Antiretroviral therapy (ART) effectively suppresses HIV levels in plasma. While HIV levels at mucosal surfaces generally also fall to undetectable levels, several groups have described detectable HIV shedding in the anogenital tissues of ART-treated individuals, and the immune correlates of HIV shedding in the context of effective ART are not well understood. Because mucosal inflammation drives increased HIV shedding in ART-naïve individuals, we hypothesized that anorectal HIV shedding in ART-treated men would be associated with activated mucosal CD4+ T cells.
Fifty-four HIV-infected, ART-treated men who have sex with men were recruited from Toronto, Canada. Anal swabs were used to test for HIV RNA levels by RT-PCR. High-resolution anoscopy was performed to collect anal biopsies, and lymphocytes isolated from collagenase-treated biopsies were stained for flow cytometric analysis. Markers included: CD38/HLA-DR (immune activation), CD25/FoxP3 (Tregs), CCR6 (Th17), CCR5 (HIV co-receptor) and CCR7/CD45RA (memory subsets). HIV shedders and non-shedders were compared by Mann-Whitney (SPSS).
Fifteen (27.8%) of 54 ART-treated men had detectable anorectal HIV shedding despite plasma HIV suppression, albeit at low levels (median 206 copies/swab). Surprisingly, HIV shedders did not have increased levels of activated (CD38+HLA-DR+) CD4+ T cells (p= 0.401). However, we observed differences in anorectal CD4+ T cells memory subsets: HIV shedders had a significantly higher proportion of central memory cells (CCR7+CD45RA-; Shedders= 34.5%, Non-shedders= 17.9%; p= 0.004). All other mucosal memory subsets were enriched in HIV non-shedders, including terminally differentiated cells (CCR7-CD45RA+; p= 0.024). No other mucosal T cell differences were observed between HIV shedders and HIV non-shedders.
An increased proportion of central memory cells (TCM), but not of activated mucosal CD4+ T cells, was associated with HIV shedding. This suggests that non-inflammatory mechanisms, such as the homeostatic proliferation of latently infected cells, may be driving mucosal HIV shedding in ART-treated individuals. While the low-level HIV shedding that we observed is unlikely to contribute to sexual transmission of HIV, understanding immune correlates of compartmentalized HIV production in ART-treated individuals may help to optimize strategies for HIV eradication.