1 6482 97 TOX TRANSCRIPTIONALLY AND EPIGENETICALLY PROGRAMS CD8(+) T CELL EXHAUSTION. EXHAUSTED CD8(+) T (T(EX)) CELLS IN CHRONIC INFECTIONS AND CANCER HAVE LIMITED EFFECTOR FUNCTION, HIGH CO-EXPRESSION OF INHIBITORY RECEPTORS AND EXTENSIVE TRANSCRIPTIONAL CHANGES COMPARED WITH EFFECTOR (T(EFF)) OR MEMORY (T(MEM)) CD8(+) T CELLS. T(EX) CELLS ARE IMPORTANT CLINICAL TARGETS OF CHECKPOINT BLOCKADE AND OTHER IMMUNOTHERAPIES. EPIGENETICALLY, T(EX) CELLS ARE A DISTINCT IMMUNE SUBSET, WITH A UNIQUE CHROMATIN LANDSCAPE COMPARED WITH T(EFF) AND T(MEM) CELLS. HOWEVER, THE MECHANISMS THAT GOVERN THE TRANSCRIPTIONAL AND EPIGENETIC DEVELOPMENT OF T(EX) CELLS REMAIN UNKNOWN. HERE WE IDENTIFY THE HMG-BOX TRANSCRIPTION FACTOR TOX AS A CENTRAL REGULATOR OF T(EX) CELLS IN MICE. TOX IS LARGELY DISPENSABLE FOR THE FORMATION OF T(EFF) AND T(MEM) CELLS, BUT IT IS CRITICAL FOR EXHAUSTION: IN THE ABSENCE OF TOX, T(EX) CELLS DO NOT FORM. TOX IS INDUCED BY CALCINEURIN AND NFAT2, AND OPERATES IN A FEED-FORWARD LOOP IN WHICH IT BECOMES CALCINEURIN-INDEPENDENT AND SUSTAINED IN T(EX) CELLS. ROBUST EXPRESSION OF TOX THEREFORE RESULTS IN COMMITMENT TO T(EX) CELLS BY TRANSLATING PERSISTENT STIMULATION INTO A DISTINCT T(EX) CELL TRANSCRIPTIONAL AND EPIGENETIC DEVELOPMENTAL PROGRAM. 2019 2 2443 34 EPIGENETIC STABILITY OF EXHAUSTED T CELLS LIMITS DURABILITY OF REINVIGORATION BY PD-1 BLOCKADE. BLOCKING PROGRAMMED DEATH-1 (PD-1) CAN REINVIGORATE EXHAUSTED CD8 T CELLS (T(EX)) AND IMPROVE CONTROL OF CHRONIC INFECTIONS AND CANCER. HOWEVER, WHETHER BLOCKING PD-1 CAN REPROGRAM T(EX) INTO DURABLE MEMORY T CELLS (T(MEM)) IS UNCLEAR. WE FOUND THAT REINVIGORATION OF T(EX) IN MICE BY PD-L1 BLOCKADE CAUSED MINIMAL MEMORY DEVELOPMENT. AFTER BLOCKADE, REINVIGORATED T(EX) BECAME REEXHAUSTED IF ANTIGEN CONCENTRATION REMAINED HIGH AND FAILED TO BECOME T(MEM) UPON ANTIGEN CLEARANCE. T(EX) ACQUIRED AN EPIGENETIC PROFILE DISTINCT FROM THAT OF EFFECTOR T CELLS (T(EFF)) AND T(MEM) CELLS THAT WAS MINIMALLY REMODELED AFTER PD-L1 BLOCKADE. THIS FINDING SUGGESTS THAT T(EX) ARE A DISTINCT LINEAGE OF CD8 T CELLS. NEVERTHELESS, PD-1 PATHWAY BLOCKADE RESULTED IN TRANSCRIPTIONAL REWIRING AND REENGAGEMENT OF EFFECTOR CIRCUITRY IN THE T(EX) EPIGENETIC LANDSCAPE. THESE DATA INDICATE THAT EPIGENETIC FATE INFLEXIBILITY MAY LIMIT CURRENT IMMUNOTHERAPIES. 2016 3 6481 39 TOX IS EXPRESSED BY EXHAUSTED AND POLYFUNCTIONAL HUMAN EFFECTOR MEMORY CD8(+) T CELLS. CD8(+) T CELL EXHAUSTION IS A HALLMARK OF MANY CANCERS AND CHRONIC INFECTIONS. IN MICE, T CELL FACTOR 1 (TCF-1) MAINTAINS EXHAUSTED CD8(+) T CELL RESPONSES, WHEREAS THYMOCYTE SELECTION-ASSOCIATED HMG BOX (TOX) IS REQUIRED FOR THE EPIGENETIC REMODELING AND SURVIVAL OF EXHAUSTED CD8(+) T CELLS. HOWEVER, IT HAS REMAINED UNCLEAR TO WHAT EXTENT THESE TRANSCRIPTION FACTORS PLAY ANALOGOUS ROLES IN HUMANS. IN THIS STUDY, WE MAPPED THE EXPRESSION OF TOX AND TCF-1 AS