1 5806 131 STRATEGIES TO REINVIGORATE EXHAUSTED CD8(+) T CELLS IN TUMOR MICROENVIRONMENT. CD8(+) T CELL EXHAUSTION IS A STABLE DYSFUNCTIONAL STATE DRIVEN BY CHRONIC ANTIGEN STIMULATION IN THE TUMOR MICROENVIRONMENT (TME). DIFFERENTIATION OF EXHAUSTED CD8(+) T CELLS (CD8(+) TEXS) IS ACCOMPANIED BY EXTENSIVE TRANSCRIPTIONAL, EPIGENETIC AND METABOLIC REPROGRAMMING. CD8(+) TEXS ARE MAINLY CHARACTERIZED BY IMPAIRED PROLIFERATIVE AND CYTOTOXIC CAPACITY AS WELL AS THE INCREASED EXPRESSION OF MULTIPLE CO-INHIBITORY RECEPTORS. PRECLINICAL TUMOR STUDIES AND CLINICAL COHORTS HAVE DEMONSTRATED THAT T CELL EXHAUSTION IS FIRMLY ASSOCIATED WITH POOR CLINICAL OUTCOMES IN A VARIETY OF CANCERS. MORE IMPORTANTLY, CD8(+) TEXS ARE REGARDED AS THE MAIN RESPONDER TO IMMUNE CHECKPOINT BLOCKADE (ICB). HOWEVER, TO DATE, A LARGE NUMBER OF CANCER PATIENTS HAVE FAILED TO ACHIEVE DURABLE RESPONSES AFTER ICB. THEREFORE, IMPROVING CD8(+) TEXS MAY BE A BREAKTHROUGH POINT TO REVERSE THE CURRENT DILEMMA OF CANCER IMMUNOTHERAPY AND ELIMINATE CANCERS. STRATEGIES TO REINVIGORATE CD8(+) TEXS IN TME MAINLY INCLUDE ICB, TRANSCRIPTION FACTOR-BASED THERAPY, EPIGENETIC THERAPY, METABOLISM-BASED THERAPY AND CYTOKINE THERAPY, WHICH TARGET ON DIFFERENT ASPECTS OF EXHAUSTION PROGRESSION. EACH OF THEM HAS ITS ADVANTAGES AND APPLICATION SCOPE. IN THIS REVIEW, WE MAINLY FOCUS ON THE MAJOR ADVANCES OF CURRENT STRATEGIES TO REINVIGORATE CD8(+) TEXS IN TME. WE SUMMARIZE THEIR EFFICACY AND MECHANISMS, IDENTIFY THE PROMISING MONOTHERAPY AND COMBINED THERAPY AND PROPOSE SUGGESTIONS TO ENHANCE THE TREATMENT EFFICACY TO SIGNIFICANTLY BOOST ANTI-TUMOR IMMUNITY AND ACHIEVE BETTER CLINICAL OUTCOMES. 2023 2 5248 48 PROGRAMMED CELL DEATH 1-DIRECTED IMMUNOTHERAPY FOR ENHANCING T-CELL FUNCTION. T-CELL EXHAUSTION IS A UNIQUE STATE THAT APPEARS DURING MANY CHRONIC INFECTIONS AND CANCER AND IS CHARACTERIZED BY LOSS OF PROLIFERATIVE CAPACITY AND EFFECTOR FUNCTION. COMPLEX MECHANISMS ARE INVOLVED IN THIS T-CELL DYSFUNCTION BUT AN INHIBITORY RECEPTOR, PD-1, HAS BEEN IDENTIFIED AS A MAJOR REGULATOR OF T-CELL EXHAUSTION. BLOCKADE OF THE PD-1 PATHWAY CAN REINVIGORATE EXHAUSTED T CELLS, RESULTING IN BETTER CONTROL OF CHRONIC INFECTIONS AND CANCER. NOTABLY, RECENT CLINICAL STUDIES HAVE REVEALED THAT PD-1-DIRECTED IMMUNOTHERAPY IS HIGHLY EFFECTIVE IN CANCER PATIENTS, DEMONSTRATING THAT PD-1 IS A PROMISING THERAPEUTIC TARGET IN HUMANS. IN THIS REVIEW, WE SUMMARIZE OUR CURRENT UNDERSTANDING OF THE EPIGENETIC REGULATION OF PD-1 EXPRESSION IN T CELLS AND DISCUSS POTENTIAL COMBINATION THERAPY WITH PD-1 BLOCKADE TOWARD DEVELOPING MORE EFFECTIVE TREATMENT FOR CHRONIC INFECTIONS AND CANCER. 2013 3 1278 34 DE NOVO EPIGENETIC PROGRAMS INHIBIT PD-1 BLOCKADE-MEDIATED T CELL REJUVENATION. IMMUNE-CHECKPOINT-BLOCKADE (ICB)-MEDIATED REJUVENATION OF EXHAUSTED T CELLS HAS EMERGED AS A PROMISING APPROACH FOR TREATING VARIOUS CANCERS AND CHRONIC INFECTIONS. HOWEVER, T CELLS THAT BECOME FULLY EXHAUSTED DURING PROLONGED ANTIGEN EXPOSURE REMAIN REFRACTORY TO ICB-MEDIATED REJUVENATION. WE REPORT THAT BLOCKING DE NOVO DNA METHYLATION IN ACTIVATED CD8 T CELLS ALLOWS THEM TO RETAIN THEIR EFFECTOR FUNCTIONS DESPITE CHRONIC STIMULATION DURING A PERSISTENT VIRAL INFECTION. WHOLE-GENOME BISULFITE SEQUENCING OF ANTIGEN-SPECIFIC MURINE CD8 T CELLS AT THE EFFECTOR AND EXHAUSTION STAGES OF AN IMMUNE RESPONSE IDENTIFIED PROGRESSIVELY ACQUIRED HERITABLE DE NOVO METHYLATION PROGRAMS THAT RESTRICT T CELL EXPANSION AND CLONAL DIVERSITY DURING PD-1 BLOCKADE TREATMENT. MOREOVER, THESE EXHAUSTION-ASSOCIATED DNA-METHYLATION PROGRAMS WERE ACQUIRED IN TUMOR-INFILTRATING PD-1HI CD8 T CELLS, AND APPROACHES TO REVERSE THESE PROGRAMS IMPROVED T CELL RESPONSES AND TUMOR CONTROL DURING ICB. THESE DATA ESTABLISH DE NOVO DNA-METHYLATION PROGRAMMING AS A REGULATOR OF T CELL EXHAUSTION AND BARRIER OF ICB-MEDIATED T CELL REJUVENATION. 