Patients are randomized to one of three treatment arms: Arm I: Patients receive an infusion of chimeric monoclonal antibody (cA2) on weeks 0, 2, and 6. Arm II: Patients receive an infusion of cA2 on weeks 0 and 2, and an infusion of placebo on week 6. Arm III: Patients receive an infusion of placebo on day 1 of weeks 0, 2, and 6.