EXHIBIT A
AGREEMENT REGARDING JOINT FILING
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The undersigned, Biotechnology Value Fund, L.P., a Delaware limited
partnership, BVF Partners L.P., a Delaware limited partnership, and BVF Inc., a
Delaware corporation, hereby agree and acknowledge that the Amendment containing
the information required by Schedule 13D, to which this Agreement is attached as
an exhibit, is filed on behalf of each of them. The undersigned further agree
that any further amendments or supplements thereto shall also be filed on behalf
of each of them.
Dated: February 27, 1998
BIOTECHNOLOGY VALUE FUND, L.P.
By: BVF Partners L.P., its general partner
By: BVF Inc., its general partner
By: /s/ Xxxx X. Xxxxxxx
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Xxxx X. Xxxxxxx
President
BVF PARTNERS L.P.
By: BVF Inc., its general partner
By: /s/ Xxxx X. Xxxxxxx
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Xxxx X. Xxxxxxx
President
BVF INC.
By: /s/ Xxxx X. Xxxxxxx
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Xxxx X. Xxxxxxx
President