Sec Form 4 Filing - Polaris Venture Management Co. VI, L.L.C. @ Alector, Inc. - 2020-06-23

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 Polaris Venture Management Co. VI, L.L.C. 2. Issuer Name and Ticker or Trading Symbol Alector, Inc. [ ALEC] 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) ONE MARINA PARK DRIVE, 10TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 06/23/2020 (Street) BOSTON, MA02210 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 06/23/2020 S 4,377 ( 1 ) ( 2 ) D $ 31.5428 ( 3 ) 12,853,817 I See footnote ( 4 )

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 Polaris Venture Management Co. VI, L.L.C. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X Polaris Venture Partners VI (AIV), L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X Polaris Venture Partners Founders' Fund VI, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X Polaris Venture Partners VI, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X PVP VI (AIV) Feeder Corp. Holding Partnership, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X Signatures /s/ Lauren Crockett, as attorney in fact for Polaris Venture Management Co. VI, L.L.C. 06/25/2020 Signature of Reporting Person Date /s/ Lauren Crockett, as attorney in fact for Polaris Venture Management Co. VI, L.L.C., general partner of Polaris Venture Partners VI (AIV), L.P. 06/25/2020 Signature of Reporting Person Date /s/ Lauren Crockett, as attorney in fact for Polaris Venture Management Co. VI, L.L.C., general partner of Polaris Venture Partners Founders' Fund VI, L.P. 06/25/2020 Signature of Reporting Person Date /s/ Lauren Crockett, as attorney in fact for Polaris Venture Management Co. VI, L.L.C., general partner of Polaris Venture Partners VI, L.P. 06/25/2020 Signature of Reporting Person Date /s/ Lauren Crockett, as attorney in fact for Polaris Venture Management Co. VI, L.L.C., general partner of PVP VI (AIV) Feeder Corp. Holding Partnership, L.P. 06/25/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )242 shares were sold by Polaris Venture Partners Founders' Fund VI, L.P ("PVPFF VI"), 3,153 shares were sold by Polaris Venture Partners VI (AIV), L.P. ("PVP VI AIV") and 982 shares were sold by PVP VI (AIV) Feeder Corp. Holding Partnership, L.P. ("PVP VI Feeder" and, together with PVP VI AIV, PVPFF VI, and Polaris Venture Partners VI, L.P. ("PVP VI"), the "Polaris Funds"). The general partner of each of the Polaris Funds is Polaris Venture Management Co. VI, L.L.C. ("PVM"). Each of Amir Nashat, Brian Chee, David Barrett, Bryce Youngren, Jonathan Flint, and Terrance McGuire, a member of the Issuer's board of directors, are managing members of PVM (collectively, the "Managing Members") and may be deemed to have shared power to vote and dispose of the shares held by the Polaris Funds. ( 2 )(Continued from footnote 1) Each of the Managing Members and PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interest therein. ( 3 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $31.50 to $31.61, inclusive. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer or the staff of the Securities Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (3) to this Form 4. ( 4 )709,675 shares are held by PVPFF VI, 9,347,724 shares are held by PVP VI AIV, 2,297,950 shares are held by PVP VI Feeder and 498,468 shares are held by PVP VI. Each of the Managing Members and PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interest therein.

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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