Notice of Proposed Sale · 144

REGENXBIO Inc.

RGNXNASDAQEQUITYCurrent

Notice of Proposed Sale

Filed Jul 1, 2026Accepted Jul 1, 2026, 4:30 PM EDTFiling CIK 1700659Accession 0001950047-26-006719

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Structured filing — 144

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Notice of proposed sale. The proposed amounts below do not establish that a sale occurred.

Proposed-sale notice

Issuer: REGENXBIO Inc.
Issuer CIK: 0001590877
SEC file number: 001-37553
Phone: 2405528181
Person for whose account securities are to be sold: Stephen J. Pakola
Relationships to issuer: Officer
Street: 9804 Medical Center Drive
City: Rockville
State / country code: MD
Postal code: 20850

Securities proposed for sale

Securities proposed for sale · 1 reported row
Security	Proposed units	Aggregate market value	Units outstanding	Approximate sale date	Exchange	Broker / market maker
Common	43,206	517,607.88	51,697,621	07/01/2026	NASDAQ	Morgan Stanley Smith Barney LLC Executive Financial Services

Broker / market maker — proposed row 1, entry 1

Name: Morgan Stanley Smith Barney LLC Executive Financial Services
Street: 1 New York Plaza
Street (continued): 8th Floor
City: New York
State / country code: NY
Postal code: 10004

Acquisition of securities to be sold

Acquisition of securities to be sold · 1 reported row
Security	Acquired	Nature of acquisition	Acquired from	Amount acquired	Gift transaction	Payment date	Nature of payment
Common	07/01/2026	Exercise of Stock Options	Issuer	43,206	N	07/01/2026	Cash

Sales reported in the preceding three months

Sales reported in the preceding three months · 2 reported rows
Seller	Security	Sale date	Amount sold	Gross proceeds
10b5-1 Sales for STEPHEN PAKOLA	Common	06/29/2026	19,608	216,560.60
10b5-1 Sales for STEPHEN PAKOLA	Common	05/11/2026	15,309	168,737.84

Seller — prior-sale row 1, entry 1

Name: 10b5-1 Sales for STEPHEN PAKOLA
Street: 9804 Medical Center Drive
City: Rockville
State / country code: MD
Postal code: 20850

Seller — prior-sale row 2, entry 1

Name: 10b5-1 Sales for STEPHEN PAKOLA
Street: 9804 Medical Center Drive
City: Rockville
State / country code: MD
Postal code: 20850

Prior-sale reporting

Nothing to report for the preceding three months: N

Remarks

The securities to be sold were and will be received upon the exercise of stock options over the next three months. The dates of acquisition and payment were and will be the dates of exercise/sale.

Notice signature

Notice date: 07/01/2026
Signed: /s/ Stephen J. Pakola
Plan adoption dates: 11/12/2025

Company context

REGENXBIO is a biotechnology company on a mission to improve lives through the curative potential of gene therapy. Since its founding in 2009, REGENXBIO has pioneered the field of AAV gene therapy. REGENXBIO is advancing a late-stage pipeline of one-time treatments for rare and retinal diseases, including RGX-202 for the treatment of Duchenne; surabgene lomparvovec (ABBV-RGX-314) for the treatment of wet AMD and diabetic retinopathy, in collaboration with AbbVie, and NAVSUNLI™ (clemidsogene lanparvovec-sngl, RGX-121) for the treatment of MPS II and RGX-111 for the treatment of MPS I, both in partnership with Nippon Shinyaku. Thousands of patients have been treated with REGENXBIO's AAV platform, including those receiving Novartis' ZOLGENSMA®. REGENXBIO's investigational gene therapies have the potential to change the way healthcare is delivered for millions of people. For more information, please visit www. REGENXBIO.com.

Current securities

RGNXNASDAQ · EQUITY · Current

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