HIV Transmission Chains Exhibit Greater HLA-B Homogeneity Than Randomly Expected

Background: HIV's capacity to escape immune recognition by human leukocyte antigen (HLA) is a core component of HIV pathogenesis. A better understanding of the distribution of HLA class I in HIV-infected patients would improve our knowledge of pathogenesis in relation to the host HLA type and could better improve therapeutic strategies against HIV. Materials and Methods: Three hundred one to 325 transmission pairs and 469-496 clusters were identified for analysis among Swiss HIV Cohort Study (SHCS) participants using HIV pol sequences from the drug resistance database. HLA class I data were compiled at 3 specificity levels: 4-digit, 2-digit alleles, and HLA-B supertype. The analysis tabulated HLA-I homogeneity as 2 measures: the proportion of transmission pairs, which are HLA concordant, and the average percentage of allele matches within all clusters. These measures were compared with the mean value across randomizations with randomly assorted individuals. Results: We repeated the analysis for different HLA classification levels and separately for HLA-A,-B, and-C. Subanalyses by the risk group were performed for HLA-B. HLA-B showed significantly greater homogeneity in the transmission chains (2-digit clusters: 0.291 vs. 0.251, P value = 0.009; supertype clusters: 0.659 vs. 0.611, P value = 0.002; supertype pairs: 0.655 vs. 0.608, P value = 0.014). Risk group restriction caused the effect to disappear for men-who-have-sexwith- men but not for other risk groups. We also examined if protective HLA alleles B27 and B57 were under-or overrepresented in the transmission chains, although this yielded no significant pattern. Conclusions: The HLA-B alleles of patients within HIV-1 transmission chains segregate in homogenous clusters/pairs, potentially indicating preferential transmission among HLA-B concordant individuals.