Jameson, Stephen C.

Abstract Sensing of extracellular metabolites controls CD8+ T cell function. Their accumulation can occur through export by specialized molecules, such as the release channel Pannexin-1 (Panx1). Here, we report that T cell-specific Panx1 is needed for efficient CD8+ T cell responses to viral infection and cancer. Panx1 favors both the expansion of effector CD8+ T cells and the survival of memory CD8+ T cells. Our data suggests that, while memory CD8+ T cells require Panx1 for mitochondrial function, Panx1 promotes the glycolytic pathway in effector CD8+ T cells. Panx1 promotes memory CD8+ T cell survival together with the eATP sensor P2RX7. However, Panx1 induces effector CD8+ T cells independently of eATP. Rather, we found an unexpected link between Panx1, lactate export and the activation of effector CD8+ T cells. Therefore, Panx1 regulates effector and memory CD8+ T cells through export of distinct metabolites and by engaging different intracellular pathways.

Abstract Memory CD8+ T cells protect against secondary viral infections. They develop and maintain exclusively in circulation (e.g. central memory - Tcm) or are excluded from re-circulation (resident memory - Trm). Circulating memory CD8+ T cells arises from memory precursors (MPs) which express memory, pro-survival, and pluripotency molecules. Trm generation, in contrast, is still not fully understood. Previous reports suggest that Trm and Tcm have a common precursor present at the early effector phase; yet, the nature of this precursor is elusive. We have found that the extracellular ATP receptor P2RX7 promotes both Tcm and Trm generation. Moreover, P2RX7 is quickly upregulated in some (but not all) early effectors and early P2RX7 ablation hinders both Tcm and Trm generation. Thus, we postulated that P2RX7 in early effectors may mark a Tcm/Trm common precursor. Comparison between high (P2RX7hi) and low (P2RX7lo) P2RX7-expressing CD8+ T cells shows a correlation between memory markers and P2RX7, with CD62L+ Tcm precursors exclusively found in P2RX7hi cells. RNA-seq of P2RX7hi and P2RX7lo early effectors show survival, memory and pluripotency genes and pathways are upregulated in P2RX7hi cells. Conversely, many terminal effector and apoptosis genes are upregulated in P2RX7lo cells. P2RX7lo early effectors and MPs have increased apoptosis. Upon transfer into infection-matched mice, P2RX7hi MPs preferentially survive and form Tcm compared to P2RX7lo MPs. This is even more apparent when P2RX7hi and P2RX7lo early effectors are compared: approximately 100x more P2RX7hi cells form memory when compared to P2RX7lo cells, both Tcm and Trm. Our data suggest that P2RX7 in early effector CD8+ T cells promotes the generation of a common Tcm/Trm precursor.

Abstract Release of extracellular ATP (eATP) by dying cells is often identified as a "danger signal" by immune cells. However, eATP export by healthy cells is common, and a major transmembrane ATP exporter is the Pannexin 1 (Panx1) molecule. CD8+ T cells express Panx1 during thymic development, at steady-state and during immune response. However, the role of Panx1 on CD8+ T cell-mediated immune response is not well defined. Here, we used genetic and pharmacological ablation tools to address this question. T cell-specific Panx1 deletion does not affect CD8+ T cell thymic development or effector responses to viral infection (LCMV). In contrast, memory CD8+ T cell establishment is impaired by either pharmacological inhibition or CD8-specific Panx1 deletion. Using a tamoxifen-controlled, conditional Panx1 knockout LCMV-specific (P14) CD8+ T cell system, we found that both memory CD8+ T cell generation and survival rely on Panx1. In vitro data further supports these findings: two Panx1 inhibitors, 10Panx and Probenecid, reduce the expression of the central memory marker CD62L. Panx1-deficient CD8+ T cells develop a memory-like phenotype in response to IL-15, but fail to engage mitochondrial respiration and present decreased mitochondrial membrane potential, suggesting Panx1 promotes optimal mitochondrial function. These defects are partially reverted with exogenous eATP. Collectively, our data indicates that cell-intrinsic Panx1-mediated eATP export favors memory CD8+ T cell differentiation. We are currently testing whether CD8-intrinsic Panx1 controls memory CD8+ T cell generation solely as an autocrine eATP source, or if Panx1 also serves as a “rheostat” controlling intracellular ATP levels in antigen-responding CD8+ T cells.

