Pediatric unmanipulated haploidentical hematopoietic stem cell transplantation with post-transplant cyclophosphamide and reduced intensity, TBI-free conditioning regimens in salvage transplantations

Background. Unmanipulated haploidentical stem cell transplantation (haploSCT) with post-transplant cyclophosphamide is an option for patients with advanced hematologic malignancies. It offers a platform both for non-major histocompatibility complex-restricted alloimmunity due to killer-like immunoglobulin receptor (KIR)-mediated mechanisms of natural killer lymphocyte regulation and for classical T-cell mediated antileukemic effects. Objectives. The devastating long-term sequelae after total body irradiation (TBI) in children are encouraging omission of irradiation techniques in pediatric stem cell transplantations (SCT). Material and methods. Five children, 4 with acute leukemia and 1 with hemophagocytic lymphohistiocytosis, aged from 1 to 10 years, underwent haploSCT with post-transplantation cyclophosphamide. In all children, the conditioning regimen consisted of chemotherapy without TBI. The graft material was bone marrow (BM) in 4 cases and peripheral blood stem cells in 1 case. Three out of 5 leukemic patients showed better KIR haplotype associated with augmented alloreactivity. Results. Engraftment with complete donor chimerism was achieved in 4 patients, and 1 recipient died before leukocyte recovery. Three patients developed skin acute graft-versus-host-disease (aGvHD), 1 gut aGvHD and 1 liver aGvHD. In 2 recipients, chronic graft-versus-host-disease (cGvHD) was observed (1 limited and 1 extensive). The 4 engrafted patients were alive and in complete remission 3, 9, 32, and 36 months after transplantation. A T-cell count of 200 cells/uL was reached 90 days after haploSCT in all patients. Conclusions. HaploSCT with TBI-free protocols can be a viable option for heavily pretreated patients with advanced malignancies.