prta-20260331

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

______________________________________

FORM 10-Q

_____________________________________

(Mark One)


☒			QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended March 31, 2026


☐			TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

Commission file number: 001-35676

______________________________________

PROTHENA CORPORATION PUBLIC LIMITED COMPANY

(Exact name of registrant as specified in its charter)

______________________________________


Ireland						98-1111119
(State or other jurisdiction of incorporation or organization)						(I.R.S. Employer Identification Number)


77 Sir John Rogerson’s Quay, Block C
Grand Canal Docklands
Dublin 2,	D02 VK60,	Ireland
(Address of principal executive offices including Zip Code)

Registrant’s telephone number, including area code: 011-353-1-236-2500

______________________________________

Securities registered pursuant to Section 12(b) of the Act:


Title of Each Class	Trading Symbol	Name of Each Exchange on Which Registered
Ordinary Shares, par value $0.01 per share	PRTA	The Nasdaq Global Select Market

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.


Large accelerated filer	☐	Accelerated filer	☒
Non-accelerated filer	☐	Smaller reporting company	☐
		Emerging growth company	☐
If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.			☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

The number of ordinary shares outstanding was 52,353,237 as of April 30, 2026.

PROTHENA CORPORATION PLC

Form 10-Q – QUARTERLY REPORT

For the Quarter Ended March 31, 2026

TABLE OF CONTENTS


			Page

PART I. FINANCIAL INFORMATION			1
Item 1. Financial Statements (unaudited)			1
Condensed Consolidated Balance Sheets as of March 31, 2026 and December 31, 2025			1
Condensed Consolidated Statements of Operations for the three months ended March 31, 2026 and 2025			2
Condensed Consolidated Statements of Cash Flows for the three months ended March 31, 2026 and 2025			3
Condensed Consolidated Statements of Shareholders' Equity for the three months ended March 31, 2026 and 2025			5
Notes to Condensed Consolidated Financial Statements			6
Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations			20
Item 3. Quantitative and Qualitative Disclosures About Market Risk			32
Item 4. Controls and Procedures			33

PART II. OTHER INFORMATION			34
Item 1. Legal Proceedings			34
Item 1A. Risk Factors			34
Item 2. Unregistered Sales of Equity Securities and Use of Proceeds			69
Item 3. Defaults Upon Senior Securities			69
Item 4. Mine Safety Disclosures			69
Item 5. Other Information			69
Item 6. Exhibits			70

SIGNATURES			71

EXHIBIT INDEX			70

Note Regarding Forward-Looking Statements

In addition to historical information, this Quarterly Report on Form 10-Q contains forward-looking statements within the meaning of Section 21E of the Securities Exchange Act of 1934, as amended. Forward-looking statements may include words such as “aim,” “anticipate,” “assume,” “believe,” “contemplate,” “continue,” “could,” “due,” “estimate,” “expect,” “goal,” “intend,” “may,” “objective” “plan,” “predict,” “potential,” “positioned,” “seek,” “should,” “target,” “will,” “would,” and other similar expressions that are predictions of or indicate future events and future trends, or the negative of these terms or other comparable terminology. In addition, any statements that refer to expectations, projections, or other characterizations of future events or circumstances are forward-looking statements.

These forward-looking statements, which reflect our beliefs, assumptions, expectations, estimates, forecasts, and projections about our business and the industry in which we operated as of the date hereof, are estimates based on our best judgment. These statements relate to, among other things, our goal to continue building a biology-directed discovery engine targeting protein dysregulation; the treatment potential, designs, proposed mechanisms of action, and potential administration of our drug candidates; potential indications and attributes of epitopes and antibodies we have identified in our programs; plans for ongoing and future clinical trials of our drug candidates; our potential to advance, initiate, and complete investigational new drug (“IND”) enabling studies for our discovery and preclinical programs; the expected timing of reporting data from clinical trials of our drug candidates; our collaborations with F. Hoffman-La Roche Ltd and Hoffmann-La Roche Inc. (together “Roche”), Bristol Myers Squibb Company (“BMS”), and Novo Nordisk, and amounts we may receive under such collaborations; the sufficiency of our cash position to fund advancement of a broad pipeline and completion of our ongoing clinical trials; and our anticipated need for additional capital.

