Sec Form 4 Filing - Flagship Ventures Fund V General Partner LLC @ Kaleido Biosciences, Inc. - 2019-03-04

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 Flagship Ventures Fund V General Partner LLC 2. Issuer Name and Ticker or Trading Symbol Kaleido Biosciences, Inc. [ KLDO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 55 CAMBRIDGE PARKWAY, SUITE 800E 3. Date of Earliest Transaction (MM/DD/YY) 03/04/2019 (Street) CAMBRIDGE, MA02142 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 2,500,000 I See Footnote ( 1 ) Common Stock 03/04/2019 C 1,545,852 A 1,545,852 I See Footnote ( 3 ) Common Stock 03/04/2019 C 4,637,555 A 4,637,555 I See Footnote ( 4 ) Common Stock 03/04/2019 C 426,240 A 1,972,092 I See Footnote ( 3 ) Common Stock 03/04/2019 C 639,360 A 639,360 I See Footnote ( 6 ) Common Stock 03/04/2019 C 321,337 A 2,293,429 I See Footnote ( 3 ) Common Stock 03/04/2019 C 964,010 A 5,601,565 I See Footnote ( 4 ) Common Stock 03/04/2019 C 1,285,347 A 1,285,347 I See Footnote ( 9 ) Common Stock 03/04/2019 C 625,625 A 6,227,190 I See Footnote ( 4 ) Common Stock 03/04/2019 C 625,625 A 1,910,972 I See Footnote ( 9 ) Common Stock 03/04/2019 P 266,667 A $ 15 2,560,096 I See Footnote ( 3 ) Common Stock 03/04/2019 P 333,333 A $ 15 6,560,523 I See Footnote ( 4 ) Common Stock 03/04/2019 P 333,333 A $ 15 2,244,305 I See Footnote ( 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 A Preferred Stock ( 2 ) 03/04/2019 C 3,091,704 ( 2 ) ( 2 ) Common Stock 1,545,852 ( 2 ) 0 I See Footnote ( 3 ) Series A Preferred Stock ( 2 ) 03/04/2019 C 9,275,111 ( 2 ) ( 2 ) Common Stock 4,637,555 ( 2 ) 0 I See Footnote ( 4 ) Series A-1 Preferred Stock ( 5 ) 03/04/2019 C 852,480 ( 5 ) ( 5 ) Common Stock 426,240 ( 5 ) 0 I See Footnote ( 3 ) Series A-1 Preferred Stock ( 5 ) 03/04/2019 C 1,278,720 ( 5 ) ( 5 ) Common Stock 639,360 ( 5 ) 0 I See Footnote ( 6 ) Series B Preferred Stock ( 7 ) 03/04/2019 C 642,674 ( 7 ) ( 7 ) Common Stock 321,337 ( 7 ) 0 I See Footnote ( 3 ) Series B Preferred Stock ( 7 ) 03/04/2019 C 1,928,021 ( 7 ) ( 7 ) Common Stock 964,010 ( 7 ) 0 I See Footnote ( 4 ) Series B Preferred Stock ( 7 ) 03/04/2019 C 2,570,694 ( 7 ) ( 7 ) Common Stock 1,285,347 ( 7 ) 0 I See Footnote ( 9 ) Series C Preferred Stock ( 8 ) 03/04/2019 C 1,251,251 ( 8 ) ( 8 ) Common Stock 625,625 ( 8 ) 0 I See Footnote ( 4 ) Series C Preferred Stock ( 8 ) 03/04/2019 C 1,251,251 ( 8 ) ( 8 ) Common Stock 625,625 ( 8 ) 0 I See Footnote ( 9 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Flagship Ventures Fund V General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X X Flagship Ventures Fund V, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Flagship VentureLabs V LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Flagship VentureLabs V Manager LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Flagship Pioneering Inc. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Nutritional Health Disruptive Innovation Fund, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Nutritional Health Side Fund, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Flagship Ventures Opportunities Fund I, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Flagship Ventures Opportunities Fund I General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X AFEYAN NOUBAR 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X X Signatures Flagship Ventures Fund V General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 03/06/2019 Signature of Reporting Person Date Flagship Ventures Fund V, L.P., By: Flagship Ventures Fund V General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 03/06/2019 Signature of Reporting Person Date Flagship Pioneering, Inc., By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Sole Director 03/06/2019 Signature of Reporting Person Date Flagship VentureLabs V Manager LLC, By: Flagship Pioneering, Inc., its manager, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Sole Director 03/06/2019 Signature of Reporting Person Date Flagship VentureLabs V LLC, By: Flagship VentureLabs V Manager LLC, its manager, By: Flagship Pioneering, Inc., its manager, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Sole Director 03/06/2019 Signature of Reporting Person Date Nutritional Health Disruptive Innovation Fund, L.P., By: Flagship Ventures Fund V General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 03/06/2019 Signature of Reporting Person Date Nutritional Health Side