Sec Form 3 Filing - Polaris Venture Management Co. VI, L.L.C. @ Alector, Inc. - 2019-02-06

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 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) 02/06/2019 (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

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 A-1 Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 500,000 I See footnote ( 2 ) Series A-2 Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 5,274,725 I See footnote ( 3 ) Series B Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 2,500,000 I See footnote ( 4 ) Series C Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 2,808,989 I See footnote ( 5 ) Series D Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 1,246,883 I See footnote ( 6 ) Series E Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 527,597 I See footnote ( 7 )

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 PVP VI (AIV) Feeder Corp. Holding Partnership, 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 Signatures /s/ Terrance McGuire, Managing Member of Polaris Venture Management Co. VI, L.L.C. 02/06/2019 Signature of Reporting Person Date /s/ Terrance McGuire, Managing Member of Polaris Venture Management Co. VI, L.L.C., general partner of Polaris Venture Partners VI (AIV), L.P. 02/06/2019 Signature of Reporting Person Date /s/ Terrance McGuire, Managing Member of Polaris Venture Management Co. VI, L.L.C., general partner of Polaris Venture Partners Founders' Fund VI, L.P. 02/06/2019 Signature of Reporting Person Date /s/ Terrance McGuire, Managing Member of Polaris Venture Management Co. VI, L.L.C., general partner of PVP VI (AIV) Feeder Corp. Holding Partnership, L.P. 02/06/2019 Signature of Reporting Person Date /s/ Terrance McGuire, Managing Member of Polaris Venture Management Co. VI, L.L.C., general partner of Polaris Venture Partners VI, L.P. 02/06/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each of the Series A-1 Preferred Stock, Series A-2 Preferred Stock, Series B Preferred Stock, Series C Preferred Stock, Series D Preferred Stock and Series E Preferred Stock is convertible into Common Stock on a one-for-one basis into the number of shares of Common Stock shown in Column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 2 )27,606 shares are held by Polaris Venture Partners Founders' Fund VI, L.P ("PVPFF VI"), 379,174 shares are held by Polaris Venture Partners VI (AIV), L.P. ("PVP VI AIV") and 93,220 shares are held 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"). PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that PVM is the beneficial owner of such securities, except to the extent of its pecuniary interest therein, if any. ( 3 )291,223 shares are held by PVPFF VI, 4,000,075 shares are held by PVP VI AIV and 983,427 shares are held by PVP VI Feeder. PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that PVM is the beneficial owner of such securities, except to the extent of its pecuniary interest therein, if any. ( 4 )138,030 shares are held by PVPFF VI, 1,895,867 shares are held by PVP VI AIV and 466,103 shares are held by PVP VI Feeder. PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that PVM is the beneficial owner of such securities, except to the extent of its pecuniary interest therein, if any. ( 5 )155,087 shares are held by PVPFF VI, 2,130,190 shares are held by PVP VI AIV and 523,712 shares are held by PVP VI Feeder. PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that PVM is the beneficial owner of such securities, except to the extent of its pecuniary interest therein, if any. ( 6 )68,842 shares are held by PVPFF VI, 945,571 shares are held by PVP VI AIV and 232,470 shares are held by PVP VI Feeder. PVM disclaims beneficial ownership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that PVM is the beneficial owner of such securities, except to the extent of its pecuniary interest therein, if any. ( 7 )29,129 shares are held by PVPFF VI and 498,468 shares are held by PVP VI. PVM disclaims beneficial own ership of the securities held by the Polaris Funds, and this report shall not be deemed an admission that PVM is the beneficial owner of such securities, 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.

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