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*
22NW, LP	

(Last)	(First)	(Middle)	
1455 NW LEARY WAY, SUITE 400	

(Street) 
SEATTLE	WA	98107	

(City)	(State)	(Zip)	
	2. Date of Event Requiring Statement (Month/Day/Year)
03/13/2019 	3. Issuer Name and Ticker or Trading Symbol 
MERRIMACK PHARMACEUTICALS INC [ MACK ] 		
		4. Relationship of Reporting Person(s) to Issuer 
(Check all applicable) 
	Director	X	10% Owner	
	Officer (give title below)	X	Other (specify below)	
See Explanation of Responses 	
	5. If Amendment, Date of Original Filed (Month/Day/Year)				
			6. Individual or Joint/Group Filing (Check Applicable Line) 
	Form filed by One Reporting Person	
X	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(1) 	1,092,263	I	By: 22NW Fund, LP(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) 	
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares				
1. Name and Address of Reporting Person*
22NW, LP	

(Last)	(First)	(Middle)	
1455 NW LEARY WAY, SUITE 400	

(Street) 
SEATTLE	WA	98107	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
22NW Fund, LP	

(Last)	(First)	(Middle)	
1455 NW LEARY WAY	
SUITE 400	

(Street) 
SEATTLE	WA	98107	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
22NW Fund GP, LLC	

(Last)	(First)	(Middle)	
1455 NW LEARY WAY, SUITE 400	

(Street) 
SEATTLE	WA	98107	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
English Aron R.	

(Last)	(First)	(Middle)	
1455 NW LEARY WAY, SUITE 400	

(Street) 
SEATTLE	WA	98107	

(City)	(State)	(Zip)	
	
Explanation of Responses:	
1. This Form 3 is filed jointly by 22NW Fund, LP ("22NW Fund"), 22NW, LP ("22NW"), 22NW Fund GP, LLC ("22NW GP") and Aron R. English (collectively, the "Reporting Persons"). Each of the Reporting Persons may be deemed to be a member of a Section 13(d) group that collectively beneficially owns more than 10% of the Issuer's outstanding shares of Common Stock. Each of the Reporting Persons disclaims beneficial ownership of the securities of the Issuer owned directly by other members of the Section 13(d) group and this report shall not be deemed an admission that the Reporting Persons are the beneficial owners of such securities for purposes of Section 16 or for any other purpose. Further, each of the Reporting Persons expressly disclaims beneficial ownership of the securities reported herein except to the extent of his or its pecuniary interest therein.	
2. Securities owned directly by 22NW Fund. As the general partner and investment adviser to 22NW Fund, 22NW may be deemed to beneficially own the securities owned directly by 22NW Fund. As the general partner of 22NW, 22NW GP may be deemed to beneficially own the securities owned directly by 22NW Fund. Mr. English, as the Portfolio Manager of 22NW and Managing Member of 22NW GP, may be deemed to beneficially own the securities owned directly by 22NW Fund.	
	22NW Fund, LP; By: 22NW, LP; By: 22NW Fund GP, LLC; By: /s/ Aron R. English, Managing Member	03/20/2019	
	22NW, LP; By: 22NW Fund GP, LLC; By: /s/ Aron R. English, Managing Member	03/20/2019	
	22NW Fund GP, LLC; By: /s/ Aron R. English, Managing Member	03/20/2019	
	/s/ Aron R. English	03/20/2019	
	** 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.