Time- and tissue-dependent roles of regulatory T cells in the immune response to HSV-2

Abstract Herpes simplex virus 2 (HSV-2) is a chronic sexually transmitted infection that causes recurrent genital ulcers and increases HIV susceptibility. Efforts to design a vaccine have assumed regulatory T cells (Tregs) restrain immune activation and impede viral clearance. However, we have previously shown that in a mouse model of vaginal primary HSV-2 infection, Treg removal leads to impaired T cell priming and migration. This suggests an alternative model where Treg function is location- and context-dependent. Additionally, research suggests that tissue-resident memory T cells (Trm) localized in the vaginal tract (VT) are crucial for efficient viral control, and Trm are likely regulated by local Tregs. These findings underscore the importance of understanding the specific contributions of VT Tregs during viral infection and vaccination. We performed RNA sequencing of VT and lymph node (LN) Tregs after HSV-2 infection to reveal a highly activated transcriptional profile in VT Tregs compared to LN Tregs. Using flow cytometry, we confirmed an elevated activation and tissue residency phenotype in VT Tregs, exacerbated after HSV-2 infection. Notably, we found that VT Tregs express Granzyme B (GzmB) by both RNA-sequencing and flow cytometry. These Tregs persist in the VT up to 90 days, suggesting that they remain poised to respond to HSV-2 reencounter by restraining memory Trm to prevent tissue damage, possibly through GzmB-mediated toxicity. Tregs from healthy human VT corroborated mouse VT Treg phenotypes. These results suggest that VT Tregs are distinct and uniquely poised to respond to viral infection. Studies are ongoing to interrogate the signals that drive Treg migration into the VT and that lead to the tissue-specific Treg phenotype.