424B5

424B5 1 d138057d424b5.htm 424B5 424B5

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-291466

Prospectus Supplement

(To Prospectus Dated November 12, 2025)

LOGO

3,532,609 Shares of Common Stock

We are offering 3,532,609 shares of our common stock, par value $0.0001 per share, or common stock, pursuant to this prospectus supplement and the accompanying prospectus.

Our common stock is listed on the Nasdaq Capital Market under the symbol “NKTR”. On April 21, 2026, the last reported sale price for our common stock on the Nasdaq Capital Market was $98.16 per share.

We are a “smaller reporting company” under the federal securities laws and, as such, we have elected to comply with certain reduced public company reporting requirements for this prospectus supplement and for future filings. See “Prospectus Supplement Summary—Implications of Being a Smaller Reporting Company.”


	Per Share		Total
Public offering price	$	92.00	$	325,000,028.00
Underwriting discounts and commissions⁽¹⁾	$	5.52	$	19,500,001.68
Proceeds to us, before expenses	$	86.48	$	305,500,026.32

(1)	See “Underwriting” for a description of the compensation payable to the underwriters.

We have granted the underwriters an option for a period of 30 days to purchase an additional 529,891 shares of our common stock from us, at the public offering price, less the underwriting discounts and commissions.

Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page S-11 of this prospectus supplement and page 6 of the accompanying prospectus, and in the documents incorporated by reference herein. You should read the entire prospectus supplement and the accompanying prospectus, including any information incorporated by reference, carefully, before investing in our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares of common stock to purchasers on or about April 23, 2026.

Joint Bookrunning Managers


Jefferies		TD Cowen		Piper Sandler

Bookrunner

Citigroup

Prospectus Supplement dated April 21, 2026

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT


	Page
ABOUT THIS PROSPECTUS SUPPLEMENT		S-1
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		S-3
PROSPECTUS SUPPLEMENT SUMMARY		S-5
RISK FACTORS		S-11
USE OF PROCEEDS		S-13
DILUTION		S-14
DIVIDEND POLICY		S-16
MATERIAL U.S. FEDERAL INCOME TAX CONSIDERATIONS FOR NON-U.S. HOLDERS		S-17
UNDERWRITING		S-22
LEGAL MATTERS		S-31
EXPERTS		S-31
WHERE YOU CAN FIND MORE INFORMATION		S-31
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE		S-32

PROSPECTUS


	Page
ABOUT THIS PROSPECTUS		1
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		3
ABOUT THE COMPANY		4
RISK FACTORS		6
USE OF PROCEEDS		7
DIVIDEND POLICY		8
GENERAL DESCRIPTION OF SECURITIES		9
DESCRIPTION OF CAPITAL STOCK		10
DESCRIPTION OF DEBT SECURITIES		15
DESCRIPTION OF WARRANTS		22
DESCRIPTION OF UNITS		23
PLAN OF DISTRIBUTION		26
LEGAL MATTERS		29
EXPERTS		29
WHERE YOU CAN FIND MORE INFORMATION		29
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE		30

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of common stock and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part is the accompanying prospectus dated November 12, 2025, included in our registration statement on Form S-3 (File No. 333-291466), along with the documents incorporated by reference therein, which provides more general information, some of which may not apply to this offering. Generally, when we refer to this prospectus, we are referring to both parts of this document combined.

To the extent there is a conflict between the information contained in this prospectus supplement and the information contained in the accompanying prospectus or in any document incorporated by reference that was filed with the Securities and Exchange Commission, or the SEC, before the date of this prospectus supplement, you should rely on the information in this prospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.

This prospectus supplement and the accompanying prospectus are part of a “shelf” registration statement that we filed with the SEC. Under the shelf registration process, we may offer from time to time various securities, of which this offering of shares of our common stock is a part. Such registration statement also includes exhibits that provide more detail on the matters discussed in this prospectus supplement and the accompanying prospectus. You should read this prospectus supplement, the accompanying prospectus, including the information incorporated by reference, the exhibits filed with the SEC, and any free writing prospectus that we have authorized for use in connection with this offering, in their entirety before making an investment decision.

You should rely only on the information contained or incorporated by reference in this prospectus supplement, the accompanying prospectus and any free writing prospectus prepared by us or on our behalf. We have not, and the underwriters have not, authorized any other person to provide you with information different from that contained in this prospectus supplement and the accompanying prospectus or incorporated by reference in this prospectus supplement and the accompanying prospectus. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the underwriters are not, making an offer to sell or soliciting an offer to buy these securities under any circumstance in any jurisdiction where the offer or solicitation is not permitted. You should assume that the information contained in this prospectus supplement, the accompanying prospectus and any free writing prospectus prepared by us or on our behalf is accurate only as of the date of the respective document in which the information appears, and that any information in documents that we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus supplement or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.

It is important for you to read and consider all of the information contained in this prospectus supplement and the accompanying prospectus before making your investment decision. We include cross-references in this prospectus supplement and the accompanying prospectus to captions in these materials where you can find additional related discussions. The table of contents in this prospectus supplement provides the pages on which these captions are located. You should read both this prospectus supplement and the accompanying prospectus, together with the additional information described in the sections entitled “Where You Can Find More Information” and “Incorporation of Certain Information By Reference” of this prospectus supplement, before investing in our securities.

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We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference herein were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

We and the underwriters are offering to sell, and seeking offers to buy, our securities only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the accompanying prospectus and the offering of the securities in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, the offering of the securities and the distribution of this prospectus supplement and the accompanying prospectus outside the United States. This prospectus supplement and the accompanying prospectus do not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement and the accompanying prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

Except as otherwise indicated herein or as the context otherwise requires, references in this prospectus supplement, the accompanying prospectus and the information incorporated by referenced herein or therein to “Nektar,” “the Company,” “we,” “us,” “our” and similar terms refer to Nektar Therapeutics, a Delaware corporation.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement and the information incorporated by reference herein, contains “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. All statements, other than statements of historical facts, included in this prospectus, including the documents that we incorporate by reference, are “forward-looking statements,” including any projections of market size, earnings, revenue, milestone payments, royalties, sales or other financial items, any statements of the plans and objectives of management for future operations (including, but not limited to, our preliminary financial estimates, which represent management’s current estimates and are subject to change; preclinical development, clinical trials and manufacturing), any statements related to our financial condition and future working capital needs, any statements regarding potential future financing alternatives including non-dilutive financings, any statements related to our strategic reorganization and cost restructuring plans, any statements concerning proposed drug candidates and our future research and development plans, any statements regarding the timing for the start or end of clinical trials or submission of regulatory approval filings, any statements regarding future economic conditions or performance, any statements regarding the initiation, formation, or success of any collaboration arrangements, commercialization activities and product sales levels and future payments that may come due to us under these arrangements, any statements regarding our plans and objectives to initiate or continue clinical trials, any statements related to potential, anticipated, or ongoing litigation (including the timing for court hearings and trials) and any statements of assumptions underlying any of the foregoing. In some cases, forward-looking statements can be identified by the use of terminology such as “believe,” “may,” “will,” “expects,” “plans,” “anticipates,” “estimates,” “potential” or “continue,” or the negative thereof or other comparable terminology. Although we believe that the expectations reflected in the forward-looking statements contained herein are reasonable, such expectations or any of the forward-looking statements may prove to be incorrect and actual results could differ materially from those projected or assumed in the forward-looking statements.

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. We have included important factors in the cautionary statements included in this prospectus, including the documents that we incorporate by reference, particularly in our “critical accounting estimates” described in Part II, Item 7 “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies and Significant Judgments and Estimates” and in Part I, Item 1A “Risk Factors” of our most recent Annual Report on Form 10-K and our subsequent Quarterly Reports on Form 10-Q filed with the SEC, which are incorporated by reference in this prospectus, and in the “Risk Factors” section of this prospectus, that could cause actual results or events to differ materially from the forward-looking statements that we make. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures, collaborations or investments that we may make.

You should read this prospectus supplement, the accompanying prospectus and the documents that we incorporate by reference herein and therein completely and with the understanding that our actual future results may be materially different from what we expect. We do not assume any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this prospectus supplement and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and you are cautioned not to unduly rely upon these statements.

This prospectus supplement, the accompanying prospectus and the documents incorporated herein and therein by reference, and any free writing prospectus that we may have authorized for use in connection with this

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offering, contains estimates, projections and other information concerning our industry, our business and the markets for our product candidates, including data regarding the estimated size of such markets and the incidence of certain medical conditions. We obtained the industry, market and similar data set forth in this prospectus from our internal estimates and research and from academic and industry research, publications, surveys and studies conducted by third parties, including governmental agencies. In some cases, we do not expressly refer to the sources from which this data is derived. Information that is based on estimates, forecasts, projections, market research or similar methodologies is inherently subject to uncertainties and actual events or circumstances may differ materially from events and circumstances that are assumed in this information. You are cautioned not to give undue weight to any such information, projections and estimates.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information about us and this offering and does not contain all of the information that you should consider before investing in our securities. You should read this prospectus supplement carefully, especially the risks of investing in our securities discussed under “Risk Factors” beginning on page S-11 of this prospectus supplement and in Part I, Item 1A “Risk Factors” of our most recent Annual Report on Form 10-K, and any Quarterly Report on Form 10-Q or Current Report on Form 8-K we file after the date of this prospectus supplement, which are incorporated by reference in this prospectus supplement, along with our consolidated financial statements and notes to those consolidated financial statements and the other information incorporated by reference in this prospectus supplement, before making an investment decision.

Overview

We are a clinical stage, research-based drug discovery biopharmaceutical company focused on discovering and developing innovative medicines in the field of immunotherapy. Within this growing field, we direct our efforts toward creating new immunomodulatory agents that selectively induce, amplify, attenuate or prevent immune responses in order to achieve desired therapeutic outcomes. We apply our deep understanding of immunology to identify and create innovative drug candidates and use our drug development expertise to advance these molecules through preclinical and clinical development. Our pipeline of clinical-stage and preclinical-stage immunomodulatory agents targets the treatment of autoimmune diseases (e.g. rezpegaldesleukin and NKTR-0165, respectively) and cancer (e.g. NKTR-255). We continue to make significant investments in building and advancing our pipeline of drug candidates as we believe that this is the best strategy to build long-term stockholder value.

Our Drug Candidates and Pipeline

By modulating the immune system, our drug candidates target pathways that play critical roles in a wide range of serious diseases. In autoimmune diseases, our focus is on addressing imbalances in the immune system to restore the body’s self-tolerance mechanisms and to achieve immune homeostasis. In oncology, we are focused on activating the immune system’s natural tumor-fighting mechanisms.

Autoimmune diseases

We recognize that many autoimmune diseases are caused by an imbalance in the body’s immune system. A failure of the body’s self-tolerance mechanisms enables the formation of pathogenic T cells that cause the immune system to mistakenly attack and damage healthy cells in a person’s body. Current systemic treatments for autoimmune diseases, including corticosteroids and anti-TNF agents, suppress the immune system broadly and come with severe side effects. Pharmaceutical agents designed to rebalance the immune system by increasing the function of regulatory T cells, or Treg cells, powerful inhibitory immune cells, could be used to treat patients suffering from autoimmune disorders and inflammatory diseases.

Rezpegaldesleukin

Our drug candidate rezpegaldesleukin is a potential first-in-class resolution therapeutic that may address this underlying immune system imbalance in people with autoimmune disorders and inflammatory diseases. It is designed to target the interleukin-2, or IL-2, receptor complex in the body in order to stimulate proliferation of powerful inhibitory immune cells known as Treg cells. Describing the critical role of Treg cells in maintaining balance in the immune system earned Drs. Mary E. Brunkow, Fred Ramsdell and Shimon Sakaguchi, the Nobel Prize in medicine on October 6, 2025. By activating these cells, rezpegaldesleukin may act to bring the immune system back into balance. Rezpegaldesleukin is being developed as a self-administered injection for a number of autoimmune disorders and inflammatory diseases.

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NKTR-0165 and NKTR-0166

We believe that our preclinical tumor necrosis factor, or TNF, receptor type II, or TNFR2, agonist asset, NKTR-0165, is a potentially unique bivalent antibody that selectively stimulates TNFR2 receptor activity, without modulation of the TNFR1 signaling. TNFR2 signaling drives immunoregulatory function and is an important gatekeeper of inflammation and its absence or deficit is associated with a broad range of autoimmune diseases. TNFR2 is highly expressed on Tregs, neuronal cells and endothelial cells and has been shown to potentiate the suppressive effects and overall functional properties of Tregs. NKTR-0165 is being developed for potential treatment of autoimmune diseases, such as ulcerative colitis, multiple sclerosis and vitiligo. We are currently conducting Investigational New Drug, or IND, enabling studies for this program, after having exercised an option to gain an exclusive license to specified agonistic antibodies and other materials that were developed pursuant to a research collaboration and license option agreement we entered into with Biolojic Design, Ltd. in 2021. We have also designed a unique bispecific antibody, NKTR-0166, that incorporates the TNFR2 agonist epitope and an antagonist epitope validated in the treatment of rheumatology diseases. As a dual agonist: antagonist of known pathways associated with disease pathogenesis, this investigational antibody is being developed to address a number of rheumatic disorders.

Oncology

NKTR-255

In oncology, we focus on developing medicines based on targeting biological pathways that stimulate and sustain the body’s immune response in order to fight cancer. NKTR-255 is an investigational biologic that is designed to target the interleukin-15, or IL-15, pathway in order to activate the body’s innate and adaptive immunity.

Activation of the IL-15 pathway enhances the survival and function of natural killer, or NK, cells and induces survival of both effector and CD8+ memory T cells. Recombinant human IL-15 is rapidly cleared from the body and must be administered frequently and in high doses limiting its utility due to toxicity. Through optimal engagement of the IL-15 receptor complex, NKTR-255 is designed to enhance functional NK cell populations and the formation of long-term immunological memory, which may lead to sustained and durable anti-tumor immune response.

Future Funding Requirements

Our ability to advance our development programs is dependent upon our ability to secure additional capital in both the near and long-term, through public or private securities offerings; royalty or fixed-rate financing; convertible debt or other debt financings; and/or potential strategic opportunities, including licensing agreements, drug product development, marketing collaboration arrangements, pharmaceutical research cooperation arrangements, and/or other similar transactions in geographic markets, including the United States, and/or through potential grants and other funding commitments from United States government agencies, in each case, if available. We have engaged with potential counterparties in various markets seeking non-dilutive financing opportunities and will continue to pursue non-dilutive sources of capital as well as potential private and public securities offerings to fund our operations and future clinical trials. There can be no assurance, however, that we will be able to identify and enter into public or private securities offerings on acceptable terms and in amounts sufficient to meet our needs or qualify for non-dilutive funding opportunities under any grant programs sponsored by United States government agencies, private foundations, or leading academic institutions, or identify and enter into any strategic transactions that will provide the additional capital, including non-dilutive capital, that we will require. If none of these alternatives is available, or if available and we are unable to raise sufficient capital through such transactions, we potentially could be forced to limit or cease our development activities, as well as modify or cease our operations, either of which would have a material adverse effect on our business, financial condition, and results of operations.

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Recent Developments

On April 20, 2026, we announced new results from a blinded 16-week treatment extension period in its Phase 2b REZOLVE-AA study. The study is evaluating investigational rezpegaldesleukin, a first-in-class IL-2 pathway agonist and regulatory T-cell (Treg) biologic, in patients with severe-to-very-severe alopecia areata.

REZOLVE-AA is a global study being conducted in 92 patients with severe-to-very-severe alopecia areata. During the initial 36-week induction phase, patients were randomized (3:3:2) to receive one of two rezpegaldesleukin doses or placebo, administered as twice-monthly subcutaneous injections. Mean baseline Severity of Alopecia Tool (SALT) Scores for patients enrolled in the study were 78.5 in the rezpegaldesleukin treatment arms as compared to 76.6 in placebo. Median time from onset of disease was 6.9 years in the treatment arms and 6.1 years in placebo. Following completion of the induction phase, patients with a SALT Score greater than 20 at week 36 who also demonstrated hair growth were eligible to continue on rezpegaldesleukin at their induction dose level in a blinded 16-week exploratory treatment extension through week 52.

