Isatuximab for Delayed Red Cell Engraftment after Allogeneic Hematopoietic Cell Transplantation.

Isatuximab is an IgG1-derived monoclonal antibody against CD38 approved for the treatment of adult patients with multiple myeloma. Here we describe the successful treatment of a therapy-refractory pure red cell aplasia case following ABO-mismatched allogeneic stem cell transplantation with isatuximab. Our patient was a 75-year-old female with acute myeloid leukemia who received an HLA-B antigen mismatched, unrelated peripheral blood stem cell transplant with a major ABO incompatibility (blood group A+ in the donor and blood group O+ in the recipient). The patient developed persistent red cell aplasia and anti-A antibodies for more than 500 days from transplant. She received therapy with rituximab, bortezomib, prednisone, and darbepoetin alfa with partial to no response. After repeated insurance denials for daratumumab, isatuximab was obtained from the manufacturer through their CareASSIST program. Following the completion of 2 cycles of isatuximab (8 doses), significant and sustained red cell recovery was observed.