Early CD8 T-cell memory precursors and terminal effectors exhibit equipotent in vivo degranulation.
ABSTRACT: Early after priming, effector CD8 T cells are distinguished into memory precursor and short-lived effector cell subsets (MPECs and SLECs). Here, we delineated a distinct in vivo heterogeneity in killer cell lectin-like receptor G1 (KLRG-1) expression, which was strongly associated with diverse MPEC and SLEC fates. These in vivo MPECs and SLECs expressed equivalent levels of cytotoxic molecules and effector cytokines. Using a unique in vivo degranulation assay, we found that the MPECs and SLECs similarly encountered infected target cells and elaborated equivalent levels of cytotoxicity in vivo. These data provide direct in vivo evidence that memory-fated cells pass through a robust effector phase. Additionally, the preferential localization of the MPECs in the lymph nodes, where a lesser degree of cytotoxicity was elaborated, suggests that the MPECs may be protected from excessive stimulation and terminal differentiation by virtue of their differential tissue localization. These data provide novel mechanistic insights into the linear decreasing potential model of memory differentiation.
Project description:As acute infections resolve, effector CD8(+) T cells differentiate into interleukin-7 receptor(lo) (IL-7R(lo)) short-lived effector cells (SLECs) and IL-7R(hi) memory precursor effector cells (MPECs) capable of generating long-lived memory CD8(+) T cells. By using another SLEC marker, KLRG1, we found that KLRG1(hi) effector cells began appearing early during infection and were committed to downregulating IL-7R. Unlike IL-7R(hi) MPECs, KLRG1(hi) IL-7R(lo) SLECs relied on IL-15, but IL-15 could not sustain their long-term maintenance or homeostatic turnover. The decision between SLEC and MPEC fates was regulated by the amount of inflammatory cytokines (i.e., IL-12) present during T cell priming. According to the amount of inflammation, a gradient of T-bet was created in which high T-bet expression induced SLECs and low expression promoted MPECs. These results elucidate a mechanism by which the innate immune system sets the relative amounts of a lineage-determining transcription factor in activated CD8(+) T cells and, correspondingly, regulates their memory cell potential.
Project description:Naïve antigen-specific CD8 T cells expand in response to infection and can be phenotypically separated into distinct effector populations, which include memory precursor effector cells (MPECs) and short-lived effector cells (SLECs). In the days before the peak of the T cell response, a third population called early effector cells (EECs) predominate the antigen-specific response. However, the contribution of the EEC population to the CD8 T cell differentiation program during an antimicrobial immune response is not well understood. To test if EEC populations were pre-committed to either an MPEC or SLEC fate, we purified EECs from mice infected with Listeria monocytogenes (LM) or vesicular stomatitis virus (VSV), where the relative frequency of each population is known to be different at the peak of the response. Sorted EECs transferred into uninfected hosts revealed that EECs were pre-programmed to differentiate based on early signals received from the distinct infectious environments. Surprisingly, when these same EECs were transferred early into mismatched infected hosts, the transferred EECs could be diverted from their original fate. These results delineate a model of differentiation where EECs are programmed to form MPECs or SLECs, but remain susceptible to additional inflammatory stimuli that can alter their fate.
Project description:CD8+ T cells play an important role in host resistance to many viral infections, but the underlying transcriptional mechanisms governing their differentiation and functionality remain poorly defined. By using a highly virulent systemic and respiratory poxvirus infection in mice, we show that the transcription factor Bcl11b provides a dual trigger that sustains the clonal expansion of virus-specific effector CD8+ T cells, while simultaneously suppressing the expression of surface markers associated with short-lived effector cell (SLEC) differentiation. Additionally, we demonstrate that Bcl11b supports the acquisition of memory precursor effector cell (MPEC) phenotype and, thus, its absence causes near complete loss of lymphoid and lung-resident memory cells. Interestingly, despite having normal levels of T-bet and Eomesodermin, Bcl11b-deficient CD8+ T cells failed to execute effector differentiation needed for anti-viral cytokine production and degranulation, suggesting a non-redundant role of Bcl11b in regulation of this program. Thus, Bcl11b is a critical player in fate decision of SLECs and MPECs, as well as effector function and memory formation.