Fund, L.P., By: Flagship Ventures Fund V General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 03/06/2019 Signature of Reporting Person Date Flagship Ventures Opportunities Fund I General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 03/06/2019 Signature of Reporting Person Date Flagship Ventures Opportunities Fund I, L.P., By: Flagship Ventures Opportunities Fund I General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager 03/06/2019 Signature of Reporting Person Date Noubar B. Afeyan, Ph.D., By: /s/ Noubar B. Afeyan 03/06/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Shares held by Flagship VentureLabs V LLC ("VentureLabs V"). Flagship Ventures Fund V, L.P. ("Flagship Fund V") is a member of VentureLabs V. Flagship Ventures Fund V General Partner LLC ("Flagship Fund V GP") is the general partner of Flagship Fund V. Flagship VentureLabs V Manager LLC ("VentureLabs V Manager") serves as manager of VentureLabs V. Flagship Pioneering, Inc. ("Flagship Pioneering") is the manager of VentureLabs V Manager. Noubar B. Afeyan, Ph.D. serves as sole manager of Flagship Fund V GP and as sole director of Flagship Pioneering. Each of these entities and Noubar B. Afeyan, Ph.D. may be deemed to share voting and investment power with respect to all shares held by VentureLabs V. Each of the reporting persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. ( 2 )Each share of Series A Preferred Stock converted into shares of the Issuer's common stock, par value $0.001 ("Common Stock"), on a one-for-two basis upon the closing of the Issuer's initial public offering. ( 3 )Shares held by Flagship Fund V. Flagship Fund V GP is the general partner of Flagship Fund V. Noubar B. Afeyan, Ph.D. serves as sole manager of Flagship Fund V GP and may be deemed to possess sole voting and investment power with respect to all shares held by Flagship Fund V. Each of the reporting persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. ( 4 )Shares held by Nutritional Health Disruptive Innovation Fund, L.P. ("Nutritional Innovation Fund"). Flagship Fund V GP is the general partner of Nutritional Innovation Fund. Noubar B. Afeyan, Ph.D. serves as sole manager of Flagship Fund V GP and may be deemed to possess sole voting and investment power with respect to all shares held by Nutritional Innovation Fund. Each of the reporting persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. ( 5 )Each share of Series A-1 Preferred Stock converted into shares of the Issuer's Common Stock on a one-for-two basis upon the closing of the Issuer's initial public offering. ( 6 )Shares held by Nutritional Health Side Fund, L.P. ("Nutritional Health Side Fund"). Flagship Fund V GP is the general partner of Nutritional Health Side Fund. Noubar B. Afeyan, Ph.D. serves as sole manager of Flagship Fund V GP and may be deemed to possess sole voting and investment power with respect to all shares held by Nutritional Health Side Fund. Each of the reporting persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. ( 7 )Each share of Series B Preferred Stock converted into shares of the Issuer's Common Stock on a one-for-two basis upon the closing of the Issuer's initial public offering. ( 8 )Each share of Series C Preferred Stock converted into shares of the Issuer's Common Stock on a one-for-two basis upon the closing of the Issuer's initial public offering. ( 9 )Shares held by Flagship Ventures Opportunities Fund I, L.P. ("Flagship Opportunities I"). Flagship Ventures Opportunities Fund I General Partner LLC ("Flagship Opportunities GP") is the general partner of Flagship Opportunities I. Noubar B. Afeyan, Ph.D. serves as sole manager of Flagship Opportunities GP and may be deemed to possess sole voting and investment power with respect to all shares held by Flagship Opportunities I. Each of the reporting persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

Remarks: Due to limitations of the electronic filing system, each of Flagship Ventures Fund IV General Partner LLC, Flagship Ventures Fund IV, L.P., Flagship VentureLabs IV LLC, Flagship Ventures 2007 General Partner LLC, Flagship Ventures Fund 2007, L.P., Cadena LLC, Edwin M. Kania Jr. and Noubar B. Afeyan, Ph.D. are filing a separate Form 4 with respect to securities of the Issuer.

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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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