Haploidentical hematopoietic stem cell transplantation with a megadose T-cell-depleted graft: harnessing natural and adaptive immunity.

For patients with high-risk acute leukemia who do not have a matched donor or who urgently need a transplant, transplantation from a full human leukocyte antigen (HLA) haplotype mismatched family donor should be considered a viable option. Clinical trials have shown that a strategy for haploidentical transplantation based on the infusion of high numbers of T-cell– depleted hematopoietic progenitor cells and no post-transplant immunosuppression controls bi-directional T-cell alloreactivity, ie, graft rejection and graft-versus-host disease (GvHD) in patients with leukemia. Overall, event-free survival compares favorably with reports of transplants using sources of stem cells other than the matched sibling. This transplant modality has highlighted the crucial role of donor-versus-recipient natural killer cell (NK) alloreactivity in the control of leukemia relapse. Current studies are focusing on rebuilding post-transplant immunity to improve clinical outcomes.