Genzyme Corp. and partner Bayer Schering Pharma AG dosed the first patient in the first of two Phase III studies comparing alemtuzumab to Rebif in multiple sclerosis patients.

The randomized, rater-blinded CARE-MS I (Comparison of Alemtuzumab and Rebif Efficacy in Multiple Sclerosis) trial is designed to compare Genzyme's monoclonal antibody to Rebif, a formulation of interferon beta-1a sold by Geneva-based Merck Serono SA, in up to 525 patients with relapsing-remitting MS, including those who have not yet begun treatment with any MS drug.

Alemtuzumab will be given in two annual cycles, while Rebif will be administered three times per week. The co-primary endpoints are the time to sustained accumulation of disability and the annualized relapse rate. All patients will be followed from their entry into the trial until two from the date that the last patient is randomized to treatment.

Genzyme and Bayer hope results will confirm interim data from a previous Phase II study, which indicated that alemtuzumab-treated patients had a statistically significant reduction compared to those treated with Rebif in the risk for sustained accumulation of disability and the risk for relapse for 24 months.

Results from 36-month data are expected to be presented at an upcoming scientific conference.

A second Phase III study, the CARE-MS-II trial, is set to start soon and will enroll patients who have continued to experience relapse episodes while on currently available disease-modifying therapies.

Pending positive results from both Phase III trials, Genzyme and Bayer anticipate filing for approval in MS in 2011. Alemtuzumab, which targets the CD52 receptor, already is marketed as Campath (MabCampath outside the U.S.) in B-cell chronic lymphocytic leukemia.

Cambridge, Mass.-based Genzyme and Berlin-based Bayer are co-developing the compound in oncology, MS and other indications, with Bayer holding exclusive, worldwide marketing and distribution rights.

Shares of Genzyme (NASDAQ:GENZ) closed at $63.13 Wednesday, unchanged.