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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* Sendek Joel (Last) (First) (Middle) C/O SPERO THERAPEUTICS, INC. 675 MASSACHUSETTS AVENUE, 14TH FLOOR (Street) CAMBRIDGE MA 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) Director 10% Owner X Officer (give title below) Other (specify below) Chief Financial Officer	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)

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)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series C Preferred Stock	(1)	(1)	Common Stock	10,181(2)	(1)	I	Joel D. Sendek Retained Annuity Trust No. 1
Stock Option (Right to Buy)	(3)	07/05/2027	Common Stock	67,852(4)	$5.9(4)	D
Stock Option (Right to Buy)	(5)	07/05/2027	Common Stock	99,981(4)	$5.9(4)	D

Explanation of Responses:

1. 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.

2. The share number gives effect to the 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017.

3. The shares underlying this option vest as to 25% on May 1, 2018, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

4. The number of underlying shares of common stock and the exercise price reported reflect a 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017.

5. The shares underlying this option vest as to 25% on May 1, 2018, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

Remarks:

Exhibit 24.1 - Power of Attorney

	/s/ Matthew Tikonoff, Attorney-in-Fact for Joel Sendek	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).
** 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.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.