Transmaternal cell flow leads to antigen-experienced cord blood

Umbilical Cord Blood (UCB) is used for hematopoietic stem cell transplantation (HSCT). It is known that UCB can comprise antigen specific T cells. Here we question whether solely transmaternal cell flow may immunize UCB. Hereto, twenty-three female UCB samples were collected from healthy mothers and analyzed for minor Histocompatibility antigen HY-specific responses. Forty-two out of 104 tetramerpos T cell clones, isolated from 16 out of 17 UCB samples, showed male-specific lysis in vitro . Male microchimerism was present in 6 out of 12 UCB samples analyzed. In conclusion; female UCB comprises HY specific cytotoxic T cells. The immunization is presumably caused by transmaternal cell flow of male microchimerism present in the mother. The presence of immune cells in UCB that are not directed against maternal foreign antigens is remarkable and may explain the reported clinical observation of improved HSCT outcome with younger sibling donors.