Redefining GVHD Prophylaxis: The Expanding Horizon of Posttransplant Cyclophosphamide.

Posttransplant cyclophosphamide (PTCy) represents a paradigm shift in the prevention of graft-versus-host disease (GVHD) following allogeneic hematopoietic stem cell transplantation (HSCT). As a high-dose, posttransplant immunomodulatory agent, PTCy offers a unique mechanism to facilitate graft tolerance, mitigate GVHD, and preserve graft-versus-leukemia (GVL) effects. The beneficial effects of PTCy on GVHD appears to be independent of donor type, graft source, or conditioning regimen intensity. This chapter provides an in-depth analysis of the mechanisms underlying PTCy and its clinical applications in haploidentical, HLA-matched, and -mismatched HSCT, highlighting its transformative impact in transplantation medicine. PTCy is emerging as a new standard GVHD prophylaxis for all HSCT settings.