Successful Engraftment Following Second Cord Blood Transplantation After Graft Failure in a Child With Relapsed B-ALL

Primary graft failure is a rare but life-threatening complication after umbilical cord blood transplantation (UCBT), especially in pediatric patients with relapsed acute lymphoblastic leukemia (ALL). Optimal salvage strategies, including conditioning regimens and donor selection for second transplantation, have not been established. This report describes the case of a 9-year-old boy with relapsed B-cell precursor ALL who developed primary graft failure following the first UCBT performed during his second complete remission. The initial transplant had used a cord blood unit with a low CD34-positive cell dose and significant human leukocyte antigen (HLA) and ABO mismatch. Despite myeloablative conditioning, neutrophil engraftment failed, and donor chimerism remained minimal. An urgent second UCBT was performed using a different cord blood unit with improved HLA compatibility and markedly higher total nucleated and CD34-positive cell doses, following reduced-intensity conditioning with fludarabine and low-dose total body irradiation. Sustained neutrophil engraftment was achieved on day +34, with stable full donor chimerism thereafter. Post-transplant complications, including hemophagocytic syndrome, sinusoidal obstruction syndrome, acute graft-versus-host disease, and viral reactivation, were successfully managed. This pediatric case demonstrates that, in the absence of a suitable donor and with prompt intervention, a second UCBT is a feasible salvage option after primary graft failure.