HIV replication occurs in follicular CD4+ T helper cells localized within germinal centers (GC) of secondary lymphoid follicles, and exclusion of CTL within GC is thought to contribute to the maintenance of the viral reservoir. Recent studies have identified a CD8+ T cell population termed follicular CD8+ T cells that expresses the chemokine receptor CXCR5, which is associated with trafficking into GCs, which secrete its ligand CXCL13. However, the frequency, precise localization and antiviral function of HIV-specific CXCR5+ CD8+ T cells within lymph nodes have not been determined. We investigated the frequency, function and localization of HIV-specific CXCR5+ CD8+ T cells in lymph nodes (LN) and peripheral blood (PB) during treated and untreated chronic clade C HIV-1 infection.
Biopsied LN and paired PB samples from 5 chronic untreated, 2 treated in chronic phase and 2 subjects treated during hyperacute HIV infection were analyzed. MHC class I tetramers and ICS assays were used to characterize HIV-specific responses. Immunohistochemistry (IHC) staining for Gag p24 was used to identify the location of HIV infected cells. IHC was also used to locate CXCR5+ CD8+ T cells within LN.
Comparative analysis of HIV-specific CD8+ T cells of the same tetramer specificity in LN and paired PB illustrated phenotypic and functional dissimilarities. Notably, in contrast to PB responses, LN cells were significantly more activated (CD38+HLA-DR+), more exhausted (PD-1 high) and secreted less cytokines upon ex vivo stimulation with mitogens (SEB). IHC revealed limited overlap between Gag p24+ CD4+ T cells and CD8+ T cells. The frequencies of CXCR5+ tetramer+ CD8+ T cells were very low in PB averaging about 0.9% (IQR 0.0:3.2), but were readily detectable in LMC samples by flowcytometry as well as in LN tissues by IHC. More importantly the frequency of CXCR5+ tetramer+ CD8+ T cells in LN inversely correlated with plasma viral load (Spearman’s r=−0.8; p=0.01).
Taken together our results indicate that HIV-specific CD8+ T cells in LN are functionally more impaired than PB responses. Within LN, CXCR5+ tetramer+ CD8+ T cells may contribute to enhanced virus control. Therefore, efforts aimed at redirecting HIV-specific CD8+ T cells into GC though induction of CXCR5 expression may contribute to enhanced virus suppression.