Haploidentical Hematopoietic Stem Cell Transplantation in Pediatric Patients with Acquired Hypocellular Bone Marrow Failure

•Pediatric patients with severe aplastic anemia and refractory cytopenia of childhood who lack matched donors and fail or relapse after immunosuppressive therapy need novel therapies.•In our experience, haploidentical hematopoietic stem cell transplantation (HSCT) allows sustained engraftment in all patients with good overall survival.•Haploidentical HSCT offers a curative therapy for these patients.•In our cohort of SAA pediatric patients heavily pretreated with immunosuppressive therapy, haploidentical HSCT demonstrated significant toxicity, with transplantation-associated microangiopathy and chronic graft-versus-host disease the most worrisome. Children with acquired hypocellular bone marrow failure of unknown cause (AHBMF) are usually diagnosed either with severe aplastic anemia (SAA) or refractory cytopenia of childhood (RCC). Patients with AHBMF who lack a matched donor and who failed or relapsed after immunosuppressive therapy (IST) need alternative therapies. Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) offers a curative treatment for these patients. We report a multicenter Spanish experience with haplo-HSCT in pediatric patients with AHBMF. Eleven pediatric patients (SAA, n = 9; RCC, n = 2) underwent haplo-HSCT with different lymphodepletion strategies. Most patients (10 of 11) had previously failed to respond or relapsed after IST. The conditioning regimen was reduced intensity in SAA and myeloablative in RCC. Patients with SAA received low-dose radiotherapy as part of their conditioning regimen. All patients engrafted. Viral reactivation was common (8 of 11). Acute GVHD grade ≥II was seen in 5 patients. Chronic GVHD was diagnosed in 4 of the long-term survivors. Transplantation-associated microangiopathy was a frequent complication in SAA patients and was related to worse outcome. Two patients died of transplantation-related complications. Overall survival was 81%, with a median follow-up of 36 months. Haplo-HSCT can be a successful salvage curative treatment for pediatric patients with AHBMF, but with significant toxicities that must be addressed. Transplantation-associated microangiopathy was the most critical complication.