Company: RGNX
Filing Date: 2025-06-25
Form Type: 424B3
Source: 0001193125-25-146911
Chunk: 6

Company: REGENXBIO Inc.
Filing Date: 2025-06-25
Form: 424B3
Chunk 6
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 supplement relating to a particular offering of our securities. These risks and uncertainties are not the only risks and uncertainties we face. Additional risks and uncertainties not presently known to us, or
that we currently view as immaterial, may also impair our business. If any of the risks or uncertainties described in our SEC filings or any prospectus supplement, or if any additional risks or uncertainties actually occur, our business, financial
condition and results of operations could be materially and adversely affected. In that case, the trading price of our securities could decline and you might lose all or part of your investment.

3

USE OF PROCEEDS

We will not receive any proceeds from the sale of the Shares. All proceeds from the sale of the Shares will be for the account of the Selling
Stockholder. However, the Company will receive the proceeds of any cash exercise of the Warrant. If the Warrant is exercised in full for cash, we would receive aggregate proceeds of approximately $4.0 million.

We will bear all other costs, fees and expenses incurred in effecting the registration of the Shares covered by this prospectus, including
without limitation, registration, qualification, filing fees, Nasdaq listing fees and fees and expenses of our counsel and our accountants. The Selling Stockholder will pay any discounts, commissions, and fees of underwriters, selling brokers,
dealer managers or similar securities industry professionals incurred by such Selling Stockholder in disposing of the Shares covered by this prospectus.

4

DESCRIPTION OF CAPITAL STOCK

The following description is a general summary of the terms of the shares of common stock and shares of preferred stock that we may issue. The
description below, and in any prospectus supplement, does not include all of the terms of the shares of common stock or shares of preferred stock and should be read together with our restated certificate of incorporation and amended and restated
bylaws, copies of which have been filed previously with the SEC. For more information on how you can obtain copies of our restated certificate of incorporation and amended and restated bylaws, see the section titled “Where You Can Find More Information.”

Authorized Capital Stock

Our authorized capital stock consists of 110,000,000 shares, of which 100,000,000 shares are designated as common stock, par value $0.0001 per
share, and 10,000,000 shares are designated as preferred stock, par value $0.0001 per share. The outstanding shares of our common stock are fully paid and non-assessable.