These forward-looking statements are not guarantees of future performance or development and involve known and unknown risks, uncertainties, and other factors that are in some cases beyond our control. As a result, any or all of our forward-looking statements in this Quarterly Report on Form 10-Q may turn out to be inaccurate. Factors that could cause our actual results to differ materially include, but are not limited to, the risks and uncertainties set forth below, those discussed under Part II Item 1A “Risk Factors” of this Quarterly Report on Form 10-Q, and in our other filings with the U.S. Securities and Exchange Commission.

Except as required by law or by the rules and regulations of the U.S. Securities and Exchange Commission, we undertake no obligation to revise or update any forward-looking statements to reflect any event or circumstance that arises after the date of this Quarterly Report on Form 10-Q, including without limitation:

•our ability to obtain additional financing in future offerings and/or obtain funding from future collaborations;

•our operating losses;

•our ability to successfully complete research and development of our drug candidates;

•our ability to develop, manufacture and commercialize products;

•our collaborations and other agreements with third parties, including Roche, BMS, and Novo Nordisk;

•our ability to protect our patents and other intellectual property;

•our ability to hire and retain key employees;

•our ability to maintain financial flexibility and sufficient cash, cash equivalents and investments and other assets capable of being monetized to meet our liquidity requirements;

•the timing, receipt, and amount of any capital investments, cost-sharing contributions or reimbursements, milestone payments, or royalties that we might receive under current or potential future collaborations, including any milestone payments pursuant to our agreement with Novo Nordisk;

•potential disruptions in the U.S. and global capital and credit markets, including by geopolitical conflicts and pandemics;

•government regulation of our industry;

•the volatility of the market price of our ordinary shares; and

• business disruptions.

Summary of Risks Affecting Our Business

Our business is subject to numerous risks and uncertainties. The following summary highlights some of the risks you should consider with respect to our business and prospects. These risks are described more fully in Part II Item 1A “Risk Factors” of this Quarterly Report on Form 10-Q which includes a more complete discussion of the risks summarized below as well as a discussion of other risks related to our business, our prospects, and your investment.

•We anticipate that we will incur losses for the foreseeable future and we may never sustain profitability.

•We will require additional capital to fund our operations, and if we are unable to obtain such capital, we will be unable to successfully develop and commercialize drug candidates.

•Our success is largely dependent on the success of our research and development programs; our drug candidates are in various stages of development and we may not be able to successfully discover, develop, obtain regulatory approval for, or commercialize any drug candidates.

•We have entered into agreements to develop and bring to market drug candidates with Roche, BMS, and Novo Nordisk and may enter into additional agreements in the future, and we might not realize the anticipated benefits of such agreements including receiving anticipated milestone payments pursuant to these agreements.

•If clinical trials of our drug candidates are prolonged, delayed, suspended, or terminated, we may be unable to commercialize our drug candidates on a timely basis, which would require us to incur additional costs and delay our receipt of any revenue from potential product sales.

•Even if any of our drug candidates receives regulatory approval, if such approved product does not achieve broad market acceptance, the revenues that we generate from sales of the product will be limited.

•If we are unable to adequately protect or enforce the intellectual property relating to our drug candidates our ability to successfully commercialize our drug candidates will be harmed.

•Our future success depends on our ability to retain key personnel and to attract, retain, and motivate qualified personnel.

PART I. FINANCIAL INFORMATION

ITEM 1. FINANCIAL STATEMENTS

Prothena Corporation plc and Subsidiaries

Condensed Consolidated Balance Sheets (unaudited)

(in thousands, except share and per share data)