2017 4 2446 37 EPIGENETIC STRATEGIES SYNERGIZE WITH PD-L1/PD-1 TARGETED CANCER IMMUNOTHERAPIES TO ENHANCE ANTITUMOR RESPONSES. IMMUNOTHERAPY STRATEGIES TARGETING THE PROGRAMMED CELL DEATH LIGAND 1 (PD-L1)/PROGRAMMED CELL DEATH 1 (PD-1) PATHWAY IN CLINICAL TREATMENTS HAVE ACHIEVED REMARKABLE SUCCESS IN TREATING MULTIPLE TYPES OF CANCER. HOWEVER, OWING TO THE HETEROGENEITY OF TUMORS AND INDIVIDUAL IMMUNE SYSTEMS, PD-L1/PD-1 BLOCKADE STILL SHOWS SLOW RESPONSE RATES IN CONTROLLING MALIGNANCIES IN MANY PATIENTS. ACCUMULATING EVIDENCE HAS SHOWN THAT AN EFFECTIVE RESPONSE TO ANTI-PD-L1/ANTI-PD-1 THERAPY REQUIRES ESTABLISHING AN INTEGRATED IMMUNE CYCLE. DAMAGE IN ANY STEP OF THE IMMUNE CYCLE IS ONE OF THE MOST IMPORTANT CAUSES OF IMMUNOTHERAPY FAILURE. IMPAIRMENTS IN THE IMMUNE CYCLE CAN BE RESTORED BY EPIGENETIC MODIFICATION, INCLUDING REPROGRAMMING THE ENVIRONMENT OF TUMOR-ASSOCIATED IMMUNITY, ELICITING AN IMMUNE RESPONSE BY INCREASING THE PRESENTATION OF TUMOR ANTIGENS, AND BY REGULATING T CELL TRAFFICKING AND REACTIVATION. THUS, A RATIONAL COMBINATION OF PD-L1/PD-1 BLOCKADE AND EPIGENETIC AGENTS MAY OFFER GREAT POTENTIAL TO RETRAIN THE IMMUNE SYSTEM AND TO IMPROVE CLINICAL OUTCOMES OF CHECKPOINT BLOCKADE THERAPY. 2020 5 5358 31 REBALANCING TGFBETA1/BMP SIGNALS IN EXHAUSTED T CELLS UNLOCKS RESPONSIVENESS TO IMMUNE CHECKPOINT BLOCKADE THERAPY. T CELL DYSFUNCTIONALITY PREVENTS THE CLEARANCE OF CHRONIC INFECTIONS AND CANCER. FURTHERMORE, EPIGENETIC PROGRAMMING IN DYSFUNCTIONAL CD8(+) T CELLS LIMITS THEIR RESPONSE TO IMMUNOTHERAPIES, INCLUDING IMMUNE CHECKPOINT BLOCKADE (ICB). HOWEVER, IT IS UNCLEAR WHICH UPSTREAM SIGNALS DRIVE ACQUISITION OF DYSFUNCTIONAL EPIGENETIC PROGRAMS, AND WHETHER THERAPEUTICALLY TARGETING THESE SIGNALS CAN REMODEL TERMINALLY DYSFUNCTIONAL T CELLS TO AN ICB-RESPONSIVE STATE. HERE WE INNOVATE AN IN VITRO MODEL SYSTEM OF STABLE HUMAN T CELL DYSFUNCTION AND SHOW THAT CHRONIC TGFBETA1 SIGNALING IN POSTEFFECTOR CD8(+) T CELLS ACCELERATES THEIR TERMINAL DYSFUNCTION THROUGH STABLE EPIGENETIC CHANGES. CONVERSELY, BOOSTING BONE MORPHOGENETIC PROTEIN (BMP) SIGNALING WHILE BLOCKING TGFBETA1 PRESERVED EFFECTOR AND MEMORY PROGRAMS IN CHRONICALLY STIMULATED HUMAN CD8(+) T CELLS, INDUCING SUPERIOR RESPONSES TO TUMORS AND SYNERGIZING THE ICB RESPONSES DURING CHRONIC VIRAL INFECTION. THUS, REBALANCING TGFBETA1/BMP SIGNALS PROVIDES AN EXCITING NEW APPROACH TO UNLEASH DYSFUNCTIONAL CD8(+) T CELLS AND ENHANCE T CELL IMMUNOTHERAPIES. 2023 6 5895 17 T CELL EXHAUSTION: AN EPIGENETICALLY IMPRINTED PHENOTYPIC AND FUNCTIONAL MAKEOVER. A RECENT ARTICLE IN CELL DEMONSTRATES THAT THE ABSENCE OF A SINGLE DNA METHYLTRANSFERASE, DNMT3A, PREVENTS CYTOTOXIC T CELLS FROM ACQUIRING THE HYPOFUNCTIONAL OR EXHAUSTED PHENOTYPE TYPICALLY SEEN IN CHRONIC VIRAL INFECTIONS AND TUMORS. UPON ESTABLISHING A CAUSAL RELATIONSHIP BETWEEN EXHAUSTION-ASSOCIATED EPIGENETIC CHANGES AND REDUCED CD8(+) T CELL FUNCTION, THE AUTHORS PROVIDED MECHANISTIC EVIDENCE THAT EXHAUSTION CONSTITUTES A SPECIFIC DIFFERENTIATION PROGRAM. 