Extended Twice-Monthly Treatment with Rezpegaldesleukin Improved SALT Scores at 52 Weeks

A total of 31 patients continued into the blinded 16-week treatment extension period with 27 patients in the twice-monthly rezpegaldesleukin dose arms (low dose of 18 µg/kg, n=14) and (high dose of 24 µg/kg, n=13) and 4 patients continuing in the placebo arm.

From week 36 to week 52, 29% of patients at low dose and 31% of patients at high dose achieved new SALT Score ≤20 responses as compared to none in the placebo arm. A SALT Score ≤20 is achieved when a patient has 80% or more of their scalp covered by hair.

At week 52 for overall study population, patients who achieved SALT Score ≤20 were 25.8% in low dose rezpegaldesleukin arm (versus 14.8% at week 36) and 27.6% in high dose rezpegaldesleukin arm (versus 15.6% at week 36) as compared to 6.7% with placebo (versus 6.7% at week 36) with a p-value of 0.049.

At week 52 for overall study population, patients who achieved SALT Score ≤30 were 30.2% in low dose rezpegaldesleukin arm (versus 21.9% at week 36) and 35.0% in high dose rezpegaldesleukin arm (versus 29.0% at week 36) as compared to 8.4% with placebo (versus 8.4% at week 36), with a p-value of 0.023. A SALT Score ≤30 is achieved when a patient has 70% or more of their scalp covered by hair.

At week 52 for overall study population, patients who achieved SALT₅₀ (showing at least a 50% improvement in SALT Score from baseline) were 37.7% in low dose rezpegaldesleukin arm and 38.8% in high dose rezpegaldesleukin arm as compared to 13.6% with placebo.

At week 52 for overall study population, patients who achieved SALT₃₀ (showing at least a 30% improvement in SALT Score from baseline) were 45.6% in low dose rezpegaldesleukin arm and 47.6% in high dose rezpegaldesleukin arm as compared to 24.2% with placebo.

We plan to submit the REZOLVE-AA results for presentation at a medical conference in 2026.

Rezpegaldesleukin Well Tolerated with Safety Profile Consistent with Previously Reported Results

Consistent with prior studies, a favorable safety and tolerability profile was observed with longer twice-monthly dosing for 52 weeks. Nearly all treatment-emergent adverse events (TEAEs) were mild-to-moderate in severity which resolved without intervention. 94% of patients in the blinded 16-week treatment extension completed 52 weeks of treatment and there were no patients who discontinued during the extension because of a TEAE. The most common TEAEs were injection site reactions (ISR) with the majority being mild to moderate in nature (erythema) which self-resolved within 5 days. There were no patients in the study who discontinued treatment due to an injection site reaction (ISR).

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Financial Results

Based upon preliminary estimates and information available to us as of the date of this prospectus supplement, we estimate that we had approximately $741.7 million in cash and investments in marketable securities as of April 1, 2026, which includes the completion of our at-the-market offering program that was established in November 2025.

At-the-Market Program Sales

From December 31, 2025 through the date of this prospectus supplement, the Company sold an aggregate of 1,532,850 shares of common stock under its at-the-market offering program at a weighted average sales price of $71.76 per share, resulting in gross proceeds of approximately $110.0 million. As of the date of this prospectus supplement, the Company has fully utilized the remaining capacity available under such at-the-market offering program.

Corporate History and Information

We were incorporated in California in 1990 and reincorporated in Delaware in 1998. Our principal corporate office is located at 455 Mission Bay Boulevard South, San Francisco, California 94158, and our telephone number is (415) 482-5300. Our website address is https://nektar.com. We do not incorporate the information on or accessible through our website into this prospectus, and you should not consider any information on, or that can be accessed through, our website a part of this prospectus supplement or incorporated by reference herein. For further information regarding us and our financial information, you should refer to our recent filings with the SEC. See “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

Implications of Being a Smaller Reporting Company

We are a “smaller reporting company” as defined in the Exchange Act. We may take advantage of certain of the scaled disclosures available to smaller reporting companies until the fiscal year following the determination that our voting and non-voting common stock held by non-affiliates is more than $250 million measured on the last business day of our second fiscal quarter, or our annual revenues are less than $100 million during the most recently completed fiscal year and our voting and non-voting common stock held by non-affiliates is more than $700 million measured on the last business day of our second fiscal quarter.

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THE OFFERING

Common stock offered by us

3,532,609 of shares of our common stock (or 4,062,500 shares if the underwriters exercise their option to purchase additional shares in full).

Common stock to be outstanding immediately after this offering

33,212,256 shares of common stock (or 33,742,147 shares if the underwriters exercise their option to purchase additional shares in full).

Option to purchase additional shares

We have granted the underwriters an option to purchase up to an additional 529,891 shares of our common stock from us, at the public offering price, less the underwriting discounts and commissions, for a period of 30 days after the date of this prospectus supplement.

Use of proceeds

We estimate that our net proceeds from this offering will be approximately $305.1 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by us. We intend to use the net proceeds we receive from this offering, together with our existing cash, cash equivalents and marketable securities, for general corporate purposes, which may include research and development, clinical development (including Phase 3 trials for rezpegaldesleukin in atopic dermatitis and alopecia areata) and manufacturing costs to support the advancement of our drug candidates, as well as other general corporate purposes. See “Use of Proceeds” for additional information.

Risk factors

Your investment in our common stock involves substantial risk. See “Risk Factors” beginning on page S-11 of this prospectus supplement and other information included and incorporated by reference in this prospectus supplement and the accompanying prospectus for a discussion of factors that you should carefully consider before deciding to invest in our common stock.

Nasdaq Capital Market symbol

“NKTR”.

The number of shares of our common stock that will be outstanding immediately after this offering set forth above is based on 29,679,647 shares of our common stock outstanding as of April 1, 2026. The number of shares outstanding as of April 1, 2026 as used throughout this prospectus supplement, unless otherwise indicated, excludes:

•

2,326,369 shares of common stock issuable upon the exercise of stock options and performance stock options outstanding as of April 1, 2026, at a weighted-average exercise price of $58.70 per share;

•

198,331 shares of common stock issuable upon the vesting and settlement of restricted stock unit awards, or RSUs, or performance RSUs outstanding as of April 1, 2026;

•

373,708 shares of common stock reserved for future issuance under our Amended and Restated 2017 Performance Incentive Plan as of April 1, 2026;

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•

45,858 shares of our common stock available for future issuance under our Amended and Restated Employee Stock Purchase Plan as of April 1, 2026;

•

225,790 shares of our common stock available for future issuance under our 2025 Inducement Plan as of April 1, 2026; and

•

293,103 shares of our common stock issuable upon the exercise of the pre-funded warrants outstanding as of April 1, 2026 at an exercise price of $0.0001 per share.

Unless otherwise indicated, all information in this prospectus supplement assumes no exercise of the outstanding options to purchase our common stock, no vesting or settlement of RSUs described above after April 1, 2026 and, no exercise by the underwriters of their option to purchase up to 529,891 additional shares of our common stock in this offering.

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RISK FACTORS

Investing in our securities involves a high degree of risk. Before you decide to invest in our securities, you should carefully consider the risks and uncertainties described below and in Part I, Item 1A “Risk Factors” of our most recent Annual Report on Form 10-K, and any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K and incorporated by reference herein, together with all other information contained in this prospectus supplement and in our filings with the SEC that we have incorporated by reference in this prospectus supplement. If any of the following risks actually occur, our business, financial condition or results of operations could be adversely affected, which, in turn, could have a negative impact on the price of our common stock and you may lose all or part of your investment.

Risks Related to this Offering and the Securities Offered Hereby

If you purchase securities in this offering, you may suffer immediate and substantial dilution of your investment.

The offering price per share in this offering will exceed the net tangible book value per share of our common stock outstanding prior to this offering. Therefore, if you purchase securities in this offering, you will pay an offering price per share that substantially exceeds our net tangible book value per share after this offering. To the extent shares are issued under outstanding options at exercise prices lower than the price of our common stock in this offering, you will incur further dilution. Our pro forma net tangible book value as of December 31, 2025 was $628.4 million, or $21.27 per share after giving effect to pro forma adjustments described in the section entitled “Dilution” below. After giving effect to this offering at the offering price of $92.00 per share, and after deducting the underwriting discounts and commissions and estimated offering expenses payable by us, you will experience immediate dilution of $63.78 per share, representing the difference between our as pro forma adjusted net tangible book value per share as of December 31, 2025 after giving effect to this offering at the offering price. See the section entitled “Dilution” below for a more detailed illustration of the dilution you would incur if you participate in this offering.

We have broad discretion over the use of our existing cash, cash equivalents and marketable securities and the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion over the application of our existing cash, cash equivalents and marketable securities and the net proceeds from this offering, including for any of the purposes described in the section titled “Use of Proceeds,” and you will not have the opportunity as part of your investment decision to assess whether such proceeds are being used appropriately. Because of the number and variability of factors that will determine our use of our existing cash and cash equivalents and the net proceeds from this offering, their ultimate use may vary substantially from their currently intended use. Our management might not apply our existing cash and cash equivalents and marketable securities and the net proceeds from this offering in ways that ultimately increase the value of your investment. The failure by our management to apply these funds effectively could harm our business. Pending the use of the net proceeds from this offering, we may invest such net proceeds in short-term, investment-grade, interest-bearing securities. These investments may not yield a favorable return to our stockholders. If we do not invest or apply the net proceeds from this offering in ways that enhance stockholder value, we may fail to achieve expected financial results, which could cause our stock price to decline.

You may experience future dilution as a result of future equity offerings.

In order to raise additional capital, we may in the future offer additional shares of our common stock or other securities convertible into or exchangeable for our common stock at prices that may not be the same as the price per share in this offering, including through any future “at-the-market” equity offering program we may establish.

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We may sell shares or other securities in any other offering at a price per share that is less than the price per share paid by investors in this offering, and investors purchasing shares or other securities in the future could have rights superior to those of existing stockholders. The price per share at which we sell additional shares of our common stock, or securities convertible or exchangeable into common stock, in future transactions may be higher or lower than the price per share paid by investors in this offering.

We are seeking additional non-dilutive financing, however, we may be unable to secure such financing on favorable terms or at all, which could require us to seek dilutive financing. If adequate funds are not available on acceptable terms, we may be unable to fund our capital requirements.

Future sales or issuances of our common stock in the public markets, or the perception of such sales, could depress the trading price of our common stock.

The sale of a substantial number of shares of our common stock or other securities convertible into or exchangeable for our common stock in the public markets, or the perception that such sales could occur, could depress the market price of our common stock and impair our ability to raise capital through the sale of additional equity securities. We may sell large quantities of our common stock at any time pursuant to this prospectus supplement or in one or more separate offerings. We cannot predict the effect that future sales of common stock or other equity-related securities would have on the market price of our common stock.

The trading price of the shares of our common stock could be highly volatile, and purchasers of our common stock could incur substantial losses.

The trading price of our common stock is highly volatile and subject to wide fluctuations in response to various factors, some of which we cannot control. The volatility of our common stock may affect the price at which you could sell the shares of our common stock, and the sale of substantial amounts of our common stock could adversely affect the price of our common stock. Our stock price is likely to continue to be volatile and subject to significant price and volume fluctuations in response to market and other factors, including those described in the sections captioned “Risk Factors” in this prospectus supplement, the accompanying prospectus, our most recent Annual Report on Form 10-K and the other documents incorporated by reference herein and therein.

As a result, you may not be able to sell your shares of common stock at or above the price at which you purchase them. In addition, the stock market in general, the Nasdaq Capital Market and the stock of biotechnology and pharmaceutical companies in particular, have experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of these companies. Broad market and industry factors may negatively affect the market price of our common stock, regardless of our actual operating performance.

Our preliminary financial results included in this prospectus supplement are based on information currently available to management and are subject to change.

The preliminary estimated financial results contained in “Prospectus Supplement Summary—Recent Developments - Financial Results” represents only preliminary financial results and is based on information available to management as of the date of this prospectus supplement.

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USE OF PROCEEDS

We expect that the net proceeds from our issuance and sale of 3,532,609 shares of our common stock in this offering will be approximately $305.1 million (or approximately $350.9 million if the underwriters exercise in full their option to purchase 529,891 additional shares), after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

We currently intend to use the net proceeds from this offering, together with our existing cash, cash equivalents and marketable securities, for general corporate purposes, which may include research and development, clinical development (including Phase 3 trials for rezpegaldesleukin in atopic dermatitis and alopecia areata) and manufacturing costs to support the advancement of our drug candidates in atopic dermatitis and alopecia areata. The expected use of the net proceeds from this offering represents our intentions based upon our current plans and business conditions, which could change in the future as our plans and business conditions evolve. The amounts and timing of our actual expenditures will depend on numerous factors, including the factors described under “Risk Factors” in this prospectus supplement, the accompanying prospectus, and in the documents incorporated by reference herein, as well as the amount of cash used in our operations. We may find it necessary or advisable to use the net proceeds for other purposes, and we will have broad discretion in the application of the net proceeds. Pending use of net proceeds as described above, we may temporarily invest the net proceeds in a variety of capital preservation instruments, including high quality, investment grade instruments, certificates of deposit or direct or guaranteed obligations of the U.S. government, or may hold such proceeds as cash, until they are used for their stated purpose.

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DILUTION

If you invest in this offering, your ownership interest will be diluted immediately to the extent of the difference between the public offering price per share of common stock in this offering and the as adjusted net tangible book value per share of our common stock after giving effect to the pro forma adjustments described below and in this offering.

As of December 31, 2025, we had a historical net tangible book value of $89.8 million, or $4.41 per share of common stock, based on 20,378,832 shares of common stock outstanding. Our historical net tangible book value per share represents total tangible assets less total liabilities, divided by the number of shares of common stock outstanding.

Pro forma net tangible book value represents the amount of our total tangible assets less our total liabilities, after giving effect to (i) the sale and issuance of 7,637,931 shares of our common stock at a price of $58.00 per share and 293,103 pre-funded warrants at price of $57.9999 per pre-funded warrant in an underwritten public offering (excluding the shares of common stock to be issued from exercises of the pre-funded warrants), pursuant to an underwriting agreement with Jefferies LLC, TD Securities (USA) LLC, and Piper Sandler & Co. on February 11, 2026, for net proceeds of approximately $432.0 million (excluding the proceeds received, if any, from exercises of the pre-funded warrants), after deducting underwriting discounts and commissions and estimated offering expenses, (ii) the sale and issuance of 1,532,850 shares of our common stock under our at-the-market offering program subsequent to December 31, 2025 at a weighted-average sales price of $71.76 per share for net proceeds of approximately $106.6 million. Pro forma net tangible book value per share represents pro forma net tangible book value divided by the total number of our outstanding shares of common stock as of December 31, 2025 after giving effect to the pro forma adjustments described above.

After giving effect to the sale of 3,532,609 shares of our common stock in this offering at the offering price of $92.00 per share, and after deducting the underwriting discounts and commissions and estimated offering expenses payable by us, our pro forma as adjusted net tangible book value as of December 31, 2025 would have been approximately $933.5 million, or $28.22 per share of our common stock. This represents an immediate increase in as adjusted net tangible book value of $6.95 per share to our existing stockholders and an immediate dilution of $63.78 per share to investors purchasing our securities in this offering. The following table illustrates this dilution on a per share basis:


Public offering price per share			$	92.00
Historical net tangible book value per share as of December 31, 2025	$	4.41
Increase per share attributable to the pro forma adjustments	$	16.86
Pro forma net tangible book value per share as of December 31, 2025	$	21.27
Increase in pro forma net tangible book value per share attributable to investors purchasing shares in this offering	$	6.95

Pro forma as adjusted net tangible book value per share after this offering			$	28.22

Dilution in net tangible book value per share to investors purchasing shares in this offering			$	63.78

If the underwriters exercise their option to purchase up to 529,891 additional shares in full at the public offering price of $92.00 per share, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, the pro forma as-adjusted net tangible book value would be $29.14 per share, representing an immediate increase in net tangible book value of $7.87 per share to existing stockholders and an

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immediate dilution in as-adjusted net tangible book value of $62.86 per share to new investors purchasing shares of our common stock in this offering.

