Activated-memory T cells influence naïve T cell fate: A non-cytotoxic function of human CD8 T cells

T cells are endowed with the capacity to sense their environment including other T cells 48 around them. They do so to set their numbers and activation thresholds. This form of regulation has been well-studied within a given T cell population – i.e., within the naïve or memory pool; however, less is known about the cross-talk between T cell subsets. Here, we tested whether memory T cells interact with and influence surrounding naïve T cells. We report that human naïve CD8 T cells (TN) undergo phenotypic and transcriptional changes in the presence of autologous activated-memory CD8 T cells (TMem). Following in vitro co-culture with activated central memory cells (TCM), ~3% of the TN acquired activation/memory canonical markers (CD45RO and CD95) in an MHC-I dependent-fashion. Using scRNA-seq, we also observed that ~3% of the TN acquired an activated/memory signature, while ~84% developed a unique activated transcriptional profile hybrid between naïve and activated memory. Pseudotime trajectory analysis provided further evidence that TN with an activated/memory or hybrid phenotype were derived from TN. Our data reveal a non-cytotoxic function of TMem with potential to activate autologous TN into the activated/memory pool. These findings may have implications for host-protection and autoimmunity that arises after vaccination, infection or transplantation CD8 T cells subsets were sorted from one healthy donor pbmcs. Activated TCM cells (150K) were labeled with CFSE and co-cultured with resting CTV labeled naïve CD8 T cells (50K) at a 3:1 ratio respectively for 7 days. As for controls, isolated naïve T cells or activated TCM were cultured separately in similar conditions. Thereafter, live naïve and activated TCM cells were sorted, while only CTV+ cells (which included both CTV+ CD45RO- and CD45RO+ subpopulations) were sorted following co-culture of naïve with activated TCM cells. Each sorted sample was then labelled with cell hashing antibodies (Totalseq-C, Biolegend) for later demultiplexing, then pooled together and sequenced in one flow cell.