2017 7 6060 50 THE DEVELOPMENT OF CD8 T-CELL EXHAUSTION HETEROGENEITY AND THE THERAPEUTIC POTENTIALS IN CANCER. CD8(+) T CELLS ARE ESSENTIAL LYMPHOCYTES WITH CYTOTOXIC PROPERTIES FOR ANTITUMOR IMMUNOTHERAPY. HOWEVER, DURING CHRONIC INFECTION OR TUMORIGENESIS, THESE CELLS OFTEN BECOME DYSFUNCTIONAL WITH A GRADUALLY DEPLETED ABILITY TO RELEASE CYTOKINES AND THE EXHIBITION OF REDUCED CYTOTOXICITY, THE STATE REFERRED TO AS "T-CELL EXHAUSTION" (TEX). THIS UNIQUE STATE WAS CHARACTERIZED BY THE INCREASING EXPRESSION OF INHIBITORY CHECKPOINT RECEPTORS, AND INTERVENTIONS TARGETING IMMUNE CHECKPOINT BLOCKADES (ICBS) HAVE BEEN CONSIDERED AS A PROMISING STRATEGY TO STIMULATE T-CELL KILLING. RECENT INVESTIGATIONS HAVE DEMONSTRATED THAT EXHAUSTED T CELLS NOT ONLY DISPLAY FUNCTIONAL, METABOLIC, TRANSCRIPTIONAL, AND EPIGENETIC DIFFERENCES BUT ALSO COMPRISE A HETEROGENEOUS GROUP OF CELLS. IN THIS REVIEW, WE SUMMARIZE THE CURRENT FINDINGS ON DYNAMIC DIFFERENTIATION PROCESS DURING TEX HETEROGENEITY DEVELOPMENT IN CANCER AND CHRONIC INFECTION. WE DISCUSS HOW THE RESPONSES TO IMMUNOTHERAPY ARE DETERMINED BY THESE DISTINCT SUBSETS AND HIGHLIGHT PROSPECTIVE APPROACHES FOR IMPROVING THE EFFICACY OF ICB THERAPY FOR CANCER BY LEVERAGING THE HETEROGENEITY OF T CELLS. 2023 8 790 32 CELLULAR AND MOLECULAR MECHANISMS OF CD8(+) T CELL DIFFERENTIATION, DYSFUNCTION AND EXHAUSTION. T CELLS FOLLOW A TRIPHASIC DISTINCT PATHWAY OF ACTIVATION, PROLIFERATION AND DIFFERENTIATION BEFORE BECOMING FUNCTIONALLY AND PHENOTYPICALLY "EXHAUSTED" IN SETTINGS OF CHRONIC INFECTION, AUTOIMMUNITY AND IN CANCER. EXHAUSTED T CELLS PROGRESSIVELY LOSE CANONICAL EFFECTOR FUNCTIONS, EXHIBIT ALTERED TRANSCRIPTIONAL NETWORKS AND EPIGENETIC SIGNATURES AND GAIN CONSTITUTIVE EXPRESSION OF A BROAD COINHIBITORY RECEPTOR SUITE. THIS REVIEW OUTLINES RECENT ADVANCES IN OUR UNDERSTANDING OF EXHAUSTED T CELL BIOLOGY AND EXAMINES CELLULAR AND MOLECULAR MECHANISMS BY WHICH A STATE OF DYSFUNCTION OR EXHAUSTION IS ESTABLISHED, AND MECHANISMS BY WHICH EXHAUSTED T CELLS MAY STILL CONTRIBUTE TO PATHOGEN OR TUMOUR CONTROL. FURTHER, THIS REVIEW DESCRIBES OUR UNDERSTANDING OF EXHAUSTED T CELL HETEROGENEITY AND OUTLINES THE MECHANISMS BY WHICH CHECKPOINT BLOCKADE DIFFERENTIALLY ENGAGES EXHAUSTED T CELL SUBSETS TO OVERCOME EXHAUSTION AND RECOVER T CELL FUNCTION. 2020 9 2718 44 EXHAUSTED T CELLS AND EPIGENETIC STATUS. EXHAUSTED T CELLS ARE A GROUP OF DYSFUNCTIONAL T CELLS, WHICH ARE PRESENT IN CHRONIC INFECTIONS OR TUMORS. THE MOST SIGNIFICANT CHARACTERISTICS OF EXHAUSTED T CELLS ARE ATTENUATED EFFECTOR CYTOTOXICITY, REDUCED CYTOKINE PRODUCTION, AND UPREGULATION OF MULTIPLE INHIBITORY MOLECULAR RECEPTORS (E.G., PD-1, TIM-3, AND LAG-3). THE INTRACELLULAR METABOLIC CHANGES, ALTERED EXPRESSION OF TRANSCRIPTION FACTORS, AND A UNIQUE EPIGENETIC LANDSCAPE CONSTITUTE THE EXHAUSTION PROGRAM. RECENTLY, RESEARCHERS HAVE MADE PROGRESS IN UNDERSTANDING EXHAUSTED T CELLS, WITH THE DEFINITION AND IDENTIFICATION OF EXHAUSTED T CELLS CHANGING FROM PHENOTYPE-BASED TO BEING CLASSIFIED AT THE TRANSCRIPTIONAL AND EPIGENETIC LEVELS. RECENT STUDIES HAVE REVEALED THAT EXHAUSTED T CELLS CAN BE SEPARATED INTO TWO SUBGROUPS, NAMELY TCF1(+)PD-1(+) PROGENITOR-LIKE PRECURSOR EXHAUSTED CELLS AND TCF1(-)PD-1(+) TERMINALLY DIFFERENTIATED EXHAUSTED T CELLS. MOREOVER, THE PROGENITOR-LIKE PRECURSOR CELL POPULATION