The number of shares of our common stock to be outstanding after this offering set forth above is based on 20,378,832 shares of our common stock outstanding as of December 31, 2025. The number of shares outstanding as of December 31, 2025, unless otherwise indicated, excludes:

•

2,461,719 shares of common stock issuable upon the exercise of stock options or performance stock options outstanding as of December 31, 2025, at a weighted-average exercise price of $59.34 per share;

•

208,100 shares of common stock issuable upon the vesting and settlement of RSUs or performance RSUs outstanding as of December 31, 2025;

•

353,240 shares of common stock reserved for future issuance under our Amended and Restated 2017 Performance Incentive Plan as of December 31, 2025; and

•

45,858 shares of our common stock available for future issuance under our Amended and Restated Employee Stock Purchase Plan as of December 31, 2025; and

•

231,690 shares of our common stock available for future issuance under our 2025 Inducement Plan as of December 31, 2025; and

•

293,103 shares of our common stock issuable upon the exercise of the pre-funded warrants outstanding as of April 1, 2026 at an exercise price of $0.0001 per share.

To the extent that outstanding options outstanding as of December 31, 2025 or pre-funded warrants have been or may be exercised or other shares issued, investors purchasing our common stock in this offering may experience further dilution. In addition, we may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders.

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DIVIDEND POLICY

We have never declared or paid any cash dividends on our capital stock. We do not anticipate paying any dividends on our capital stock in the foreseeable future. We currently intend to retain all available funds and any future earnings to fund the development and growth of our business. Any future determination to declare dividends will be subject to the discretion of our board of directors and will depend on various factors, including applicable laws, our results of operations, financial condition, future prospects and any other factors deemed relevant by our board of directors. Investors should not purchase our common stock with the expectation of receiving cash dividends.

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MATERIAL U.S. FEDERAL INCOME TAX CONSIDERATIONS FOR NON-U.S. HOLDERS

The following discussion is a summary of material U.S. federal income tax considerations applicable to non-U.S. holders (as defined below) with respect to their ownership and disposition of shares of our common stock issued pursuant to this offering, or the Shares, but does not purport to be a complete analysis of all potential tax effects. The Shares are collectively referred to herein as our “securities.” All prospective holders of our securities should consult their tax advisors with respect to the U.S. federal, state, local and non-U.S. tax consequences of the purchase, ownership and disposition of our securities. For purposes of this discussion, a non-U.S. holder means a beneficial owner of our common stock that is, for U.S. federal income tax purposes:

•

a non-resident alien individual;

•

a corporation or any other organization taxable as a corporation for U.S. federal income tax purposes that is created or organized in or under laws other than the laws of the United States, any state thereof, or the District of Columbia;

•

an estate, the income of which is not subject to U.S. federal income tax on a net income basis; or

•

a trust that (1) (a) has not made an election to be treated as a U.S. person under applicable U.S. Treasury regulations and (b) either (i) is not subject to the primary supervision of a court within the United States or (ii) is not subject to the substantial control of one or more U.S. persons or (2) the income of which is not subject to U.S. federal income tax on a net income basis.

This discussion does not address the tax treatment of partnerships or other entities or arrangements that are treated as partnerships or disregarded entities for U.S. federal income tax purposes or persons that hold their shares of our common stock through partnerships or disregarded entities. The tax treatment of a partner in an entity treated as a partnership for U.S. federal income tax purposes generally will depend upon the status of the partner and the activities of the partnership. A partner in a partnership or an investor in a disregarded entity that will hold our common stock should consult his, her or its tax advisor regarding the tax consequences of acquiring, holding and disposing of our common stock through a partnership or disregarded entity, as applicable.

This discussion is based on current provisions of the Internal Revenue Code of 1986, as amended, or the Code, existing and proposed U.S. Treasury regulations promulgated thereunder, current administrative rulings and judicial decisions, all as in effect as of the date of this prospectus and, all of which are subject to change or to differing interpretation, possibly with retroactive effect. Any such change or differing interpretation could alter the tax consequences to non-U.S. holders described in this prospectus. We have not sought and will not seek any rulings from the Internal Revenue Service, or the IRS, regarding the matters discussed below and there can be no assurance that the IRS will not challenge one or more of the tax consequences described herein or that any such challenge would not be sustained by a court. We assume in this discussion that a non-U.S. holder holds shares of our common stock as a “capital asset” within the meaning of Section 1221 of the Code, which is generally property held for investment.

This discussion does not address all aspects of U.S. federal income taxation that may be relevant to a particular non-U.S. holder in light of that non-U.S. holder’s individual circumstances, including the alternative minimum tax, the Medicare tax on net investment income, the special tax accounting rules under Section 451(b) of the Code, the rules relating to “qualified small business stock” within the meaning of Section 1202 of the Code, any U.S. federal tax other than the income tax (including, for example, the estate or gift tax), or any aspects of U.S. state, local or non-U.S. taxes. This discussion also does not consider any specific facts or circumstances that may apply to a non-U.S. holder and does not address the special tax rules applicable to particular non-U.S. holders, such as:

1.	insurance companies;

2.	tax-exempt or governmental organizations;

3.	banks or other financial institutions;

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4.	brokers or dealers in securities;

5.	regulated investment companies;

6.	pension plans;

7.	“controlled foreign corporations,” “passive foreign investment companies,” and corporations that accumulate earnings to avoid U.S. federal income tax;

8.	“qualified foreign pension funds” as defined in Section 897(I)(2) of the Code and entities all of the interests of which are held by qualified foreign pension funds;

9.	persons that own, or are deemed to own, actually or constructively, more than 5% of our capital stock;

10.	persons deemed to sell our common stock under the constructive sale provisions of the Code;

11.	persons that hold our common stock as part of a straddle, hedge, conversion transaction, synthetic security or other integrated investment;

12.	persons who hold or receive our common stock pursuant to the exercise of any employee stock option or otherwise as compensation; and

13.	U.S. expatriates and former citizens or long-term residents of the United States.

This discussion is for general information only and is not tax advice. Accordingly, all prospective non-U.S. holders of our common stock should consult their tax advisors with respect to the U.S. federal, state, local, estate and non-U.S. tax consequences of the purchase, ownership and disposition of our common stock.

Distributions on our Common Stock

As described in the “Dividend Policy” section above, we do not intend to pay any dividends in cash or property on our common stock to our stockholders in the foreseeable future. Distributions of cash or property, if any, on shares of our common stock generally will constitute dividends for U.S. federal income tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. If a distribution exceeds our current and accumulated earnings and profits, the excess will be treated as a return of the non-U.S. holder’s investment, up to such holder’s adjusted tax basis in the shares of common stock (not below zero). Any remaining excess will be treated as capital gain, subject to the tax treatment described below in “Gain on Sale, Exchange or Other Taxable Disposition of Shares of our Common Stock.” Any such distributions will also be subject to the discussion below under the section titled “Withholding and Information Reporting Requirements—FATCA.”

Subject to the discussion in the next paragraph in this section, dividends paid to a non-U.S. holder generally will be subject to U.S. federal withholding tax at a rate of 30% of the gross amount of the dividends or such lower rate specified by an applicable income tax treaty between the United States and such holder’s country of residence. A non-U.S. holder of shares of our common stock who claims the benefit of an applicable income tax treaty between the United States and such holder’s country of residence generally will be required to provide a properly executed IRS Form W-8BEN or W-8BEN-E (or a successor form) to the applicable withholding agent and satisfy applicable certification and other requirements. Non-U.S. holders are urged to consult their tax advisors regarding their entitlement to benefits under a relevant income tax treaty. A non-U.S. holder that is eligible for a reduced rate of U.S. withholding tax under an income tax treaty may generally obtain a refund or credit of any excess amounts withheld by timely filing an appropriate claim with the IRS.

Dividends that are treated as effectively connected with a trade or business conducted by a non-U.S. holder within the United States and, if an applicable income tax treaty so provides, that are attributable to a permanent establishment or a fixed base maintained by the non-U.S. holder within the United States, are generally exempt from the 30% withholding tax if the non-U.S. holder delivers a properly executed IRS Form W-8ECI, stating that

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the dividends are so connected and satisfies applicable certification and disclosure requirements. However, such U.S. effectively connected income, net of specified deductions and credits, is taxed at the same U.S. federal income tax rates applicable to United States persons (as defined in the Code). Any U.S. effectively connected income received by a non-U.S. holder that is a corporation may also, under certain circumstances, be subject to an additional “branch profits tax” at a 30% rate or such lower rate as specified by an applicable income tax treaty between the United States and such holder’s country of residence.

Distributions on the Shares

We do not anticipate declaring or paying any future distributions. However, if we do make distributions on the Shares, such distributions will constitute dividends to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles, and will be includible in your income as ordinary income when received. However, with respect to dividends received by individuals, such dividends are generally taxed at the lower applicable long-term capital gains rates, provided certain holding period and other requirements are satisfied. If a distribution exceeds our current and accumulated earnings and profits, the excess will be treated as a tax-free return of the U.S. holder’s investment, up to such U.S. holder’s adjusted tax basis in the Shares. Any remaining excess will be treated as capital gain from the sale or exchange of such Shares, subject to the tax treatment described in “—Sale or Other Taxable Disposition of the Shares.”

Sale or Other Taxable Disposition of the Shares

Upon the sale, exchange or other taxable disposition of the Shares, a U.S. holder will generally recognize capital gain or loss equal to the difference between the amount of cash and the fair market value of any property received upon the sale, exchange or other taxable disposition and such U.S. holder’s adjusted tax basis in the Shares. This capital gain or loss will be long-term capital gain or loss if the U.S. holder’s holding period in such Shares is more than one year at the time of the sale, exchange or other taxable disposition. Long-term capital gains recognized by certain non-corporate U.S. holders, including individuals, generally will be subject to reduced rates of U.S. federal income tax. The deductibility of capital losses is subject to certain limitations.

Gains on Sale, Exchange or Other Taxable Disposition of Shares of our Common Stock

Subject to the discussion below under “Withholding and Information Reporting Requirements—FATCA,” a non-U.S. holder generally will not be subject to any U.S. federal income tax on any gain realized upon such holder’s sale, exchange or other taxable disposition of shares of our common stock unless:

•

the gain is effectively connected with the non-U.S. holder’s conduct of a U.S. trade or business and, if an applicable income tax treaty so provides, is attributable to a permanent establishment or a fixed-base maintained by such non-U.S. holder in the United States, in which case the non-U.S. holder generally will be taxed on a net income basis at the same U.S. federal income tax rates applicable to United States persons (as defined in the Code) and, if the non-U.S. holder is a foreign corporation, the branch profits tax at a 30% rate (or such lower rate as may be specified by an applicable income tax treaty between the United States and such holder’s country of residence) may also apply as described above in “Distributions on the Shares” also may apply;

•

the non-U.S. holder is a nonresident alien individual who is present in the United States for a period or periods aggregating 183 days or more in the taxable year of the disposition and certain other conditions are met, in which case the non-U.S. holder will be subject to a 30% tax (or such lower rate as may be specified by an applicable income tax treaty between the United States and such holder’s country of residence) on the gain derived from the disposition, which may be offset by certain U.S. source capital losses of the non-U.S. holder, if any (even though the individual is not considered a resident of the United States), provided that the non-U.S. holder has timely filed U.S. federal income tax returns with respect to such losses, if any; or

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•

we are, or have been, at any time during the five-year period preceding such sale or other taxable disposition (or the non-U.S. holder’s holding period, if shorter) a “U.S. real property holding corporation” (as defined in the Code), unless our common stock is regularly traded on an established securities market, within the meaning of the relevant provisions of the Code, and the non-U.S. holder holds no more than 5% of our outstanding common stock, directly or indirectly, actually or constructively, during the shorter of the five-year period ending on the date of the disposition or the period that the non-U.S. holder held the Shares. If we are determined to be a U.S. real property holding corporation and the foregoing exception does not apply, then the non-U.S. holder generally will be taxed on its gain derived from the disposition at the same U.S. federal income tax rates applicable to United States persons (as defined in the Code). Generally, a corporation is a “U.S. real property holding corporation” only if the fair market value of its “U.S. real property interests” (as defined in the Code and applicable U.S. Treasury Regulations) equals or exceeds 50% of the sum of the fair market value of its worldwide real property interests plus its other assets used or held for use in a trade or business. Although there can be no assurance, we do not believe that we are, or have been, a “U.S. real property holding corporation” for U.S. federal income tax purposes, or that we are likely to become one in the future. No assurance can be provided that our common stock will be regularly traded on an established securities market for purposes of the rules described above.

Backup Withholding and Information Reporting

We must report annually to the IRS and to each non-U.S. holder the gross amount of the distributions on shares of our common stock paid to such holder and the tax withheld, if any, with respect to such distributions.

Non-U.S. holders may have to comply with specific certification procedures to establish that the holder is not a United States person (as defined in the Code) in order to avoid backup withholding at the applicable rate with respect to distributions on shares of our common stock. Generally, a non-U.S. holder will comply with such procedures if it provides a properly executed IRS Form W-8BEN, W-8BEN-E or W-8ECI (or other applicable IRS Form W-8), or otherwise meets documentary evidence requirements for establishing that it is a non-U.S. holder, or otherwise establishes an exemption from withholding. Distributions paid to non-U.S. holders subject to withholding of U.S. federal income tax, as described above in “Distributions on the Shares,” generally will be exempt from U.S. backup withholding.

Information reporting and backup withholding will generally apply to the proceeds of a disposition of shares of our common stock by a non-U.S. holder effected by or through the U.S. office of any broker, U.S. or non-U.S., unless the holder certifies its status as a non-U.S. holder and satisfies certain other requirements, or otherwise establishes an exemption from withholding. Copies of information returns may be made available to the tax authorities of the country in which the non-U.S. holder resides or is incorporated under the provisions of a specific treaty or agreement. Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules from a payment to a non-U.S. holder can be refunded or credited against the non-U.S. holder’s U.S. federal income tax liability, if any, provided that an appropriate claim is filed with the IRS in a timely manner.

Withholding and Information Reporting Requirements—FATCA

The Foreign Account Tax Compliance Act, or FATCA, generally imposes a U.S. federal withholding tax at a rate of 30% on payments of dividends on our common stock paid to a foreign entity unless (i) if the foreign entity is a “foreign financial institution,” such foreign entity undertakes certain due diligence, reporting, withholding, and certification obligations, (ii) if the foreign entity is not a “foreign financial institution,” such foreign entity identifies certain of its U.S. investors, if any, or (iii) the foreign entity is otherwise exempt under FATCA. Such withholding may also apply to payments of gross proceeds from the sale or other disposition of shares of our common stock, although under proposed U.S. Treasury Regulations (the preamble to which specifies that taxpayers, including withholding agents, are generally permitted to rely on them pending

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finalization), no withholding will apply to payments of gross proceeds. Under certain circumstances, a non-U.S. holder may be eligible for refunds or credits of this withholding tax. An intergovernmental agreement between the United States and an applicable foreign country may modify the requirements described in this paragraph. Non-U.S. holders should consult their tax advisors regarding the possible implications of this legislation on their investment in our common stock and the entities through which they hold our shares of common stock, including, without limitation, the process and deadlines for meeting the applicable requirements to prevent the imposition of the 30% withholding tax under FATCA.