Project description:The transcriptional repressor Blimp-1 promotes the differentiation of CD8(+) T cells into short-lived effector cells (SLECs) that express the lectin-like receptor KLRG-1, but how it operates remains poorly defined. Here we show that Blimp-1 bound to and repressed the promoter of the gene encoding the DNA-binding inhibitor Id3 in SLECs. Repression of Id3 by Blimp-1 was dispensable for SLEC development but limited the ability of SLECs to persist as memory cells. Enforced expression of Id3 was sufficient to restore SLEC survival and enhanced recall responses. Id3 function was mediated in part through inhibition of the transcriptional activity of E2A and induction of genes regulating genome stability. Our findings identify the Blimp-1-Id3-E2A axis as a key molecular switch that determines whether effector CD8(+) T cells are programmed to die or enter the memory pool.
Project description:The PI3K/Akt signaling pathway impacts various aspects of CD8 T cell homeostasis, such as effect versus memory cell differentiation, during viral infection. We used microarrays to determine which downstream molecules were affected and what other signaling pathways were interconnected with the Akt pathway by constitutive activation of Akt in LCMV-infected CD8 T cells. Overall design: Splenocytes from naive P14/WT or P14/Akt mice were stained with anti-CD8 and anti-Ly5.1, and CD8 T cells were sorted using a FACSAria II instrument. Purified Ly5.1+ CD8 T cells from P14/WT or P14/Akt mice were transferred into B6 mice, which were subsequently infected with LCMV Armstrong. At day 8 post infection, splenocytes were stained with anti-CD8, anti-Ly5.1, anti-KLRG1, and anti-CD127. Following staining, short-lived effector cells (SLECs) and memory precursor effector cells (MPECs) were sorted using the FACSAria II instrument; the purity of the sorted cells was >95%. A total of 5 samples were analyzed, including WT naive, WT SLEC, WT MPEC, Akt naive and Akt SLEC.
Project description:By the peak of the CD8(+) T cell response, the effector cell pool consists of a heterogeneous population of cells that includes both those with an increased propensity to become long-lived memory cells (memory precursor effector cells; MPEC) and those that are terminally differentiated cells (short-lived effector cells; SLEC). Numerous studies have established the critical role that functional avidity plays in determining the in vivo efficacy of CD8(+) effector cells. Currently, how functional avidity differs in MPEC versus SLEC and the evolution of this property within these two populations during the expansion and contraction of the response are unknown. The data presented in this study show that at the peak of the effector response generated after poxvirus infection, SLEC were of higher functional avidity than their MPEC counterpart. Over time, however, SLEC exhibited a decrease in peptide sensitivity. This is in contrast to MPEC, which showed a modest increase in peptide sensitivity as the response reached equilibrium. The decrease in functional avidity in SLEC was independent of CD8 modulation or the amount of Ag receptor expressed by the T cell. Instead, the loss in sensitivity was correlated with decreased expression and activation of ZAP70 and Lck, critical components of TCR membrane proximal signaling. These results highlight the potential contribution of avidity in the differentiation and evolution of the T cell effector response after viral infection.
