Director — Gregory Ciongoli: The filing reports the election of a new independent director and the resignation of two directors, which constitutes a routine board composition change rather than the departure of a senior executive officer.

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Other Events. On June 29, 2026, REGENXBIO Inc. (the “Company”) announced that it has earned a milestone payment of $100.0 million from AbbVie Global Enterprises Ltd. (“AbbVie”), a subsidiary of AbbVie Inc., pursuant to the Collaboration and License Agreement, dated as of September 10, 2021 between the Company and AbbVie, as amended on August 5, 2025. The milestone payment relates to the dosing of the first patient in the Phase IIb/III trial of investigational surabgene lomparvovec (sura-vec,…

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement. On March 18, 2026, REGENXBIO Inc. (the “Company”) entered into a Settlement and Release Agreement (the “Settlement Agreement”) with GlaxoSmithKline LLC (“GSK”) to resolve non-binding mediation related to the License Agreement dated March 6, 2009, as amended on April 15, 2009, between GSK and the Company (as amended, the “GSK-REGENXBIO Sublicense”). As previously disclosed, the Company was notified of a dispute with GSK over the amount of sublicense…

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Other Events. On February 7, 2026, the Company received a CRL from the FDA regarding the Company’s BLA for RGX-121, the Company's investigational gene therapy for Mucopolysaccharidosis type II.

Regulation FD Disclosure. On February 9, 2026, REGENXBIO Inc. (the “Company”) announced that it received a Complete Response Letter ("CRL") from the U.S. Food and Drug Administration ("FDA") regarding the Company’s Biologics License Application ("BLA") for RGX-121, the Company's investigational gene therapy for Mucopolysaccharidosis type II. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K and incorporated herein by reference. The information in

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement. Amendment to License Agreement with AbbVie On August 5, 2025, REGENXBIO Inc. (the “Company”) and AbbVie Global Enterprises Ltd. (“AbbVie”), a subsidiary of AbbVie Inc., entered into a First Amendment (the “Amendment”) to the Collaboration and License Agreement, dated as of September 10, 2021 (the “Collaboration Agreement”) by and between the Company and AbbVie. The Amendment modifies the development plan and related milestone structure for the diabe…

Entry into a Material Definitive Agreement.

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. On May 16, 2025 (the “Closing Date”), a wholly owned subsidiary of REGENXBIO Inc. (the “Company”), REGENXBIO RS LLC (“REGENXBIO RS”), entered into a Loan Agreement (“Loan Agreement”) with an affiliate of HealthCare Royalty Management, LLC (“HCRx”). Under the terms of the Loan Agreement, HCRx will provide REGENXBIO RS with an aggregate limited recourse loan of up to $250 million (…

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Other Events. On March 3, 2025, the waiting period under the Hart-Scott Rodino Antitrust Improvements Act of 1976, as amended, expired with respect to the previously reported Collaboration and License Agreement (the “Collaboration and License Agreement”) between REGENXBIO Inc. (the “Company”) and Nippon Shinyaku Co., Ltd. (“Nippon Shinyaku“). On March 4, 2025, the Collaboration and License Agreement closed.

Entry into a Material Definitive Agreement. On January 14, 2025, REGENXBIO Inc. (the “Company”) and Nippon Shinyaku Co., Ltd. (“Nippon Shinyaku“) entered into a Collaboration and License Agreement (the “Agreement”) for the development and commercialization of RGX-121 for the treatment of Mucopolysaccharidosis II (“MPS II”), also known as Hunter syndrome, and RGX-111 for Mucopolysaccharidosis I (“MPS I”), also known as Hurler syndrome (each, a “Licensed Product”). The Agreement will become eff…

Regulation FD Disclosure. The Company issued a press release on January 14, 2025, announcing entry into the Collaboration and License Agreement, a copy of which is attached hereto as Exhibit 99.1 and incorporated herein by reference.

Other Events. On December 9, 2024, REGENXBIO Inc. (the “Company”) entered into a Sales Agreement (the “Sales Agreement”) with Leerink Partners LLC (the “Agent”), as sales agent, under which the Company may offer and sell shares of its common stock, par value $0.0001 per share, from time to time having an aggregate offering price of up to $150.0 million (the “Shares”). The Company will file a prospectus supplement relating to the offer and sale of the Shares pursuant to the Sales Agreement, wh…

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Chief Financial Officer — Vittal Vasista: The resignation of the Chief Financial Officer without immediate mention of a successor is a significant departure.

The company granted RSUs to its EVP, Chief Medical Officer and EVP, Chief Scientific Officer during a period of CEO transition.

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

President and Chief Executive Officer — Kenneth T. Mills: Kenneth T. Mills resigned as President and CEO, but will continue to serve as Chairman of the Board.

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 liability under that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.