Allogeneic hematopoietic stem-cell engraftment and graft failure.

Two immunologically mediated reactions, the graft-versus-host (GvH) and host-versus-graft (HvG) responses, form primary and opposing barriers to successful transplantation of allogeneic hematopoietic stem-cells (HSC). The HvG barrier is set by the strength of the allogeneic immune response, which is determined by antigenic stimulation provided by donor cells, owing to differences in histocompatibility antigens, and the capacity of host immune cells to generate a response. Risk of graft failure must be viewed as the interplay of multiple factors, including degree of human leukocyte antigen and minor histocompatibility antigen disparity, capacity of host immune response, and the capacity of donor hematopoietic and immunologic cells for overcoming residual host immunity.