Characterization of CD4⁺ T cell subsets and HIV susceptibility in the inner and outer foreskin of Ugandan men

Problem: Biological mechanisms of foreskin HIV acquisition are poorly defined. The inner foreskin is preferentially infected in explant models, so we hypothesized that this site would be enriched for HIV-susceptible CD4⁺ T cells and proinflammatory/chemoattractant cytokines. Method of study: A total of 42 HIV-uninfected Ugandan men without genital symptoms provided foreskin tissues and swabs at the time of elective penile circumcision. The immune phenotype of foreskin-derived CD4⁺ T cells and entry of a CCR5-tropic HIV pseudovirus was characterized, and specific cytokine levels assayed by multiplexed chemiluminescent ELISA. Results: Unexpectedly, outer foreskin CD4⁺ T cells more frequently expressed CCR5 (median 29.2% vs 22.9%, P = 0.01) and CD69 (median 36.5% vs 15%, P < 0.01), and on a per-cell basis, HIV entry was higher. However, overall CD4⁺ T cell density was approximately twofold higher in the inner foreskin, and several highly susceptible T cell subsets were increased at this site, including Th17 cells (20.0% vs 14.1%, P = 0.0021). Specific pro-inflammatory cytokine levels were also higher on the inner foreskin surface (IL-17, IL-8, RANTES and IL-1β; all P < 0.05). Conclusion: There was marked heterogeneity in CD4⁺ T cell populations and immune milieu between inner and outer foreskin tissues. Despite higher per-cell viral entry into CD4⁺ T cells from the outer foreskin, the higher target cell density and enriched pro-inflammatory cytokines of the inner foreskin suggest that this may be a preferential site for HIV acquisition.