REGENXBIO Inc.

Rule 10b5-1 Trading Plans

The adoption or termination of contracts, instructions or written plans for the purchase or sale of our securities by our Section 16 officers and directors for the three months ended December 31, 2025, each of which is intended to satisfy the affirmative defense of Rule 10b5-1(c) (Rule 10b5-1 Plan), were as follows:

(a)

The aggregate number of shares in this column includes shares that may be forfeited or withheld to satisfy exercise price and/or tax withholding obligations at the time of vesting.

Other than as described above, during the three months ended December 31, 2025, none of ourdirectors or Section 16 reporting officers adopted orterminated any Rule 10b5-1 trading arrangement or non-Rule 10b5-1 trading arrangement (as such terms are defined in Item 408 of the SEC's Regulation S-K).

Amendment to Bylaws

On March 4, 2026, the Board of Directors amended and restated the Company’s bylaws (as so amended and restated, the Amended and Restated Bylaws), effective immediately. The Amended and Restated Bylaws modify the Company’s prior bylaws to (i) revise the procedures and disclosure requirements governing stockholder nominations of director candidates, including to require compliance with Rule 14a-19 under the Exchange Act, (ii) update procedures and rules relating to stockholder meetings, (iii) make certain changes to conform to recent amendments to the Delaware General Corporation Law and (iv) make certain other ministerial and conforming changes. The foregoing summary is not, nor is it intended to be, a complete or comprehensive summary of all of the changes reflected in Amended and Restated Bylaws. The foregoing summary is qualified in its entirety by the full text of the Amended and Restated Bylaws, a copy of which is filed as Exhibit 3.2 hereto and incorporated herein by reference.