On the other hand, enrichment of Tsp cells was detected in the BM up to 60 times subsequent infection (Supplemental Figure 2A). was maintained in Tsp cells, indicative of the slow-cycling phenotype. Human being Tsp cells shown a definite gene-expression profile that was enriched for genes overexpressed in Trm cells. In mice, proteins encoded by Tsp signature genes, including nuclear receptor subfamily 4 group A member 1 (NR4A1) and ATP-binding cassette (ABC) transporters, influenced the function and differentiation of Trm cells. Responses to RR6 adoptive transfer of human Tsp cells into immune-deficient mice and plerixafor therapy suggested that human Tsp cell mobilization could be manipulated as a potential cellular therapy. These data identify a distinct subset of human T cells with a quiescent/slow-cycling phenotype, propensity for tissue enrichment, and potential to mobilize into circulation, which may be harnessed for adoptive cellular therapy. Introduction A fundamental property of human T cells is to provide lifelong immunity against pathogens lasting several decades (1). The complement of T cells within an individual is heterogeneous and includes naive T cells that develop from thymic precursors, short-lived effector cells, and memory T cells derived from naive T cells following antigen exposure. Maintenance of each of these components for several decades of life is essential to host defense: memory T cells for defense against previously encountered antigens and naive T cells for responses to new antigens. T cell memory is mediated by coordinated action of distinct subsets. RR6 Initial pioneering studies classified human memory T cells into effector memory T cells (Tem cells) and central memory T cells (Tcm cells) based on rapid effector function and the expression of lymphoid homing receptors, respectively (2). More recent studies have identified and characterized a subset of memory T cells resident in RR6 nonlymphoid tissues (NLT) that mediate regional immune surveillance against pathogens (3C6). Tissue-resident RR6 memory T cells (Trm cells) in NLTs outnumber memory CD8+ T cells in lymphoid tissues and represent the primary steady-state surveillance mechanism in NLTs (7). Both Tcm and Trm cells originate from a common clonal precursor, but following tissue localization, Trm cells maintain a highly regional network and persist over decades of life with apparently little homeostatic turnover (8C10). Little is known about the mechanisms that underlie the development, dormancy, and maintenance of these long-lived Trm cells, RR6 particularly in humans, and investigation of these areas will have major implications for understanding immune homeostasis within tissues. Homeostasis in adult tissues is maintained by the differentiation of a small population of adult stem cells. The capacity of T cells for long-term survival, quiescence, clonal differentiation, and self-renewal has elicited comparisons between long-lived postmitotic cells, such as memory T cells and adult stem cells (11). Indeed, prior studies have shown that murine memory T cells share a transcriptional program of self-renewal with long-term hematopoietic stem cells (HSCs) (12). Goodell et al. described the ability to efflux lipophilic Hoechst dyes as a distinct property of a subset of HSCs, termed side population (SP) cells, with enhanced regenerative potential (13, 14). The SP phenotype (i.e., dye efflux) is mediated by the expression of ATP-binding cassette (ABC) transporters (particularly ABCG2 in most HSCs and some adult stem cells), and cells with SP phenotype have been identified in putative stem cells in diverse tissues (15C18). ABC transporters efflux diverse substrates, and their expression in stem cells is postulated to protect these cells from xenotoxic, oxidative, and metabolic stress (15, 19). Human CD8+ memory T cells expressing P-glycoprotein/ABCB1 were shown to persist following cancer chemotherapy (20); however, most human T cells with ABCB1+ phenotype were later shown to be mucosa-associated invariant T (MAIT) cells (21). We hypothesized that human T cells with SP phenotype may identify a subset with distinct biologic and functional properties. Here, we show that SP phenotype marks a distinct subset of human and murine T cells. Trm cells in human and murine tissues such as the gut are highly enriched SP T cells (Tsp cells), and these cells particularly mark a Trm subset with quiescent/slow-cycling phenotype. Human Tsp cells share overlapping transcriptional gene-expression programs with Trm cells Rabbit Polyclonal to iNOS (10), including several members of the NR4A orphan nuclear receptor family, also implicated in HSC quiescence (22, 23). We also show that 2 key signature genes identified in human Tsp cells, ABC transporters and nuclear receptor subfamily 4 group A member 1 (= 20), BM (=.