HLA antibody formation within the HLA‐A1 crossreactive group in multitransfused platelet recipients

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Abstract
The formation of intragroup antibodies, HLA antibodies directed against antigens in the same crossreactive group (CREG) as those of the serum donor, may be an important cause of transfusion failures in patients receiving HLA‐matched platelets. Twenty‐two patients whose HLA types included at least one antigen in the HLA‐A1 CREG were studied. Of the ten patients who formed HLA antibodies, six produced antibodies that reacted with one or more antigens in the HLA‐A1 CREG. Five of 12 patients whose HLA types included HLA‐A3 formed antibodies directed against HLA‐A1‐10‐11 or HLA‐A1‐10. In contrast, only one of ten individuals whose phenotypes included HLA‐A1, HLA‐A11, or both produced anti‐HLA‐A3. Eleven incompatible retrospective crossmatches were observed in recipients of HLA‐matched platelets attributable to intragroup antibodies. Patients receiving incompatible platelets had unsatisfactory post‐transfusion platelet count increments. It is concluded that intragroup antibodies, such as those directed against antigens in the HLA‐A1 CREG, are an important cause of platelet transfusion failures in patients requiring long‐term platelet transfusion support. These antibodies can be identified by routinely screening recipient sera for HLA antibodies and performing retrospective crossmatches using the lymphocytotoxicity technique.