[Successful treatment of secondary graft failure in a mixed-phenotype acute leukemia patient with haploidentical hematopoietic stem cell transplantation and post-transplant cyclophosphamide administration].

A 38-year-old woman in the first remission of mixed-phenotype acute leukemia underwent unrelated bone marrow transplantation from an HLA-DR-mismatched donor in the host-versus-graft (HVG) direction with myeloablative conditioning. Neutrophil engraftment was achieved and complete donor chimera was obtained on days 21 and 29 after transplantation, respectively. Subsequently, with delayed blood cell recovery, continuous transfusion was needed to replace platelets. In the CD3 peripheral blood chimerism test, the percentage of recipient cells on days 50, 63, and 80 was 27.3%, 90%, and 95% or higher, respectively. With no relapse of leukemia observed on bone marrow examination, secondary graft failure associated with autologous hematopoietic recovery was diagnosed. Bone marrow transplantation from the patient's HLA-haploidentical sister was performed because of graft failure on day 111 after the initial transplant using post-transplant cyclophosphamide (PTCy). Neutrophil engraftment was achieved and complete donor chimera was obtained on days 14 and 21 after the second transplantation, respectively. With no serious complications or acute graft versus host disease, the patient was discharged with symptomatic improvement. According to our results, retransplant using PTCy obtained from an HLA-haploidentical sibling donor is a potential treatment for graft failure.