The preceding discussion of material U.S. federal tax considerations is for prospective investors’ information only. It is not tax advice. Prospective investors should consult their own tax advisors regarding the particular U.S. federal, state, local, and non-U.S. tax consequences of purchasing, holding, and disposing of our common stock, including the consequences of any proposed changes in applicable laws, as well as tax consequences arising under any state, local, non-U.S. or U.S. federal non-income tax laws such as estate and gift tax or under any applicable tax treaty.

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UNDERWRITING

Subject to the terms and conditions set forth in the underwriting agreement, dated April 21, 2026, by and between us and Jefferies LLC, TD Securities (USA) LLC and Piper Sandler & Co. as the representatives of the underwriters named below and the joint book-running manager of this offering, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us the respective number of shares of common stock shown opposite its name below:


Underwriter	Number of Shares
Jefferies LLC		1,324,729
TD Securities (USA) LLC		1,024,457
Piper Sandler & Co.		830,163
Citigroup Global Markets Inc.		353,260

Total		3,532,609

The underwriting agreement provides that the obligations of the several underwriters are subject to certain conditions precedent such as the receipt by the underwriters of officers’ certificates and legal opinions and approval of certain legal matters by their counsel. The underwriting agreement provides that the underwriters will purchase all of the shares of common stock. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the non-defaulting underwriters may be increased or the underwriting agreement may be terminated. We have agreed to indemnify the underwriters and certain of their controlling persons against certain liabilities, including liabilities under the Securities Act, and to contribute to payments that the underwriters may be required to make in respect of those liabilities.

The underwriters are offering the shares of common stock subject to their acceptance of the shares of common stock from us and subject to prior sale. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commission and Expenses

The underwriters have advised us that they propose to offer the shares of common stock to the public at the initial public offering price set forth on the cover page of this prospectus supplement and to certain dealers, which may include the underwriters, at that price less a concession not in excess of $3.3120 per share of common stock. After the offering, the initial public offering price, concession and reallowance to dealers may be reduced by the representatives. No such reduction will change the amount of proceeds to be received by us as set forth on the cover page of this prospectus supplement.

The following table shows the public offering price, the underwriting discounts and commissions that we are to pay the underwriters and the proceeds, before expenses, to us in connection with this offering. Such amounts are shown assuming both no exercise and full exercise of the underwriters’ option to purchase additional shares.


	Per Share		Without Option to Purchase Additional Shares		With Option to Purchase Additional Shares
Public offering price	$	92.00	$	325,000,028.00	$	373,750,000.00
Underwriting discounts and commissions paid by us	$	5.52	$	19,500,001.68	$	22,425,000.00
Proceeds to us, before expenses	$	86.48	$	305,500,026.32	$	351,325,000.00

We estimate expenses payable by us in connection with this offering, other than the underwriting discounts and commissions referred to above, will be approximately $0.4 million.

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Listing

Our common stock is listed on the Nasdaq Capital Market under the trading symbol “NKTR”.

Stamp Taxes

If you purchase shares of common stock offered in this prospectus supplement, you may be required to pay stamp taxes and other charges under the laws and practices of the country of purchase, in addition to the offering price listed on the cover page of this prospectus supplement.

Option to Purchase Additional Shares

We have granted to the underwriters an option, exercisable for 30 days from the date of this prospectus supplement, to purchase, from time to time, in whole or in part, up to an aggregate of 529,891 shares from us at the public offering price set forth on the cover page of this prospectus supplement, less underwriting discounts and commissions. If the underwriters exercise this option, each underwriter will be obligated, subject to specified conditions, to purchase a number of additional shares proportionate to that underwriter’s initial purchase commitment as indicated in the table above.

No Sales of Similar Securities

We, our executive officers and directors have agreed, subject to specified exceptions, not to directly or indirectly:

•

sell, offer, contract or grant any option to sell (including any short sale), pledge, transfer, establish an open “put equivalent position” within the meaning of Rule 16a-l(h) under the Exchange Act,

•

otherwise dispose of any shares of common stock, options or warrants to acquire shares of common stock, or securities exchangeable or exercisable for or convertible into shares of common stock currently or hereafter owned either of record or beneficially, or

•

publicly announce an intention to do any of the foregoing,

for a period of 60 days after the date of this prospectus supplement without the prior written consent of Jefferies LLC, TD Securities (USA) LLC and Piper Sandler & Co.

This restriction terminates after the close of trading of the common stock on and including the 60^th day after the date of this prospectus supplement.

With respect to the Company, this restriction does not apply to (A) the transactions contemplated by this offering, (B) the issuance by us of common stock or options to purchase common stock, or the issuance of common stock upon exercise of options, pursuant to stock options, stock bonuses or other stock plans or arrangements, (C) the issuance by us of common stock pursuant to the conversion of securities or the exercise of warrants, which securities or warrants are outstanding as of the date hereof, (D) the adoption of a new equity incentive plan, including an inducement plan, and filing of a registration statement on Form S-8 under the Securities Act to register the offer and sale of securities to be issued pursuant to such new equity incentive plan, subject to certain limitations; (E) for the thirty (30) days following the first closing date, the issuance by us of shares of our common stock or related securities not exceeding, in the aggregate, that number of shares equal to five percent (5%) of our outstanding shares at the time immediately after the first closing date, to one or more counterparties in connection with the consummation of a strategic partnership, joint venture, collaboration, merger, co-promotion or distribution arrangement, or the acquisition, in-licensing or out-licensing of any business products or technologies; provided, however, that following such thirty (30) day period, we may issue shares and related securities in excess of five percent (5%) of our outstanding shares at the time immediately after the first closing date, and that prior to any issuance under this clause (E), each recipient of such shares of common stock or related securities shall execute a lock-up agreement; (F) the facilitation of the transfer of shares

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of common stock under a trading plan pursuant to Rule 10b5-1 under the Exchange Act, or a Trading Plan, that is existing on the date hereof, (G) the facilitation of the establishment of a trading plan on behalf of a shareholder, officer or director pursuant to Rule 10b5-1 under the Exchange Act for the transfer of shares of common stock, provided that (x) such plan does not provide for the transfer of shares of common stock during the lock-up period and (y) to the extent a public announcement or filing under the Exchange Act, if any, is required of or voluntarily made by us regarding the establishment of such plan, such announcement or filing shall include a statement to the effect that no transfer of shares of common stock may be made under such plan during the lock-up period and (H) upon the earlier of: (i) the thirty-first (31st) day following the first closing date and (ii) the date on which all of the overallotment shares have been issued by us, the issuance of shares of common stock pursuant to an existing or future at the market sales programs, through which we can sell shares of common stock by means of at the market offerings from time to time.

Notwithstanding the foregoing, our executive officers and directors may transfer shares of common stock (i) by gift, or by will or intestate succession to a family member or to a trust whose beneficiaries consist exclusively of one or more of the securityholder and/or a family member, (ii) as a bona fide gift to a charity or educational institution, (iii) transfers that occur solely by operation of law pursuant to pursuant to a court order, qualified domestic order or in connection with a divorce settlement, (iv) acquired in open market transactions after the completion of the offering, provided that no filing under Section 16(a) of the Exchange Act shall be required or shall be voluntarily made in connection with subsequent sales of shares or related securities acquired in such open market transactions, (v) the transfer of shares under an existing Trading Plan, (vi) the establishment or modification of a Trading Plan for the transfer of shares or related securities, provided that such plan does not provide for any sales of shares or related securities during the lock-up period, or (vii) the transfer of shares in connection with the exercise, including by and to the extent necessary to cover any “net” or “cashless” exercise, of any options or warrants to acquire shares or the conversion of any convertible security into shares in accordance with its terms; provided, in the case of clauses (i)-(iii) above, each transferee executes and delivers an agreement stating that such transferee is receiving and holding such shares and/or related securities subject to the provisions of the lock-up agreement, in the case of clause (v) to the extent a public announcement or filing under the Exchange Act, if any, is required of or voluntarily made by or on behalf of the securityholder or us regarding such transfer, such announcement or filing shall include a statement that such transfer is in accordance with an established Trading Plan, and in the case of clauses (i)-(iii) and (vii), prior to the expiration of the lock-up period, no public disclosure or filing under the Exchange Act by any party to the transfer (donor, donee, transferor or transferee) shall be required, or made voluntarily, reporting a reduction in beneficial ownership of shares in connection with such transfer; provided that if the securityholder is required to file a report under Section 13 or Section 16(a) of the Exchange Act reporting a reduction in beneficial ownership during the lock-up period, the securityholder shall include a statement in such report detailing the reason for the transaction.

For the Company and our executive officers and directors, Jefferies, TD Securities (USA) LLC, and Piper Sandler & Co., may, in their sole discretion and at any time or from time to time before the termination of the 60-day period, release all or any portion of the securities subject to lock-up agreements. There are no existing agreements between the underwriters and any of our shareholders who will execute a lock-up agreement providing consent to the sale of shares prior to the expiration of the lock-up period.

Stabilization

The underwriters have advised us that they, pursuant to Regulation M under the Exchange Act, certain persons participating in the offering, may engage in short sale transactions, stabilizing transactions, syndicate covering transactions or the imposition of penalty bids in connection with this offering. These activities may have the effect of stabilizing or maintaining the market price of the common stock at a level above that which might otherwise prevail in the open market. Establishing short sales positions may involve either “covered” short sales or “naked” short sales.

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“Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional shares of our common stock in this offering. The underwriters may close out any covered short position by either exercising their option to purchase additional shares of our common stock or purchasing shares of our common stock in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through the option to purchase additional shares.

“Naked” short sales are sales in excess of the option to purchase additional shares of our common stock. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the shares of our common stock in the open market after pricing that could adversely affect investors who purchase in this offering.

A stabilizing bid is a bid for the purchase of shares of common stock on behalf of the underwriters for the purpose of fixing or maintaining the price of the common stock. A syndicate covering transaction is the bid for or the purchase of shares of common stock on behalf of the underwriters to reduce a short position incurred by the underwriters in connection with the offering. Similar to other purchase transactions, the underwriter’s purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. A penalty bid is an arrangement permitting the underwriters to reclaim the selling concession otherwise accruing to a syndicate member in connection with the offering if the common stock originally sold by such syndicate member are purchased in a syndicate covering transaction and therefore have not been effectively placed by such syndicate member.

Neither we, nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our common stock. The underwriters are not obligated to engage in these activities and, if commenced, any of the activities may be discontinued at any time.

The underwriters may also engage in passive market making transactions in our common stock on The Nasdaq Capital Market in accordance with Rule 103 of Regulation M during a period before the commencement of offers or sales of shares of our common stock in this offering and extending through the completion of distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security.

However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specified purchase limits are exceeded.

Electronic Distribution

A prospectus supplement in electronic format may be made available by e-mail or on the web sites or through online services maintained by one or more of the underwriters or their affiliates. In those cases, prospective investors may view offering terms online and may be allowed to place orders online. The underwriters may agree with us to allocate a specific number of shares of common stock for sale to online brokerage account holders. Any such allocation for online distributions will be made by the underwriters on the same basis as other allocations. Other than the prospectus supplement in electronic format, the information on the underwriters’ web sites and any information contained in any other web site maintained by any of the underwriters is not part of this prospectus supplement, has not been approved and/or endorsed by us or the underwriters and should not be relied upon by investors.

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Other Activities and Relationships

The underwriters and certain of its affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. The underwriters and certain of its affiliates have, from time to time, performed, and may in the future perform, various commercial and investment banking and financial advisory services for us and our affiliates, for which they received or will receive customary fees and expenses. For example, Piper Sandler & Co. is the sales agent under our ATM Sales Agreement.

In the ordinary course of their various business activities, the underwriters and certain of its affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments issued by us and our affiliates. If the underwriters or their respective affiliates have a lending relationship with us, they routinely hedge their credit exposure to us consistent with their customary risk management policies. The underwriters and their respective affiliates may hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities or the securities of our affiliates, including potentially the common stock offered hereby. Any such short positions could adversely affect future trading prices of the common stock offered hereby. The underwriters and certain of their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Notice to Prospective Investors in the European Economic Area

In relation to each Member State of the European Economic Area, or a Relevant State, no shares have been offered or will be offered pursuant to the offering to the public in that Relevant State prior to the publication of a prospectus in relation to the shares which have been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent authority in that Relevant State, all in accordance with the Prospectus Regulation, except that the shares may be offered to the public in that Relevant State at any time:

(a)	to any legal entity which is a “qualified investor” as defined under Article 2 of the Prospectus Regulation;

(b)	to fewer than 150 natural or legal persons (other than qualified investors as defined under Article 2 of the Prospectus Regulation), subject to obtaining the prior consent of representatives for any such offer; or

(c)	in any other circumstances falling within Article 1(4) of the Prospectus Regulation,

provided that no such offer of the shares shall require us or any of the representatives to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation.

For the purposes of this provision, the expression “offer to the public” in relation to the shares in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any shares to be offered so as to enable an investor to decide to purchase or subscribe for any shares, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

Notice to Prospective Investors in the United Kingdom

No shares have been offered or will be offered pursuant to the offering to the public in the United Kingdom prior to the publication of a prospectus in relation to the shares which has been approved by the Financial Conduct Authority, except that the shares may be offered to the public in the United Kingdom at any time:

(a)	to any legal entity which is a qualified investor as defined under Article 2 of the UK Prospectus Regulation;

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(b)	to fewer than 150 natural or legal persons (other than qualified investors as defined under Article 2 of the UK Prospectus Regulation), subject to obtaining the prior consent of the representatives for any such offer; or

(c)	in any other circumstances falling within Section 86 of the Financial Services and Markets Act 2000, or FSMA,

provided that no such offer of the shares shall require the Issuer or any Manager to publish a prospectus pursuant to Section 85 of the FSMA or supplement a prospectus pursuant to Article 23 of the UK Prospectus Regulation. For the purposes of this provision, the expression an “offer to the public” in relation to the shares in the United Kingdom means the communication in any form and by any means of sufficient information on the terms of the offer and any shares to be offered so as to enable an investor to decide to purchase or subscribe for any shares and the expression “UK Prospectus Regulation” means Regulation (EU) 2017/1129 as it forms part of domestic law by virtue of the European Union (Withdrawal) Act 2018.

Notice to Prospective Investors in Switzerland

The securities may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange, or SIX, or on any other stock exchange or regulated trading facility in Switzerland. This prospectus supplement has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this prospectus supplement nor any other offering or marketing material relating to the securities or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

Neither this prospectus supplement nor any other offering or marketing material relating to the offering, the Company or the securities have been or will be filed with or approved by any Swiss regulatory authority. In particular, this prospectus supplement will not be filed with, and the offer of securities will not be supervised by, the Swiss Financial Market Supervisory Authority FINMA, and the offer of securities has not been and will not be authorized under the Swiss Federal Act on Collective Investment Schemes, or CISA. The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of securities.

Notice to Prospective Investors in the Dubai International Financial Centre

This prospectus supplement relates to an “Exempt Offer” in accordance with the Offered Securities Rules of the Dubai Financial Services Authority, or DFSA. This prospectus supplement is intended for distribution only to persons of a type specified in the Offered Securities Rules of the DFSA. It must not be delivered to, or relied on by, any other person. The DFSA has no responsibility for reviewing or verifying any documents in connection with Exempt Offers. The DFSA has not approved this prospectus supplement nor taken steps to verify the information set forth herein and has no responsibility for the prospectus supplement. The shares to which this prospectus supplement relates may be illiquid and/or subject to restrictions on their resale. Prospective purchasers of the shares offered should conduct their own due diligence on the shares. If you do not understand the contents of this prospectus supplement you should consult an authorized financial advisor.

Notice to Prospective Investors in Australia

No placement document, prospectus, product disclosure statement or other disclosure document has been lodged with the Australian Securities and Investments Commission, or ASIC, in relation to the offering. This prospectus does not constitute a prospectus, product disclosure statement or other disclosure document under the Corporations Act 2001, or the Corporations Act, and does not purport to include the information required for a prospectus, product disclosure statement or other disclosure document under the Corporations Act.

