Sec Form 4 Filing - Spring Mountain Capital G.P., LLC @ IsoPlexis Corp - 2021-10-12

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 Spring Mountain Capital G.P., LLC 2. Issuer Name and Ticker or Trading Symbol IsoPlexis Corp [ ISO] 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) 650 MADISON AVENUE, 20TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 10/12/2021 (Street) NEW YORK, NY10022 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 10/12/2021 C 894,128 ( 1 ) ( 5 ) A 894,128 I By SMC Growth Capital Partners II, LP ( 2 ) Common Stock 10/12/2021 C 338,959 ( 1 ) ( 6 ) A 1,233,087 I By SMC Growth Capital Partners II, LP ( 2 ) Common Stock 10/12/2021 C 630,209 ( 1 ) ( 7 ) A 1,863,296 I By SMC Growth Capital Partners II, LP ( 2 ) Common Stock 10/12/2021 C 739,033 ( 1 ) ( 8 ) A 2,602,329 I By SMC Growth Capital Partners II, LP ( 2 ) Common Stock 10/12/2021 C 689,267 ( 1 ) ( 9 ) A 3,291,596 I By SMC Growth Capital Partners II, LP ( 2 ) Common Stock 10/12/2021 C 435,136 ( 1 ) ( 10 ) A 3,726,732 I By SMC Growth Capital Partners II, LP ( 2 ) Common Stock 10/12/2021 C 744,083 ( 1 ) ( 11 ) A 744,083 I By SMC Private Equity Holdings, LP ( 3 ) Common Stock 10/12/2021 C 459,781 ( 1 ) ( 12 ) A 1,203,864 I By SMC Private Equity Holdings, LP ( 3 ) Common Stock 10/12/2021 C 415,337 ( 1 ) ( 13 ) A 1,619,201 I By SMC Private Equity Holdings, LP ( 3 ) Common Stock 10/12/2021 C 215,950 ( 1 ) ( 14 ) A 1,835,151 I By SMC Private Equity Holdings, LP ( 3 ) Common Stock 10/12/2021 C 435,136 ( 1 ) ( 15 ) A 2,270,287 I By SMC Private Equity Holdings, LP ( 3 ) Common Stock 10/12/2021 C 67,642 ( 1 ) ( 16 ) A 67,642 I By SMC Holdings II, LP ( 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 Series A Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 107,604 ( 1 ) ( 1 ) Common Stock 860,832 ( 1 ) $ 0 0 I By SMC Growth Capital Partners II, LP ( 2 ) Series A-2 Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 39,726 ( 1 ) ( 1 ) Common Stock 317,808 ( 1 ) $ 0 0 I By SMC Growth Capital Partners II, LP ( 2 ) Series A-2 Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 87,398 ( 1 ) ( 1 ) Common Stock 699,184 ( 1 ) $ 0 0 I By SMC Private Equity Holdings, LP ( 3 ) Series A-2 Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 7,945 ( 1 ) ( 1 ) Common Stock 63,560 ( 1 ) $ 0 0 I By SMC Holdings II, LP ( 4 ) Series B Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 73,571 ( 1 ) ( 1 ) Common Stock 588,568 ( 1 ) $ 0 0 I By SMC Growth Capital Partners II, LP ( 2 ) Series B Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 53,480 ( 1 ) ( 1 ) Common Stock 427,840 ( 1 ) $ 0 0 I By SMC Private Equity Holdings, LP ( 3 ) Series B-2 Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 84,347 ( 1 ) ( 1 ) Common Stock 674,776 ( 1 ) $ 0 0 I By SMC Growth Capital Partners II, LP ( 2 ) Series B-2 Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 47,403 ( 1 ) ( 1 ) Common Stock 379,224 ( 1 ) $ 0 0 I By SMC Private Equity Holdings, LP ( 3 ) Series C Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 78,999 ( 1 ) ( 1 ) Common Stock 631,992 ( 1 ) $ 0 0 I By SMC Growth Capital Partners II, LP ( 2 ) Series C Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 24,833 ( 1 ) ( 1 ) Common Stock 198,664 ( 1 ) $ 0 0 I By SMC Private Equity Holdings, LP ( 3 ) Series C-2 Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 51,522 ( 1 ) ( 1 ) Common Stock 412,176 ( 1 ) $ 0 0 I By SMC Growth Capital Partners II, LP ( 2 ) Series C-2 Redeemable Convertible Preferred Stock ( 1 ) 10/12/2021 C 51,522 ( 1 ) ( 1 ) Common Stock 412,176 ( 1 ) $ 0 0 I By SMC Private Equity Holdings, LP ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Spring Mountain Capital G.P., LLC 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X SMC Growth Capital II GP, LLC 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X SMC Growth Capital Partners II, LP 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X SMC Private Equity Holdings GP, LLC 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X SMC Private Equity Holdings, LP 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X SMC Holdings II G.P., LLC 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X SMC Holdings II, LP 65 EAST 55TH STREET, 33RD FLOOR NEW YORK, NY10022 X Ho Gregory P. 