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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: November 19, 1997 By: /s/ Xxxx-Xxxxx Xxxx
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Name: Xxxx-Xxxxx Xxxx
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Date: November 19, 1997 By: /s/ Xx. Xxxxxx Xxxxxxxx
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Name: Xx. Xxxxxx Xxxxxxxx
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BIOTECH TARGET, S.A.
Date: November 19, 1997 By: /s/ Xx. Xxxxxxx Xxxxxx
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Name: Xx. Xxxxxxx Xxxxxx
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Date: November 19, 1997 By: /s/ Dr. Xxxxxx Xxxx
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Name: Dr. Xxxxxx Xxxx
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