Minor histocompatibility antigens: targets for tumour therapy and transplant tolerance.

Minor histocompatibility (H) antigens are allogeneic targets of T-cell mediated immune reactivity following allogeneic haematopoietic stem cell transplantation. Depending on the tissue expression profile of the minor H antigens this immune reactivity clinically results in graft-vs-host disease or in graft-vs-leukaemia effects. Targeting haematopoietic-specific minor H antigens by adoptive immunotherapy will evoke leukaemia-specific allo-immune responses, thereby enhancing graft-vs-leukaemia effects. Recently, a novel alternative role for minor H antigens in transplantation has been described; minor H antigen-specific T cells appear to be able to regulate allo-immune responses after solid organ transplantation. This diversity in immune reactivity suggests a broad clinical potential of minor H antigens, both in haematopoietic stem cell transplantation and in solid organ transplantation.