# EDGAR Filing Document

**Accession Number:** 0001559053
**File Stem:** 0001559053-26-000009
**Filing Date:** 2026-2
**Character Count:** 12268
**Document Hash:** ae230a8a061566e2dd9061236cf8f28f
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001559053-26-000009.hdr.sgml**: 20260227

**ACCESSION NUMBER**: 0001559053-26-000009

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 14

**CONFORMED PERIOD OF REPORT**: 20260227

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Other Events

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20260227

**DATE AS OF CHANGE**: 20260227

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** PROTHENA CORP PUBLIC LTD CO
- **CENTRAL INDEX KEY:** 0001559053
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** L2
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-35676
- **FILM NUMBER:** 26701062

**BUSINESS ADDRESS:**
- **STREET 1:** 77 SIR JOHN ROGERSON'S QUAY, BLOCK C
- **STREET 2:** GRAND CANAL DOCKLANDS
- **CITY:** DUBLIN 2
- **STATE:** L2
- **ZIP:** D02 VK60
- **BUSINESS PHONE:** 011-353-1-236-2500

**MAIL ADDRESS:**
- **STREET 1:** 77 SIR JOHN ROGERSON'S QUAY, BLOCK C
- **STREET 2:** GRAND CANAL DOCKLANDS
- **CITY:** DUBLIN 2
- **STATE:** L2
- **ZIP:** D02 VK60

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Prothena Corp plc
- **DATE OF NAME CHANGE:** 20121102

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Neotope Corp Ltd
- **DATE OF NAME CHANGE:** 20120926

?xml version='1.0' encoding='ASCII'? prta-20260227

**UNITED STATES**

**SECURITIES AND EXCHANGE COMMISSION**

**WASHINGTON, D.C. 20549**

_______________________________________________________

**FORM 8-K** 

_______________________________________________________

**CURRENT REPORT**

**Pursuant to Section 13 or 15(d) of the**

**Securities Exchange Act of 1934**

**Date of Report (Date of earliest event reported): February 27, 2026** 

_______________________________________________________

**PROTHENA CORPORATION PUBLIC LIMITED COMPANY**

**(Exact name of registrant as specified in its charter)**

_______________________________________________________

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| | | | | |
|:---|:---|:---|:---|:---|
| **Ireland** | **001-35676** | **001-35676** | **001-35676** | **98-1111119** |
| **(State or Other Jurisdiction<br>of Incorporation)** | **(Commission<br>File Number)** | **(Commission<br>File Number)** | **(Commission<br>File Number)** | **(IRS Employer<br>Identification No.)** |
|  | **77 Sir John Rogerson's Quay, Block C** | **77 Sir John Rogerson's Quay, Block C** | **77 Sir John Rogerson's Quay, Block C** |  |
|  | **Grand Canal Docklands** | **Grand Canal Docklands** | **Grand Canal Docklands** |  |
|  | **Dublin 2,** | **D02 VK60,** | **Ireland** |  |
| **(Address of principal executive offices, including Zip Code)** | **(Address of principal executive offices, including Zip Code)** | **(Address of principal executive offices, including Zip Code)** | **(Address of principal executive offices, including Zip Code)** | **(Address of principal executive offices, including Zip Code)** |

---

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

___________________________________________________

**(Former Name or Former Address, if Changed Since Last Report.)** 

___________________________________________________

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (*see* General Instruction A.2. below):

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

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| | | |
|:---|:---|:---|
| <u>Title of Each Class</u> | <u>Trading Symbol</u> | <u>Name of Each Exchange on Which Registered</u> |
| Ordinary Shares, par value $0.01 per share | PRTA | The Nasdaq Global Select Market |

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Indicate by check mark whether the registrant is an emerging growth company as defined in as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Emerging growth company ☐

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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. ☐

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| | |
|:---|:---|
| **Item 7.01** | **Regulation FD.** |

---

On February 27, 2026, Prothena Corporation plc (the "Company") issued a press release announcing a share repurchase plan under which the Company may repurchase up to $100.0 million of the Company's outstanding ordinary shares, par value $0.01 per share. A copy of that press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

*The information in Item 7.01 of this Current Report on Form 8-K and Exhibit 99.1 attached hereto shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section. It may only be incorporated by reference in another filing under the Exchange Act or the Securities Act of 1933, as amended, if such subsequent filing specifically incorporate by reference the information furnished pursuant to Item 7.01 (including Exhibit 99.1) of this Current Report.*

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| | |
|:---|:---|
| **Item 8.01** | **Other Events.** |

---

On February 27, 2026, the Company announced a share repurchase plan under which the Company may repurchase up to $100.0 million of the Company's outstanding ordinary shares, par value $0.01 per share. The share repurchase plan will expire on December 31, 2026, may be suspended or discontinued at any time, and does not obligate the company to acquire any amount of ordinary shares.

