One haplotype matched bone marrow grafts: an investigation using the HLA system as a marker of cellular origin

HLA antigens were used as markers to study the lymphocyte population in 31 patients with leukaemia, treated with a one-haplotype matched bone marrow transplant (BMT). In 24 patients substained engraftment was achieved and the recipient was repopulated with B and T lymphocytes of donor HLA type. Repopulation occurred at the same rate for lymphocytes of the B and T cell classes, usually within 2 weeks of grafting. In two additional cases bone marrow engraftment was successful but the lymphocyte population was chimeric and cells of both donor and host HLA type were present in the recipient for many weeks. Three patients relapsed after engraftment and peripheral blood lymphocytes were exclusively of host or donor HLA type, or a chimeric population was present. In one chimeric case, peripheral blood T lymphocytes were of donor origin, and B lymphocytes were of host origin. Mononuclear cells in the bone marrow were of host HLA type. The use of the HLA system as a marker is a useful additional approach to determine engraftment or chimerism following an allogeneic one haplotype matched bone marrow transplant.