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Any offer in Australia of the shares may only be made to persons, or the Exempt Investors, who are “sophisticated investors” (within the meaning of section 708(8) of the Corporations Act), “professional investors” (within the meaning of section 708(11) of the Corporations Act) or otherwise pursuant to one or more exemptions contained in section 708 of the Corporations Act so that it is lawful to offer the shares without disclosure to investors under Chapter 6D of the Corporations Act.

The shares applied for by “Exempt Investors” in Australia must not be offered for sale in Australia in the period of 12 months after the date of allotment under the offering, except in circumstances where disclosure to investors under Chapter 6D of the Corporations Act would not be required pursuant to an exemption under section 708 of the Corporations Act or otherwise or where the offer is pursuant to a disclosure document which complies with Chapter 6D of the Corporations Act. Any person acquiring shares must observe such Australian on-sale restrictions.

This prospectus contains general information only and does not take account of the investment objectives, financial situation or particular needs of any particular person. It does not contain any securities recommendations or financial product advice. Before making an investment decision, investors need to consider whether the information in this prospectus supplement is appropriate to their needs, objectives and circumstances, and, if necessary, seek expert advice on those matters.

Notice to Prospective Investors in Hong Kong

No securities have been offered or sold, and no securities may be offered or sold, in Hong Kong, by means of any document, other than to persons whose ordinary business is to buy or sell shares or debentures, whether as principal or agent; or to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong, or SFO, and any rules made under that Ordinance; or in other circumstances which do not result in the document being a “prospectus” as defined in the Companies Ordinance (Cap. 32) of Hong Kong, or CO, or which do not constitute an offer or invitation to the public for the purpose of the CO or the SFO. No document, invitation or advertisement relating to the securities has been issued or may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted under the securities laws of Hong Kong) other than with respect to securities which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the SFO and any rules made under that Ordinance.

This prospectus supplement has not been registered with the Registrar of Companies in Hong Kong. Accordingly, this prospectus supplement may not be issued, circulated or distributed in Hong Kong, and the securities may not be offered for subscription to members of the public in Hong Kong. Each person acquiring the securities will be required, and is deemed by the acquisition of the securities, to confirm that he is aware of the restriction on offers of the securities described in this prospectus supplement and the relevant offering documents and that he is not acquiring, and has not been offered any securities in circumstances that contravene any such restrictions.

Notice to Prospective Investors in Japan

The offering has not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948 of Japan, as amended), or FIEL, and the Initial Purchaser will not offer or sell any securities, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the FIEL and any other applicable laws, regulations and ministerial guidelines of Japan.

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Notice to Prospective Investors in Singapore

This prospectus supplement has not been and will not be lodged or registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares of common stock may not be circulated or distributed, nor may the notes be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the common stock are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

(a)	a corporation (which is not an accredited investor (as defined in Section 4A of the SFA)) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or

(b)	a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary of the trust is an individual who is an accredited investor,

securities (as defined in Section 239(1) of the SFA) of that corporation or the beneficiaries’ rights and interest (howsoever described) in that trust shall not be transferred within six months after that corporation or that trust has acquired the notes pursuant to an offer made under Section 275 of the SFA except:

(i)	to an institutional investor or to a relevant person defined in Section 275(2) of the SFA, or to any person arising from an offer referred to in Section 275(1A) or Section 276(4)(i)(B) of the SFA;

(ii)	where no consideration is or will be given for the transfer;

(iii)

where the transfer is by operation of law;

(iv)	as specified in Section 276(7) of the SFA; or

(v)	as specified in Regulation 32 of the Securities and Futures (Offers of Investments) (Shares and Debentures) Regulations 2005 of Singapore.

Notice to Prospective Investors in Canada

Resale Restrictions

Any resale of the shares of common stock in Canada must be made under applicable securities laws which may vary depending on the relevant jurisdiction, and which may require resales to be made under available statutory exemptions or under a discretionary exemption granted by the applicable Canadian securities regulatory authority. Purchasers are advised to seek legal advice prior to any resale of the securities.

Representations of Canadian Purchasers

By purchasing shares of common stock in Canada and accepting delivery of a purchase confirmation, a purchaser is representing to us and the dealer from whom the purchase confirmation is received that:

•

the purchaser is entitled under applicable provincial securities laws to purchase the shares of common stock without the benefit of a prospectus qualified under those securities laws as it is an “accredited investor” as defined under National Instrument 45-106 – Prospectus Exemptions,

•

the purchaser is a “permitted client” as defined in National Instrument 31-103 – Registration Requirements, Exemptions and Ongoing Registrant Obligations,

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•

where required by law, the purchaser is purchasing as principal and not as agent, and

•

the purchaser has reviewed the text above under Resale Restrictions.

Conflicts of Interest

Canadian purchasers are hereby notified that Jefferies LLC, TD Securities (USA) LLC and Piper Sandler & Co. are relying on the exemption set out in section 3A.3 or 3A.4, if applicable, of National Instrument 33-105 – Underwriting Conflicts from having to provide certain conflict of interest disclosure in this document.

Statutory Rights of Action

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if the offering memorandum (including any amendment thereto) such as this document contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser of these securities in Canada should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Enforcement of Legal Rights

All of our directors and officers as well as the experts named herein may be located outside of Canada and, as a result, it may not be possible for Canadian purchasers to effect service of process within Canada upon us or those persons. All or a substantial portion of our assets and the assets of those persons may be located outside of Canada and, as a result, it may not be possible to satisfy a judgment against us or those persons in Canada or to enforce a judgment obtained in Canadian courts against us or those persons outside of Canada.

Taxation and Eligibility for Investment

Canadian purchasers of shares of common stock should consult their own legal and tax advisors with respect to the tax consequences of an investment in the shares of common stock in their particular circumstances and about the eligibility of the shares of common stock for investment by the purchaser under relevant Canadian legislation.

Language of Documents

The purchaser confirms its express wish and that it has requested that this document, all documents evidencing or relating to the sale of the securities described herein and all other related documents be drawn up exclusively in the English language. L’acquéreur confirme sa volonté expresse et qu’il a demandé que le présent document, tous les documents attestant de la vente des titres décrits dans le présent document ou s’y rapportant ainsi que tous les autres documents s’y rattachant soient rédigés exclusivement en langue anglaise.

Notice to Prospective Investors in Israel

This document does not constitute a prospectus under the Israeli Securities Law, 5728-1968, or the Securities Law, and has not been filed with or approved by the Israel Securities Authority. In Israel, this prospectus is being distributed only to, and is directed only at, and any offer of the shares of common stock is directed only at, (i) a limited number of persons in accordance with the Israeli Securities Law and (ii) investors listed in the first addendum, or the Addendum, to the Israeli Securities Law, consisting primarily of joint investment in trust funds, provident funds, insurance companies, banks, portfolio managers, investment advisors, members of the Tel Aviv Stock Exchange, underwriters, venture capital funds, entities with equity in excess of NIS 50 million and “qualified individuals,” each as defined in the Addendum (as it may be amended from time to time), collectively referred to as qualified investors (in each case, purchasing for their own account or, where permitted under the Addendum, for the accounts of their clients who are investors listed in the Addendum). Qualified investors are required to submit written confirmation that they fall within the scope of the Addendum, are aware of the meaning of same and agree to it.

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LEGAL MATTERS

Goodwin Procter LLP, Redwood City, California, which has acted as our counsel in connection with this offering, will pass upon the validity of the securities offered hereby. Lowenstein Sandler LLP, New York, New York, has acted as counsel to the underwriters in connection with this offering.

EXPERTS

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2025, as set forth in their report, which is incorporated by reference in this prospectus supplement and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus supplement is part of a registration statement that we have filed with the SEC. Certain information in the registration statement has been omitted from this prospectus supplement in accordance with the rules of the SEC. We are subject to the information requirements of the Exchange Act and, in accordance therewith, file annual, quarterly and special reports, proxy statements and other information with the SEC. These documents also may be accessed through the SEC’s electronic data gathering, analysis and retrieval system, or EDGAR, via electronic means, including the SEC’s home page on the Internet (www.sec.gov). You may also inspect the registration statement and this prospectus supplement on this website.

Our website is located at https://nektar.com. Information contained on our website is not incorporated by reference into this prospectus, and, except for the documents incorporated by reference as noted below, you should not consider any information on, or that can be accessed from, our website as part of this prospectus supplement.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to incorporate by reference the information and reports we file with it, which means that we can disclose important information to you by referring you to these documents. The information incorporated by reference is an important part of this prospectus supplement, and information that we file after the date hereof with the SEC will automatically update and supersede the information already incorporated by reference. We are incorporating by reference the documents listed below, which we have already filed with the SEC, and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, except as to any portion of any future report or document that is not deemed filed under such provisions, after the date of this prospectus supplement and prior to the termination of this offering:

•

Our Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with the SEC on March 13, 2026;

•

Our Current Reports on Form 8-K, filed with the SEC on February 10, 2026 (solely with respect to Item 8.01), February 13, 2026, and April 20, 2026 (solely with respect to Item 8.01); and

•

the description of our Common Stock, which is registered under Section 12 of the Exchange Act, contained in Exhibit 4.4 to our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, filed with the SEC on February 28, 2020, including any amendments or reports filed for the purpose of updating such description.

Pursuant to Rule 412 under the Securities Act, any statement contained in a document incorporated or deemed to be incorporated by reference into this prospectus supplement will be deemed to be modified or superseded for purposes of this prospectus supplement to the extent that a statement contained in this prospectus supplement or any other subsequently filed document that is deemed to be incorporated by reference into this prospectus supplement modifies or supersedes the statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement.

Upon request, we will provide, without charge, to each person, including any beneficial owner, to whom a copy of this prospectus supplement is delivered, a copy of the documents incorporated by reference into this prospectus supplement but not delivered with the prospectus supplement. You may request a copy of these filings, and any exhibits we have specifically incorporated by reference as an exhibit in this prospectus supplement, at no cost by writing us at the following address: Nektar Therapeutics, 455 Mission Bay Boulevard South, San Francisco, CA 94158, Attention: Secretary or by telephone by calling (415) 482-5300. Our website is located at https://nektar.com. The reference to our website is intended to be an inactive textual reference and, except for the documents incorporated by reference as noted above, the information on, or accessible through, our website is not intended to be part of this prospectus supplement.

You should rely only on the information incorporated by reference or provided in this prospectus supplement. We have not authorized anyone else to provide you with different information. You should not assume that the information in this prospectus supplement or in the documents incorporated by reference is accurate as of any date other than the date on the front of this prospectus supplement or those documents. Nothing in this prospectus supplement shall be deemed to incorporate information furnished but not filed with the SEC pursuant to Item 2.02 or Item 7.01 of Form 8-K.

We advise that there have been no material changes in our affairs that have occurred since the end of the latest fiscal period for which audited financial statements were included in the latest Form 10-K and that have not been described in a Form 10-Q or Form 8-K filed under the Exchange Act.

This prospectus supplement is part of a registration statement we filed with the SEC. We have incorporated exhibits into this registration statement. You should read the exhibits carefully for provisions that may be important to you.

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PROSPECTUS

Nektar Therapeutics

LOGO

Common Stock

Preferred Stock

Debt Securities

Warrants

Units

From time to time, we may offer and sell our Common Stock, Preferred Stock, Debt Securities, Warrants or Units, in each case in one or more issuances and at prices and on terms that we will determine at the time of the offering.

This prospectus describes the general manner in which any of these securities may be offered using this prospectus. We will specify in an accompanying prospectus supplement the terms of the securities offered and other details regarding the offering thereof.

Our common stock is listed on the Nasdaq Capital Market under the symbol “NKTR.” On November 10, 2025, the closing price for our common stock, as reported on the Nasdaq Capital Market, was $57.97 per share.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” on page 6 of this prospectus (and any applicable prospectus supplement) and under any similar heading in the documents that are incorporated by reference into this prospectus, as well as “Special Note Regarding Forward-Looking Statements” on page 3 of this prospectus. You should read the entire prospectus carefully before you make your investment decision.

We are a smaller reporting company as defined under federal securities laws and, as such, may elect to comply with certain reduced public company reporting requirements for future filings.

The securities covered by this prospectus may be sold directly by us to investors, through agents designated by us from time to time or through underwriters or dealers at prices and on terms to be determined at the time of offering. We will include in an applicable prospectus supplement the names of any underwriters or agents and any applicable commissions or discounts. Additional information on the methods of sale appears under “Plan of Distribution” in this prospectus. We will also describe in an applicable prospectus supplement the way(s) in which we expect to use the net proceeds we receive from any sale.

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

This prospectus may not be used to offer or sell any securities unless accompanied by a prospectus supplement.

The date of this prospectus is November 12, 2025.

Table of Contents


	Page

ABOUT THIS PROSPECTUS		1
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		3
ABOUT THE COMPANY		4
RISK FACTORS		6
USE OF PROCEEDS		7
DIVIDEND POLICY		8
GENERAL DESCRIPTION OF SECURITIES		9
DESCRIPTION OF CAPITAL STOCK		10
DESCRIPTION OF DEBT SECURITIES		15
DESCRIPTION OF WARRANTS		22
DESCRIPTION OF UNITS		23
PLAN OF DISTRIBUTION		26
LEGAL MATTERS		29
EXPERTS		29
WHERE YOU CAN FIND MORE INFORMATION		29
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE		30

ABOUT THIS PROSPECTUS

This prospectus is part of an automatic shelf registration statement that we have filed with the Securities and Exchange Commission, or the SEC, as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended, or the Securities Act.

Under the shelf registration process, we may from time to time sell any combination of the securities described in this prospectus in one or more offerings as described in this prospectus. This prospectus describes the general manner in which we may offer the securities described in this prospectus. Each time we sell securities pursuant to the registration statement we will provide a prospectus supplement that will contain specific information about the offering and the securities offered, and may also add, update or change information contained in this prospectus. If there is any inconsistency between information in this prospectus and any accompanying prospectus supplement, you should rely on the information in the most recent applicable prospectus supplement and documents incorporated by reference herein and therein. This prospectus may not be used to offer to sell, solicit an offer to buy or consummate a sale of our securities unless it is accompanied by a prospectus supplement.

This prospectus, together with any accompanying prospectus supplement, contains important information you should know before investing in our securities, including important information about us and the securities being offered. You should carefully read both documents, as well as the additional information contained in the documents described under “Where You Can Find More Information” and “Incorporation of Certain Information by Reference” in both this prospectus and the applicable prospectus supplement, and in particular the annual, quarterly and current reports and other documents we file with the SEC. Neither this prospectus nor any accompanying prospectus supplement is an offer to sell these securities or is soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

You should rely only on the information contained or incorporated by reference in this prospectus and in an applicable prospectus supplement to this prospectus. We have not authorized any other person to provide you with different or additional information. If anyone provides you with different, additional or inconsistent information, you should not rely on it. We do not take responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are not making an offer to sell these securities or soliciting any offer to buy these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus, any applicable prospectus supplement or any free writing prospectus we authorize to be delivered to you is accurate only as of the date of that document or any other date set forth in that document. Additionally, any information we have incorporated by reference in this prospectus or in any applicable prospectus supplement is accurate only as of the date of the document incorporated by reference or other date set forth in that document, regardless of the time of delivery of this prospectus, any applicable prospectus supplement or any sale of securities. Our business, financial condition, results of operations, cash flow and prospects may have changed since that date.

This prospectus, any applicable prospectus supplement and the information incorporated herein or therein by reference contains market data, industry statistics and other data that have been obtained or compiled from information made available by independent third parties. We have not independently verified the accuracy and completeness of such data. This prospectus, any applicable prospectus supplement and the information incorporated herein or therein by reference include trademarks, service marks and trade names owned by us or other companies. Solely for convenience, we may refer to our trademarks included or incorporated by reference in this prospectus, any applicable prospectus supplement or any free writing prospectus without the TM or ^® symbols, but any such references are not intended to indicate that we will not assert, to the fullest extent permitted under applicable law, our rights to our trademarks or other intellectual property. All trademarks, service marks and trade names included or incorporated by reference in this prospectus, any applicable prospectus supplement or any related free writing prospectus are the property of their respective owners.

