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EXHIBIT 4
JOINT FILING AGREEMENT
We, the undersigned, hereby express our agreement that the attached
Schedule 13D (including all amendments thereto) is filed on behalf of each of
the undersigned.
BB BIOTECH AG
Date: February 9, 1998 By: /s/ Xxxx-Xxxxx Xxxx
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Name: Xxxx-Xxxxx Xxxx
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Date: February 9, 1998 By: /s/ Xx. Xxxxxx Xxxxxxxx
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Name: Xx. Xxxxxx Xxxxxxxx
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BIOTECH TARGET, S.A.
Date: February 9, 1998 By: /s/ Xx. Xxxxxxx Xxxxxx
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Name: Xx. Xxxxxxx Xxxxxx
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Date: February 9, 1998 By: /s/ Dr. Xxxxxx Xxxx
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Name: Dr. Xxxxxx Xxxx
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