Sec Form 3 Filing - Syncona Portfolio Ltd @ Nightstar Therapeutics plc - 2019-01-01

FORM 3 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 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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1. Name and Address of Reporting Person Syncona Portfolio Ltd 2. Issuer Name and Ticker or Trading Symbol Nightstar Therapeutics plc [ NITE] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) ARNOLD HOUSE, ST JULIAN'S AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 01/01/2019 (Street) ST PETER PORT, Y7GY1 3RD 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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 (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 Ordinary Shares 13,203,922 ( 1 ) D ( 2 )

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Syncona Portfolio Ltd ARNOLD HOUSE, ST JULIAN' S AVENUE ST PETER PORT, Y7GY1 3RD X Syncona Holdings Ltd ARNOLD HOUSE, ST JULIAN'S AVENUE ST PETER PORT, Y7GY1 3RD X Syncona Ltd ARNOLD HOUSE, ST JULIAN'S AVENUE ST PETER PORT, Y7GY1 3RD X Signatures Syncona Portfolio Limited, By: Rob Hutchinson, Director, /s/ Rob Hutchinson 01/01/2019 Signature of Reporting Person Date Syncona Holdings Limited, By: Rob Hutchinson, Director, /s/ Rob Hutchinson 01/01/2019 Signature of Reporting Person Date Syncona Limited, By: Jeremy Tigue, Director, /s/ Jeremy Tigue 01/01/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Consists of 11,203,922 ordinary shares and 2,000,000 American Depository Share ("ADS") held by Syncona Portfolio Limited. Each ADS represents one ordinary share, nominal value 0.01 GBP per share, of the Issuer. ( 2 )The shares are owned directly by Syncona Portfolio Limited ("Syncona Portfolio") and indirectly by Syncona Holdings Limited ("Syncona Holdings") and Syncona Limited ("Syncona Limited"). Syncona Portfolio is a wholly owned subsidiary of Syncona Holdings and Syncona Holdings is a wholly controlled subsidiary of Syncona Limited ("Syncona Limited"), a publicly-listed company. Investment and voting decisions with respect to these shares are made by Syncona Portfolio, acting upon the recommendation of an investment committee of Syncona Investment Management Limited, also a subsidiary of Syncona Holdings. Each of these entities disclaims beneficial ownership except to the extent of its pecuniary interest therein, if any.

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 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).

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