Rapid Response with Daratumumab for Pure Red Cell Aplasia in a Case of Aplastic Anemia with Mixed Chimerism After ABO-Mismatched Stem Cell Transplant

Pure red cell aplasia (PRCA) following major ABO-mismatched allogeneic hematopoietic stem cell transplantation (HSCT) is a challenging complication, affecting 7–10% of patients and significantly impacts quality of life. Despite half of patients showing a resolution within three–six months after HSCT, PRCA might require treatment. Various therapeutic approaches have been investigated, including erythropoietin, plasmapheresis or immunomodulatory therapies (rituximab, bortezomib, corticosteroids, donor lymphocyte infusion (DLI), or the early tapering of immunosuppressive drugs), and TPO-mimetic agents, though responses have generally remained suboptimal. Recently, daratumumab has emerged as a promising, safe, and effective treatment for PRCA, documented by numerous case reports and series. We present a case of PRCA arising in a patient with mixed chimerism following a sibling HSCT for aplastic anemia (AA). In line with the literature, our findings highlight the effectiveness of daratumumab in PRCA from the first dose, although daratumumab administrations were delayed by the onset of infectious complications. Our case supports the earlier introduction of daratumumab in the treatment strategy of PRCA to avoid patient exposure to ineffective therapies that carry risks of increased immunosuppression and infections. Indeed, in our specific case, the early introduction of daratumumab may interrupt the immune hematologic mechanism underlying PRCA, which, in the context of mixed chimerism, could increase the risk of graft failure.