The impact of HIV infection on the frequencies, function, spatial localization and heterogeneity of T follicular regulatory cells (TFRs) within human lymph nodes.

BACKGROUND: HIV eradication efforts have been unsuccessful partly due to virus persistence in immune sanctuary sites such as germinal centres within lymph node (LN) tissues. Recent evidence suggests that LNs harbour a novel subset of regulatory T cells, termed follicular regulatory T cells (TFRs), but their role in HIV pathogenesis is not fully elucidated. RESULTS: Paired excisional LN and peripheral blood samples obtained from 20 HIV-uninfected and 31 HIV-infected treated and 7 chronic untreated, were used to determine if and how HIV infection modulate frequencies, function and spatial localization of TFRs within LN tissues. Imaging studies showed that most TFRs are localized in extra-follicular regions. Co-culture assays showed TFRs suppression of TFH help to B cells. Importantly, epigenetic and transcriptional studies identified DPP4 and FCRL3 as novel phenotypic markers that define four functionally distinct TFR subpopulations in human LNs regardless of HIV status. Imaging studies confirmed the regulatory phenotype of DPP4+TFRs. CONCLUSION: Together these studies describe TFRs dynamic changes during HIV infection and reveal previously underappreciated TFR heterogeneity within human LNs.

Hypermethylation at the CXCR5 gene locus limits trafficking potential of CD8+ T cells into B-cell follicles during HIV-1 infection.

CD8+ T cells play an important role in HIV control. However, in human lymph nodes (LNs), only a small subset of CD8+ T cells express CXCR5, the chemokine receptor required for cell migration into B-cell follicles, which are major sanctuaries for HIV persistence in individuals on therapy. Here, we investigate the impact of HIV infection on follicular CD8+ T cell (fCD8) frequencies, trafficking patterns, and CXCR5 regulation. We show that, although HIV infection results in a marginal increase in fCD8s in LNs, the majority of HIV-specific CD8+ T cells are CXCR5- (non-fCD8s) (P < .003). Mechanistic investigations using Assay for Transposase-Accessible Chromatin using sequencing showed that non-fCD8s have closed chromatin at the CXCR5 transcriptional start site (TSS). DNA bisulfite sequencing identified DNA hypermethylation at the CXCR5 TSS as the most probable cause of closed chromatin. Transcriptional factor footprint analysis revealed enrichment of transforming growth factors (TGFs) at the TSS of fCD8s. In vitro stimulation of non-fCD8s with recombinant TGF-ß resulted in a significant increase in CXCR5 expression (fCD8s). Thus, this study identifies TGF-ß signaling as a viable strategy for increasing fCD8 frequencies in follicular areas of the LN where they are needed to eliminate HIV-infected cells, with implications for HIV cure strategies.