Horse ATG/CsA in Aplastic Anemia Patients Unresponsive to or With a Suboptimal Response to Rabbit ATG/CsA Treatment

• Number of Participants With Complete Response at 3 Months. [ Time Frame: 3-months ]

  The primary endpoint was hematologic response at 3 months, defined as no longer meeting criteria for Severe Aplastic Anemia (SAA) defined as bone marrow cellularity of less than 30% and severe pancytopenia with at least two of the following peripheral blood count criteria: (i) absolute neutrophil count less than 0.5×109/L; (ii) absolute reticulocyte count less than 60×109/L; and (iii) platelet count less than 20×109/L.

  A complete response was defined as absolute neutrophil count (ANC) above 1.0×109/L, Hgb > 10 g/dL, and platelet count > 100×109/L.

  A partial response was defined as a hematologic response that was not sufficient for a complete response.

  
  
• Number of Participants With Complete Response at 3 Months. [ Time Frame: 3 months ]

  The primary endpoint was hematologic response at 3 months, defined as no longer meeting criteria for Severe Aplastic Anemia (SAA).

  A complete response was defined as absolute neutrophil count (ANC) above 1.0×109/L, Hgb > 10 g/dL, and platelet count > 100×109/L.

  A partial response was defined as a hematologic response that was not sufficient for a complete response.

  In subjects with a non-robust hematologic response at 3 months, improvement in one or more of the listed peripheral blood parameter (a,b,c) were recorded as a response: a) ANC - if baseline ANC below 0.5×109/L, increase in ANC by > 0.3×109/L, if baseline ANC above 0.5×109/L, any increase in ANC by > 0.5×109/L of blood; (b) platelets - if baseline platelet count < 50×109/L, any increase in platelet count by > 20×109/L of blood; c) hemoglobin - any increase in hemoglobin by 1.5 g/dl of blood in transfusion-independent patients and in absolute reticulocyte count to > 60×109/L of blood in transfusion-dependent patients.

  
  

Severe aplastic anemia (SAA), characterized by pancytopenia and a hypocellular bone marrow, is effectively treated by immunosuppressive therapy, usually a combination of antithymocyte globulin (ATG) and cyclosporine (CsA). Survival rates following this regimen are equivalent to those achieved with allogeneic stem cells transplantation. However, approximately 1/3 of patients will not show blood count improvement after ATG/CsA. General experience and small pilot studies have suggested that such patients benefit from further immunosuppression. Furthermore, analysis of our own clinical data suggests that patients with minimal blood count responses to a single course of ATG, even when transfusion independence is achieved, have a markedly worse prognosis than patients with robust hematologic improvement.

The majority of the experience in the US and worldwide has been with horse ATG (h-ATG) plus CsA as initial therapy in SAA. Rabbit ATG (r-ATG) plus CsA has been employed successfully in about 1/3 of cases in those who are refractory to initial h-ATG/CsA (current NHLBI Protocol 03-H-0249). In recent years, h-ATG and r-ATG have been used interchangeably in treatment-naive patients, and initial therapy with r-ATG/CsA is now frequent in the US and the only option in Europe and Japan, where h-ATG is no longer available. An active NHLBI randomized study is comparing the efficacy of h- and r-ATG as initial therapy in SAA, and the results from a recently completed interim analysis suggest that the hematologic response rate ultimately may not be comparable between these two agents (Protocol 06-H-0034). There is no published report on the outcome of repeat immunosuppressive therapy in those patients refractory to initial r-ATG/CsA, and thus the management of these patients is uncertain. We therefore propose this study of h-ATG/CsA in SAA patients who are refractory or have a suboptimal response to r-ATG.

The primary endpoint will be the response rate at 3 months where response is defined as no longer meeting criteria for SAA.

The primary objective is to evaluate the effectiveness (response rate) at 3 months of a second course of immunosuppression with h-ATG/CsA in subjects refractory to or with a suboptimal response to a course of r-ATG/CsA or cyclophosphamide at least 3 months post treatment.

Secondary objectives include robustness of hematologic recovery, relapse, response rate at 6 months, clonal evolution and overall survival.

The primary endpoint will be changes in absolute neutrophil count, platelet count, reticulocyte count at 3 months.

Secondary endpoints will include time to relapse, changes in cytogenetics, time to death.