When used in this prospectus, the terms “Nektar,” “we,” “our” and “us” refer to Nektar Therapeutics, a Delaware corporation, unless otherwise specified or the context otherwise requires.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, together with any accompanying prospectus supplement, includes and incorporates by reference “forward-looking statements” within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act. All statements other than statements of historical fact are “forward-looking statements” for purposes of this prospectus, including any financial projections, any statements of the plans and objectives of management for future operations, any statements related to our financial condition and future working capital needs, any statements regarding potential future financing alternatives, any statements concerning proposed drug candidates and our future research and development plans, any statements regarding the timing for the start or end of clinical trials or submission of regulatory approval filings, any statements regarding future economic conditions or performance, any statements regarding the initiation, formation, or success of our collaboration arrangements, any statements regarding future payments that may come due to us, any statements regarding our plans and objectives to initiate or continue clinical trials and any statements of assumptions underlying any of the foregoing. In some cases, forward-looking statements can be identified by the use of terminology such as “believe,” “may,” “will,” “expects,” “plans,” “anticipates,” “estimates,” “potential” or “continue,” or the negative thereof or other comparable terminology. Although we believe that the expectations reflected in the forward-looking statements contained herein are reasonable, such expectations or any of the forward-looking statements may prove to be incorrect and actual results could differ materially from those projected or assumed in the forward-looking statements. Our future financial condition and results of operations, as well as any forward-looking statements, are subject to inherent risks and uncertainties, including, but not limited to, those described under “Risk Factors” in this prospectus, any applicable prospectus supplement and any related free writing prospectus, and in any other documents incorporated herein or therein (including in our most recent annual report on Form 10-K, subsequent quarterly reports on Form 10-Q and other filings we make with the SEC pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act). All forward-looking statements and reasons why results may differ included in this prospectus are made as of the date hereof and we do not intend to update any forward-looking statements except as required by law or applicable regulations.

ABOUT THE COMPANY

The following highlights information about us and our business contained elsewhere or incorporated by reference in this prospectus. It is not complete and does not contain all of the information that you should consider before investing in any of our securities. You should carefully read this prospectus together with the more detailed information incorporated by reference in this prospectus. Unless the context otherwise requires, references in this prospectus to “Nektar,” “the company,” “we,” “us,” and “our” refer to Nektar Therapeutics.

Overview

Our Drug Candidates and Pipeline

Autoimmune diseases

We recognize that many autoimmune diseases are caused by an imbalance in the body’s immune system. A failure of the body’s self-tolerance mechanisms enables the formation of pathogenic T cells that cause the immune system to mistakenly attack and damage healthy cells in a person’s body. Current systemic treatments for autoimmune diseases, including corticosteroids and anti-TNF agents, suppress the immune system broadly and come with severe side effects. Pharmaceutical agents designed to rebalance the immune system by increasing the function of regulatory T cells (Treg cells), powerful inhibitory immune cells, could be used to treat patients suffering from autoimmune disorders and inflammatory diseases.

Rezpegaldesleukin

Our drug candidate rezpegaldesleukin is a potential first-in-class resolution therapeutic that may address this underlying immune system imbalance in people with autoimmune disorders and inflammatory diseases. It is designed to target the interleukin-2 (IL-2) receptor complex in the body in order to stimulate proliferation of Treg cells. By activating these cells, rezpegaldesleukin may act to bring the immune system back into balance. Rezpegaldesleukin is being developed as a once or twice monthly self-administered injection for a number of autoimmune disorders and inflammatory diseases.

NKTR-0165

We believe that our preclinical tumor necrosis factor (TNF) receptor type II (TNFR2) agonist asset is a potentially unique bivalent antibody that selectively stimulates TNFR2 receptor activity, without modulation of the TNFR1 signaling. TNFR2 signaling drives immunoregulatory function and can provide a direct protective

effect for tissue cells. TNFR2 is highly expressed on Tregs, neuronal cells and endothelial cells and has been shown to potentiate the suppressive effects and overall functional properties of Tregs. Our focus is on TNFR2 antibody candidates that show selective Treg cell binding and signaling profiles that may be potentially developed for treatment of autoimmune diseases, such as ulcerative colitis, multiple sclerosis and vitiligo. We are currently conducting Investigational New Drug (IND) enabling studies for this program, after having exercised an option to gain an exclusive license to specified agonistic antibodies and other materials that were developed pursuant to a research collaboration and license option agreement we entered into with Biolojic Design, Ltd. in 2021, with the goal of preparing for a future IND submission.

Oncology

NKTR-255

In oncology, we focus on developing medicines based on targeting biological pathways that stimulate and sustain the body’s immune response in order to fight cancer. NKTR-255 is an investigational biologic that is designed to target the interleukin-15 (IL-15) pathway in order to activate the body’s innate and adaptive immunity.

Activation of the IL-15 pathway enhances the survival and function of natural killer (NK) cells and induces survival of both effector and CD8+ memory T cells. Recombinant human IL-15 is rapidly cleared from the body and must be administered frequently and in high doses limiting its utility due to toxicity. Through optimal engagement of the IL-15 receptor complex, NKTR-255 is designed to enhance functional NK cell populations and the formation of long-term immunological memory, which may lead to sustained and durable anti-tumor immune response.

Corporate History and Information

We were incorporated in California in 1990 and reincorporated in Delaware in 1998. Our principal corporate office is located at 455 Mission Bay Boulevard South, San Francisco, California 94158, and our telephone number is (415) 482-5300. Our website address is https://nektar.com. We do not incorporate the information on or accessible through our website into this prospectus, and you should not consider any information on, or that can be accessed through, our website a part of this prospectus or incorporated by reference herein. For further information regarding us and our financial information, you should refer to our recent filings with the SEC. See “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

Implications of Being a Smaller Reporting Company

RISK FACTORS

Investing in our securities involves certain risks. Before you invest in any of our common stock, preferred stock, debt securities, warrants or any combination thereof, in addition to the other information included in, or incorporated by reference into, this prospectus, you should carefully consider the risk factors contained in Item 1A under the caption “Risk Factors” and elsewhere in our annual report on Form 10-K for the period ended December 31, 2024, which is incorporated into this prospectus by reference, as updated by our annual or quarterly reports for subsequent fiscal years or fiscal quarters that we file with the SEC and that are so incorporated. See “Where You Can Find More Information” for information about how to obtain a copy of these documents. You should also carefully consider the risks and other information that may be contained in, or incorporated by reference into, any prospectus supplement relating to specific offerings of securities.

USE OF PROCEEDS

Unless otherwise described in the applicable prospectus supplement, we intend to use the net proceeds from the sale of any securities described in this prospectus for general corporate purposes, which may include research and development and clinical development costs to support the advancement of our drug candidates, including conducting pre-clinical studies and clinical trials, as applicable, for rezpegaldesleukin, NKTR-0165 and NKTR-255; working capital; capital expenditures; general and administrative expenses; and other general corporate purposes. We may also use net proceeds to fund potential acquisitions of, or investments in, complementary businesses, products, services and technologies. We have not entered into any agreements or commitments with respect to any material acquisitions or investments at this time.

We may set forth additional information concerning our expected use of net proceeds from sales of securities in the applicable prospectus supplement relating to the specific offering. Pending use of net proceeds as described above, we may temporarily invest the net proceeds in a variety of capital preservation instruments, including high quality, investment grade instruments, certificates of deposit or direct or guaranteed obligations of the U.S. government, or may hold such proceeds as cash, until they are used for their stated purpose. We have not determined the amount of net proceeds to be used specifically for such purposes. As a result, management will retain broad discretion over the allocation of net proceeds.

DIVIDEND POLICY

GENERAL DESCRIPTION OF SECURITIES

We may offer shares of common or preferred stock, various series of senior or subordinated debt securities, warrants, or units consisting of combinations of the foregoing, in each case from time to time under this prospectus, together with the applicable prospectus supplement, at prices and on terms to be determined by market conditions at the time of offering. This prospectus provides you with a general description of the securities we may offer. At the time we offer a particular type or series of securities, we will provide an applicable prospectus supplement describing the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

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designation or classification;

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aggregate principal amount or aggregate offering price;

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voting or other rights;

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rates and times of payment of interest, dividends or other payments;

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liquidation preference;

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original issue discount;

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maturity;

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ranking;

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restrictive covenants;

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redemption, conversion, exercise, exchange, settlement or sinking fund terms, including prices or rates, and any provisions for changes to or adjustments in such prices or rates and in the securities or other property receivable upon conversion, exercise, exchange or settlement;

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any securities exchange or market listing arrangements; and

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important U.S. federal income tax considerations.

This prospectus may not be used to offer or sell securities unless accompanied by an applicable prospectus supplement. The applicable prospectus supplement may add, update or change information contained in this prospectus or in documents incorporated by reference in this prospectus. You should read the prospectus supplement related to any securities being offered.

We may sell the securities directly to or through underwriters, dealers or agents. We and our underwriters, dealers or agents reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities through underwriters or agents, we will include in the applicable prospectus supplement (i) the names of the underwriters or agents and applicable fees, discounts and commissions to be paid to them; (ii) details regarding over-allotment options, if any; and (iii) net proceeds to us.

The following descriptions are not complete and may not contain all the information you should consider before investing in any securities we may offer hereunder; such descriptions are summarized from, and qualified by reference to, our amended and restated certificate of incorporation, our amended and restated bylaws and the other documents referred to in the descriptions, all of which are or will be publicly filed with the SEC, as applicable. See “Where You Can Find More Information.”

DESCRIPTION OF CAPITAL STOCK

The following summary description of our common stock and preferred stock, together with the additional information we include in any applicable prospectus supplements, summarizes the material terms and provisions of our capital stock. The following description of our capital stock does not purport to be complete and is subject to, and qualified in its entirety by, our amended and restated certificate of incorporation and amended and restated bylaws, which are exhibits to the registration statement of which this prospectus forms a part, and by applicable law. The terms of our common stock and preferred stock may also be affected by Delaware law.

General

Our authorized capital stock consists of 390,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share, all of which are undesignated. As of November 10, 2025, we had 20,341,589 shares of common stock outstanding and no shares of preferred stock outstanding.

Common Stock

The holders of common stock are entitled to one vote for each share held of record on all matters submitted to a vote of the stockholders. Directors are elected by a plurality vote and the holders of common stock are not entitled to cumulative voting rights with respect to the election of directors. Accordingly, holders of a majority of the voting stock are able to elect all of the directors.

Subject to preferences that may be applicable to any shares of preferred stock currently outstanding or issued in the future, holders of common stock are entitled to receive ratably such dividends as may be declared by our board of directors out of funds legally available therefor. In the event of our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preference of any then outstanding preferred stock. Holders of common stock have no preemptive rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to the common stock. All outstanding shares of common stock are fully paid and non-assessable.

Exchange Listing

Our common stock is listed on Nasdaq under the symbol “NKTR.” On November 10, 2025, the closing price for our common stock, as reported on Nasdaq, was $57.97 per share. As of November 10, 2025, we had approximately 136 stockholders of record.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A.

Preferred Stock

Undesignated Preferred Stock

Our board of directors has the authority, without further vote or action by the stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series and to fix, by filing a certificate of designation pursuant to the Delaware General Corporation Law, or the DGCL, the rights, preferences, privileges and restrictions thereof, including dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of such series. We will incorporate by reference as an exhibit to the registration statement, which includes this prospectus, the form of any certificate of designation that describes the terms of any series of preferred stock we may offer pursuant to this prospectus.

The DGCL provides that the holders of preferred stock will have the right to vote separately as a class on a proposed amendment to our certificate of incorporation involving certain fundamental changes in the rights of holders of that preferred stock. This right is in addition to any voting rights that may be provided in the applicable certificate of designation. The issuance of preferred stock could adversely affect the voting power, conversion rights or other rights of holders of common stock and reduce the likelihood that holders of common stock will receive dividend payments and payments upon liquidation. Issuance of preferred stock could delay or prevent a change in control of our company or make removal of management more difficult. Additionally, the issuance of preferred stock could have the effect of decreasing the market price of our common stock. The rights of holders of our common stock described above will be subject to, and may be adversely affected by, the rights of any preferred stock that we may designate and issue in the future.

The existence of authorized but unissued shares of undesignated preferred stock may enable our board of directors to render more difficult or to discourage an attempt to obtain control of us by means of a merger, tender offer, proxy contest or otherwise. For example, if in the due exercise of its fiduciary obligations, our board of directors were to determine that a takeover proposal is not in the best interests of us or our stockholders, our board of directors could cause shares of preferred stock to be issued without stockholder approval in one or more private offerings or other transactions that might dilute the voting or other rights of the proposed acquirer, stockholder or stockholder group.

Authorized but Unissued Capital Stock

The DGCL does not require stockholder approval for any issuance of authorized shares. However, the listing requirements of Nasdaq, which would apply so long as our common stock remains listed on Nasdaq, require stockholder approval of certain issuances equal to or exceeding 20% of the then outstanding voting power or then outstanding number of shares of common stock. These additional shares may be used for a variety of corporate purposes, including for future public offerings, to raise additional capital or to facilitate acquisitions. Issuance of unissued and unreserved common stock or preferred stock may render more difficult or discourage an attempt to obtain control of our company by means of a merger, tender offer, proxy contest or otherwise.

Anti-Takeover Effects of Provisions of Delaware Law and Our Certificate of Incorporation and Bylaws

Certain provisions of the DGCL and of our certificate of incorporation and bylaws could have the effect of delaying, deferring or discouraging another party from acquiring control of us. These provisions, which are summarized below, are expected to discourage certain types of coercive takeover practices and inadequate takeover bids and, as a consequence, they might also inhibit temporary fluctuations in the market price of our common stock that often result from actual or rumored hostile takeover attempts. These provisions are also designed in part to encourage anyone seeking to acquire control of us to first negotiate with our board of directors. These provisions might also have the effect of preventing changes in our management. It is possible that these provisions could make it more difficult to accomplish transactions that stockholders might otherwise deem to be in their best interests. However, we believe that the advantages gained by protecting our ability to negotiate with any unsolicited and potentially unfriendly acquirer outweigh the disadvantages of discouraging such proposals, including those priced above the then-current market value of our common stock, because, among other reasons, the negotiation of such proposals could improve their terms.

Delaware Takeover Statute

We are subject to the provisions of Section 203 of the DGCL, or Section 203. In general, Section 203 prohibits a publicly held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a three-year period following the time that this stockholder becomes an interested stockholder, unless the business combination is approved in a prescribed manner. Under Section 203, a business combination

between a corporation and an interested stockholder is prohibited unless it satisfies one of the following conditions:

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before the stockholder became interested, our board of directors approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder;

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upon consummation of the transaction which resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the voting stock outstanding, shares owned by persons who are directors and also officers, and employee stock plans, in some instances, but not the outstanding voting stock owned by the interested stockholder; or

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at or after the time the stockholder became interested, the business combination was approved by our board of directors and authorized at an annual or special meeting of the stockholders by the affirmative vote of at least two-thirds of the outstanding voting stock which is not owned by the interested stockholder.

Section 203 defines a business combination to include:

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any merger or consolidation involving the corporation and the interested stockholder;

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any sale, transfer, lease, pledge, exchange, mortgage or other disposition involving the interested stockholder of 10% or more of the assets of the corporation;

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subject to exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;

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subject to exceptions, any transaction involving the corporation that has the effect of increasing the proportionate share of the stock of any class or series of the corporation beneficially owned by the interested stockholder; or

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the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits provided by or through the corporation.

