Alemtuzumab to Treat Severe Aplastic Anemia

Hematopoietic stem cell destruction in many human bone marrow failure syndromes is now recognized to be secondary to immune mechanisms. Severe aplastic anemia (SAA) is a life-threatening blood disease which can be effectively treated with immunosuppressive drug regimens. However, a significant minority of patients with SAA fail to respond to a single course of horse antithymocyte globulin and cyclosporine, and other patients experience relapse, especially on discontinuation of therapy. Pancytopenia secondary to refractory or relapsed aplastic anemia has a poor prognosis, with death usually resulting from infectious complications. Alemtuzumab (Campath ) is a humanized IgG1 monoclonal antibody directed against the CD52 protein; CD52 is expressed on all lymphocytes and monocytes. Alemtuzumab (Campath ) produces profound and persistent lymphopenia. The antibody has been used to treat a wide range of autoimmune diseases, lymphoid malignancies, and in solid organ and hematopoietic stem cell transplantation. In our limited experience with alemtuzumab for the treatment of SAA refractory to horse antithymocyte globulin, meaningful hematologic responses have been observed and toxicity has been modest. We therefore propose a non-randomized pilot phase II study of this humanized monoclonal antibody in SAA relapsed or refractory to ATG. Commercially available alemtuzumab (Campath ) will be administered at 10 mg per day subcutaneously for 10 days total. The primary end point of the study is the response rate at 6 months, defined as no longer satisfying blood count criteria for SAA. Relapse, robustness of the hematopoietic recovery at 3 and 6 months, 3 months responses, survival, and clonal evolution to myelodysplasia and acute leukemia will be secondary end points.