MAY BE A SUBSET OF T CELLS THAT CAN RESPOND TO IMMUNOTHERAPY. STUDIES HAVE ALSO FOUND THAT TOX INITIATES AND DOMINATES THE DEVELOPMENT OF EXHAUSTED T CELLS AT THE TRANSCRIPTIONAL AND EPIGENETIC LEVELS. TOX ALSO MAINTAINS T CELL SURVIVAL AND MAY AFFECT DECISIONS REGARDING TREATMENT STRATEGIES. IN THIS REVIEW, WE DISCUSS THE LATEST DEVELOPMENTS IN T CELL EXHAUSTION IN REGARDS TO DEFINITIONS, SUBPOPULATIONS, DEVELOPMENT MECHANISMS, DIFFERENCES IN DIVERSE DISEASES, AND TREATMENT PROSPECTS FOR EXHAUSTED T CELLS. FURTHERMORE, WE HYPOTHESIZE THAT THE EPIGENETIC STATE REGULATED BY TOX MIGHT BE THE KEY POINT, WHICH CAN DETERMINE THE REVERSIBILITY OF EXHAUSTION AND THE EFFICACY OF IMMUNOTHERAPY. 2020 10 2367 34 EPIGENETIC REGULATION OF T CELL EXHAUSTION. CHRONIC ANTIGEN STIMULATION DURING VIRAL INFECTIONS AND CANCER CAN LEAD TO T CELL EXHAUSTION, WHICH IS CHARACTERIZED BY REDUCED EFFECTOR FUNCTION AND PROLIFERATION, AND THE EXPRESSION OF INHIBITORY IMMUNE CHECKPOINT RECEPTORS. RECENT STUDIES HAVE DEMONSTRATED THAT T CELL EXHAUSTION RESULTS IN WHOLESCALE EPIGENETIC REMODELING THAT CONFERS PHENOTYPIC STABILITY TO THESE CELLS AND PREVENTS T CELL REINVIGORATION BY CHECKPOINT BLOCKADE. HERE, WE REVIEW FOUNDATIONAL TECHNOLOGIES TO PROFILE THE EPIGENOME AT MULTIPLE SCALES, INCLUDING MAPPING THE LOCATIONS OF TRANSCRIPTION FACTORS AND HISTONE MODIFICATIONS, DNA METHYLATION AND THREE-DIMENSIONAL GENOME CONFORMATION. WE DISCUSS HOW THESE TECHNOLOGIES HAVE ELUCIDATED THE DEVELOPMENT AND EPIGENETIC REGULATION OF EXHAUSTED T CELLS AND FUNCTIONAL IMPLICATIONS ACROSS VIRAL INFECTION, CANCER, AUTOIMMUNITY AND ENGINEERED T CELL THERAPIES. FINALLY, WE COVER EMERGING MULTI-OMIC AND GENOME ENGINEERING TECHNOLOGIES, CURRENT AND UPCOMING OPPORTUNITIES TO APPLY THESE TO T CELL EXHAUSTION, AND THERAPEUTIC OPPORTUNITIES FOR T CELL ENGINEERING IN THE CLINIC. 2022 11 198 34 ACQUIRED TRANSCRIPTIONAL PROGRAMMING IN FUNCTIONAL AND EXHAUSTED VIRUS-SPECIFIC CD8 T CELLS. PURPOSE OF REVIEW: FAILURE TO CONTROL VIRAL INFECTIONS SUCH AS HIV RESULTS IN T-CELL RECEPTOR (TCR) AND INHIBITORY RECEPTOR DRIVEN EXHAUSTION OF ANTIGEN-SPECIFIC T CELLS. PERSISTENT SIGNALING BY THESE RECEPTORS DURING CHRONIC VIRAL INFECTION SCULPTS THE TRANSCRIPTIONAL REGULATORY PROGRAMS OF VIRUS-SPECIFIC T CELLS. THE RESULTING GENE EXPRESSION PROFILE IS TAILORED TO TEMPER THE POTENTIALLY DAMAGING EFFECTOR FUNCTIONS OF CYTOTOXIC T CELLS AND ADAPT THEM TO AN ANTIGEN-RICH AND INFLAMMATION-RICH ENVIRONMENT. HERE WE REVIEW RECENT STUDIES INVESTIGATING MECHANISMS OF TRANSCRIPTIONAL REGULATION OF EFFECTOR, FUNCTIONAL MEMORY, AND EXHAUSTED T-CELL FUNCTIONS DURING ACUTE VERSUS CHRONIC INFECTIONS. RECENT FINDINGS: PATTERNS OF GENE EXPRESSION IN VIRUS-SPECIFIC CD8 T CELLS ARE A RESULT OF A COMBINATION OF PRO AND INHIBITORY SIGNALS FROM ANTIGEN PRESENTATION (TCR-MEDIATED) AND CO-INHIBITORY RECEPTOR LIGATION (PD-1, 2B4). FURTHER, MEMORY-SPECIFIC TRANSCRIPTIONAL REGULATION OF 2B4 EXPRESSION AND SIGNALING IMPOSE A SELF-LIMITING SECONDARY EFFECTOR RESPONSE TO A PROLONGED VIRAL INFECTION. ADDITIONALLY, DIFFERENTIATION OF FUNCTIONAL MEMORY CD8 T CELLS IS COUPLED WITH ACQUISITION OF A REPRESSIVE EPIGENETIC PROGRAM FOR PD-1 EXPRESSION. HOWEVER, CHRONIC INFECTION PROVIDES A SIGNAL THAT BLOCKS THE ACQUISITION OF THESE EPIGENETIC MODIFICATIONS REINFORCING THE SUPPRESSION OF CYTOTOXIC LYMPHOCYTE (CTL) FUNCTIONS IN EXHAUSTED CELLS. SUMMARY: CURRENT FINDINGS SUGGEST THAT THE MECHANISM(S) THAT DELINEATE FUNCTIONAL MEMORY VERSUS EXHAUSTION ARE COUPLED WITH ACQUISITION OF TRANSCRIPTIONAL PROGRAMS AT THE EFFECTOR STAGE OF DIFFERENTIATION, REINFORCED BY CESSATION OR PERSISTENCE OF TCR SIGNALING. 