Occult alloimmunization to the D antigen (RhD) related to graft versus host disease and its treatment

Alloimmunization to red blood cell (RBC) antigens post-allogeneic stem cell transplantation (allo-SCT) appears to be quite rare. The D antigen (RhD) is considered the most immunogenic RBC antigen with possibly a third of RhD-negative individuals exposed to RhD-positive RBC transfusions becoming alloimmunized. Though variable, most are detectable within a year of exposure, and the median time between exposure and detection is estimated to be about a month. We report the detection of anti-D in an allogeneic bone marrow transplant (allo-BMT) recipient about five years following last exposure to RhD-positive RBC.