Abstract Resident memory T cells (TRM) provide localized protective immunity in non-lymphoid tissues, but the signals and interactions within non-lymphoid tissues involved in generating TRM are incompletely defined. Inducible T-cell costimulator (ICOS) is a costimulatory molecule with well elaborated roles in regulating differentiation of CD4+ T cell populations, its function in CD8+ T cells is largely unexplored. With acute infection models, we found that ICOS-deficient CD8+ T cells showed minimal defects in the initial effector expansion and the generation of recirculating memory subsets. However, consistent with its high expression in TRM, ICOS deficiency significantly compromised the establishment of CD8+ TRM cells in diverse non-lymphoid tissues. We further confirmed that rather than pre-programming the TRM fate during initial T cell priming, the interaction between ICOS ligand (ICOSL) and ICOS in the non-lymphoid tissues during CD8+ T cell recruitment is critical for efficient tissue retention and acquisition of tissue residency signatures. ICOS signaling through PI3K pathway is key for TRM generation and ICOS stimulation promotes downregulation of KLF2, a transcription factor that regulates T cell trafficking, in CD8+ T cells after entering non-lymphoid tissues. Altogether, our data illustrate that engagement of ICOS is one of the critical local costimulatory cues that promote the establishment of tissue-resident populations, with potential implication for therapeutic manipulation.

Abstract Tissue-derived extracellular ATP (eATP) is a “danger signal” sensed by immune cells via purinergic receptors (e.g. P2RX7). In addition, healthy cells can export eATP through transmembrane channels, such as the hemichannel Pannexin-1 (Panx1). CD8+ T cells express Panx1 constitutively throughout developmental and immune response stages. However, the biological role of Panx1 in CD8+ T cells is undefined. Here, we used genetic and pharmacological tools to address this question. T-cell specific Panx1 deletion did not affect CD8+ T cell thymic development. In contrast, CD8+ T cell responses to viral infection (LCMV) are impaired by Panx1 inhibition or deletion. This is true for effector expansion of CD8+ T cells and for the survival of memory CD8+ T cells. Using adoptive transfer of tamoxifen-conditional Panx1 knockout LCMV-specific (P14) cells into LCMV-infected mice, we showed that memory CD8+ T cell survival requires sustained Panx1 – except for small intestinal-resident cells. Mechanistically, Panx1 promotes memory CD8+ T cell survival via P2RX7, which also favors memory CD8+ T cells - as suggested by our data with Panx1/P2RX7-double knockout P14 cells. The role of Panx1 for effector CD8+ T cell expansion, however, is unlikely to be via P2RX7 since this receptor does not have a role in effector CD8+ T cells. Our transcriptional and metabolic data suggests that, while memory CD8+ T cells require Panx1 for optimal mitochondrial function and expression of pro-memory genes, effector CD8+ T cells lacking Panx1 had decreased activation of the glycolytic pathway. Collectively, these results suggest that, in response to acute virus, Panx1 induces CD8+ T cell effector expansion and memory survival through distinct metabolic pathways. Supported by grants from NIH (R00 AI139381, NIAID).

Abstract The objective of this study was to test the hypothesis that the increasing global incidence of allergy and atopy are due in part to improved hygiene and decreased microbial exposure. We have adopted a novel mouse model of normalized microbial exposure to test the impact of immune experience on subsequent responses to airway allergens. In this model, specific pathogen free (SPF) B6 mice are cohoused with mice from pet stores and become “dirty” – many commensals and pathogens are transmitted through cohousing and influence the immune cell populations systemically and in the lungs. We treated mice intranasally with a single dose of A. alternata fungal extract (Alt) and assessed production of type 2 cytokines. IL5 and IL13 levels in the lungs and bronchoalveolar lavage fluid were dramatically elevated by Alt in SPF mice but were not significantly increased by Alt in dirty mice. Type 2 innate lymphoid cells (ILC2) are the cells responsible for IL5 and IL13 after acute Alt treatment, and interestingly the number of lung ILC2 was unaltered by cohousing and their activation status appeared similar in both housing conditions. We treated mice with recombinant IL33, the alarmin released by lung epithelial cells in response to allergens, and the results suggest an impaired response to IL33 by dirty lung ILC2. In a repeated Alt exposure model, ILC2 cells expanded in SPF lungs and recruited eosinophils, neutrophils, and T cells. Most dirty mouse lungs contained these cell populations at steady state but were only modestly recruited with repeated Alt exposure. Lung function experiments are in progress. This study suggests that increased microbial exposure leads to more type-2 associated immune cells in the lungs, however responses to airway allergens are dampened.