2012 12 1763 31 EARLY TRANSCRIPTIONAL AND EPIGENETIC DIVERGENCE OF CD8+ T CELLS RESPONDING TO ACUTE VERSUS CHRONIC INFECTION. DURING A MICROBIAL INFECTION, RESPONDING CD8+ T CELLS GIVE RISE TO EFFECTOR CELLS THAT PROVIDE ACUTE HOST DEFENSE AND MEMORY CELLS THAT PROVIDE SUSTAINED PROTECTION. AN ALTERNATIVE OUTCOME IS EXHAUSTION, A STATE OF T CELL DYSFUNCTION THAT OCCURS IN THE CONTEXT OF CHRONIC INFECTIONS AND CANCER. ALTHOUGH IT IS EVIDENT THAT EXHAUSTED CD8+ T (TEX) CELLS ARE PHENOTYPICALLY AND MOLECULARLY DISTINCT FROM EFFECTOR AND MEMORY CD8+ T CELLS, THE FACTORS REGULATING THE EARLIEST EVENTS IN THE DIFFERENTIATION PROCESS OF TEX CELLS REMAIN INCOMPLETELY UNDERSTOOD. HERE, WE PERFORMED SINGLE-CELL RNA-SEQUENCING AND SINGLE-CELL ATAC-SEQUENCING OF CD8+ T CELLS RESPONDING TO LCMV-ARMSTRONG (LCMV-ARM) OR LCMV-CLONE 13 (LCMV-CL13), WHICH RESULT IN ACUTE OR CHRONIC INFECTIONS, RESPECTIVELY. COMPARED TO CD8+ T CELLS THAT HAD UNDERGONE THEIR FIRST DIVISION IN RESPONSE TO LCMV-ARM (DIV1ARM) CELLS, CD8+ T CELLS THAT HAD UNDERGONE THEIR FIRST DIVISION IN RESPONSE TO LCMV-CL13 (DIV1CL13) EXPRESSED HIGHER LEVELS OF GENES ENCODING TRANSCRIPTION FACTORS PREVIOUSLY ASSOCIATED WITH EXHAUSTION, ALONG WITH HIGHER LEVELS OF EZH2, THE CATALYTIC COMPONENT OF THE POLYCOMB REPRESSIVE COMPLEX 2 (PRC2) COMPLEX, WHICH MEDIATES EPIGENETIC SILENCING. MODULATION OF EZH2 RESULTED IN ALTERED EXPRESSION OF EXHAUSTION-ASSOCIATED MOLECULES BY CD8+ T CELLS RESPONDING TO LCMV-CL13, THOUGH THE SPECIFIC CELLULAR AND INFECTIOUS CONTEXTS, RATHER THAN SIMPLY THE LEVEL OF EZH2 EXPRESSION, LIKELY DETERMINE THE EVENTUAL OUTCOME. TAKEN TOGETHER, THESE FINDINGS SUGGEST THAT THE DIFFERENTIATION PATHS OF CD8+ T CELLS RESPONDING TO ACUTE VERSUS CHRONIC INFECTIONS MAY DIVERGE EARLIER THAN PREVIOUSLY APPRECIATED. 2023 13 4177 46 MEMORY T CELL, EXHAUSTION, AND TUMOR IMMUNITY. CD8(+)T CELLS ARE IMPORTANT IN PROTECTIVE IMMUNITY AGAINST INTRACELLULAR PATHOGENS AND TUMORS. IN CHRONIC INFECTIONS OR CANCER, CD8(+)T CELLS ARE CONSTANTLY EXPOSED TO ANTIGENS AND INFLAMMATORY SIGNALS. SUCH EXCESSIVE AND CONSTITUTIVE SIGNALS LEAD TO THE DETERIORATION OF T CELL FUNCTION, CALLED 'EXHAUSTION'. EXHAUSTED T CELLS ARE CHARACTERIZED BY LOW PROLIFERATION IN RESPONSE TO ANTIGEN STIMULATION, PROGRESSIVE LOSS OF EFFECTOR FUNCTION (CYTOKINE PRODUCTION AND KILLING FUNCTION), EXPRESSION OF MULTIPLE INHIBITORY RECEPTORS SUCH AS PD-1, TIM3, AND LAG3, AND METABOLIC ALTERATIONS FROM OXIDATIVE PHOSPHORYLATION TO GLYCOLYSIS. THESE DYSFUNCTIONS ARE ASSOCIATED WITH ALTERED TRANSCRIPTIONAL PROGRAMS AND EPIGENETIC REGULATIONS AND RECENT STUDIES SUGGESTED THAT NR4A AND TOX TRANSCRIPTION FACTORS ARE DEEPLY INVOLVED IN EXHAUSTION PHENOTYPES. HOWEVER, AN INCREASE THE EARLY MEMORY T CELLS INCLUDING STEM CELL MEMORY T (T(SCM)) CELLS IS CRITICAL FOR T CELL PERSISTENCE AND EFFICIENT TUMOR KILLING ESPECIALLY FOR ADOPTIVE CANCER IMMUNOTHERAPY SUCH AS CAR-T CELL THERAPY. AN INCREASING AMOUNT OF EVIDENCE SUPPORTS THE THERAPEUTIC POTENTIAL OF TARGETING EXHAUSTED T CELLS AND T(SCM) CELLS. WE HAVE BEGUN TO UNDERSTAND THE MOLECULAR MECHANISMS OF T CELL EXHAUSTION AND EARLY MEMORY FORMATION, AND THE CLINICAL APPLICATION OF CONVERTING EXHAUSTED T CELLS TO REJUVENATED EARLY MEMORY T CELLS IS THE GOAL OF OUR STUDY. 