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| | |
|:---|:---|
| **Item 9.01** | **Financial Statements and Exhibits.** |

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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(d) Exhibits.

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| | |
|:---|:---|
| **<u>Exhibit No.</u>** | **<u>Description</u>** |
| 99.1 | <u>[Press Release dated February 27, 2026](a2026febexx991sharerepurch.htm)</u>  |
| 104 | Cover Page Interactive Data File (embedded within the Inline XBRL document) |

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**SIGNATURES**

&nbsp;&nbsp;&nbsp;&nbsp;Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

---

| | | | |
|:---|:---|:---|:---|
| Date: | February 27, 2026 | **PROTHENA CORPORATION PLC** | **PROTHENA CORPORATION PLC** |
|  |  | By: | /s/ Tran B. Nguyen |
|  |  | Name: | Tran B. Nguyen |
|  |  | Title: | Chief Strategy Officer and Chief Financial Officer |

---

## Exhibit 99.1

**EXHIBIT 99.1**

![image_0a.jpg](image_0a.jpg)

**PRESS RELEASE**

**Prothena Announces up to $100 Million Share Repurchase Plan**

DUBLIN, Ireland, February 27, 2026 -- Prothena Corporation plc (NASDAQ:PRTA), a late-stage clinical biotechnology company with a robust pipeline of investigational therapeutics built on protein dysregulation expertise, today announced that its Board of Directors has authorized a Share Repurchase Plan under which the Company may repurchase up to $100.0 million of the Company's outstanding ordinary shares, par value $0.01 per share.

Prothena had cash, cash equivalents and restricted cash of $308.4 million and no debt as of December 31, 2025. Excluding any potential purchases under this Share Repurchase Plan, Prothena expects to end the year with approximately $255 million in cash, cash equivalents, and restricted cash. This financial guidance does not include the potential to earn up to $105 million of aggregate clinical milestone payments from strategic partners in 2026 related to the advancement of both coramitug for ATTR amyloidosis with cardiomyopathy by Novo Nordisk and PRX019 for neurodegenerative diseases by Bristol Myers Squibb.

Prothena may repurchase the shares from time to time in open market transactions, which may be structured to occur in accordance with the requirements of Rule 10b-18 of the Securities Exchange Act of 1934, as amended. Prothena may also enter into Rule 10b5-1 plans to facilitate repurchases. The timing, number of shares repurchased, and prices paid for the shares under this program will depend on general business and market conditions as well as corporate and regulatory limitations, prevailing share prices, and other considerations. The Share Repurchase Plan will expire on December 31, 2026, may be suspended or discontinued at any time, and does not obligate the company to acquire any amount of ordinary shares. No amount or any amount of outstanding ordinary shares may be acquired by the expiration of the Share Repurchase Plan, at Prothena's sole discretion.

**About Prothena**

Prothena Corporation plc 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

<br> <br> <br>

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deep scientific expertise built over decades of research, Prothena 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. Prothena'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<sup>®</sup> technology to target a broad spectrum of intracellular disease pathways in the brain and periphery. For more information, please visit the Company's website at www.prothena.com and follow the Company on X (formerly Twitter) @ProthenaCorp.

**Forward-Looking Statements** 

*This press release contains forward-looking statements. These statements relate to, among other things, our plans and expectations regarding the Share Repurchase Plan, capital allocation, and other objectives and expectations; our anticipated cash burn and projected year end cash, cash equivalents, and restricted cash; and the receipt of clinical milestone payments in 2026. These statements are based on estimates, projections and assumptions that may prove not to be accurate, and actual results could differ materially from those anticipated due to known and unknown risks, uncertainties and other factors, including but not limited to uncertainties related to the completion of operational and financial closing procedures, audit adjustments and other developments that may arise that would require adjustments to the preliminary financial results included in this press release, as well as those described in the "Risk Factors" sections of our Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 27, 2026, and discussions of potential risks, uncertainties, and other important factors in our subsequent filings with the SEC. We undertake no obligation to update publicly any forward-looking statements contained in this press release as a result of new information, future events, or changes in our expectations.* 

**Contacts:**

Mark Johnson, CFA, Vice President, Investor Relations

650-837-8550

IR@prothena.com

Media@prothena.com

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