Project description:Memory T cells are critical for vaccines and T-cell-based therapies. However, the differentiation path of memory T cells is not completely understood. Early bulk cell population-based studies support a linear model, in which effector T cells lose the effector program and dedifferentiate into memory T cells. Recent research supports a bifurcation model, where T cells choose one of the two paths, either the effector or the memory path, at an early stage of T cell responses. Terminal effector T cells lose the capacity to become memory T cells. Here, we first demonstrate that the expression of granzyme A is largely distinct from that of granzyme B and marks terminal cytotoxic effector CD8+ T cells with reduced polyfunctionality. Using a granzyme A-fate mapping mouse line and an acute viral infection model, we discovered that early memory T cells are largely derived from cells lacking a history of granzyme A expression, supporting the bifurcation model. Progressively, granzyme A-expressing terminal effector T cells dedifferentiate into functional long-term memory T cells. At the late memory phase, memory T cells are a mixed population composed of cells with different differentiation paths (i.e., the linear and the bifurcated paths) that coordinate to provide balanced immune protection.
Project description:CD8 effector T cells with a CD127hi KLRG1- phenotype are considered precursors to the long-lived memory pool, while KLRG1+ CD127low cells are viewed as short-lived effectors. Nevertheless, we and others have shown that a KLRG1+ CD127low population persists into the memory phase and that these T cells (termed long-lived effector cells or LLEC) display robust protective function during acute re-challenge with bacteria or viruses. Whether these T cells represent a true memory population or are instead a remnant effector cell population that failed to undergo initial contraction has remained unclear. Here, we show that LLEC from mice express a distinct phenotypic and transcriptional signature that shares characteristics of both early effectors and long-lived memory cells. Furthermore, we find that LLEC are exclusively derived from day 12 KLRG1+ effector cells. Our work challenges the concept that the KLRG1+ CD127low population is dominated by short-lived cells and shows that KLRG1 downregulation is not a prerequisite to become a long-lived protective memory T cell.
Project description:Memory T cells are heterogeneous in terms of their phenotype and functional properties. We investigated the molecular profiles of human CD8 naïve (TN), central memory (TCM), effector memory (TEM), and effector memory RA (TEMRA) T cells using gene expression microarrays and phospho-protein-specific intracellular flow cytometry. We demonstrate that TCM have a gene expression and cytokine signaling signature that lies between that of TN and TEM or TEMRA cells, whereas TEM and TEMRA are closely related. Our data define the molecular basis for the different functional properties of central and effector memory subsets. We show that TEM and TEMRA cells strongly express genes with known importance in CD8 T cell effector function. In contrast, TCM are characterized by high basal and cytokine-induced STAT5 phosphorylation, reflecting their capacity for self-renewal. Altogether, our results distinguish TCM and TEM/TEMRA at the molecular level and are consistent with the concept that TCM represent memory stem cells.
Project description:Memory CD8+ T cells are indispensable for maintaining long-term immunity against intracellular pathogens and tumors. Despite their presence in oxygen-deprived tissues of infection sites or tumors, the impact of local oxygen pressure on memory CD8+ T cells has remained largely unclear. We sought to elucidate how oxygen pressure impacted memory CD8+ T cells arising after infection with Listeria monocytogenes-OVA. Our data revealed that reduced oxygen pressure during in vitro culture switched CD8+ T cell metabolism from an OXPHOS to a glycolytic phenotype. Quantitative proteomic analysis showed that limiting oxygen conditions increased the expression of glucose transporters and components of the glycolytic pathway, while decreasing TCA cycle and mitochondrial respiratory chain proteins. The altered CD8+ T cell metabolism did not affect the expansion potential, but enhanced the granzyme B and IFN- production capacity. Memory CD8+ T cells cultured under low oxygen pressure were able to persist long-term in vivo and provided protection against bacterial rechallenge. Taken together, our study indicates that strategies of cellular immune therapy may benefit from reducing oxygen during culture to develop memory CD8+ T cells with superior effector functions .