2020 14 5853 40 SUBSETS OF EXHAUSTED CD8(+) T CELLS DIFFERENTIALLY MEDIATE TUMOR CONTROL AND RESPOND TO CHECKPOINT BLOCKADE. T CELL DYSFUNCTION IS A HALLMARK OF MANY CANCERS, BUT THE BASIS FOR T CELL DYSFUNCTION AND THE MECHANISMS BY WHICH ANTIBODY BLOCKADE OF THE INHIBITORY RECEPTOR PD-1 (ANTI-PD-1) REINVIGORATES T CELLS ARE NOT FULLY UNDERSTOOD. HERE WE SHOW THAT SUCH THERAPY ACTS ON A SPECIFIC SUBPOPULATION OF EXHAUSTED CD8(+) TUMOR-INFILTRATING LYMPHOCYTES (TILS). DYSFUNCTIONAL CD8(+) TILS POSSESS CANONICAL EPIGENETIC AND TRANSCRIPTIONAL FEATURES OF EXHAUSTION THAT MIRROR THOSE SEEN IN CHRONIC VIRAL INFECTION. EXHAUSTED CD8(+) TILS INCLUDE A SUBPOPULATION OF 'PROGENITOR EXHAUSTED' CELLS THAT RETAIN POLYFUNCTIONALITY, PERSIST LONG TERM AND DIFFERENTIATE INTO 'TERMINALLY EXHAUSTED' TILS. CONSEQUENTLY, PROGENITOR EXHAUSTED CD8(+) TILS ARE BETTER ABLE TO CONTROL TUMOR GROWTH THAN ARE TERMINALLY EXHAUSTED T CELLS. PROGENITOR EXHAUSTED TILS CAN RESPOND TO ANTI-PD-1 THERAPY, BUT TERMINALLY EXHAUSTED TILS CANNOT. PATIENTS WITH MELANOMA WHO HAVE A HIGHER PERCENTAGE OF PROGENITOR EXHAUSTED CELLS EXPERIENCE A LONGER DURATION OF RESPONSE TO CHECKPOINT-BLOCKADE THERAPY. THUS, APPROACHES TO EXPAND THE POPULATION OF PROGENITOR EXHAUSTED CD8(+) T CELLS MIGHT BE AN IMPORTANT COMPONENT OF IMPROVING THE RESPONSE TO CHECKPOINT BLOCKADE. 2019 15 2879 43 FUNDAMENTALS TO THERAPEUTICS: EPIGENETIC MODULATION OF CD8(+) T CELL EXHAUSTION IN THE TUMOR MICROENVIRONMENT. IN THE SETTING OF CHRONIC ANTIGEN EXPOSURE IN THE TUMOR MICROENVIRONMENT (TME), CYTOTOXIC CD8(+) T CELLS (CTLS) LOSE THEIR IMMUNE SURVEILLANCE CAPABILITIES AND ABILITY TO CLEAR TUMOR CELLS AS A RESULT OF THEIR DIFFERENTIATION INTO TERMINALLY EXHAUSTED CD8(+) T CELLS. IMMUNE CHECKPOINT BLOCKADE (ICB) THERAPIES REINVIGORATE EXHAUSTED CD8(+) T CELLS BY TARGETING SPECIFIC INHIBITORY RECEPTORS, THUS PROMOTING THEIR CYTOLYTIC ACTIVITY TOWARDS TUMOR CELLS. DESPITE EXCITING RESULTS WITH ICB THERAPIES, MANY PATIENTS WITH SOLID TUMORS STILL FAIL TO RESPOND TO SUCH THERAPIES AND PATIENTS WHO INITIALLY RESPOND CAN DEVELOP RESISTANCE. RECENTLY, THROUGH NEW SEQUENCING TECHNOLOGIES SUCH AS THE ASSAY FOR TRANSPOSASE-ACCESSIBLE CHROMATIN WITH SEQUENCING (ATAC-SEQ), EPIGENETICS HAS BEEN APPRECIATED AS A CONTRIBUTING FACTOR THAT ENFORCES T CELL DIFFERENTIATION TOWARD EXHAUSTION IN THE TME. IMPORTANTLY, SPECIFIC EPIGENETIC ALTERATIONS AND EPIGENETIC FACTORS HAVE BEEN FOUND TO CONTROL CD8(+) T CELL EXHAUSTION PHENOTYPES. IN THIS REVIEW, WE WILL EXPLAIN THE BACKGROUND OF T CELL DIFFERENTIATION AND VARIOUS EXHAUSTION STATES AND DISCUSS HOW EPIGENETICS PLAY AN IMPORTANT ROLE IN THESE PROCESSES. THEN WE WILL OUTLINE SPECIFIC EPIGENETIC CHANGES AND CERTAIN EPIGENETIC AND TRANSCRIPTION FACTORS THAT ARE KNOWN TO CONTRIBUTE TO CD8(+) T CELL EXHAUSTION. WE WILL ALSO DISCUSS THE MOST RECENT METHODOLOGIES THAT ARE USED TO STUDY AND DISCOVER SUCH EPIGENETIC MODULATIONS. FINALLY, WE WILL EXPLAIN HOW EPIGENETIC REPROGRAMMING IS A PROMISING APPROACH THAT MIGHT FACILITATE THE DEVELOPMENT OF NOVEL EXHAUSTED T CELL-TARGETING IMMUNOTHERAPIES. 