Background/Case Studies: Alloimmunization to HLA antibodies is found in 1-2% of the general male blood donor population. HLA sensitization has significant implications in transfusion and transplantation medicine, including increased risk of transfusion reactions, transfusion-refractory thrombocytopenia, and allograft rejection. HLA sensitization can occur after transfusion, transplantation, or pregnancy. Our previous pilot study suggested that men who have sex with men (MSM) have a higher prevalence of HLA sensitization than that of the general male blood donor population. To confirm these findings, we conducted a larger study to determine the prevalence of HLA sensitization and examined correlations with recent sexual practices in a cohort of HIV-negative MSM.
Study
Design/Methods: Banked serum samples were obtained from sexually active, HIV-negative MSM who participated in the Emory Involvement study (2010-2014). HLA sensitization was detected by flow cytometry screen (FlowPRA). Positive FlowPRA screens were then tested with single antigen bead testing (LABScreen) to provide antibody specificity. Antibody specificities were used to determine degree of sensitization, reported as a calculated PRA (CPRA) value. The prevalence of HLA sensitization was determined, and the correlation between sexual practices (sex with anyone, sex with men, protected anal intercourse with men, unprotected anal intercourse with men) and HLA sensitization was assessed by the Student’s t test or the Chi-squared test, as appropriate.
Results/Findings: Serum samples from 395 MSM (median age 26 years) revealed that 25% (100/395) had HLA antibodies. HLA class I antibodies alone occurred in 79/100, class II antibodies alone in 14/100, and class I and class II antibodies in 7/100. Among those with HLA antibody, sensitization levels ranged from < 1% to 99% CPRA (see figure). No significant correlation was found between HLA sensitization and either sexual practices or number of partners. Conclusions: This study found that 25% of MSM have HLA sensitization. As the FDA considers an "individual risk" approach to HIV screening, more MSM will be eligible to donate blood. Screening MSM for HLA antibodies during plasma-based blood product donation could mitigate the risk of transfusion reactions such as transfusion-related acute lung injury. The study did not find a correlation between HLA antibodies and sexual behavior, but some individuals like MSM may be more susceptible to alloimmunization than others, regardless of the number of partners (i.e., responders). Future research should explore whether the number of sexual encounters with a single partner may be a more relevant factor than the total number of partners, in terms of repeated exposure to the same HLA antibody specificities.
Importance of research: Results show that MSM may have a higher prevalence of HLA antibodies than that reported for the general male blood donor population. The findings have implications for blood recipients, transplant patients, and blood donors, as the FDA explores an "individual risk" approach for HIV screening, which could increase MSM donor eligibility. Screening MSM for HLA antibodies during plasma-based blood product donation may mitigate the risk of certain transfusion reactions.
