Insights into platelet post-transfusional human leukocyte antigen I immunization

Although human leukocyte antigen (HLA) class I alloimmunization is asymptomatic, it nevertheless introduces a degree of complexity in the context of transplantation or allogeneic transfusion. In practice, it is evidenced by the presence of anti-HLA-I alloantibodies in patient circulation, which can lead to graft rejection or, of interest in this work, platelet transfusion refractoriness. Exposure of HLA-I antigens during pregnancy or after a transfusion does not lead systematically to the production of alloantibodies. We discuss here recent studies that illustrate the nature of the intrinsic and extrinsic factors involved in regulating humoral response following platelet transfusion. We highlight the importance of the factors related to the 'donor/blood product/recipient triad'. Understanding their relative importance may help us to develop a stewardship of strategies to prevent the production of antibodies with potential to interfere with transfusions or transplants. We also underscore new directions to orient research in the field.