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BACKGROUND: Women whose fetuses were treated with intrauterine transfusions (IUTs) for alloimmune hemolytic disease are high responders to red blood cell (RBC) antigens. We investigated the risk for HLA alloimmunization.

STUDY DESIGN AND METHODS: Women and their children treated with IUT between 1987 and 2008 were included. Participants were HLA antigen typed and studied for the prevalence of HLA antibodies compared to age-matched parous nontransfused blood donors. Anti-D titer, the formation of new RBC antibodies after IUT, and the degree of fetomaternal HLA mismatches on HLA antibody formation and/or persistence were analyzed.

RESULTS: A higher prevalence of HLA Class I antibodies was observed in these women compared to controls (41% vs. 23%). Both a higher anti-D titer (>8000) and formation of new RBC antibodies after IUT were associated with increased HLA immunization. HLA antibody formation was associated with the number of fetomaternal triplet epitope mismatches. Antigens within HLA-Bw4, HLA-B35/51/52/53/18/78-complex and A1/A9, were higher and mismatches within HLA-C were less immunogenic than expected. HLA antibodies against the IUT-treated fetus were more persistent than other antibodies.

CONCLUSION: Women whose fetuses were treated with IUT had a high risk of developing and maintain fetal-specific HLA Class I antibodies. Factors associated with increased HLA immunization were a higher amount of fetomaternal HLA triplet mismatches, higher anti-D titer, and additional RBC antibody formation. We presume that the induction of HLA Class I antibodies is the result of increased fetomaternal hemorrhage during IUT, eliciting antibodies in women with an increased susceptibility to alloimmunization.