Twelve patients with acute leukemia and nine with aplastic anemia received marrow transplants from donors other than genotypically HLA-identical siblings. All donor-recipient pairs were genotypically identical for one HLA haplotype and shared antigens of the other. Of nine transplants between siblings, three were HLA-D incompatible and one HLA-A and B incompatible as a consequence of B-D recombination. One such recipient survives in good health at day 485. Three sibling pairs had parents homozygous for HLA-A and B and heterozygous for HLA-D. One rejected the transplant, one died of interstitial pneumonia, and one died of persistent leukemia. Two sibling pairs had parents homozygous for HLA-D but not for HLA-A and B. One recipient died of graft rejection on day 93, and one survives in good health at day 339. Three patients had parent donors identical for HLA-A, B, and D. One survives at day 742. Of two recipients whose parent donors were HLA-A and B compatible and D incompatible, one has minimal graft-versus-host disease (GVHD) at day 361, and one died of graft rejection at day 47. Six recipients had parent donors matched for HLA-D but not for HLA-A or B. One survives with recurrent leukemia in postchemotherapy remission at day 690, three died of graft rejection and two of GVHD. One recipient was HLA-D homozygous, received marrow from his HLA-A-mismatched, HLA-D heterozygous parent and died of graft rejection on day 47. The experience of GVHD was within the range encountered in transplants between genotypically HLA-identical siblings. The number of patients receiving transplants is much too small to permit any conclusions about the relative importance of various degrees and varieties of mismatching, but the results encourage further studies of well defined deviations from the HLA-identical sibling relationship in marrow transplantation.
There is an increasing number of reports of marrow transplantation between identical twins or genotypically HLA-identical siblings as part of the therapy of aplastic anemia or hematological malignancy (1–5). We are extending our studies of marrow transplantation by performing allogeneic marrow transplants from donors other than HLA-matched siblings to evaluate the effects of precise histocompatibility differences. This paper reports our experience in this endeavor and presents the details of 21 such transplants.