Ownership Submission
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

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
Yoo Stephen
   2. Issuer Name and Ticker or Trading Symbol
REGENXBIO Inc. [RGNX] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
Chief Medical Officer
(Last)
(First)
(Middle)
C/O REGENXBIO INC., 9600 BLACKWELL ROAD, SUITE 210		 3. Date of Earliest Transaction (Month/Day/Year)
09/05/2017
(Street)

ROCKVILLE, MD 20850		 4. If Amendment, Date Original Filed(Month/Day/Year)
 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction 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 09/05/2017   M(1)   31,803 A $ 0.85 31,803 D  
Common Stock 09/05/2017   S(1)   31,803 D $ 25 0 D  
Common Stock 09/06/2017   M(1)   855 A $ 0.85 855 D  
Common Stock 09/06/2017   S(1)   855 D $ 25 0 D  

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction 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
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(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 09/05/2017   M(1)     31,803   (2) 11/03/2024 Common Stock 31,803 $ 0 171,097 D  
Employee Stock Option (Right to Buy) $ 0.85 09/06/2017   M(1)     855   (2) 11/03/2024 Common Stock 855 $ 0 170,242 D  

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
Yoo Stephen
C/O REGENXBIO INC.
9600 BLACKWELL ROAD, SUITE 210
ROCKVILLE, MD 20850		       Chief Medical Officer  

Signatures

 /s/ Stephen Yoo   09/07/2017
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(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 247,900 shares, became exercisable as follows: 165,200 of the shares subject to the option are initial shares ("Initial Shares") and 82,700 of the shares subject to the option are contingent shares ("Contingent Shares"). 23,600 of the Initial Shares vested on October 13, 2014, 35,400 of the Initial Shares vested on October 13, 2015 and an additional 2,950 of the Initial Shares vest upon each month of continuous service to the Company thereafter. 15% of the Contingent Shares were deemed vested as of October 13, 2014 on January 13, 2015 due to a subsequent event. The remainder of the Contingent Shares vest over four years of service following October 13, 2014, with 25% of the remaining 85% of Contingent Shares having vested on October 13, 2015 and the remaining Contingent Shares vesting in 36 equal monthly installments thereafter.

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