Sec Form 3 Filing - VIKING GLOBAL INVESTORS LP @ Adaptive Biotechnologies Corp - 2019-06-26

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 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) 06/26/2019 (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 1,425,000 I See Explanation of Responses ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 )

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 ( 1 ) ( 1 ) ( 1 ) Common Stock 18,908,945 I See Explanation of Responses ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) Series E Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 15,524,350 I See Explanation of Responses ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) Series F Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 2,007,740 I See Explanation of Responses ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) Series F-1 Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 290,572 I See Explanation of Responses ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 )

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 (8)(9) 06/26/2019 Signature of Reporting Person Date /s/ David C. Ott (8)(9) 06/26/2019 Signature of Reporting Person Date /s/ Rose S. Shabet (8)(9) 06/26/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Pursuant to the Amended and Restated Certificate of Incorporation of the Issuer, upon the closing of its initial public offering (the "IPO"), each share of convertible preferred stock will be automatically converted into shares of common stock of the Issuer ("Common Stock") on a one-to-one basis. The 38,156,607 shares of stock reported on this form will convert into 38,156,607 shares of Common Stock upon the closing of the IPO. ( 2 )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"), ("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"). ( 3 )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. ( 4 )VGEM directly holds 14,006,625 shares of Series D Preferred Stock, 10,789,973 shares of Series E Preferred Stock, 1,411,467 shares of Series F Preferred Stock and 197,888 shares of Series F-1 Preferred Stock. VGE II directly holds 285,850 shares of Series D Preferred Stock, 220,204 shares of Series E Preferred Stock, 28,805 shares of Series F Preferred Stock and 4,039 shares of Series F-1 Preferred Stock. VLFM directly holds 4,616,470 shares of Series D Preferred Stock, 4,514,173 shares of Series E Preferred Stock, 567,468 shares of Series F Preferred Stock and 88,645 shares of Series F-1 Preferred Stock. Opportunities Fund directly holds 1,425,000 shares of Common Stock. ( 5 )VGI provides managerial services to the Viking Funds. Because of the relationship between VGI and the Viking Funds, VGI may be deemed to beneficially own the shares directly held by the Viking Funds. 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 directly held by VGE II and VGEM. 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 directly held by VLFM. ( 6 )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 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 held directly by Opportunities Fund. ( 7 )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: (8)The Reporting Persons are jointly filing this Form 3 pursuant to Rule 16a-3(j) under the Exchange Act.(9)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-M ASTER LP.(10)Because no more than 10 reporting persons can file any one Form 3 through the SEC's EDGAR system, VGP, VGE II, VGEM, VLFGP and VLFM have jointly filed with the Reporting Persons on a separate Form 3 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).

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