Immunological studies in patients with aplastic anemia who rejected marrow grafts from HLA-identical sibling donors

Marrow graft rejection after transplantation from an HLA-identical sibling for the treatment of aplastic anemia has an immunological basis in most cases. We previously studied the post-transplantation sera of 20 consecutive patients using the chromium release assays of complement-dependent cytotoxicity (CDC) and/or antibody-dependent cell-mediated cytotoxicity (ADCC). Reactivity against peripheral blood mononuclear cells of the marrow donors was found which was associated with graft rejection. Sera of 17 consecutive patients who rejected their grafts have now been studied. Donor cells susceptible to cytotoxicity in both the CDC and ADCC assays were composed of both adherent and nonadherent cells not forming spontaneous rosettes with sheep red blood cells. Absorption studies demonstrated that the reactivities were mediated by antibody, and inhibition studies with 2-mercaptoethanol indicated that the active component was IgM.