Immunohaematological aspects of bone marrow transplantation

Abstract

A successful bone marrow transplant results in chimerism, but various haematological markers are necessary to prove that a true chimera exists. Differences in the red cell antigens between the donor and the recipient of a bone marrow transplant provide ideal markers to confirm chimerism. In this paper, experience with the immunohaematological aspects of bone marrow transplantation will be discussed. It is now well established that red cell antigens, and in particular the ABO system, are not important in long-term marrow graft survival or graft versus host reaction. There are, however, practical considerations and difficulties in crossing the ABO barrier, and interesting immunohaematological questions are posed regarding tolerance and the nature of red cell antigens. Large volume plasma exchange with donor group fresh frozen plasma and infusion of A substance (when indicated) followed by a small transfusion of ABO incompatible red cells prior to marrow infusion, has been our standard approach to crossing the ABO barrier. In most cases, anti-A or anti-B isoagglutinins can be effectively reduced to undetectable levels and bone marrow infusion has been uneventful. In each case, anti-A or anti-B isoagglutinin titres have returned rapidly while awaiting engraftment, but have subsequently disappeared following marrow engraftment without clinical evidence of haemolysis. Haptoglobin levels have fallen to undetectable levels during this engraftment period, during which time mixed field ABO blood group reactions were present. IgG anti-A and anti-B have been present in most cases to high titre but have not been effectively removed by plasma exchange, However, in no case did the presence of IgG antibodies appear to be clinically significant. Some interesting changes in blood group antigens have been observed. In one case the emergence of the A 2 antigen clearly preceded the A 1 antigen in the transformation of 0 to A, and a second case of anti-A 1 developed in an A 1 to A 1 graft.