A FUNCTION OF DIFFERENTIATION AND SPECIFICITY IN THE HUMAN CD8(+) T CELL LANDSCAPE. HERE, WE DEMONSTRATE THAT CIRCULATING TOX(+) CD8(+) T CELLS EXIST IN MOST HUMANS, BUT THAT TOX IS NOT EXCLUSIVELY ASSOCIATED WITH EXHAUSTION. EFFECTOR MEMORY CD8(+) T CELLS GENERALLY EXPRESSED TOX, WHEREAS NAIVE AND EARLY-DIFFERENTIATED MEMORY CD8(+) T CELLS GENERALLY EXPRESSED TCF-1. CYTOLYTIC GENE AND PROTEIN EXPRESSION SIGNATURES WERE ALSO DEFINED BY THE EXPRESSION OF TOX. IN THE CONTEXT OF A RELENTLESS IMMUNE CHALLENGE, EXHAUSTED HIV-SPECIFIC CD8(+) T CELLS COMMONLY EXPRESSED TOX, OFTEN IN CLUSTERS WITH VARIOUS ACTIVATION MARKERS AND INHIBITORY RECEPTORS, AND EXPRESSED LESS TCF-1. HOWEVER, POLYFUNCTIONAL MEMORY CD8(+) T CELLS SPECIFIC FOR CYTOMEGALOVIRUS (CMV) OR EPSTEIN-BARR VIRUS (EBV) ALSO EXPRESSED TOX, EITHER WITH OR WITHOUT TCF-1. A SIMILAR PHENOTYPE WAS OBSERVED AMONG HIV-SPECIFIC CD8(+) T CELLS FROM INDIVIDUALS WHO MAINTAINED EXCEPTIONAL IMMUNE CONTROL OF VIRAL REPLICATION. COLLECTIVELY, THESE DATA DEMONSTRATE THAT TOX IS EXPRESSED BY MOST CIRCULATING EFFECTOR MEMORY CD8(+) T CELL SUBSETS AND NOT EXCLUSIVELY LINKED TO EXHAUSTION. 2020 4 2409 41 EPIGENETIC SCARRING OF EXHAUSTED T CELLS HINDERS MEMORY DIFFERENTIATION UPON ELIMINATING CHRONIC ANTIGENIC STIMULATION. EXHAUSTED CD8 T CELLS (T(EX)) ARE A DISTINCT STATE OF T CELL DIFFERENTIATION ASSOCIATED WITH FAILURE TO CLEAR CHRONIC VIRUSES AND CANCER. IMMUNOTHERAPIES SUCH AS PD-1 BLOCKADE CAN REINVIGORATE T(EX) CELLS, BUT REINVIGORATION IS NOT DURABLE. A MAJOR UNANSWERED QUESTION IS WHETHER T(EX) CELLS DIFFERENTIATE INTO FUNCTIONAL DURABLE MEMORY T CELLS (T(MEM)) UPON ANTIGEN CLEARANCE. HERE, USING A MOUSE MODEL, WE FOUND THAT UPON ELIMINATING CHRONIC ANTIGENIC STIMULATION, T(EX) CELLS PARTIALLY (RE)ACQUIRE PHENOTYPIC AND TRANSCRIPTIONAL FEATURES OF T(MEM) CELLS. THESE 'RECOVERING' T(EX) CELLS ORIGINATED FROM THE T CELL FACTOR (TCF-1(+)) T(EX) PROGENITOR SUBSET. NEVERTHELESS, THE RECALL CAPACITY OF THESE RECOVERING T(EX) CELLS REMAINED COMPROMISED AS COMPARED TO T(MEM) CELLS. CHROMATIN-ACCESSIBILITY PROFILING REVEALED A FAILURE TO RECOVER CORE MEMORY EPIGENETIC CIRCUITS AND MAINTENANCE OF A LARGELY EXHAUSTED OPEN CHROMATIN LANDSCAPE. THUS, DESPITE SOME PHENOTYPIC AND TRANSCRIPTIONAL RECOVERY UPON ANTIGEN CLEARANCE, EXHAUSTION LEAVES DURABLE EPIGENETIC SCARS CONSTRAINING FUTURE IMMUNE RESPONSES. THESE RESULTS SUPPORT EPIGENETIC REMODELING INTERVENTIONS FOR T(EX) CELL-TARGETED IMMUNOTHERAPIES. 