STUDIES OF THE RESPONSE IN MIXED LEUKOCYTE CULTURE OF CELLS FROM PATIENTS WITH APLASTIC ANEMIA TO CELLS FROM HLA-IDENTICAL SIBLINGS

Abstract

We have studied the mixed leukocyte culture (MLC) reactions of 64 patients with severe aplastic anemia. Their peripheral blood mononuclear cells showed an increased relative response (RR) to cells from HLA-identical siblings as compared to cells from normal HLA-identical siblings, confirming the results reported in an earlier series of 34 patients. Elevated RRs were associated with patient antidonor lymphocyte antibodies as detected by the antibody-dependent cell-mediated cytotoxicity assay, but were not associated with antidonor complement-dependent cytotoxic antibodies or with antidonor cytotoxic T lymphocytes. Among 98 patients receiving marrow grafts from HLA-identical sibling donors, those with elevated RRs before transplantation were more apt to reject the transplant than those without (P < 0.0001). There was no elevation of the RR in 10 untransfused patients, although positive RRs were noted in 2 patients within 12 to 24 hr of their first transfusions. Five patients with identical twins were also tested, and elevated RRs were noted in three. Although blood transfusion appears to be responsible for the increased RRs observed in some aplastic patients, genetic differences between donor and recipient were not always necessary for eliciting an increased MLC response, suggesting that mechanisms other than alloimmunization are involved.