SEC FORM 3

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

FORMELA JEAN FRANCOIS

(Last)

(First)

(Middle)

C/O SPERO THERAPEUTICS, INC.

675 MASSACHUSETTS AVENUE, 14TH FLOOR

(Street)

CAMBRIDGE

02139

(City)

(State)

(Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
11/01/2017

3. Issuer Name and Ticker or Trading Symbol
Spero Therapeutics, Inc. [ SPRO ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director	10% Owner
	Officer (give title below)	Other (specify below)

5. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	42,781⁽¹⁾	I	See Footnote⁽²⁾

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
1. Title of Derivative Security (Instr. 4)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
Junior Preferred Stock	⁽³⁾	⁽³⁾	Common Stock	245,605⁽⁴⁾	⁽³⁾	I	See Footnote⁽²⁾
Series A Preferred Stock	⁽⁵⁾	⁽⁵⁾	Common Stock	246,272⁽⁴⁾	⁽⁵⁾	I	See Footnote⁽²⁾
Series B Preferred Stock	⁽⁶⁾	⁽⁶⁾	Common Stock	328,992⁽⁴⁾	⁽⁶⁾	I	See Footnote⁽²⁾
Series C Preferred Stock	⁽⁷⁾	⁽⁷⁾	Common Stock	513,318⁽⁴⁾	⁽⁷⁾	I	See Footnote⁽²⁾
Series C Preferred Stock	⁽⁷⁾	⁽⁷⁾	Common Stock	602,589⁽⁴⁾	⁽⁷⁾	I	See Footnote⁽⁸⁾

Explanation of Responses:

1. The number of shares reported reflects a 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017.

2. Shares held by Atlas Venture Fund IX, L.P. ("Atlas Venture Fund IX"). The general partner of Atlas Venture Fund IX is Atlas Venture Associates IX, L.P. ("AVA IX LP"). Atlas Venture Associates IX, LLC ("AVA IX LLC") is the general partner of AVA IX LP. Dr. Formela is a member of AVA IX LLC and disclaims beneficial ownership of such shares, except to the extent of his pecuniary interest therein, if any.

3. The shares of Junior preferred stock are convertible into the number of shares of common stock shown in Column 3, calculated using the conversion ratio set forth in the Issuer's Amended and Restated Certificate of Incorporation, as amended, at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The shares have no expiration date.

4. Share numbers give effect to the 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017.

5. The shares of Series A preferred stock are convertible into the number of shares of common stock shown in Column 3, calculated using the conversion ratio set forth in the Issuer's Amended and Restated Certificate of Incorporation, as amended, at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The shares have no expiration date.

6. The shares of Series B preferred stock are convertible into the number of shares of common stock shown in Column 3, calculated using the conversion ratio set forth in the Issuer's Amended and Restated Certificate of Incorporation, as amended, at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The shares have no expiration date.

7. The shares of Series C preferred stock are convertible into the number of shares of common stock shown in Column 3, calculated using the conversion ratio set forth in the Issuer's Amended and Restated Certificate of Incorporation, as amended, at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The shares have no expiration date.

8. Shares held by Atlas Venture Fund X, L.P. ("Atlas Venture Fund X") The general partner of Atlas Venture Fund X is Atlas Venture Associates X, L.P. ("AVA X LP"). Atlas Venture Associates X, LLC ("AVA X LLC") is the general partner of AVA X LP. Dr. Formela is a member of AVA X LLC and disclaims beneficial ownership of such shares, except to the extent of his pecuniary interest therein, if any.

Remarks:

Exhibit 24.1 - Power of Attorney

	/s/ Frank Castellucci, Attorney-in-Fact for Jean-Francois Formela	11/01/2017
	** Signature of Reporting Person	Date
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 5 (b)(v).
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