JOINT FILING AGREEMENT
Exhibit
A
The
undersigned hereby agree that the Statement on this Schedule 13D, dated June 3,
2008 (the “Schedule 13D”), with respect to the Common Stock, par value
$.001 per share, of NxStage Medical, Inc. is filed on behalf of each
of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under
the Securities Exchange Act of 1934, as amended, and that this Agreement shall
be included as an Exhibit to this Schedule 13D. Each of the
undersigned agrees to be responsible for the timely filing of the Schedule 13D,
and for the completeness and accuracy of the information concerning itself
contained therein. This Agreement may be executed in any number of
counterparts, all of which taken together shall constitute one and the same
instrument.
IN
WITNESS WHEREOF, the undersigned have executed this Agreement as of the 3rd day of
June, 2008.
| OrbiMed Advisors LLC | |||
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By:
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/s/ Xxxxxx X. Xxxxx | ||
| Name: Xxxxxx X. Xxxxx | |||
| Title: Managing Partner | |||
| OrbiMed Capital GP III LLC | |||
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By:
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/s/ Xxxxxx X. Xxxxx | ||
| Name: Xxxxxx X. Xxxxx | |||
| Title: Managing Partner | |||
|
|
|
By:
|
/s/ Xxxxxx X. Xxxxx | ||
| Name: Xxxxxx X. Xxxxx |