2022 16 2410 30 EPIGENETIC SCARS OF CD8(+) T CELL EXHAUSTION PERSIST AFTER CURE OF CHRONIC INFECTION IN HUMANS. T CELL EXHAUSTION IS AN INDUCED STATE OF DYSFUNCTION THAT ARISES IN RESPONSE TO CHRONIC INFECTION AND CANCER. EXHAUSTED CD8(+) T CELLS ACQUIRE A DISTINCT EPIGENETIC STATE, BUT IT IS NOT KNOWN WHETHER THAT CHROMATIN LANDSCAPE IS FIXED OR PLASTIC FOLLOWING THE RESOLUTION OF A CHRONIC INFECTION. HERE WE SHOW THAT THE EPIGENETIC STATE OF EXHAUSTION IS LARGELY IRREVERSIBLE, EVEN AFTER CURATIVE THERAPY. ANALYSIS OF CHROMATIN ACCESSIBILITY IN HCV- AND HIV-SPECIFIC RESPONSES IDENTIFIES A CORE EPIGENETIC PROGRAM OF EXHAUSTION IN CD8(+) T CELLS, WHICH UNDERGOES ONLY LIMITED REMODELING BEFORE AND AFTER RESOLUTION OF INFECTION. MOREOVER, CANONICAL FEATURES OF EXHAUSTION, INCLUDING SUPER-ENHANCERS NEAR THE GENES TOX AND HIF1A, REMAIN 'EPIGENETICALLY SCARRED.' T CELL EXHAUSTION IS THEREFORE A CONSERVED EPIGENETIC STATE THAT BECOMES FIXED AND PERSISTS INDEPENDENT OF CHRONIC ANTIGEN STIMULATION AND INFLAMMATION. THERAPEUTIC EFFORTS TO REVERSE T CELL EXHAUSTION MAY REQUIRE NEW APPROACHES THAT INCREASE THE EPIGENETIC PLASTICITY OF EXHAUSTED T CELLS. 2021 17 769 41 CD8 T CELL EXHAUSTION DURING CHRONIC VIRAL INFECTION AND CANCER. EXHAUSTED CD8 T (TEX) CELLS ARE A DISTINCT CELL LINEAGE THAT ARISE DURING CHRONIC INFECTIONS AND CANCERS IN ANIMAL MODELS AND HUMANS. TEX CELLS ARE CHARACTERIZED BY PROGRESSIVE LOSS OF EFFECTOR FUNCTIONS, HIGH AND SUSTAINED INHIBITORY RECEPTOR EXPRESSION, METABOLIC DYSREGULATION, POOR MEMORY RECALL AND HOMEOSTATIC SELF-RENEWAL, AND DISTINCT TRANSCRIPTIONAL AND EPIGENETIC PROGRAMS. THE ABILITY TO REINVIGORATE TEX CELLS THROUGH INHIBITORY RECEPTOR BLOCKADE, SUCH AS ALPHAPD-1, HIGHLIGHTS THE THERAPEUTIC POTENTIAL OF TARGETING THIS POPULATION. EMERGING INSIGHTS INTO THE MECHANISMS OF EXHAUSTION ARE INFORMING IMMUNOTHERAPIES FOR CANCER AND CHRONIC INFECTIONS. HOWEVER, LIKE OTHER IMMUNE CELLS, TEX CELLS ARE HETEROGENEOUS AND INCLUDE PROGENITOR AND TERMINAL SUBSETS WITH UNIQUE CHARACTERISTICS AND RESPONSES TO CHECKPOINT BLOCKADE. HERE, WE REVIEW OUR CURRENT UNDERSTANDING OF TEX CELL BIOLOGY, INCLUDING THE DEVELOPMENTAL PATHS, TRANSCRIPTIONAL AND EPIGENETIC FEATURES, AND CELL INTRINSIC AND EXTRINSIC FACTORS CONTRIBUTING TO EXHAUSTION AND HOW THIS KNOWLEDGE MAY INFORM THERAPEUTIC TARGETING OF TEX CELLS IN CHRONIC INFECTIONS, AUTOIMMUNITY, AND CANCER. 2019 18 4726 31 NOT-SO-OPPOSITE ENDS OF THE SPECTRUM: CD8(+) T CELL DYSFUNCTION ACROSS CHRONIC INFECTION, CANCER AND AUTOIMMUNITY. CD8(+) T CELLS ARE CRITICAL MEDIATORS OF CYTOTOXIC EFFECTOR FUNCTION IN INFECTION, CANCER AND AUTOIMMUNITY. IN CANCER AND CHRONIC VIRAL INFECTION, CD8(+) T CELLS UNDERGO A PROGRESSIVE LOSS OF CYTOKINE PRODUCTION AND CYTOTOXICITY, A STATE TERMED T CELL EXHAUSTION. IN AUTOIMMUNITY, AUTOREACTIVE CD8(+) T CELLS RETAIN THE CAPACITY TO EFFECTIVELY MEDIATE THE DESTRUCTION OF HOST TISSUES. ALTHOUGH THE CLINICAL OUTCOME DIFFERS IN EACH CONTEXT, CD8(+) T CELLS ARE CHRONICALLY EXPOSED TO ANTIGEN IN ALL THREE. THESE CHRONICALLY STIMULATED CD8(+) T CELLS SHARE SOME COMMON PHENOTYPIC FEATURES, AS WELL AS TRANSCRIPTIONAL AND EPIGENETIC PROGRAMMING, ACROSS DISEASE CONTEXTS. A BETTER UNDERSTANDING OF THESE CD8(+) T CELL STATES MAY REVEAL NOVEL STRATEGIES TO AUGMENT CLEARANCE OF CHRONIC VIRAL INFECTION AND CANCER AND TO MITIGATE SELF-REACTIVITY LEADING TO TISSUE DAMAGE IN AUTOIMMUNITY. 