Abstract Expression of the purinergic receptor P2RX7 by CD8+ T cells promotes the generation of memory populations following acute infections. However, data suggest that P2RX7 may limit the efficacy of antitumor responses. Herein, we show that P2RX7 is beneficial for optimal melanoma control in a mouse CD8+ T-cell adoptive transfer model. Tumor-specific P2rx7–/– CD8+ T cells exhibited impaired mitochondrial maintenance and function but did not display signs of overt exhaustion early in the antitumor response. However, as the tumor burden increased, the relative frequency of P2RX7-deficient CD8+ T cells declined within the tumor; this correlated with reduced proliferation, increased apoptosis, and mitochondrial dysfunction. Extending these studies, we found that the transient in vitro stimulation of P2RX7 using the ATP analogue BzATP led to enhanced B16 melanoma control by CD8+ T cells. These findings are in keeping with the concept that extracellular ATP (eATP) sensing by P2RX7 on CD8+ T cells is required for their ability to efficiently eliminate tumors by promoting mitochondrial fitness and underscore the potential for P2RX7 stimulation as a novel therapeutic treatment to enhance tumor immunotherapy.

Abstract Development of CD8+ central memory T (Tcm) and resident memory T (Trm) cells, which promote immunity in the circulation and in barrier tissues, respectively, is not completely understood. Tcm and Trm cells may arise from common precursors; however, their fate-inducing signals are elusive. We found that virus-specific effector CD8+ T cells display heterogeneous expression of the extracellular ATP sensor P2RX7. P2RX7-high expression is confined, at peak effector phase, to CD62L+ memory precursors, which preferentially form Tcm cells. Among early effector CD8+ T cells, asymmetrical P2RX7 distribution correlated with distinct transcriptional signatures, with P2RX7-high cells enriched for memory and tissue residency sets. P2RX7-high early effectors preferentially form both Tcm and Trm cells. Defective Tcm and Trm cell formation in P2RX7 deficiency is significantly reverted when the transcriptional repressor Zeb2 is ablated. Mechanistically, P2RX7 negatively regulates Zeb2 expression, at least partially through TGF-β sensing in early effector CD8+ T cells. Our study indicates that unequal P2RX7 upregulation in effector CD8+ T cells is a foundational element of the early Tcm/Trm fate.

Abstract The impact of microbes on restraining the immune response to allergens has been extensively studied and is a key element of the hygiene hypothesis. Lung type 2 innate lymphoid cell responses to airway allergens can be inhibited by administration of a number of microbial products; however, it is unclear whether such an effect would be observed with natural infections and how sustained any observed inhibitory effects would be. To answer these questions, we used a murine model of physiological microbial exposures through cohousing SPF laboratory mice with pet store mice and examined the acute type 2 response to intranasally delivered fungal allergen extract Alternaria alternata. We found laboratory mice cohoused with pet store mice for two weeks display a suppressed ILC2 response to A. alternata which resulted in reduced eosinophilia. By comparison, mice cohoused for at least two months had ILC2 and eosinophil responses similar to SPF mice despite dramatic changes to the composition of the immune cell populations in the lungs. Lung ILC2 in two-month cohoused mice were still sensitive to subsequent inflammatory cues, as administration of poly(I:C) was able to suppress ILC2 activation and eosinophilia equally well in SPF and two-month cohoused animals. These findings suggest ILC2 dynamically respond to their environment and are not easily desensitized long-term.

Senescent cells exacerbate COVID-19 Cellular senescence is a state elicited in response to stress signals and is associated with a damaging secretory phenotype. The number of senescent cells increases with advanced age and this in turn drives age-related diseases. Camell et al. show that senescent cells have an amplified inflammatory response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (see the Perspective by Cox and Lord). This response is communicated to nonsenescent cells, suppressing viral defense mechanisms and increasing the expression of viral entry proteins. In old mice infected with a SARS-CoV-2–related virus, treatment with senolytics to reduce the senolytic cell burden reduced mortality and increased antiviral antibodies. Science , abe4832, this issue p. eabe4832 ; see also abi4474, p. 281