Sec Form 4 Filing - Flagship Ventures Fund IV General Partner LLC @ Kaleido Biosciences, Inc. - 2021-02-08

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 IV 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) _____ 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) 02/08/2021 (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 02/08/2021 P 71,666 ( 1 ) A $ 11.5 1,685,444 I See Footnote ( 2 ) Common Stock 02/08/2021 P 71,667 ( 3 ) A $ 11.5 2,982,639 I See Footnote ( 4 ) Common Stock 02/08/2021 P 71,667 ( 5 ) A $ 11.5 738,333 I See Footnote ( 6 ) Common Stock 42,865 I See Footnote ( 7 ) Common Stock 2,500,000 I See Footnote ( 8 ) Common Stock 2,560,096 I See Footnote ( 9 ) Common Stock 639,360 I See Footnote ( 10 ) Common Stock 6,560,523 I See Footnote ( 11 ) Common Stock 216,451 I See Footnote ( 12 ) Common Stock 1,649,999 I See Footnote ( 13 )

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 Flagship Ventures Fund IV General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Flagship Ventures Fund IV, 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 Flagship Ventures Opportunities Fund I, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Nutritional Health LTP Fund General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Nutritional Health LTP Fund, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X AFEYAN NOUBAR 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA02142 X Signatures Flagship Ventures Fund IV General Partner LLC, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 02/10/2021 Signature of Reporting Person Date Flagship Ventures Fund IV, L.P., By: Flagship Ventures Fund IV General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 02/10/2021 Signature of Reporting Person Date Flagship Ventures Opportunities Fund I General Partner LLC, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 02/10/2021 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, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 02/10/2021 Signature of Reporting Person Date Nutritional Health LTP Fund General Partner LLC, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 02/10/2021 Signature of Reporting Person Date Nutritional Health LTP Fund, L.P., By: Nutritional Health LTP Fund General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 02/10/2021 Signature of Reporting Person Date Noubar B. Afeyan, Ph.D. By: /s/ Noubar B. Afeyan, Ph.D. 02/10/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On February 8, 2021, Flagship Ventures Fund IV, L.P. ("Flagship Fund IV") acquired 71,666 shares pursuant to an underwritten public offering of common stock by the Issuer (the "Offering"). ( 2 )Shares held by Flagship Fund IV. Flagship Ventures Fund IV General Partner LLC ("Flagship Fund IV GP") is the general partner of Flagship Fund IV. Noubar B. Afeyan, Ph.D. ("Dr. Afeyan") is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 3 )On February 8, 2021, Flagship Ventures Opportunities Fund I, L.P. ("Flagship Opportunities I") acquired 71,667 shares pursuant to the Offering. ( 4 )Shares held by Flagship Opportunities I. Flagship Ventures Opportunities Fund I General Partner LLC ("Flagship Opportunities GP") is the general partner of Flagship Opportunities I. Dr. Afeyan serves as sole manager of Flagship Opportunities GP. Each of the reporting persons except for Flagship Opportunities I disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 5 )On February 8, 2021, Nutritional Health LTP Fund, L.P. ("Nutritional LTP") acquired 71,667 shares pursuant to the Offering. ( 6 )Shares held by Nutritional LTP. Nutritional Health LTP Fund General Partner LLC ("Nutritional LTP GP") is the general partner of Nutritional LTP. Dr. Afeyan is the sole member and manager of Nutritional LTP GP. Each of the reporting persons except for Nutritional LTP disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 7 )Shares held by Flagship VentureLabs IV, LLC ("VentureLabs IV"). Flagship Fund IV is a member of VentureLabs IV and also serves as its manager. Flagship Fund IV GP is the general partner of Flagship Fund IV. Dr. Afeyan is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for VentureLabs IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 8 )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. Dr. Afeyan serves as sole manager of Flagship Fund V GP and as sole director of Flagship Pioneering. Each of the reporting persons except for VentureLabs V disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 9 )Shares held by Flagship Fund V. Flagship Fund V GP is the general partner of Flagship Fund V. Dr. Afeyan serves as sole manager of Flagship Fund V GP. Each of the reporting persons except for Flagship Fund V disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 10 )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. Dr. Afeyan serves as sole manager of Flagship Fund V GP. Each of the reporting persons except for Nutritional Health Side Fund disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 11 )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. Dr. Afeyan serves as sole manager of Flagship Fund V GP. Each of the reporting persons except for Nutritional Innovation Fund disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 12 )Shares held by Flagship Ventures Fund 2007, L.P. ("Flagship Fund 2007"). Flagship Ventures 2007 General Partner LLC ("Fund 2007 GP") is the general partner of Flagship Fund 2007. Dr. Afeyan is the sole manager of Fund 2007 GP. Each of the reporting persons except for Flagship Fund 2007 disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. ( 13 )Shares held by Cadena LLC ("Cadena"). Dr. Afeyan is the sole manager of Cadena. Each of the reporting persons except for Cadena disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.

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