	March 31,		December 31,
	2026		2025
Assets
Current assets:
Cash and cash equivalents	$	329,462	$	307,531
Prepaid expenses and other current assets	9,739		7,662
Total current assets	339,201		315,193
Non-current assets:
Property and equipment, net	1,960		2,144
Operating lease right-of-use assets	7,391		8,125
Restricted cash, non-current	860		860
Other non-current assets	482		482
Total non-current assets	10,693		11,611
Total assets	$	349,894	$	326,804
Liabilities and Shareholders’ Equity
Current liabilities:
Accounts payable	$	4,299	$	5,875
Accrued research and development	4,611		4,329
Deferred revenue, current	1,630		2,664
Restructuring liability	8,585		13,303
Lease liability, current	2,893		2,886
Other current liabilities	10,499		11,786
Total current liabilities	32,517		40,843
Non-current liabilities:
Lease liability, non-current	4,761		5,487
Total non-current liabilities	4,761		5,487
Total liabilities	37,278		46,330
Commitments and contingencies (Note 6)
Shareholders’ equity:
Euro deferred shares, €22 nominal value:	—		—
Authorized shares — 10,000 at March 31, 2026 and December 31, 2025
Issued and outstanding shares — none at March 31, 2026 and December 31, 2025
Ordinary shares, $0.01 par value:	530		538
Authorized shares — 100,000,000 at March 31, 2026 and December 31, 2025
Issued and outstanding shares — 53,077,225 and 53,832,982 at March 31, 2026 and December 31, 2025, respectively
Additional paid-in capital	1,625,798		1,626,369
Accumulated deficit	(1,313,712)		(1,346,433)
Total shareholders’ equity	312,616		280,474
Total liabilities and shareholders’ equity	$	349,894	$	326,804

See accompanying Notes to Condensed Consolidated Financial Statements.

Prothena Corporation plc and Subsidiaries

Condensed Consolidated Statements of Operations

(in thousands, except per share data)

(unaudited)


	Three Months Ended March 31,
	2026		2025
Collaboration revenue	1,034		2,778
Revenue from license and intellectual property	50,050		50
Total revenue	51,084		2,828
Operating expenses:
Research and development	12,627		50,811
General and administrative	12,666		17,598
Restructuring costs	(4,244)		—
Total operating expenses	21,049		68,409
Income (loss) from operations	30,035		(65,581)
Other income (expense):
Interest income	2,416		4,348
Other income (expense), net	271		(140)
Total other income, net	2,687		4,208
Income (loss) before income taxes	32,722		(61,373)
Provision for (benefit from) income taxes	1		(1,178)
Net income (loss)	$	32,721	$	(60,195)
Basic net income (loss) per ordinary share	$	0.61	$	(1.12)
Diluted net income (loss) per ordinary share	$	0.60	$	(1.12)
Shares used to compute basic net income (loss) per share	53,708		53,827
Shares used to compute diluted net income (loss) per share	54,109		53,827

See accompanying Notes to Condensed Consolidated Financial Statements.

Prothena Corporation plc and Subsidiaries

Condensed Consolidated Statements of Cash Flows

(in thousands)

(unaudited)


	Three Months Ended March 31,
	2026		2025
Operating activities
Net income (loss)	$	32,721	$	(60,195)
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation	184		223
Share-based compensation	6,915		10,949
Deferred income taxes	—		(1,672)
Reduction in the carrying amount of right-of-use assets	734		686
Reduction in restructuring liability - non-cash	(5,198)		—
Loss on disposal of fixed assets	—		2
Changes in operating assets and liabilities:
Prepaid and other assets	(2,984)		(843)
Accounts payable, accruals and other liabilities	(2,222)		910
Deferred revenue	(1,034)		(2,778)
Restructuring liability	480		—
Operating lease liabilities	(719)		(645)
Net cash provided by (used in) operating activities	28,877		(53,363)
Investing activities
Purchases of property and equipment	—		(42)
Net cash used in investing activities	—		(42)
Financing activities
Repurchase of ordinary shares	(6,946)		—
Proceeds from issuance of ordinary shares in at-the-market offering, net	—		(48)
Net cash used in financing activities	(6,946)		(48)
Net increase (decrease) in cash, cash equivalents and restricted cash	21,931		(53,453)
Cash, cash equivalents and restricted cash, beginning of the year	308,391		472,248
Cash, cash equivalents and restricted cash, end of the period	$	330,322	$	418,795

Supplemental disclosures of cash flow information
U.S. Federal	$	—	$	—
U.S. State and Local	—		—
Cash paid for income taxes	$	—	$	—

Supplemental disclosures of non-cash investing and financing activities
Share repurchase costs included in accounts payable and accrued liabilities	$	548	$	—
Acquisition of property and equipment included in accounts payable and accrued liabilities	$	—	$	49

See accompanying Notes to Condensed Consolidated Financial Statements.