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X Steffens John 650 MADISON AVENUE, 20TH FLOOR NEW YORK, NY10022 X Signatures Spring Mountain Capital G.P., LLC, by Gregory P. Ho, as Managing Member /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date SMC Growth Capital II GP, LLC, by Spring Mountain Capital G.P., LLC, as Managing Member /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date SMC Growth Capital Partners II, LP, by SMC Growth Capital II GP, LLC, as its general partner /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date SMC Private Equity Holdings G.P., LLC, by Spring Mountain Capital G.P., LLC, as Managing Member /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date SMC Private Equity Holdings, LP, by SMC Private Equity Holdings G.P., as its general partner /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date SMC Holdings II G.P., LLC, by Gregory P. Ho, as Managing Member /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date SMC Holdings II, LP, by SMC Holdings II G.P., LLC, as its general partner /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date Gregory P. Ho /s/Gregory P. Ho 10/14/2021 Signature of Reporting Person Date John L. Steffens /s/John L. Steffens 10/14/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Shares of Series A Redeemable Convertible Preferred Stock, par value $0.001, of the Issuer, Series A-2 Redeemable Convertible Preferred Stock, par value $0.001, of the Issuer, Series B Redeemable Convertible Preferred Stock, par value $0.001, of the Issuer, Series B-2 Redeemable Convertible Preferred Stock, par value $0.001, of the Issuer, Series C Redeemable Convertible Preferred Stock, par value $0.001, of the Issuer and Series C-2 Redeemable Convertible Preferred Stock, par value $0.001, of the Issuer (collectively, the "Preferred Stock") were convertible on a one-for-eight basis into shares of Common Stock of the Issuer at the option of the holder at any time and automatically converted upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date. ( 2 )The securities are directly held by SMC Growth Capital Partners II, LP ("GCII"). SMC Growth Capital II GP, LLC, a Delaware limited liability company ("GCII GP"), is the general partner of GCII, and Spring Mountain Capital G.P., LLC, a Delaware limited liability company ("SMC GP"), is the managing member of GCII GP. John L. Steffens and Gregory P. Ho each serves as a managing member of SMC GP. Each of GCII GP, SMC GP, Mr. Steffens and Mr. Ho may be deemed to indirectly hold the securities held by GCII. GCII holds voting and dispositive power over the securities it holds. Each of Mr. Steffens, Mr. Ho, GCII GP and SMC GP disclaims beneficial ownership of these securities, except to the extent of their respective pecuniary interests therein. ( 3 )The securities are directly held by SMC Private Equity Holdings, LP ("PEH"). SMC Private Equity Holdings G.P., LLC, a Delaware limited liability company ("PEH GP"), is the general partner of PEH, and SMC GP is the managing member of PEH GP. Mr. Steffens and Mr. Ho each serves as a managing member of SMC GP. Each of PEH GP, SMC GP, Mr. Steffens and Mr. Ho may be deemed to indirectly hold the securities held by PEH. PEH holds voting and dispositive power over the securities it holds. Each of Mr. Steffens, Mr. Ho, PEH GP and SMC GP disclaims beneficial ownership of these securities, except to the extent of their respective pecuniary interests therein. ( 4 )The securities are directly held by SMC Holdings II, LP ("Holdings"). SMC Holdings II G.P., LLC, a Delaware limited liability company ("Holdings GP"), is the general partner of Holdings. Mr. Steffens and Mr. Ho each serves as a managing member of Holdings GP. Each of Holdings GP, Mr. Steffens and Mr. Ho may be deemed to indirectly hold the securities held by Holdings. Holdings holds voting and dispositive power over the securities it holds. Each of Mr. Steffens, Mr. Ho and Holdings GP disclaims beneficial ownership of these securities, except to the extent of their respective pecuniary interests therein. ( 5 )Includes 33,296 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 6 )Includes 21,151 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 7 )Includes 41,641 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 8 )Includes 64,257 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 9 )Includes 57,275 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 10 )Includes 22,960 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 11 )Includes 44,899 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 12 )Includes 31,941 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 13 )Includes 36,113 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 14 )Includes 17,286 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 15 )Includes 22,960 shares of Common Stock issued per dividends accrued to but not including October 12, 2021. ( 16 )Includes 4,082 shares of Common Stock issued per dividends accrued to but not including October 12, 2021.

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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