In general, Section 203 defines an interested stockholder as any entity or person beneficially owning 15% or more of the outstanding voting stock of the corporation and any entity or person affiliated with or controlling or controlled by the entity or person.

Provisions of Our Certificate of Incorporation and Bylaws

Our certificate of incorporation provides for our board of directors to be divided into three classes, with staggered three-year terms. As a result, only one class of directors will be elected at each annual meeting of stockholders, with the other classes continuing for the remainder of their respective three-year terms. Stockholders have no cumulative voting rights. Subject to the rights of the holders of any outstanding series of preferred stock, directors may not be removed without cause. Any vacancies on the board of directors shall be filled by the affirmative vote of a majority of the directors then in office, unless the board of directors otherwise determines that the vacancy shall be filled by stockholders entitled to vote for directors.

Our certificate of incorporation also requires that any action required or permitted to be taken by our stockholders must be effected at a duly called annual or special meeting of the stockholders and may not be effected by a consent in writing. This limit may lengthen the amount of time required to take stockholder actions and would prevent the amendment of our bylaws or removal of directors by our stockholder without holding a meeting of stockholders. The stockholders may amend our bylaws, or adopt new bylaws, and may amend certain provisions of our certificate of incorporation, including the provisions related to stockholder actions and the calling of special meetings of stockholders, only by the affirmative vote of the holders of 66.67% of the voting power of all of the outstanding shares of the voting stock of our company entitled to vote at an election of directors. These provisions may have the effect of delaying, deferring or preventing a change in control of our company.

The classification of our board of directors and lack of cumulative voting may make it more difficult for our existing stockholders to replace our board of directors or for another party to obtain control of us by replacing our board of directors. Since our board of directors has the power to retain and discharge our officers, these provisions could also make it more difficult for existing stockholders or another party to effect a change in management. These and other provisions may have the effect of deterring hostile takeovers or delaying changes in control or management. These provisions are intended to enhance the likelihood of continued stability in the composition of our board of directors and in the policies of our board of directors and to discourage certain types of transactions that may involve an actual or threatened change in control. These provisions are designed to reduce our vulnerability to an unsolicited acquisition proposal and to discourage certain tactics that may be used to replace our board of directors. However, such provisions could have the effect of discouraging others from making tender offers for our shares and, as a consequence, such provisions also may inhibit increases in the market price of our shares that could result from actual or rumored takeover attempts.

Our bylaws establish advance notice procedures with regard to stockholder proposals relating to the nomination of candidates for election as directors or new business to be brought before meetings of our stockholders. These procedures provide that notice of stockholder proposals must be timely given in writing to our secretary prior to the meeting at which the action is to be taken. Generally, to be timely, notice must be received at our principal executive offices not less than the close of business on the 60th day nor earlier than the close of business on the 90th day prior to the first anniversary of the annual meeting for the preceding year. The notice must contain certain information specified in the bylaws. These provisions may have the effect of precluding the conduct of certain business at a meeting if the proper procedures are not followed. These provisions may also discourage or deter a potential acquirer from conducting a solicitation of proxies to elect the acquirer’s own slate of directors or otherwise attempting to obtain control of our company.

Our bylaws provide that, unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware, or, if the Court of Chancery of the State of Delaware does not have jurisdiction, the Superior Court of the State of Delaware, or, if the Superior Court of the State of Delaware does not have jurisdiction, the United States District Court for the District of Delaware will be the sole and exclusive forum for any state law claim for: (1) any derivative action or proceeding brought on behalf of our company, (2) any action asserting a claim of breach of a fiduciary duty owed by any director, officer or other employee of our company to us or to our stockholders, (3) any action asserting a claim arising pursuant to any provision of the DGCL, our certificate of incorporation or our bylaws, (4) any action to interpret, apply, enforce or determine the validity of our certificate of incorporation or our bylaws or (5) any action asserting a claim governed by the internal affairs doctrine. The choice of forum provision does not apply to any actions arising under the Securities Act or the Exchange Act.

Our certificate of incorporation also contains provisions that limit the liability of our directors for monetary damages to the fullest extent permitted by Delaware law. Consequently, our directors will not be personally liable to us or our stockholders for monetary damages for any breach of fiduciary duties as directors, except liability for:

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any breach of the director’s duty of loyalty to us or our stockholders;

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any act or omission not in good faith or that involves intentional misconduct or a knowing violation of law;

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unlawful payments of dividends or unlawful stock repurchases or redemptions as provided in Section 174 of the DGCL; or

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any transaction from which the director derived an improper personal benefit.

Each of our certificate of incorporation and bylaws provides that we are required to indemnify our directors and officers, in each case to the fullest extent permitted by Delaware law. Our bylaws also obligate us to advance expenses incurred by a director or officer in advance of the final disposition of any action or proceeding, and

permit us to secure insurance on behalf of any officer, director, employee or other agent for any liability arising out of such person’s actions in that capacity regardless of whether we would otherwise be permitted to indemnify such person under Delaware law. We have entered into agreements to indemnify our directors, executive officers and other employees as determined by our board of directors. With specified exceptions, these agreements provide for indemnification for related expenses including, among other things, attorneys’ fees, judgments, fines and settlement amounts incurred by any of these individuals in any action or proceeding. We believe that these bylaw provisions and indemnification agreements are necessary to attract and retain qualified persons as directors and officers. We also maintain directors’ and officers’ liability insurance. The limitation of liability and indemnification provisions in our certificate of incorporation and bylaws may discourage stockholders from bringing a lawsuit against our directors and officers for breach of their fiduciary duty. They may also reduce the likelihood of derivative litigation against our directors and officers, even though an action, if successful, might benefit us and our stockholders. Further, a stockholder’s investment may be adversely affected to the extent that we pay the costs of settlement and damage.

DESCRIPTION OF DEBT SECURITIES

This section describes the general terms and provisions of our debt securities that we may issue from time to time. We may issue debt securities, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any future debt securities we may offer under this prospectus, the applicable prospectus supplement or free writing prospectus will describe the specific terms of any debt securities offered through that prospectus supplement or free writing prospectus. The terms of any debt securities we offer under a prospectus supplement or free writing prospectus may differ from the terms we describe below. Unless the context requires otherwise, whenever we refer to the “indentures,” we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue any senior debt securities under the senior indenture that we will enter into with the trustee named in the senior indenture. We will issue any subordinated debt securities under the subordinated indenture that we will enter into with the trustee named in the subordinated indenture. We have filed forms of these documents as exhibits to the registration statement, of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The indentures will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We use the term “trustee” to refer to either the trustee under the senior indenture or the trustee under the subordinated indenture, as applicable.

The following summaries of material provisions of the senior debt securities, the subordinated debt securities and the indentures are subject to, and qualified in their entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplement or free writing prospectus and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete applicable indenture that contains the terms of the debt securities. Except as we may otherwise indicate, the terms of the senior indenture and the subordinated indenture are identical.

General

We will describe in the applicable prospectus supplement or free writing prospectus the terms of the series of debt securities being offered, including:

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the title;

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the principal amount being offered, and if a series, the total amount authorized and the total amount outstanding;

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any limit on the amount that may be issued;

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whether or not we will issue the series of debt securities in global form, and, if so, the terms and who the depository will be;

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the maturity date;

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whether and under what circumstances, if any, we will pay additional amounts on any debt securities held by a person who is not a United States person for tax purposes, and whether we can redeem the debt securities if we have to pay such additional amounts;

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the annual interest rate, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

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whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

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the terms of the subordination of any series of subordinated debt;

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the place where payments will be payable;

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restrictions on transfer, sale or other assignment, if any;

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our right, if any, to defer payment of interest and the maximum length of any such deferral period;

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the date, if any, after which, the conditions upon which, and the price at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

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the date, if any, on which, and the price at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option, to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

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whether the indenture will restrict our ability to:

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incur additional indebtedness;

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issue additional securities;

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create liens;

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pay dividends or make distributions in respect of our capital stock or the capital stock;

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redeem capital stock;

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make investments or other restricted payments;

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sell or otherwise dispose of assets;

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enter into sale-leaseback transactions;

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engage in transactions with stockholders or affiliates; or

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effect a consolidation or merger.

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whether the indenture will require us to maintain any interest coverage, fixed charge, cash flow-based, asset-based or other financial ratios;

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a discussion of certain material or special United States federal income tax considerations applicable to the debt securities;

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information describing any book-entry features;

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provisions for a sinking fund purchase or other analogous fund, if any;

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the applicability of the provisions in the indenture on discharge;

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whether the debt securities are to be offered at a price such that they will be deemed to be offered at an “original issue discount” as defined in paragraph (a) of Section 1273 of the Internal Revenue Code of 1986, as amended;

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the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

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the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars; and

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any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, including any additional events of default or covenants provided with respect to the debt securities, and any terms that may be required by us or advisable under applicable laws or regulations or advisable in connection with the marketing of the debt securities.

Conversion or Exchange Rights

We will set forth in the applicable prospectus supplement or free writing prospectus the terms on which a series of debt securities may be convertible into or exchangeable for our common stock, our preferred stock or other securities (including securities of a third-party). We will include provisions as to whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock, our preferred stock or other securities (including securities of a third- party) that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, the indentures will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of all or substantially all of our assets. However, any successor to or acquirer of such assets must assume all of our obligations under the indentures or the debt securities, as appropriate. If the debt securities are convertible into or exchangeable for other securities of ours or securities of other entities, the person with whom we consolidate or merge or to whom we sell all or substantially all of our property must make provisions for the conversion of the debt securities into securities that the holders of the debt securities would have received if they had converted the debt securities before the consolidation, merger or sale.

Events of Default Under the Indenture

Unless we provide otherwise in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, the following are events of default under the indentures with respect to any series of debt securities that we may issue:

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if we fail to pay interest when due and payable and our failure continues for 90 days and the time for payment has not been extended;

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if we fail to pay the principal, premium or sinking fund payment, if any, when due and payable at maturity, upon redemption or repurchase or otherwise, and the time for payment has not been extended;

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if we fail to observe or perform any other covenant contained in the debt securities or the indentures, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive notice from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

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if specified events of bankruptcy, insolvency or reorganization occur.

We will describe in each applicable prospectus supplement or free writing prospectus any additional events of default relating to the relevant series of debt securities.

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the unpaid principal, premium, if any, and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indentures, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity or security satisfactory to it against any loss, liability or expense. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

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the direction so given by the holder is not in conflict with any law or the applicable indenture; and

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subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

A holder of the debt securities of any series will have the right to institute a proceeding under the indentures or to appoint a receiver or trustee, or to seek other remedies if:

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the holder has given written notice to the trustee of a continuing event of default with respect to that series;

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the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request, and such holders have offered reasonable indemnity to the trustee or security satisfactory to it against any loss, liability or expense or to be incurred in compliance with instituting the proceeding as trustee; and

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the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities, or other defaults that may be specified in the applicable prospectus supplement or free writing prospectus.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indentures.

Modification of Indenture; Waiver

Subject to the terms of the indenture for any series of debt securities that we may issue, we and the trustee may change an indenture without the consent of any holders with respect to the following specific matters:

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to fix any ambiguity, defect or inconsistency in the indenture;

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to comply with the provisions described above under “Description of Debt Securities-Consolidation, Merger or Sale;”

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to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act;

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to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

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to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided under “Description of Debt Securities-General,” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

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to evidence and provide for the acceptance of appointment hereunder by a successor trustee;

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to provide for uncertificated debt securities and to make all appropriate changes for such purpose;

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to add to our covenants such new covenants, restrictions, conditions or provisions for the benefit of the holders, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred to us in the indenture; or

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to change anything that does not materially adversely affect the interests of any holder of debt securities of any series.

In addition, under the indentures, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, subject to the terms of the indenture for any series of debt securities that we may issue or as otherwise provided in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

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extending the stated maturity of the series of debt securities;

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reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption or repurchase of any debt securities; or

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reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Discharge

Each indenture provides that, subject to the terms of the indenture and any limitation otherwise provided in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

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replace stolen, lost or mutilated debt securities of the series;

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maintain paying agencies;

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hold monies for payment in trust;

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recover excess money held by the trustee;

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compensate and indemnify the trustee; and

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appoint any successor trustee.

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of and any premium and interest on the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we otherwise specify in the applicable prospectus supplement or free writing prospectus, in denominations of $1,000 and any integral multiple thereof. The indentures provide that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company or another depository named by us and identified in a prospectus supplement or free writing prospectus with respect to that series.

At the option of the holder, subject to the terms of the indentures and the limitations applicable to global securities described in the applicable prospectus supplement or free writing prospectus, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indentures and the limitations applicable to global securities set forth in the applicable prospectus supplement or free writing prospectus, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will make no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement or free writing prospectus the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series. If we elect to redeem the debt securities of any series, we will not be required to:

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issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

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register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of such person’s own affairs.

Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indentures at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement or free writing prospectus any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indentures and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

Ranking of Debt Securities

The subordinated debt securities will be subordinate and junior in priority of payment to certain of our other indebtedness to the extent described in a prospectus supplement or free writing prospectus. The subordinated indenture does not limit the amount of subordinated debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

The senior debt securities will rank equally in right of payment to all our other senior unsecured debt. The senior indenture does not limit the amount of senior debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

DESCRIPTION OF WARRANTS

The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the warrants that we may offer under this prospectus and the related warrant agreements and warrant certificates. While the terms summarized below will apply generally to any warrants that we may offer, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. If we indicate in the prospectus supplement, the terms of any warrants offered under that prospectus supplement may differ from the terms described below. Specific warrant agreements will contain additional important terms and provisions and will be incorporated by reference as an exhibit to the registration statement, which includes this prospectus.

General

We may issue warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or together with common stock, preferred stock and/or debt securities, and the warrants may be attached to or separate from these securities.

We will evidence each series of warrants by warrant certificates that we will issue under a separate warrant agreement. We will enter into the warrant agreement with a warrant agent. We will indicate the name and address of the warrant agent in the applicable prospectus supplement relating to a particular series of warrants.

We will describe in the applicable prospectus supplement the terms of the series of warrants, including:

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the offering price and aggregate number of warrants offered;

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the currency for which the warrants may be purchased;

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if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

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if applicable, the date on and after which the warrants and the related securities will be separately transferable;

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in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased upon such exercise;

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in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

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the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreement and the warrants;

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the terms of any rights to redeem or call the warrants;

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any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;

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the periods during which, and places at which, the warrants are exercisable;

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the manner in which the warrants are exercisable;

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the dates on which the right to exercise the warrants will commence and expire;

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the manner in which the warrant agreement and warrants may be modified;

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U.S. federal income tax consequences of holding or exercising the warrants;

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the terms of the securities issuable upon exercise of the warrants; and

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any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

DESCRIPTION OF UNITS

We may issue units comprised of shares of common stock, shares of preferred stock, debt securities and warrants in any combination. We may issue units in such amounts and in as many distinct series as we wish. This section outlines certain provisions of the units that we may issue. If we issue units, they will be issued under one or more unit agreements to be entered into between us and a bank or other financial institution, as unit agent. The information described in this section may not be complete in all respects and is qualified entirely by reference to the unit agreement with respect to the units of any particular series. The specific terms of any series of units offered will be described in the applicable prospectus supplement. If so described in a particular supplement, the specific terms of any series of units may differ from the general description of terms presented below. We urge you to read any prospectus supplement related to any series of units we may offer, as well as the complete unit agreement and unit certificate that contain the terms of the units. If we issue units, forms of unit agreements and unit certificates relating to such units will be incorporated by reference as exhibits to the registration statement, which includes this prospectus.

Each unit that we may issue will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date. The applicable prospectus supplement may describe:

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the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;

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any provisions of the governing unit agreement;

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the price or prices at which such units will be issued;

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the applicable United States federal income tax considerations relating to the units;

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any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units; and

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any other terms of the units and of the securities comprising the units.