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the statement of financial position that sum to the total of the same such amounts shown in the Condensed Consolidated Statements of Cash Flows.


	Three Months Ended March 31,
	2026		2025
Cash and cash equivalents	$	329,462	$	417,935
Restricted cash, non-current	860		860
Total cash, cash equivalents and restricted cash, end of the period	$	330,322	$	418,795

Prothena Corporation plc and Subsidiaries

Condensed Consolidated Statements of Shareholders' Equity

(in thousands, except share data)

(unaudited)


	Ordinary Shares			Additional Paid-in Capital		Accumulated Deficit		Total Shareholders' Equity
	Shares	Amount
Balances at December 31, 2025	53,832,982	$	538	$	1,626,369	$	(1,346,433)	$	280,474
Share-based compensation				6,915				6,915
Issuance of ordinary shares upon vesting of restricted stock units	33,233	—		—				—
Repurchase of ordinary shares	(788,990)	(8)		(7,486)		—		(7,494)
Net income						32,721		32,721
Balances at March 31, 2026	53,077,225	530		1,625,798		(1,313,712)		312,616


	Ordinary Shares			Additional Paid-in Capital		Accumulated Deficit		Total Shareholders' Equity
	Shares	Amount
Balances at December 31, 2024	53,826,982	$	538	$	1,588,729	$	(1,102,341)	$	486,926
Share-based compensation				10,949				10,949
Net loss						(60,195)		(60,195)
Balances at March 31, 2025	53,826,982	538		1,599,678		(1,162,536)		437,680

See accompanying Notes to Condensed Consolidated Financial Statements.

Notes to the Condensed Consolidated Financial Statements

(unaudited)

1.Organization

Description of Business

Prothena Corporation plc (“Prothena” or the “Company”) is a late-stage clinical biotechnology company with expertise in protein dysregulation with the potential to change the course of devastating neurodegenerative and rare peripheral amyloid diseases.

Fueled by its deep scientific expertise built over decades of research, the Company is advancing a pipeline of therapeutic candidates for a number of indications and novel targets for which its ability to integrate scientific insights around neurological dysfunction and the biology of misfolded proteins can be leveraged. The Company’s pipeline includes both wholly-owned and partnered programs being developed for the potential treatment of diseases including Parkinson’s disease, ATTR amyloidosis with cardiomyopathy, Alzheimer’s disease, Amyotrophic lateral sclerosis (ALS) and a number of other neurodegenerative diseases. Prothena is developing and applying its proprietary CYTOPE® technology to target a broad spectrum of intracellular targets in the brain and periphery.

The Company was formed on September 26, 2012, under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. The Company's ordinary shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012, and currently trade on The Nasdaq Global Select Market.

Liquidity and Business Risks

As of March 31, 2026, the Company had an accumulated deficit of $1.3 billion and cash and cash equivalents of $329.5 million.

Based on the Company's business plans, management believes that the Company’s cash and cash equivalents at March 31, 2026, are sufficient to meet its obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on research and development programs significantly above current long-term plans or enters into potential licenses and/or other acquisitions of complementary technologies, products or companies, the Company may need additional capital. Additionally, in order to develop and obtain regulatory approval for our potential products the Company will need to raise substantial additional capital. The Company expects to continue to finance future capital needs that exceed its existing cash and cash equivalents from payments pursuant to its agreements with Roche, BMS, and Novo Nordisk, and, to the extent necessary, other collaborative agreements with corporate partners, or other arrangements, and through proceeds from public or private equity or debt financings, and loans. The Company cannot assume that such additional financings will be available on acceptable terms, if at all, and such financings may only be available on terms dilutive to its shareholders.

