Impact of fetal-maternal tolerance in hematopoietic stem cell transplantation.

Allogeneic hematopoietic stem cell transplantation (HSCT) is known to cure various hematological disorders; however, its widespread use is limited due to a lack of histocompatible donors. Reciprocal cell traffic between the mother and fetus during pregnancy gives rise to postpartum fetal-maternal lymphohematopoietic microchimerism, which is frequently detected in the blood or tissue of healthy individuals. Studies in clinical and experimental transplantation provide evidence that exposure to non-inherited maternal antigens (NIMAs) during pregnancy may result in long-lasting fetomaternal microchimerism and tolerance induction. Studies of HLA-mismatched HSCT have suggested a relatively lower incidence of severe graft-versus-host disease (GVHD) after transplantation from a NIMA-mismatched donor. Studies using a mouse model have also demonstrated a "child-to-mother" bone marrow transplantation from an NIMA-exposed donor to reduce the morbidity and mortality of GVHD in an antigen-specific manner while preserving the graft-versus-leukemia effects and favoring the immune reconstitution, thus resulting in a marked improvement in outcome after HSCT. Prospective clinical studies are therefore warranted to confirm these beneficial effects of fetal-maternal tolerance in allogeneic HSCT.