Cytolytic effector memory HIV- and SIV-specific CD8+ T cells are key correlates for natural and vaccine-induced viral control. While assumed, it remains unknown if these cells leave the blood to access HIV reservoirs in lymphoid and peripheral tissues. To directly address this question, we present for the first time a spatial map of the tissue egressing (recirculating) immune system by sampling blood, lymph nodes (LNs) and thoracic duct lymph (TDL) in HIV-seronegative and seropositive individuals.
We isolated LNs and matched human blood and TDL mononuclear cells through thoracic duct cannulation of HIV-seronegative and seropositive individuals on and off antiretroviral therapy. Functional and phenotypic assays on total and HIV+ lymphocytes were performed by flow cytometry and transcriptional data was collected through RNAseq using the SMARTseq2 platform. The results were analyzed using RStudio, FlowJo, and GraphPad Prism.
Through transcriptional, functional and phenotypic analysis, we show that expression of cytolytic molecules by effector memory CD8+ T cells are almost entirely confined to blood, while their phenotypic counterparts in the thoracic duct, and many tissues, represent non-cytolytic T cells with a higher regenerative capacity. Unlike their blood counterparts, HIV- and CMV-specific CD8+ T cells in TDL and LNs generally lack cytolytic molecule expression and killing ability. We further demonstrate that those HIV-specific CD8+ T cells detectable in the TDL possess an intermediate differentiation status (CCR7-CD45RA-CD27+), thereby defining the identity of HIV-specific CD8+ T cells capable of accessing HIV reservoirs in peripheral tissues.
Our results demonstrate that not all types of memory CD8+ T cells survey tissues and reveal that cytolytic molecule expression is mostly confined to effector memory HIV-specific CD8+ T cells in blood during steady-state and chronic HIV disease. These data also suggest that the intermediate differentiation status of peripheral blood HIV-specific CD8+ T cells is a marker of tissue recirculation rather than a dysfunctional state as previously assumed.