2.Summary of Significant Accounting Policies

Basis of Preparation and Presentation of Financial Information

These accompanying Condensed Consolidated Financial Statements have been prepared in accordance with the accounting principles generally accepted in the U.S. (“GAAP”) and with the instructions for Form 10-Q and Regulation S-X statements. Accordingly, they do not include all of the information and notes required for complete financial statements. These Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes thereto contained in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission (the “SEC”) on February 27, 2026 (the “2025 Form 10-K”). These unaudited interim Condensed Consolidated Financial Statements are presented in U.S. dollars, which is the functional currency of the Company and its consolidated subsidiaries. These Condensed Consolidated Financial Statements include the accounts of the Company and its consolidated subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Unaudited Interim Financial Information

The accompanying Condensed Consolidated Financial Statements and related disclosures are unaudited, have been prepared on the same basis as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for a fair presentation of the results of operations for the periods presented. The year-end condensed consolidated balance sheet data was derived from audited financial statements,

however certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted. The condensed consolidated results of operations for any interim period are not necessarily indicative of the results to be expected for the full year or for any other future year or interim period.

Use of Estimates

The preparation of the Condensed Consolidated Financial Statements in conformity with U.S. GAAP requires the Company to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosures. On an ongoing basis, management evaluates its estimates, including critical accounting policies or estimates related to revenue recognition and research and development expenses. The Company bases its estimates on historical experience and on various other market specific and other relevant assumptions that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Because of the uncertainties inherent in such estimates, actual results may differ materially from these estimates.

Significant Accounting Policies

Except for the accounting policy for repurchases of ordinary shares, which was added below as a result of the Company’s February 2026 announcement of a share repurchase plan, there were no significant changes to the accounting policies during the three months ended March 31, 2026, from the significant accounting policies described in Note 2 of the Notes to Consolidated Financial Statements in the 2025 Form 10-K.

Repurchases of Ordinary Shares

The Company may repurchase its ordinary shares from time to time in open market transactions. All shares repurchased are immediately retired. Repurchased ordinary shares are recorded at cost and the excess of the repurchase cost over the par value of repurchased ordinary shares is charged against additional paid in capital (“APIC”) or to retained earnings once APIC is reduced to zero. The par value of repurchased ordinary shares is charged against the ordinary shares par account. The Company accrues for the cost of shares repurchased based on the trade date.

Concentration of Risks and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents. The Company places its cash equivalents with high credit quality financial institutions and, by policy, limits the amount of credit exposure with any one financial institution. Deposits held with banks have exceeded, and will continue to exceed, federally insured limits. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash and cash equivalents. The Company has not experienced any losses on its deposits of cash and cash equivalents and its credit risk exposure is up to the extent recorded on the Company's Consolidated Balance Sheet.

The Company’s business is primarily conducted in U.S. dollars except for its agreements with contract manufacturers for drug supplies which are primarily denominated in euros. For the three months ended March 31, 2026, the Company recorded a gain on foreign currency exchange rate differences of approximately $271,000 and a loss of $140,000 during the three months ended March 31, 2025. If the Company increases its business activities that require the use of foreign currencies, it may be exposed to losses if the euro and other such currencies continue to strengthen against the U.S. dollar.

The Company’s revenue during the three months ended March 31, 2026 was primarily from revenue from the development milestone payment received from Novo Nordisk, and to a lesser extent, collaboration revenue recognized under the Company’s Collaboration Agreement with BMS, while the revenue during the three months ended March 31, 2025 was primarily from collaboration revenue recognized under the Company’s Collaboration Agreement with BMS. During the three months ended March 31, 2026, and 2025, the Company derived its revenue from foreign countries and none from Ireland.

As of March 31, 2026, and December 31, 2025, $2.0 million and $2.1 million, respectively, of the Company’s property and equipment, net were held in the U.S. and a nominal amount were in Ireland.

The Company does not own or operate facilities for the manufacture, packaging, labeling, storage, testing or distribution of nonclinical or clinical supplies of any of its drug candidates. The Company instead contracts with and relies on third-parties to manufacture, package, label, store, test and distribute all preclinical development and clinical supplies of our drug candidates, and it plans to continue to do so for the foreseeable future. The Company also relies on third-party consultants to assist in managing these third-parties and assist with its manufacturing strategy.

