Germinal Center T Follicular Helper Cells Are Highly Permissive to HIV-1 and Alter Their Phenotype during Virus Replication

Abstract

HIV-1 replication is concentrated within CD4+ T cells in B-cell follicles of secondary lymphoid tissues during asymptomatic disease. Limited data suggest that a subset of T follicular helper cells (TFH) within germinal centers (GC) is highly permissive to HIV-1. Whether GC TFH are the major HIV-1 virus-producing cells in vivo has not been established. Here, we investigated TFH permissivity to HIV-1 ex vivo by spinoculating and culturing tonsil cells with HIV-1 GFP reporter viruses. Using flow cytometry, higher percentages of GC TFH (CXCR5highPD-1high) and CXCR5+PD-1low cells were GFP+ than non-GC TFH (CXCR5+PD-1intermediate) or extrafollicular (CXCR5-) cells. When sorted prior to spinoculation, however, GC TFH were substantially more permissive than CXCR5+PD-1low or extrafollicular cells, suggesting that many GC TFH transition to a CXCR5+PD-1low phenotype during productive infection. In situ hybridization on inguinal lymph node sections from untreated HIV-1-infected individuals without AIDS revealed higher frequencies of HIV-1 RNA+ cells in GC than non-GC regions of follicle or extrafollicular regions. Superinfection of HIV-1-infected individuals’ lymph node cells with GFP reporter virus confirmed the permissivity of follicular cells ex vivo. Lymph node immunostaining revealed 96% of CXCR5+CD4+ cells were located in follicles. Within sorted lymph node cells from four HIV-infected individuals, CXCR5+ subsets harbored 11- to 66-fold more HIV-1 RNA than CXCR5-subsets, as determined by RT PCR. Thus, GC TFH are highly permissive to HIV-1, but downregulate PD-1 and to a lesser extent CXCR5 during HIV-1 replication. These data further implicate GC TFH as the major HIV-1-producing cells in chronic asymptomatic HIV-1 infection.

The receptor repertoire and functional profile of follicular T cells in HIV-infected lymph nodes

“…The enrichment of HIV antigens (10, 11) and the highly pro-inflammatory milieu (12, 13) in the LNs could lead to antigen-driven and/or bystander T cell expansion. To address whether proliferation of T FH cells is antigen-dependent, we tested whether HIV induces selective proliferation of certain T cell clones.…”

Immunologic characteristics of HIV‐infected individuals who make broadly neutralizing antibodies

“…In vitro, GC Tfh cells are more susceptible to infection with HIV‐1 than non‐GC Tfh cells or CXCR5 − extrafollicular CD4 + T cells,170, 171 and in vivo they have been shown to constitute the major CD4 T‐cell compartment for virus replication in both HIV‐1 172, 173 and SIV174, 175 infections. Furthermore, Tfh cell populations in both LNs and blood constitute a major (although not the only) site of SIV/HIV latency in macaques/humans receiving antiretroviral therapy 171, 176, 177, 178, 179.…”

T FH in HIV Latency and as Sources of Replication-Competent Virus

“…T FH from human tonsils are highly permissive to both CCR5- and CXCR4-tropic HIV compared to other CD4+ T cell subsets ex vivo [8, 9]. The heightened permissivity of tonsillar T FH cannot be fully explained by differences in memory subsets, cellular activation, or chemokine co-receptor expression [9].…”

“…T FH from human tonsils are highly permissive to both CCR5- and CXCR4-tropic HIV compared to other CD4+ T cell subsets ex vivo [8, 9]. The heightened permissivity of tonsillar T FH cannot be fully explained by differences in memory subsets, cellular activation, or chemokine co-receptor expression [9]. Importantly, in an HIV-model system using humanized mice, T FH rapidly accumulate in gut and female reproductive tract mucosal tissues and are the most permissive CD4+ T cell subset to HIV [10], suggesting that gut and vaginal T FH may play a key role in establishment of HIV infection as well as ongoing virus replication.…”