Edgar Filing: Nielsen Ulrik B.

Ownership Submission

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person ^*

Â Nielsen Ulrik B.

2. Date of Event Requiring Statement (Month/Day/Year)
01/31/2012

3. Issuer Name and Ticker or Trading Symbol
MERRIMACK PHARMACEUTICALS INC [MACK]

(Last)

(First)

(Middle)

C/O MERRIMACK PHARMACEUTICALS, INC.,Â ONE KENDALL SQUARE, SUITE B7201

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

_____ Director	_____ 10% Owner
__X__ Officer (give title below)	_____ Other (specify below)
SVP and CSO

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

(Street)

CAMBRIDGE,Â MAÂ 02139

6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

(City)

(State)

(Zip)

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	247,443	D	Â

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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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 of Derivative Security: 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		6. Nature of Indirect Beneficial Ownership (Instr. 5)
Stock Option (right to buy)	Â ⁽¹⁾	08/02/2012	Common Stock	4,368	$ 2.19	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	05/08/2013	Common Stock	10,483	$ 2.19	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	08/30/2014	Common Stock	150,000	$ 1.25	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	08/03/2015	Common Stock	82,977	$ 1.71	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	08/03/2015	Common Stock	17,023	$ 1.71	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	10/03/2016	Common Stock	48,175	$ 2.47	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	10/03/2016	Common Stock	26,825	$ 2.47	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	10/04/2017	Common Stock	53,378	$ 2.59	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	10/04/2017	Common Stock	146,622	$ 2.59	D	Â
Stock Option (right to buy)	Â ⁽¹⁾	09/21/2018	Common Stock	250,000	$ 1.81	D	Â
Stock Option (right to buy)	Â ⁽²⁾	11/04/2019	Common Stock	180,000	$ 2.12	D	Â
Stock Option (right to buy)	Â ⁽³⁾	01/31/2020	Common Stock	100,000	$ 2.12	D	Â
Stock Option (right to buy)	Â ⁽⁴⁾	10/14/2020	Common Stock	60,000	$ 2.69	D	Â
Stock Option (right to buy)	Â ⁽⁵⁾	12/21/2020	Common Stock	50,000	$ 2.69	D	Â
Stock Option (right to buy)	Â ⁽⁶⁾	05/02/2021	Common Stock	100,000	$ 5.54	D	Â

Reporting Owners

Reporting Owner Name / Address	Relationships
Reporting Owner Name / Address	Director	10% Owner	Officer	Other
Nielsen Ulrik B. C/O MERRIMACK PHARMACEUTICALS, INC. ONE KENDALL SQUARE, SUITE B7201 CAMBRIDGE,Â MAÂ 02139	Â	Â	Â SVP and CSO	Â

Signatures

/s/ Jeffrey A. Munsie, attorney-in-fact		02/01/2012
^**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	This option is fully vested.
(2)	This option vested as to 1/12th of the shares on each of November 5, 2009 and February 1, 2010 and vests in equal quarterly installments thereafter until August 1, 2012.
(3)	This option vested as to 1/12th of the shares on April 1, 2010 and vests in equal quarterly installments thereafter until January 1, 2013.
(4)	This option vested as to 1/12th of the shares on each of October 15, 2010 and January 1, 2011 and vests in equal quarterly installments thereafter until July 1, 2013.
(5)	This option vested as to 1/6th of the shares on January 1, 2011 and vests in equal quarterly installments thereafter until July 1, 2013.
(6)	This option vested as to 1/12th of the shares on August 1, 2011 and vests in equal quarterly installments thereafter until May 1, 2014.

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