Segment Information

The Company currently manages its operations as a single segment focused on the discovery and development of novel therapies to treat diseases caused by protein dysregulation. A single management team reports to the chief operating decision maker (“CODM”) who comprehensively manages the entire business. All clinical programs are included in one operating segment because the majority of the Company’s clinical programs have similar economic and other characteristics, including the nature of the clinical programs and production processes, and regulatory environment.

Consistent with the Company’s operational structure, the chief executive officer, as the CODM, manages and allocates resources at the global corporate level using consolidated, single-segment GAAP financial statement reported profit and loss and consolidated budget and forecast information for the purpose of evaluating performance, allocating resources, setting incentive targets, and planning and forecasting future periods. Managing and allocating resources at the global corporate level enables the CODM to assess both the overall level of resources available and how to best deploy these resources across functions, therapeutic areas and research and development projects in line with our overarching long-term corporate-wide strategic goals, rather than on a clinical program basis. The Company is not organized by market and is managed and operated as one business. As a single reportable segment entity, the determined measure of profit or loss is the Company’s consolidated net income (loss). Consolidated asset information for the Company’s single-segment is presented in the Company’s consolidated Balance Sheet.

The following table sets forth significant research and development (“R&D”) expenses by program as regularly provided to the CODM (in thousands):


	Three Months Ended March 31,
	2026		2025
Birtamimab (NEOD001)	$	31	$	25,914
PRX012	5,353		18,075
PRX019	2,127		2,102
Other R&D	5,116		4,720
Total R&D	$	12,627	$	50,811

Recent Accounting Pronouncements

On November 4, 2024, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (ASU) 2024-03, Income Statement — Reporting Comprehensive Income — Expense Disaggregation Disclosures, which requires public business entities to disclose, on an annual and interim basis, disaggregated information about certain income statement line items in a tabular format in the notes to the financial statements. This guidance will be effective for the Company’s annual period ending December 31, 2027, and interim periods beginning January 1, 2028. Early adoption is permitted. Entities may apply the guidance prospectively or retrospectively. The Company is currently evaluating the impact of this new standard on its financial statement disclosures.

There have been no other recent accounting pronouncements or changes in accounting pronouncements during the three months ended March 31, 2026 that are of significance or potential significance to the Company.

3.Fair Value Measurements

The Company measures certain financial assets and liabilities at fair value on a recurring basis, including cash equivalents. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. A three-tier fair value hierarchy is established as a basis for considering such assumptions and for inputs used in the valuation methodologies in measuring fair value:

Level 1 — inputs are quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2 — inputs are other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly.

Level 3 — inputs are unobservable inputs that are supported by little or no market activities, which would require the Company to develop its own assumptions.

The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The carrying amounts reflected in the Condensed Consolidated Balance Sheets for cash equivalents, prepaid expenses and other current assets, accounts payable and accrued liabilities, approximate their fair value due to their short-term nature.

Based on the fair value hierarchy, the Company classifies its cash equivalents within Level 1. This is because the Company values its cash equivalents using quoted market prices. The Company’s Level 1 securities consisted of $305.2 million and $275.4 million in money market funds included in cash and cash equivalents at March 31, 2026, and December 31, 2025, respectively.

4.Composition of Certain Balance Sheet Items

Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):


	March 31,		December 31,
	2026		2025
Prepaid R&D expenses	$	3,813	$	5,270
Prepaid G&A expenses	2,171		639
Other	3,755		1,753
Prepaid expenses and other current assets	$	9,739	$	7,662

Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):


	March 31,		December 31,
	2026		2025
Machinery and equipment	$	7,068	$	7,068
Purchased computer software	2,128		2,128
	9,196		9,196
Less: accumulated depreciation	(7,236)		(7,052)
Property and equipment, net	$	1,960	$	2,144

Depreciation expense was $0.2 million and $0.2 million for the three months ended March 31, 2026 and 2025, respectively.

