The appearance and expansion of donor white blood cells in a recipient after transfusion has many potential biologic ramifications. Although patients with HIV infection are ostensibly at high risk for microchimerism, transfusion-associated graft-versus-host disease (TA-GVHD) is rare. The purpose of this study was to search for sustained microchimerism in such patients. Blood samples were collected from 93 HIV-infected women (a
subset from the Viral Activation Transfusion Study, an NHLBI multicenter randomized trial comparing leukoreduced versus unmodified red blood cell [RBC] transfusions) before and after transfusions from male donors. Donor lymphocytes were detected in posttransfusion specimens using a quantitative Y-chromosome-specific polymerase chain reaction (PCR) assay, and donor-specific human leukocyte antigen (HLA) alleles were identified with allele-specific PCR primers and probes. Five of 47 subjects randomized to receive nonleukoreduced RBCs had detectable male lymphocytes 1 to 2 weeks after transfusion, but no subject had detectable male cells more than 4 weeks after a transfusion. In 4 subjects studied, donor-specific HLA haplotypes were detected in posttransfusion specimens, consistent with one or more donors' cells. None of 46 subjects randomized to receive leukoreduced RBCs had detectable male lymphocytes in the month after transfusion. Development of sustained microchimerism after transfusion in HIV-infected patients is rare; HIV-infected patients do not appear to be at risk for TA-GVHD.