Company: RGNX
Filing Date: 2025-06-25
Form Type: 424B3
Source: 0001193125-25-146911
Chunk: 14

Company: REGENXBIO Inc.
Filing Date: 2025-06-25
Form: 424B3
Chunk 14
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 bear all fees and expenses incident to our obligation to register the Shares. The Selling Stockholder may sell all or a portion of the Shares beneficially owned by it and offered hereby from time to time directly to one or more purchasers or to or through one or more underwriters, broker-dealers or agents or through a combination of any of these methods. If the Shares are sold through underwriters or broker-dealers, the Selling Stockholder will be responsible for underwriting discounts or commissions or agent’s commissions in connection with the sale of the Shares. The Shares may be sold on any national securities exchange on which the Shares may be listed at the time of sale, in the over-the-countermarket or in transactions other than on such exchange or in the over-the-countermarket and in one or more transactions at fixed prices, at prevailing market prices at the time of the sale, at varying prices determined at the time of sale, or at privately negotiated prices. These sales may be effected in transactions, which may involve crosses or block transactions. The Selling Stockholder may use any one or more of the following methods when disposing of the Shares:

| • |     | ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers; |

| • |     | block trades in which the broker-dealer will attempt to sell the Shares as agent, but may position and resell a 
 portion of the block as principal to facilitate the transaction;                                                |

| • |     | purchases by a broker-dealer as principal and resale by the broker-dealer for its account; |

| • |     | an over-the-counter distribution; |

| • |     | an exchange distribution in accordance with the rules of the applicable exchange; |

| • |     | privately negotiated transactions; |

| • |     | short sales effected after the effective date of the registration statement of which this prospectus is a part; |

| • |     | through the writing or settlement of options or other hedging transactions, whether through an options exchange 
 or otherwise;                                                                                                   |

| • |     | in “at the market” offerings, as defined in Rule 415 under the Securities Act, at negotiated prices, at                                                                                                                                             
 prices prevailing at the time of sale or prices related to such prevailing market prices, including sales made directly on a national securities exchange or sales made through a market maker other than on an exchange or other similar offerings 
 through sales agents;                                                                                                                                                                                                                               |

| • |     | through trading plans entered into by the Selling Stockholder pursuant to Rule