SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* Flynn James E (Last) (First) (Middle) 780 THIRD AVENUE, 37TH FLOOR (Street) NEW YORK NY 10017 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 09/16/2015	3. Issuer Name and Ticker or Trading Symbol REGENXBIO Inc. [ RGNX ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) X Other (specify below) Possible Member of 10% Group	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series C Convertible Preferred Stock	(1)	(1)	Common Stock	771,963(1)	(1)	I	Through Deerfield Private Design Fund III, L.P.(3)(4)
Series D Convertible Preferred Stock	(2)	(2)	Common Stock	397,079(2)	(2)	I	Through Deerfield Private Design Fund III, L.P.(3)(4)

1. Name and Address of Reporting Person* Flynn James E (Last) (First) (Middle) 780 THIRD AVENUE, 37TH FLOOR (Street) NEW YORK NY 10017 (City) (State) (Zip)

1. Name and Address of Reporting Person* Deerfield Mgmt III, L.P. (Last) (First) (Middle) 780 THIRD AVENUE, 37TH FLOOR (Street) NEW YORK NY 10017 (City) (State) (Zip)

1. Name and Address of Reporting Person* DEERFIELD MANAGEMENT CO (Last) (First) (Middle) 780 THIRD AVENUE, 37TH FLOOR (Street) NEW YORK NY 10017 (City) (State) (Zip)

1. Name and Address of Reporting Person* Deerfield Private Design Fund III, L.P. (Last) (First) (Middle) 780 THIRD AVENUE, 37TH FLOOR (Street) NEW YORK NY 10017 (City) (State) (Zip)

Explanation of Responses:

1. Each share of Series C Convertible Preferred Stock is convertible into one (1) of the Issuer's shares of common stock. Shares of Series C Convertible Preferred Stock will automatically convert into shares of common stock upon the closing of the Issuer's initial public offering of common stock.

2. Each share of Series D Convertible Preferred Stock is convertible into one (1) of the Issuer's shares of common stock. Shares of Series D Convertible Preferred Stock will automatically convert into shares of common stock upon the closing of the Issuer's initial public offering of common stock.

3. This Form 3 is being filed by the undersigned as well as the entities listed on the Joint filer Information Statement attached as an exhibit hereto (the "Reporting Persons"). Deerfield Mgmt III, L.P. is the general partner of Deerfield Private Design Fund III, L.P. (the "Fund"). Deerfield Management Company, L.P. is the investment manager of the Fund. James E. Flynn is the sole member of the general partner of each of Deerfield Mgmt III, L.P. and Deerfield Management Company, L.P. In accordance with Instruction 5 (b)(iv) to Form 3, the entire amount of the Issuer's securities held by the Fund is reported herein.

4. For purposes of Section 16 of the Securities Exchange Act of 1934, as amended, each Reporting Person disclaims beneficial ownership of any such securities, except to the extent of his/its indirect pecuniary interest therein, if any, and this report shall not be deemed an admission that such Reporting Person is the beneficial owner of such securities for purposes of Section 16 or otherwise.

Remarks:

Please see Joint Filer Information Statement attached as Exhibit 99 hereto. Jonathan Isler, signing as Attorney-in-Fact: Power of Attorney, incorporated by reference to Exhibit 24 to a Form 3 with regard to Avalanche Biotechnologies, Inc. filed with the Securities and Exchange Commission on July 30, 2014 by Deerfield Mgmt, L.P., Deerfield Mgmt III, L.P., Deerfield Special Situations Fund, L.P., Deerfield Special Situations International Master Fund, L.P., Deerfield Private Design Fund III, L.P. and James E. Flynn.

	/s/ Jonathan Isler	09/16/2015
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (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).
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