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^*

Parr Thomas R JR

(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)

	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	Chief Scientific 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)
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)
Stock Option (Right to Buy)	⁽¹⁾	07/05/2027	Common Stock	13,687⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽³⁾	07/05/2027	Common Stock	10,037⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽⁴⁾	07/05/2027	Common Stock	3,454⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽⁵⁾	07/05/2027	Common Stock	411⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽⁶⁾	07/05/2027	Common Stock	411⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽⁷⁾	07/05/2027	Common Stock	8,920⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽⁸⁾	07/05/2027	Common Stock	6,371⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽⁹⁾	07/05/2027	Common Stock	20,932⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽¹⁰⁾	07/05/2027	Common Stock	46,195⁽²⁾	$5.9⁽²⁾	D
Stock Option (Right to Buy)	⁽¹¹⁾	07/05/2027	Common Stock	31,981⁽²⁾	$5.9⁽²⁾	D

Explanation of Responses:

1. The shares underlying this option vested as to 25% on April 14, 2015, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

2. 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.

3. The shares underlying this option vested to 25% on August 24, 2016, 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 shares underlying this option vested as to 25% on August 24, 2016, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

5. The shares underlying this option vested as to 25% on December 1, 2016, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

6. The shares underlying this option vested as to 25% on December 1, 2016, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

7. The shares underlying this option vested as to 25% on April 28, 2017, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

8. The shares underlying this option vested as to 25% on April 28, 2017, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

9. All shares underlying this option were fully vested as of July 6, 2017.

10. The shares underlying this option vest as to 25% on July 6, 2018, with the remainder vesting in 36 equal monthly installments thereafter, subject to the Reporting Person's continued service through the applicable vesting date.

11. The shares underlying this option vest as to 25% on July 6, 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 Thomas Parr Jr.	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.