Project description:The PI3K/Akt signaling pathway impacts various aspects of CD8 T cell homeostasis, such as effect versus memory cell differentiation, during viral infection. We used microarrays to determine which downstream molecules were affected and what other signaling pathways were interconnected with the Akt pathway by constitutive activation of Akt in LCMV-infected CD8 T cells. Splenocytes from naive P14/WT or P14/Akt mice were stained with anti-CD8 and anti-Ly5.1, and CD8 T cells were sorted using a FACSAria II instrument. Purified Ly5.1+ CD8 T cells from P14/WT or P14/Akt mice were transferred into B6 mice, which were subsequently infected with LCMV Armstrong. At day 8 post infection, splenocytes were stained with anti-CD8, anti-Ly5.1, anti-KLRG1, and anti-CD127. Following staining, short-lived effector cells (SLECs) and memory precursor effector cells (MPECs) were sorted using the FACSAria II instrument; the purity of the sorted cells was >95%. A total of 5 samples were analyzed, including WT naive, WT SLEC, WT MPEC, Akt naive and Akt SLEC.
Project description:In response to infection, CD8(+) T cells integrate multiple signals and undergo an exponential increase in cell numbers. Simultaneously, a dynamic differentiation process occurs, resulting in the formation of short-lived effector cells (SLECs; CD127(low)KLRG1(high)) and memory precursor effector cells (CD127(high)KLRG1(low)) from an early effector cell that is CD127(low)KLRG1(low) in phenotype. CD8(+) T cell differentiation during vesicular stomatitis virus infection differed significantly than during Listeria monocytogenes infection with a substantial reduction in early effector cell differentiation into SLECs. SLEC generation was dependent on Ebi3 expression. Furthermore, SLEC differentiation during vesicular stomatitis virus infection was enhanced by administration of CpG-DNA, through an IL-12-dependent mechanism. Moreover, CpG-DNA treatment enhanced effector CD8(+) T cell functionality and memory subset distribution, but in an IL-12-independent manner. Population dynamics were dramatically different during secondary CD8(+) T cell responses, with a much greater accumulation of SLECs and the appearance of a significant number of CD127(high)KLRG1(high) memory cells, both of which were intrinsic to the memory CD8(+) T cell. These subsets persisted for several months but were less effective in recall than memory precursor effector cells. Thus, our data shed light on how varying the context of T cell priming alters downstream effector and memory CD8(+) T cell differentiation.
Project description:Mucosal immunity to reinfection with a highly virulent virus requires the accumulation and persistence of memory CD8 T cells at the site of primary infection. These cells may derive from memory precursor effector cells (MPECs), which are distinct from short-lived effector cells that provide acute protection but are often destined to die. Using respiratory virus infection, we show that herpes virus entry mediator (HVEM; TNFRSF14), a member of the TNF receptor superfamily, provides key signals for MPEC persistence. HVEM-deficient CD8 T cells expanded normally but were skewed away from MPECs with resultant poor development of circulating and lung-resident memory cells. HVEM was selectively expressed on MPECs whereas MPECs deficient in HVEM failed to survive in adoptive transfer recipients. As a consequence, HVEM-deficient recipients failed to afford protection against respiratory reinfection with influenza virus. HVEM therefore represents a critical signal for MPECs and development of protective mucosal CD8 T cell memory.
Project description:Generating and maintaining a robust CD8(+) T cell response in the face of high viral burden is vital for host survival. Further, balancing the differentiation of effectors along the memory precursor effector cell pathway versus the short-lived effector cell (SLEC) pathway may be critical in controlling the outcome of virus infection with regard to clearance and establishing protection. Although recent studies have identified several factors that have the capacity to regulate effector CD8(+) T cell differentiation-for example, inflammatory cytokines-we are far from a complete understanding of how cells choose the memory precursor effector cell versus SLEC fate following infection. In this study, we have modulated the infectious dose of the poxvirus vaccinia virus as an approach to modulate the environment present during activation and expansion of virus-specific effector cells. Surprisingly, in the face of a high virus burden, the number of SLECs was decreased. This decrease was the result of increased natural regulatory T cells (Tregs) generated by high viral burden, as depletion of these cells restored SLECs. Our data suggest Treg modulation of differentiation occurs via competition for IL-2 during the late expansion period, as opposed to the time of T cell priming. These findings support a novel model wherein modulation of the Treg response as a result of high viral burden regulates late-stage SLEC number.