Statement of Changes in Beneficial Ownership (4)

FORM 4

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

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3235-0287

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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person * Mills Kenneth T.	2. Issuer Name and Ticker or Trading Symbol REGENXBIO Inc. [ RGNX ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director                    _____ 10% Owner __X__ Officer (give title below)    _____ Other (specify below) President and CEO
(Last)          (First)          (Middle) C/O REGENXBIO INC., 9600 BLACKWELL ROAD, SUITE 210	3. Date of Earliest Transaction (MM/DD/YYYY) 2/25/2021
(Street) ROCKVILLE, MD 20850 (City)        (State)        (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) _X _ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	2/25/2021		M(1)		1500.00	A	$0.85	282484.00	D
Common Stock	2/25/2021		S(1)		1500.00	D	$40.77	280984.00	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Employee Stock Option (Right to Buy)	$0.85	2/25/2021		M (1)			1500.00	(2)	9/23/2024	Common Stock	1500.00	$0.00	39670.00	D

Explanation of Responses:
(1)	This transaction was effected pursuant to a Rule 10b5-1 trading plan.
(2)	The previously granted option, representing a right to purchase a total of 708,200 shares, became exercisable as follows: 474,490 of the shares subject to the option are initial shares ("Initial Shares") and 233,710 of the shares subject to the option are contingent shares ("Contingent Shares"). 120,394 of the Initial Shares vested on September 17, 2014, 88,524 of the Initial Shares vested on September 17, 2015 and an additional 7,377 of the Initial Shares vested upon each month of continuous service to the Company thereafter. 25% of the Contingent Shares were deemed vested as of September 17, 2014 on January 13, 2015 due to a subsequent event. The remainder of the Contingent Shares vested over four years of service following September 17, 2014, with 25% of the remaining 75% of Contingent Shares having vested on September 17, 2015 and the remaining Contingent Shares having vested in 36 equal monthly installments thereafter.

Reporting Owners
Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Mills Kenneth T. C/O REGENXBIO INC. 9600 BLACKWELL ROAD, SUITE 210 ROCKVILLE, MD 20850	X		President and CEO

Signatures
/s/ Patrick J. Christmas as attorney-in-fact		3/1/2021
**Signature of Reporting Person		Date