Sec Form 4 Filing - VIKING GLOBAL INVESTORS LP @ Adaptive Biotechnologies Corp - 2019-07-01

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 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 VIKING GLOBAL INVESTORS LP 2. Issuer Name and Ticker or Trading Symbol Adaptive Biotechnologies Corp [ ADPT] 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) 55 RAILROAD AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 07/01/2019 (Street) GREENWICH, CT06830 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 Common Stock 07/01/2019 P 250,000 ( 1 ) A $ 20 1,675,000 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Common Stock 07/01/2019 C 18,908,945 A 20,583,945 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Common Stock 07/01/2019 C 15,524,350 A 36,108,295 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Common Stock 07/01/2019 C 2,007,740 A 38,116,035 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Common Stock 07/01/2019 C 290,572 A 38,406,607 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 )

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 Series D Preferred Stock ( 2 ) 07/01/2019 C 18,908,945 ( 2 ) ( 2 ) Common Stock 18,908,945 ( 2 ) 0 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Series E Preferred Stock ( 2 ) 07/01/2019 C 15,524,350 ( 2 ) ( 2 ) Common Stock 15,524,350 ( 2 ) 0 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Series F Preferred Stock ( 2 ) 07/01/2019 C 2,007,740 ( 2 ) ( 2 ) Common Stock 2,007,740 ( 2 ) 0 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Series F-1 Preferred Stock ( 2 ) 07/01/2019 C 290,572 ( 2 ) ( 2 ) Common Stock 290,572 ( 2 ) 0 I See explanation of responses ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other VIKING GLOBAL INVESTORS LP 55 RAILROAD AVENUE GREENWICH, CT06830 X Viking Global Opportunities Illiquid Investments Sub-Master LP 55 RAILROAD AVENUE GREENWICH, CT06830 X Viking Global Opportunities Portfolio GP LLC 55 RAILROAD AVENUE GREENWICH, CT06830 X Viking Global Opportunities GP LLC 55 RAILROAD AVENUE GREENWICH, CT06830 X HALVORSEN OLE ANDREAS 55 RAILROAD AVENUE GREENWICH, CT06830 X Ott David C. 55 RAILROAD AVENUE GREENWICH, CT06830 X Shabet Rose Sharon 55 RAILROAD AVENUE GREENWICH, CT06830 X Signatures /s/ O. Andreas Halvorsen (10)(11) 07/02/2019 Signature of Reporting Person Date /s/ David C. Ott (10)(11) 07/02/2019 Signature of Reporting Person Date /s/ Rose S. Shabet (10)(11) 07/02/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On July 1, 2019, the Viking Funds (defined below) acquired an aggregate of 250,000 shares of common stock of the Issuer ("Common Stock") at a price of $20 per share in connection with the Issuer's initial public offering ("IPO"). VGEM acquired 173,010 shares in the IPO, VGE II acquired 3,531 shares in the IPO, VLFM acquired 64,122 shares in the IPO and Opportunities Fund acquired 9,337 shares in the IPO. ( 2 )On July 1, 2019 in connection with the closing of the IPO, the shares of Series D Preferred Stock, Series E Preferred Stock, Series F Preferred Stock and Series F-1 Preferred Stock held by the Reporting Persons (defined below) automatically converted into shares of Common Stock on a one-to-one basis. ( 3 )O. Andreas Halvorsen, David C. Ott and Rose S. Shabet are Executive Committee members of certain management entities, including Viking Global Partners LLC, the general partner of Viking Global Investors LP ("VGI"), Viking Global Performance LLC ("VGP"), Viking Long Fund GP LLC ("VLFGP") and Viking Global Opportunities GP LLC ("Opportunities GP"), the sole owner of Viking Global Opportunities Portfolio GP LLC ("Opportunities Portfolio GP"). VGI provides managerial services to various investment funds, including Viking Global Equities II LP ("VGE II"), Viking Global Equities Master Ltd. ("VGEM"), Viking Long Fund Master Ltd. ("VLFM") and Viking Global Opportunities Illiquid Investments Sub-Master LP ("Opportunities Fund," and together with VLFM, VGEM and VGE II, the "Viking Funds"). ( 4 )VGP is the general partner of VGE II. Opportunities Portfolio GP is the general partner of Opportunities Fund. VLFGP serves as the investment manager of VLFM. Each of the Viking Funds, VGI, VGP, VLFGP, Opportunities Portfolio GP, Mr. Halvorsen, Mr. Ott and Ms. Shabet (collectively, the "Reporting Persons") may be deemed to beneficially own the shares reported on this form. ( 5 )VGI provides managerial services to (i) VGEM, which directly holds 26,578,963 shares of Common Stock; (ii) VGE II, which directly holds 542,429 shares of Common Stock; (iii) VLFM, which directly holds 9,850,878 shares of Common Stock; and (iv) Opportunities Fund, which directly holds 1,434,337 shares of Common Stock. Because of the relationship between VGI and the Viking Funds, VGI may be deemed to beneficially own the shares of Common Stock directly held by the Viking Funds. ( 6 )VGP is the general partner of VGE II and the investment manager of VGEM. Because of the relationships between VGP and VGE II and VGEM, respectively, VGP may be deemed to beneficially own the shares of Common Stock directly held by VGE II and VGEM. ( 7 )VLFGP serves as the investment manager of VLFM. Because of the relationship between VLFGP and VLFM, VLFGP may be deemed to beneficially own the shares of Common Stock directly held by VLFM. ( 8 )Opportunities Portfolio GP is the general partner of Opportunities Fund. Because of the relationship between Opportunities Portfolio GP and Opportunities Fund, Opportunities Portfolio GP may be deemed to beneficially own the shares of Common Stock held directly by Opportunities Fund. Opportunities GP is the sole owner of Opportunities Portfolio GP. Because of the relationship between Opportunities GP and Opportunities Portfolio GP, Opportunities GP may be deemed to beneficially own the shares of Common Stock held directly by Opportunities Fund. ( 9 )The Reporting Persons disclaim beneficial ownership of these securities except to the extent of their pecuniary interest therein, and the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of the reported securities for purposes of Section 16 or for any other purpose.

Remarks: (10) The Reporting Persons are jointly filing this Form 4 pursuant to Rule 16a-3(j) under the Exchange Act.(11) Each of O. Andreas Halvorsen, David C. Ott and Rose S. Shabet is signing individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP.(12) Because no more than 10 reporting persons can file any one Form 4 through the SEC's EDGAR system, VGP, VGE II, VGEM, VLFGP and VLFM have jointly filed with the Reporting Persons on a separate Form 4 filing submitted on the same day hereof.

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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