Three Immunosuppressive Treatment Regimens for Severe Aplastic Anemia

Study Summary

Severe aplastic anemia (SAA) is a life-threatening bone marrow failure disorder characterized by pancytopenia and a hypocellular bone marrow. Allogeneic bone marrow transplantation offers the opportunity for cure in 70% of patients, but most patients are not suitable candidates for hematopoietic stem cell transplantation (HSCT) due to advanced age or lack of a histocompatible donor. For these patients, comparable long term survival is attainable with immunosuppressive treatment with anti-thymocyte globulin (ATG) and cyclosporine (CsA). However, of those patients treated with horse ATG(h-ATG)/CsA, one quarter to one third will not respond, and about 50% of responders relapse. Auto-reactive T cells may be resistant to the effect of ATG/CsA (non-responders), while in others residual auto-reactive T cells expand post-treatment, leading to hematopoietic stem cell destruction and recurrent pancytopenia (relapse). As long term survival is correlated to response rates and robustness of hematopoietic recovery, novel immunosuppressive regimens that can achieve hematologic response and decrease relapse rates are needed. This trial will compare the effectiveness of three immunosuppressive regimens as first line therapies in patients with SAA with early hematologic response as the primary endpoint, as well as assess the role of extended CsA treatment after h-ATG in reducing numbers of late events of relapse and clonal evolution. Randomization is employed to obtain an equal distribution of subject to each arm; comparisons of early hematologic responses will be made among the rates observed among the three concurrent arms (rabbit-ATG \[r-ATG\] versus standard h-ATG; alemtuzumab vs standard h-ATG). For long course CSA, comparison of primary end points will be to well established historic relapse rate of 38% at 2-3 years and a cumulative rate of clonal evolution of 15%.

Primary Outcome

Hematologic response is defined as subjects having blood counts no longer meeting the standard ("Camitta") criteria for severe pancytopenia in Severe Aplastic Anemia, equivalent to 2 of the following values obtained on 2 serial blood count measurements at least one week apart at landmark time points (3, 6 and 12 months) * Absolute neutrophil count \> 500/ μL * Platelet count \> 20,000/ μL * Reticulocyte count \> 60,000/ μL Improvement in counts that are dependent upon exogenously administered

Interventions

• DRUG Alemtuzumab
• DRUG Cyclosporine
• BIOLOGICAL Anti-thymocyte globulin (rabbit)
• BIOLOGICAL Anti-thymocyte globulin (horse)