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

1. Name and Address of Reporting Person *

Breum Casper 		2. Issuer Name and Ticker or Trading Symbol

Spero Therapeutics, Inc. [ SPRO ] 		5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

__ X __ Director                      _____ 10% Owner
_____ Officer (give title below)      _____ Other (specify below)
(Last)          (First)          (Middle)

C/O LUNDBECKFOND INVEST A/S, SCHERFIGSVEJ 7 		3. Date of Earliest Transaction (MM/DD/YYYY)

11/6/2017
(Street)

COPENHAGEN, G7 DK-2100
(City)        (State)        (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)

 
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 Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. 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   11/6/2017     C    289102   A   (2) 289102   I   Lundbeckfond Invest A/S   (3)
Common Stock   11/6/2017     C    179450   A   (2) 468552   I   Lundbeckfond Invest A/S   (3)
Common Stock   11/6/2017     C    408937   A   (2) 877489   I   Lundbeckfond Invest A/S   (3)
Common Stock   11/6/2017     P    214285   (1) A $14.00   1091774   I   Lundbeckfond Invest A/S   (3)

Table II - Derivative Securities Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3) 		2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. 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 7. Title and Amount of Securities Underlying Derivative Security
(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 Preferred Stock     (2) 11/6/2017     C         1153846      (2)   (2) Common Stock   289102   $0.00   0   I   Lundbeckfond Invest A/S   (3)
Series B Preferred Stock     (2) 11/6/2017     C         681818      (2)   (2) Common Stock   179450   $0.00   0   I   Lundbeckfond Invest A/S   (3)
Series C Preferred Stock     (2) 11/6/2017     C         2485272      (2)   (2) Common Stock   408937   $0.00   0   I   Lundbeckfond Invest A/S   (3)

Explanation of Responses:
(1)  Reflects shares of the Issuer's common stock that were purchased in connection with the Issuer's initial public offering.
(2)  Amount of underlying securities reflects the application of the applicable conversion ratio as set forth in the Issuer's Amended and Restated Certificate of Incorporation in effect immediately prior to the closing of the initial public offering (as adjusted by the 1-for-6.0774 reverse stock split of the Issuer's common stock effected on October 20, 2017). The preferred stock had no expiration date.
(3)  Shares held by Lundbeckfond Invest A/S. The Reporting Person shares voting and investment power with respect to the shares held by Lundbeckfond Invest A/S and disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
Breum Casper
C/O LUNDBECKFOND INVEST A/S
SCHERFIGSVEJ 7
COPENHAGEN, G7 DK-2100 		X



Signatures
/s/ Matthew Tikonoff, Attorney-in-Fact for Casper Breum 11/7/2017
** 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 4(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 control number.
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