Other Current Liabilities

Other current liabilities consisted of the following (in thousands):


	March 31,		December 31,
	2026		2025
Payroll and related expenses	$	9,529	$	11,350
Professional services	356		222
Other	614		214
Other current liabilities	$	10,499	$	11,786

5.Net Income (Loss) Per Ordinary Share

Net income (loss) per ordinary share was determined as follows (in thousands, except per share amounts):


	Three Months Ended March 31,
	2026		2025
Numerator:
Net income (loss)	$	32,721	$	(60,195)
Denominator:
Weighted-average ordinary shares outstanding used in per share calculations - basic	53,708		53,827
Dilutive restricted stock units outstanding	384		—
Dilutive stock options outstanding	17		—
Weighted-average ordinary shares outstanding used in per share calculations - diluted	54,109		53,827
Net income (loss) per ordinary share:
Basic	$	0.61	$	(1.12)
Diluted	$	0.60	$	(1.12)

Potentially issuable ordinary shares were not used in computing diluted net loss per ordinary share as their effect would be anti-dilutive due to the loss recorded during the three months ended March 31, 2025, and therefore diluted net loss per share is equal to basic net loss per share.

The equivalent ordinary shares not included in diluted net income (loss) per share because their effect would be anti-dilutive are as follows (in thousands):


	Three Months Ended March 31,
	2026	2025
Stock options to purchase ordinary shares	10,640	12,835
Restricted Stock Units (RSU)	259	291
Total	10,899	13,126

6. Commitments and Contingencies

Lease Commitments

As of March 31, 2026, the Company currently has three leases relating to its facilities in the United States and Dublin, Ireland.

Dublin

In June 2021, the Company entered into a lease agreement for office space in Dublin, Ireland, which commenced in August 2021 and had an initial term of one year. In addition, the Company entered into a lease agreement for additional office space in Dublin, Ireland, which commenced in August 2023 and had an initial term of one year. Both leases have an automatic renewal clause, pursuant to which each agreement will be extended automatically for successive periods equal to their current terms, unless each agreement is cancelled by the Company. In April 2026, the Company renewed the August 2023 lease for another one year term. The August 2021 lease was not renewed and will terminate pursuant to its terms on July 31, 2026.

Brisbane Facility

On October 28, 2022, the Company entered into a noncancelable operating sublease (the "Brisbane Sublease") to sublease approximately 31,157 square feet of office and laboratory space located in Brisbane, California (the “Brisbane Facility”) with Arcus Biosciences, Inc., (the "Sublandlord"). The Brisbane Sublease became effective on October 28, 2022. The Brisbane Sublease provides that the Company's obligation to pay rent commenced on July 1, 2023, which is subject to abatement for the first six months following such date, with the exception of the seventh rent payment that was due upon execution of the Brisbane Sublease. The Company is obligated to make lease payments totaling approximately $14.9 million over the lease term, which expires on September 30, 2028, unless terminated earlier. The Brisbane Sublease further provides that the Company is obligated to pay the Sublandlord certain costs, including taxes and operating expenses. The Company has the option to extend

the sublease by providing written notice at least nine months prior to the expiration of the sublease term. As of March 31, 2026, the Brisbane Sublease has a remaining lease term of 2.5 years.

Total operating lease cost for the Brisbane Sublease was $0.8 million and $0.8 million for the three months ended March 31, 2026 and 2025, respectively. Total cash paid against the operating lease liability was $0.8 million and $0.7 million for the three months ended March 31, 2026 and 2025, respectively.

In conjunction with the Brisbane Sublease, the Company obtained a standby letter of credit in the initial amount of $0.9 million, which may be drawn down by the Sublandlord in the event the Company fails to fully and faithfully perform all of its obligations under the Brisbane Sublease and to compensate the Sublandlord for all losses and damages the Sublandlord may suffer as a result of the occurrence of any default on the part of the Company not cured within the applicable cure period. As of March 31, 2026, none of the standby letter of credit amount of $0.9 million has been used.

The following table sets out a maturity analysis of payments under the Company’s operating leases, including a reconciliation to the lease liabilities recognized in the Condensed Consolidated Balance Sheets as of March 31, 2026 (in thousands):


Year Ended December 31,	Operating Leases
2026 (9 months)	$	2,462
2027	3,269
2028	2,523
Thereafter	—

SEC Form 10-Q filed by Prothena Corporation plc