2021 19 1309 42 DEFINING AND TARGETING PATTERNS OF T CELL DYSFUNCTION IN INBORN ERRORS OF IMMUNITY. INBORN ERRORS OF IMMUNITY (IEIS) ARE A GROUP OF MORE THAN 450 MONOGENIC DISORDERS THAT IMPAIR IMMUNE DEVELOPMENT AND FUNCTION. A SUBSET OF IEIS BLEND INCREASED SUSCEPTIBILITY TO INFECTION, AUTOIMMUNITY, AND MALIGNANCY AND ARE KNOWN COLLECTIVELY AS PRIMARY IMMUNE REGULATORY DISORDERS (PIRDS). WHILE MANY ASPECTS OF IMMUNE FUNCTION ARE ALTERED IN PIRDS, ONE KEY IMPACT IS ON T-CELL FUNCTION. BY THEIR NATURE, PIRDS PROVIDE UNIQUE INSIGHTS INTO HUMAN T-CELL SIGNALING; ALTERATIONS IN INDIVIDUAL SIGNALING MOLECULES TUNE DOWNSTREAM SIGNALING PATHWAYS AND EFFECTOR FUNCTION. QUANTIFYING T-CELL DYSFUNCTION IN PIRDS AND THE UNDERLYING CAUSATIVE MECHANISMS IS CRITICAL TO IDENTIFYING EXISTING THERAPIES AND POTENTIAL NOVEL THERAPEUTIC TARGETS TO TREAT OUR RARE PATIENTS AND GAIN DEEPER INSIGHT INTO THE BASIC MECHANISMS OF T-CELL FUNCTION. THOUGH THERE ARE MANY TYPES OF T-CELL DYSFUNCTION, HERE WE WILL FOCUS ON T-CELL EXHAUSTION, A KEY PATHOPHYSIOLOGICAL STATE. EXHAUSTION HAS BEEN DESCRIBED IN BOTH HUMAN AND MOUSE MODELS OF DISEASE, WHERE THE CHRONIC PRESENCE OF ANTIGEN AND INFLAMMATION (E.G., CHRONIC INFECTION OR MALIGNANCY) INDUCES A STATE OF ALTERED IMMUNE PROFILE, TRANSCRIPTIONAL AND EPIGENETIC STATES, AS WELL AS IMPAIRED T-CELL FUNCTION. SINCE A SUBSET OF PIRDS AMPLIFY T-CELL RECEPTOR (TCR) SIGNALING AND/OR INFLAMMATORY CYTOKINE SIGNALING CASCADES, IT IS POSSIBLE THAT THEY COULD INDUCE T-CELL EXHAUSTION BY GENETICALLY MIMICKING CHRONIC INFECTION. HERE, WE REVIEW THE FUNDAMENTALS OF T-CELL EXHAUSTION AND ITS POSSIBLE ROLE IN IEIS IN WHICH GENETIC MUTATIONS MIMIC PROLONGED OR AMPLIFIED T-CELL RECEPTOR AND/OR CYTOKINE SIGNALING. GIVEN THE POTENTIAL INSIGHT FROM THE MANY FORMS OF PIRDS IN UNDERSTANDING T-CELL FUNCTION AND THE CHALLENGES IN OBTAINING PRIMARY CELLS FROM THESE RARE DISORDERS, WE ALSO DISCUSS ADVANCES IN CRISPR-CAS9 GENOME-EDITING TECHNOLOGIES AND POTENTIAL APPLICATIONS TO EDIT HEALTHY DONOR T CELLS THAT COULD FACILITATE FURTHER STUDY OF MECHANISMS OF IMMUNE DYSFUNCTIONS IN PIRDS. EDITING T CELLS TO MATCH PIRD PATIENT GENETIC VARIANTS WILL ALLOW INVESTIGATIONS INTO THE MECHANISMS UNDERPINNING STATES OF DYSREGULATED T-CELL FUNCTION, INCLUDING T-CELL EXHAUSTION. 2022 20 6530 37 TRANSCRIPTIONAL REGULATION AND T CELL EXHAUSTION. PURPOSE OF REVIEW: THIS REVIEW HIGHLIGHTS THE CONTROL OF TRANSCRIPTIONAL NETWORKS, INCLUDING INDUCTION OF INHIBITORY RECEPTORS, BY T CELL-SPECIFIC TRANSCRIPTION FACTORS IN EXHAUSTED T CELLS THAT ACCUMULATE IN CHRONIC VIRAL INFECTIONS INCLUDING HIV. RECENT FINDINGS: TRANSCRIPTIONAL PROFILING HAS ESTABLISHED DISTINCT MOLECULAR PHENOTYPES FOR EXHAUSTED CD4 AND CD8 T CELLS IN CHRONIC VIRAL INFECTION MODELS. THERE EXISTS A SUBSET OF TRANSCRIPTION FACTORS ASSOCIATED WITH EXHAUSTION, NOTABLY BLIMP-1, BASIC LEUCINE ZIPPER TRANSCRIPTION FACTOR, ATF-LIKE AND HELIOS. EPIGENETIC PHENOMENA ARE LIKELY IMPORTANT IN REGULATING GENE EXPRESSION NETWORKS DURING EXHAUSTION AS ILLUSTRATED BY PROGRAMMED DEATH 1 PROMOTER METHYLATION PATTERNS. SUMMARY: FOLLOWING CHRONIC VIRAL INFECTIONS, CD4 AND CD8 T CELLS DEFINED FUNCTIONALLY AND PHENOTYPICALLY AS EXHAUSTED HAVE DISTINCT TRANSCRIPTIONAL PROFILES. THESE STUDIES HAVE IDENTIFIED A CORE SET OF TRANSCRIPTION FACTORS THAT HAVE BEEN IMPLICATED IN PROMOTING EXHAUSTION. HOWEVER, NO SINGLE FACTOR APPEARS TO BE AN EXHAUSTION DETERMINING FACTOR, SUGGESTING THAT T CELL EXHAUSTION REFLECTS A COMBINATORIAL MECHANISM WITH MULTIPLE TRANSCRIPTION FACTORS INTERACTING TO INFLUENCE THE DEVELOPMENT OF FUNCTIONALLY EXHAUSTED T CELLS AS WELL AS DIFFERENT T EFFECTOR POPULATIONS. 2014