Platelet transfusions irradiated with ultraviolet-B light may have a role in reducing recipient alloimmunization

The recipients of multiple platelet transfusions frequently develop alloantibodies directed against the human leucocyte antigens (HLA) present on both leucocytes and platelets. Such alloimmunization (AI) may result in refractoriness to further platelet transfusions. Contaminating leucocytes bearing Class II HLA and present in platelet concentrates (PC) are responsible for the formation of HLA antibodies and their removal by filtration reduces the rate of recipient AI. Ultraviolet irradiation (UVR) of PC at an appropriate dose inactivates the contaminating mononuclear leucocytes so that responses in vitro to mitogens and alloantigens are abrogated. It seems likely that UV-irradiation of donor dendritic cells (DC) is important in preventing in vitro responses to alloantigens and in vivo allosensitization. At the same time, satisfactory platelet function and structure is retained when measured by in vitro tests. In vivo assessments of platelet recovery and survival in healthy subjects and the ability to correct the bleeding time in thrombocytopenic patients are comparable to non-irradiated PC. Prospective studies are now in progress to determine if UVR will reduce recipient AI to HLA in multiply-transfused patients with leukaemia and lymphoma.