Three escalating doses of alemtuzumab will be considered to determine the maximum tolerated dose (MTD). In this design, a cohort of 3-6 patients will be treated at each dose level. Dose-limiting toxicity (DLT) will be defined as any life-threatening anaphylaxis due to an alemtuzumab infusion, any grade 4 non-hematologic toxicity directly related to alemtuzumab during the 12 week assessment period, any grade 4 hematological toxicity, and any grade 4 infectious complication that requires hospitalization. CMV reactivation secondary to alemtuzumab is an expected complication of alemtuzumab and will not be considered a DLT unless grade 4 CMV disease occurs. CMV DNA levels will be closely monitored and preemptive therapy for CMV will be initiated if there is evidence of CMV reactivation.