The provisions described in this section, as well as those described under “Description of Capital Stock,” “Description of Debt Securities” and “Description of Warrants” will apply to the securities included in each unit, to the extent relevant and as may be updated in any prospectus supplements.

Issuance in Series

We may issue units in such amounts and in as many distinct series as we wish. This section summarizes terms of the units that apply generally to all series. The financial and other specific terms of a particular series of units will be described in the applicable prospectus supplement.

Unit Agreements

We will issue the units under one or more unit agreements to be entered into between us and a bank or other financial institution, as unit agent. We may add, replace or terminate unit agents from time to time. We will identify the unit agreement under which each series of units will be issued and the unit agent under that agreement in the applicable prospectus supplement.

The following provisions will generally apply to all unit agreements unless otherwise stated in the applicable prospectus supplement:

Modification without Consent

We and the applicable unit agent may amend any unit or unit agreement without the consent of any holder:

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to cure any ambiguity;

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to cure any provisions of the governing unit agreement that differ from those described below;

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to correct or supplement any defective or inconsistent provision; or

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to make any other change that we believe is necessary or desirable and will not adversely affect the interests of the affected holders in any material respect.

We do not need any approval to make changes that affect only units to be issued after the changes take effect. We may also make changes that do not adversely affect a particular unit in any material respect, even if they adversely affect other units in a material respect. In those cases, we do not need to obtain the approval of the holder of the unaffected unit; we need only obtain any required approvals from the holders of the affected units.

Modification with Consent

We may not amend any particular unit or a unit agreement with respect to any particular unit unless we obtain the consent of the holder of that unit, if the amendment would:

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impair any right of the holder to exercise or enforce any right under a security included in the unit if the terms of that security require the consent of the holder to any changes that would impair the exercise or enforcement of that right; or

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reduce the percentage of outstanding units or any series or class the consent of whose holders is required to amend that series or class, or the applicable unit agreement with respect to that series or class, as described below.

Any other change to a particular unit agreement and the units issued under that agreement would require the following approval:

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If the change affects only the units of a particular series issued under that agreement, the change must be approved by the holders of a majority of the outstanding units of that series; or

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If the change affects the units of more than one series issued under that agreement, it must be approved by the holders of a majority of all outstanding units of all series affected by the change, with the units of all the affected series voting together as one class for this purpose.

These provisions regarding changes with majority approval also apply to changes affecting any securities issued under a unit agreement, as the governing document. In each case, the required approval must be given by written consent.

Unit Agreements Will Not Be Qualified under Trust Indenture Act

No unit agreement will be qualified as an indenture, and no unit agent will be required to qualify as a trustee, under the Trust Indenture Act. Therefore, holders of units issued under unit agreements will not have the protections of the Trust Indenture Act with respect to their units.

Mergers and Similar Transactions Permitted; No Restrictive Covenants or Events of Default

The unit agreements will not restrict our ability to merge or consolidate with, or sell our assets to, another corporation or other entity or to engage in any other transactions. If at any time we merge or consolidate with, or

sell our assets substantially as an entirety to, another corporation or other entity, the successor entity will succeed to and assume our obligations under the unit agreements. We will then be relieved of any further obligation under these agreements.

The unit agreements will not include any restrictions on our ability to put liens on our assets, nor will they restrict our ability to sell our assets. The unit agreements also will not provide for any events of default or remedies upon the occurrence of any events of default.

Governing Law

The unit agreements and the units will be governed by New York or Delaware law.

Form, Exchange and Transfer

We will issue each unit in global (book-entry) form only. Units in book-entry form will be represented by a global security registered in the name of a depositary, which will be the holder of all the units represented by the global security. Those who own beneficial interests in a unit will do so through participants in the depositary’s system, and the rights of these indirect owners will be governed solely by the applicable procedures of the depositary and its participants. We will describe book-entry securities, and other terms regarding the issuance and registration of the units in the applicable prospectus supplement. Each unit and all securities comprising the unit will be issued in the same form.

If we issue any units in registered, non-global form, the following terms will apply to them:

The units will be issued in the denominations stated in the applicable prospectus supplement. Holders may exchange their units for units of smaller denominations or combined into fewer units of larger denominations, as long as the total amount is not changed.

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Holders may exchange or transfer their units at the office of the unit agent. Holders may also replace lost, stolen, destroyed or mutilated units at that office. We may appoint another entity to perform these functions or perform them ourselves.

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Holders will not be required to pay a service charge to transfer or exchange their units, but they may be required to pay for any tax or other governmental charge associated with the transfer or exchange. The transfer or exchange, and any replacement, will be made only if our transfer agent is satisfied with the holder’s proof of legal ownership. The transfer agent may also require an indemnity before replacing any units.

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If we have the right to redeem, accelerate or settle any units before their maturity, and we exercise our right as to less than all those units or other securities, we may block the exchange or transfer of those units during the period beginning 15 days before the day we mail the notice of exercise and ending on the day of that mailing. We may also refuse to register transfers of or exchange any unit selected for early settlement, except that we will continue to permit transfers and exchanges of the unsettled portion of any unit being partially settled. We may also block the transfer or exchange of any unit in this manner if the unit includes securities that are or may be selected for early settlement.

Only the depositary will be entitled to transfer or exchange a unit in global form, since it will be the sole holder of the unit.

Payments and Notices

In making payments and giving notices with respect to our units, we will follow the procedures as described in the applicable prospectus supplement.

PLAN OF DISTRIBUTION

We may sell the offered securities in and outside the United States (1) through underwriters or dealers, (2) directly to one or more purchasers, including to a limited number of institutional purchasers, to a single purchaser or to our affiliates and stockholders, (3) through agents or (4) through a combination of any of these methods.

If underwriters or dealers are used in the sale, the securities will be acquired by the underwriters or dealers for their own account and may be resold from time to time in one or more transactions, including:

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in one or more transactions at a fixed price or prices, which may be changed from time to time;

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in “at-the-market offerings,” within the meaning of Rule 415(a)(4) of the Securities Act, into an existing trading market, on an exchange or otherwise;

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through a market maker or into an existing trading market on an exchange or otherwise;

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at prices related to those prevailing market prices; or

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at negotiated prices.

The applicable prospectus supplement will set forth the following information to the extent applicable:

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the terms of the offering;

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the names of any underwriters, dealers or agents;

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the name or names of any managing underwriter or underwriters;

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the purchase price of the securities;

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the net proceeds from the sale of the securities;

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any delayed delivery arrangements;

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any underwriting discounts, commissions and other items constituting underwriters’ compensation;

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any initial public offering price;

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any discounts or concessions allowed or reallowed or paid to dealers; and

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any commissions paid to agents.

Sale through Underwriters or Dealers

If any securities are offered through underwriters, the underwriters will acquire the securities for their own account and may resell them from time to time in one or more transactions, including negotiated transactions, at a fixed public offering price or at varying prices determined at the time of sale. Underwriters may offer and sell securities to the public either through underwriting syndicates represented by one or more managing underwriters or directly by one or more firms acting as underwriters. Unless otherwise provided in the applicable prospectus supplement, the obligations of the underwriters to purchase the securities will be subject to certain conditions, and the underwriters will be obligated to purchase all of the offered securities if they purchase any of them. In connection with the sale of securities, underwriters may be deemed to have received compensation from us in the form of underwriting discounts or commissions and dealers may receive compensation from the underwriters in the form of discounts or concessions. The underwriters may change from time to time any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers.

In order to facilitate the offering of securities, the underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the securities. Specifically, the underwriters may over allot in

connection with the offering, creating a short position in the securities for their account. In addition, to cover overallotments or to stabilize the price of the shares, the underwriters may bid for, and purchase, shares in the open market. Finally, an underwriting syndicate may reclaim selling concessions allowed to an underwriter or a dealer for distributing the securities in the offering if the syndicate repurchases previously distributed shares in transactions to cover syndicate short positions, in stabilization transactions, or otherwise. Any of these activities may stabilize or maintain the market price of the offered securities above independent market levels. The underwriters are not required to engage in these activities, and may discontinue any of these activities at any time.

Some or all of the securities that we offer through this prospectus may be new issues of securities with no established trading market. Any underwriters to whom we sell securities for public offering and sale may make a market in those securities, but they will not be obligated to do so and they may discontinue any market making at any time without notice. Accordingly, we cannot assure you of the liquidity of, or continued trading markets for, any securities offered pursuant to this prospectus.

If any securities are offered through dealers, we will sell the securities to them as principals. They may then resell those securities to the public at varying prices determined by the dealers at the time of resale.

Direct Sales and Sales through Agents

We may sell the securities directly to purchasers. If the securities are sold directly to institutional investors or others who may be deemed to be underwriters within the meaning of the Securities Act with respect to any sale of those securities, we will describe the terms of any such sales in the applicable prospectus supplement. We may also sell the securities through agents designated from time to time. Sales may be made by means of ordinary brokers’ transactions on Nasdaq at market prices, in block transactions and such other transactions as agreed by us and any agent. In the applicable prospectus supplement, we will name any agent involved in the offer or sale of the offered securities, and we will describe any commissions payable to the agent. Unless otherwise provided in the applicable prospectus supplement, any agent will agree to use its reasonable best efforts to solicit purchases for the period of its appointment.

At-the-Market Offerings

To the extent that we make sales through one or more underwriters or agents in at-the-market offerings, we will do so pursuant to the terms of a sales agency financing agreement or other at-the-market offering arrangement between us and the underwriters or agents. If we engage in at-the-market sales pursuant to any such agreement, we will issue and sell our securities through one or more underwriters or agents, which may act on an agency basis or a principal basis. During the term of any such agreement, we may sell securities on a daily basis in exchange transactions or otherwise as we agree with the underwriters or agents. Any such agreement will provide that any securities sold will be sold at prices related to the then-prevailing market prices for our securities. Therefore, exact figures regarding proceeds that will be raised or commissions to be paid cannot be determined at this time. Pursuant to the terms of the agreement, we may agree to sell, and the relevant underwriters or agents may agree to solicit offers to purchase, blocks of our common stock or other securities. The terms of any such agreement will be set forth in more detail in the applicable prospectus supplement.

Remarketing Arrangements

Offered securities may also be offered and sold, if we so indicate in the applicable prospectus supplement, in connection with a remarketing upon their purchase, in accordance with a redemption or repayment pursuant to their terms, or otherwise, by one or more remarketing firms, acting as principals for their own accounts or as our agents. Any remarketing firm will be identified and the terms of its agreements, if any, with us and its compensation will be described in the applicable prospectus supplement. Remarketing firms may be deemed to be underwriters of the offered securities under the Securities Act.

Delayed Delivery Contracts

If we so indicate in the applicable prospectus supplement, we may authorize agents, underwriters or dealers to solicit offers by certain institutions to purchase securities from us pursuant to contracts providing for payment and delivery on a specified future date. The applicable prospectus supplement will describe the conditions to those contracts and the commission payable for solicitation of those contracts.

General Information

We may have agreements with the agents, dealers, underwriters and remarketing firms to indemnify them against certain civil liabilities, including liabilities under the Securities Act, or to contribute with respect to payments that the agents, dealers or underwriters may be required to make. Agents, dealers, underwriters and remarketing firms may be customers of, engage in transactions with or perform services for us in the ordinary course of their businesses.

Each underwriter, dealer and agent participating in the distribution of any of the securities that are issuable in bearer form will agree that it will not offer, sell or deliver, directly or indirectly, securities in bearer form in the United States or to United States persons, other than qualifying financial institutions, during the restricted period, as defined in United States Treasury Regulations Section 1.163-5(c)(2)(i)(D)(7).

LEGAL MATTERS

Certain legal matters in connection with this offering will be passed upon for us by Goodwin Procter LLP, Redwood City, California. Any underwriters, dealers and agents will also be advised about the validity of the securities and other legal matters by their own counsel, which will be named in the prospectus supplement.

EXPERTS

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2024, as set forth in their report, which is incorporated by reference in this prospectus and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of an automatic shelf registration statement that we have filed with the SEC. This prospectus and any applicable prospectus supplement do not contain all of the information set forth in the registration statement and its exhibits and schedules in accordance with SEC rules and regulations. For further information with respect to us and the securities being offered by this prospectus and the applicable prospectus supplement, you should read the registration statement, including its exhibits and schedules. Statements contained in this prospectus and the applicable prospectus supplement, including documents that we have incorporated by reference, as to the contents of any contract or other document referred to are not necessarily complete, and, with respect to any contract or other document filed as an exhibit to the registration statement or any other such document, each such statement is qualified in all respects by reference to the corresponding exhibit. You should review the complete contract or other document to evaluate these statements. You may obtain copies of the registration statement and its exhibits via the SEC’s EDGAR database or our website.

We file annual, quarterly and current reports, proxy statements and other documents with the SEC under the U.S. Securities Exchange Act of 1934, as amended, or the Exchange Act. The SEC maintains a website that contains reports, proxy and information statements and other information regarding issuers, including us, that file electronically with the SEC. You may obtain documents that we file with the SEC at www.sec.gov. We also make these documents available on our website at https://nektar.com. Our website and the information contained or connected to our website is not incorporated by reference in this prospectus or any prospectus supplement, and you should not consider it part of this prospectus or any prospectus supplement.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

SEC rules permit us to incorporate information by reference in this prospectus and the applicable prospectus supplement. This means that we can disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is considered to be part of this prospectus and the applicable prospectus supplement, except for information superseded by information contained in this prospectus or the applicable prospectus supplement itself or in any subsequently filed incorporated document. This prospectus and the applicable prospectus supplement incorporate by reference the documents set forth below that we have previously filed with the SEC, other than information in such documents that is deemed to be furnished and not filed. These documents contain important information about us and our business and financial condition.

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Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on March 14, 2025;

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Quarterly Reports on Form 10-Q for the fiscal quarters ended March 31, 2025, June 30, 2025 and September 30, 2025, filed with the SEC on May 9, 2025, August 8, 2025 and November 7, 2025, respectively;

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Current Reports on Form 8-K, filed with the SEC on February 4, 2025, February 24, 2025, March 28, 2025, April 4, 2025, May 28, 2025, June 4, 2025, June 6, 2025, June 24, 2025, June 27, 2025, July 1, 2025, September 18, 2025 and November 10, 2025; and

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All documents that we file (but not those that we furnish) pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act, after the date of the initial registration statement of which this prospectus is a part and prior to the effectiveness of the registration statement shall be deemed to be incorporated by reference into this prospectus and will automatically update and supersede the information in this prospectus, and any previously filed documents.

Any statement contained herein or in a document incorporated or deemed to be incorporated by reference in this prospectus or the applicable prospectus supplement shall be deemed to be modified or superseded for purposes of this prospectus and such applicable prospectus supplement to the extent that a statement contained in this prospectus or such applicable prospectus supplement, or in any other subsequently filed document which also is or is deemed to be incorporated by reference in this prospectus and such applicable prospectus supplement, modifies or supersedes such earlier statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus or such applicable prospectus supplement. Nothing in this prospectus shall be deemed to incorporate information furnished but not filed with the SEC pursuant to Item 2.02 or Item 7.01 of Form 8-K.

Upon request, we will provide, without charge, to each person, including any beneficial owner, to whom a copy of this prospectus or an applicable prospectus supplement is delivered, a copy of the documents incorporated by reference into this prospectus or such prospectus supplement but not delivered with this prospectus or such prospectus supplement. You may request a copy of these filings, and any exhibits we have specifically incorporated by reference as an exhibit in this prospectus or such prospectus supplement, at no cost by writing us at the following address: Nektar Therapeutics, 455 Mission Bay Boulevard South, San Francisco, CA 94158, Attention: Secretary or by telephone by calling (415) 482-5300.

LOGO

3,532,609 Shares of Common Stock

Prospectus Supplement

Joint Bookrunning Managers


Jefferies		TD Cowen		Piper Sandler

Bookrunner

Citigroup

April 21, 2026

SEC Form 424B5 filed by Nektar Therapeutics