RGNX · REGENXBIO Inc.

Represents shares purchased in an open-market transaction. The price reported in Column 4 is a weighted average price. This transaction was executed in multiple trades at prices ranging from $9.17 to $9.4525. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

Represents shares purchased in an open-market transaction. The price reported in Column 4 is a weighted average price. This transaction was executed in multiple trades at prices ranging from $8.67 to $9.35. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

The option will vest over a three year period, with 1/3rd of the option vesting on August 25, 2027 and the remaining portion of the option vesting in equal monthly installments over the 24 months thereafter, while the optionee provides continuous service to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 1/3rd of the shares subject to the RSU award shall vest on each of August 25, 2027, August 25, 2028 and August 25, 2029, while the recipient provides continuous service to the Issuer.

Represents shares of common stock withheld to pay taxes upon the vesting of restricted stock units originally granted to the reporting person on August 1, 2024. The number of shares withheld was determined based on the closing price of the issuer's common stock on August 1, 2026.

Represents shares of common stock withheld to pay taxes upon the vesting of restricted stock units originally granted to the reporting person on August 1, 2024. The number of shares withheld was determined based on the closing price of the issuer's common stock on August 1, 2026.

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

The previously granted option, representing a right to purchase a total of 103,698 shares, became exercisable as follows: 25% of the shares subject to this option vested on January 2, 2026, and the balance vests in equal monthly installments over the 36 months thereafter while the optionee provides continuous service to the Issuer.

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

The previously granted option, representing a right to purchase a total of 103,698 shares, became exercisable as follows: 25% of the shares subject to this option vested on January 2, 2026, and the balance vests in equal monthly installments over the 36 months thereafter while the optionee provides continuous service to the Issuer

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

Represents shares of common stock withheld to pay taxes upon the vesting of restricted stock units originally granted to the reporting person on July 1, 2024. The number of shares withheld was determined based on the closing price of the issuer's common stock on July 1, 2026.

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

The reporting person is voluntarily reporting the acquisition of shares of the Issuer's common stock pursuant to the ESPP for the ESPP purchase period of January 1, 2026 through June 30, 2026. This transaction is exempt under Rule 16b-3(c).

In accordance with the ESPP, these shares were purchased based on 85% of the closing price of the Issuer's common stock on June 30, 2026.

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

This transaction was executed in multiple trades at prices ranging from $11.00 to $11.18. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

The option will vest on May 29, 2027 subject to the continuous service of the optionee to the Issuer.

The option will vest on May 29, 2027 subject to the continuous service of the optionee to the Issuer.

The option will vest on May 29, 2027 subject to the continuous service of the optionee to the Issuer.

The option will vest on May 29, 2027 subject to the continuous service of the optionee to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

The option will vest in 12 equal monthly installments following May 29, 2027 subject to the continuous service of the optionee to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

The option will vest May 29, 2027 subject to the continuous service of the optionee to the Issuer.

The option will vest on May 29, 2027 subject to the continuous service of the optionee to the Issuer.

The option will vest on May 29, 2027 subject to the continuous service of the optionee to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

The option will vest on May 29, 2027 subject to the continuous service of the optionee to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 100% of the shares subject to this RSU will vest on May 29, 2027 subject to the continuous service of the recipient to the Issuer.

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

This transaction was executed in multiple trades at prices ranging from $11.00 to $11.10. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

This transaction was effected pursuant to a Rule 10b5-1 trading plan.

Represents shares of common stock withheld to pay taxes upon the vesting of restricted stock units originally granted to the reporting person on August 1, 2024. The number of shares withheld was determined based on the closing price of the issuer's common stock on February 1, 2026.

Represents shares of common stock withheld to pay taxes upon the vesting of restricted stock units originally granted to the reporting person on August 1, 2024. The number of shares withheld was determined based on the closing price of the issuer's common stock on February 1, 2026.

The previously granted option, representing a right to purchase a total of 225,000 shares, became exercisable as follows: 25% of the shares subject to this option vested on January 28, 2017, and the balance vested in equal monthly installments over the 36 months thereafter.

The previously granted option, representing a right to purchase a total of 225,000 shares, became exercisable as follows: 25% of the shares subject to this option vested on January 28, 2017, and the balance vested in equal monthly installments over the 36 months thereafter.

Represents shares of common stock withheld to satisfy the exercise price and pay taxes upon the exercise of options originally granted to the reporting person on January 28, 2016, which were set to expire on January 28, 2026. The number of shares withheld was determined based on the closing price of the issuer's common stock on January 27, 2026. The transaction did not involve any open-market sale of securities.

25% of the shares subject to this option shall vest after 12 months of continuous service with the Issuer. The balance will vest in equal monthly installments over the 36 months following January 6, 2027 while the optionee provides continuous service to the Issuer.

25% of the shares subject to this option shall vest after 12 months of continuous service with the Issuer. The balance will vest in equal monthly installments over the 36 months following January 6, 2027 while the optionee provides continuous service to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 25% of the shares subject to this RSU will vest on each of January 6, 2027, January 6, 2028, January 6, 2029 and January 6, 2030 while the recipient provides continuous service to the Issuer.

25% of the shares subject to this option shall vest after 12 months of continuous service with the Issuer. The balance will vest in equal monthly installments over the 36 months following January 6, 2027 while the optionee provides continuous service to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 25% of the shares subject to this RSU will vest on each of January 6, 2027, January 6, 2028, January 6, 2029 and January 6, 2030 while the recipient provides continuous service to the Issuer.

25% of the shares subject to this option shall vest after 12 months of continuous service with the Issuer. The balance will vest in equal monthly installments over the 36 months following January 6, 2027 while the optionee provides continuous service to the Issuer.

25% of the shares subject to this option shall vest after 12 months of continuous service with the Issuer. The balance will vest in equal monthly installments over the 36 months following January 6, 2027 while the optionee provides continuous service to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 25% of the shares subject to this RSU will vest on each of January 6, 2027, January 6, 2028, January 6, 2029 and January 6, 2030 while the recipient provides continuous service to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 25% of the shares subject to this RSU will vest on each of January 6, 2027, January 6, 2028, January 6, 2029 and January 6, 2030 while the recipient provides continuous service to the Issuer.

Represents shares of common stock underlying a time-based restricted stock unit award (RSU). 25% of the shares subject to this RSU will vest on each of January 6, 2027, January 6, 2028, January 6, 2029 and January 6, 2030 while the recipient provides continuous service to the Issuer.