Evidence of involvement of cytotoxic antibodies directed against patient’s HLA class II produced by transfused donor‐derived B cells in post‐transfusion graft‐versus‐host disease

Post-transfusion graft-versus-host disease (PTGVHD) is one of the most severe side-effects of blood transfusion. To characterize the effector cells causing this disease, we cloned lymphocytes from a PTGVHD patient's peripheral blood. T-cell and B-cell clones were established, the origins of which were proven to be transfused donor lymphocytes. It was found that the B cells produced IgG that mediated complement-dependent cytotoxicity to the cells bearing the patient's HLA class II genotype. Our results suggest, for the first time, the involvement of B-cell-produced cytotoxic antibodies directed against patient's HLA class II in the pathogenesis of PTGVHD.