Facilitating cells: Novel promoters of stem cell alloengraftment and donor-specific transplantation tolerance in the absence of GVHD

Bone marrow transplantation (BMT) is the treatment of choice for many hematological malignancies and immunopathologies. Unfortunately, success is often impeded by engraftment failure and graft-versus-host disease (GVHD). A rare bone marrow population known as the facilitating cell (FC) has been identified which facilitates stem cell engraftment and circumvents these obstacles in murine experimental models. This review discusses the identification and characterization of this rare population and provides an emerging portrait of FC origin, ontogeny and function. The promotion of durable stem cell engraftment in MHC disparate recipients, GVHD inhibition and tolerance induction by the FC suggests that future therapies in hematopoietic cell transplantation and tolerance induction for solid organ transplants may be significantly improved through the application of FC transplantation.