Genzyme

(GENZ)

said Wednesday that it has begun a cash tender offer of $22.50 a share to acquire all of the outstanding shares of

SangStat Medical Group

(SANG)

.

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Fremont, Calif.-based SangStat makes an antibody product used in organ transplantation and has a product-development program for immune-mediated diseases.

The offer and withdrawal rights will expire after midnight on Sept. 10, the company said.

Genzyme

first announced the agreement on Aug. 4. At that time, the company had said the acquisition would dilute earnings through 2004 due to amortization. Shares of the biotechnology company were down about 2.7%, or $1.26, at $45.39 in late

Nasdaq

trading.