Precision Alemtuzumab Dosing for Allogeneic Hematopoietic Cell Transplantation

Alemtuzumab levels at Day 0 can affect: * the chances of developing acute graft versus host disease (GVHD), which is an immune reaction of the donor cells against your own tissues * the chances of developing mixed chimerism, which is having a mixture of your own cells and donor cells after HCT, and * recovery of your immune system following transplant. High levels of alemtuzumab are associated with more mixed chimerism and slower immune recovery, while low levels are associated with more acute GVHD. The investigators have developed a plan to adjust the alemtuzumab dose for patients to target Day 0 levels to fall within an ideal effective range of 0.15-0.9 ug/mL. This range may minimize the risks of these complications. The investigators are conducting this study to determine if the current plan for alemtuzumab dosing will be successful in the majority of patients and evaluate the impact on the clinical outcomes of acute GVHD, mixed chimerism, and immune recovery.