2021 5 5853 34 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 6 559 31 BACH2 ENFORCES THE TRANSCRIPTIONAL AND EPIGENETIC PROGRAMS OF STEM-LIKE CD8(+) T CELLS. DURING CHRONIC INFECTION AND CANCER, A SELF-RENEWING CD8(+) T CELL SUBSET MAINTAINS LONG-TERM IMMUNITY AND IS CRITICAL TO THE EFFECTIVENESS OF IMMUNOTHERAPY. THESE STEM-LIKE CD8(+) T CELLS DIVERGE FROM OTHER CD8(+) SUBSETS EARLY AFTER CHRONIC VIRAL INFECTION. HOWEVER, PATHWAYS GUARDING STEM-LIKE CD8(+) T CELLS AGAINST TERMINAL EXHAUSTION REMAIN UNCLEAR. HERE, WE SHOW THAT THE GENE ENCODING TRANSCRIPTIONAL REPRESSOR BACH2 IS TRANSCRIPTIONALLY AND EPIGENETICALLY ACTIVE IN STEM-LIKE CD8(+) T CELLS BUT NOT TERMINALLY EXHAUSTED CELLS EARLY AFTER INFECTION. BACH2 OVEREXPRESSION ENFORCED STEM-LIKE CELL FATE, WHEREAS BACH2 DEFICIENCY IMPAIRED STEM-LIKE CD8(+) T CELL DIFFERENTIATION. SINGLE-CELL TRANSCRIPTOMIC AND EPIGENOMIC APPROACHES REVEALED THAT BACH2 ESTABLISHED THE TRANSCRIPTIONAL AND EPIGENETIC PROGRAMS OF STEM-LIKE CD8(+) T CELLS. IN ADDITION, BACH2 SUPPRESSED THE MOLECULAR PROGRAM DRIVING TERMINAL EXHAUSTION THROUGH TRANSCRIPTIONAL REPRESSION AND EPIGENETIC SILENCING. THUS, OUR STUDY REVEALS A NEW PATHWAY THAT ENFORCES COMMITMENT TO STEM-LIKE CD8(+) LINEAGE AND PREVENTS AN ALTERNATIVE TERMINALLY EXHAUSTED CELL FATE. 2021 7 770 28 CD8(+) T CELL DYSFUNCTION BY TOX INTOXICATION: A PROTUMORIGENIC EVENT IN THE TUMOR MICROENVIRONMENT. ACCUMULATING EVIDENCE SUGGESTS THE ROLE OF CELLULAR COMPONENTS IN ACHIEVING ANTITUMOR TO PROTUMOR MICROENVIRONMENTS. AMONG THE VARIOUS TYPES OF CELLS WITHIN THE TUMOR NICHE, THE STATE OF CD8(+) T CELLS APPARENTLY CHANGES FROM CYTOTOXIC T EFFECTOR CELLS AND MEMORY T CELLS TO EXHAUSTED CD8(+) T CELLS. THESE CHANGES IN THE PHENOTYPE OF CD8(+) T CELLS PROMOTE THE PROTUMOR MICROENVIRONMENT. RECENTLY, COMPREHENSIVE EXPERIMENTAL DATA DELINEATED THE ROLE OF THYMOCYTE SELECTION-ASSOCIATED HIGH-MOBILITY GROUP-BOX PROTEIN (TOX), WHICH REGULATES THE TRANSCRIPTIONAL PROCESS AND EPIGENETIC REMODELING, WITH IMPLICATIONS IN TUMOR AND CHRONIC VIRAL INFECTIONS. THIS PERSPECTIVE SUMMARIZES THE MOLECULAR MECHANISMS THAT LINK CD8(+) T CELLS, TOX, AND TRANSCRIPTIONAL AND EPIGENETIC REPROGRAMMING AS WELL AS FUTURE DIRECTIONS FOR DETERMINING NEW AVENUES OF CANCER THERAPEUTICS. 2021 8 1379 33 DEVELOPMENTAL RELATIONSHIPS OF FOUR EXHAUSTED CD8(+) T CELL SUBSETS REVEALS UNDERLYING TRANSCRIPTIONAL AND EPIGENETIC LANDSCAPE CONTROL MECHANISMS. CD8(+) T CELL EXHAUSTION IS A MAJOR BARRIER TO CURRENT ANTI-CANCER IMMUNOTHERAPIES. DESPITE THIS, THE DEVELOPMENTAL BIOLOGY OF EXHAUSTED CD8(+) T CELLS (TEX) REMAINS POORLY DEFINED, RESTRAINING IMPROVEMENT OF STRATEGIES AIMED AT "RE-INVIGORATING" TEX CELLS. HERE, WE DEFINED A FOUR-CELL-STAGE DEVELOPMENTAL FRAMEWORK FOR TEX CELLS. TWO TCF1(+) PROGENITOR SUBSETS WERE IDENTIFIED, ONE TISSUE RESTRICTED AND QUIESCENT AND ONE MORE BLOOD ACCESSIBLE, THAT GRADUALLY LOST TCF1 AS IT DIVIDED AND CONVERTED TO A THIRD INTERMEDIATE TEX SUBSET. THIS INTERMEDIATE SUBSET RE-ENGAGED SOME EFFECTOR BIOLOGY AND INCREASED UPON PD-L1 BLOCKADE BUT ULTIMATELY CONVERTED INTO A FOURTH, TERMINALLY EXHAUSTED SUBSET. BY USING TRANSCRIPTIONAL AND EPIGENETIC ANALYSES, WE IDENTIFIED THE CONTROL MECHANISMS UNDERLYING SUBSET TRANSITIONS AND DEFINED A KEY INTERPLAY BETWEEN TCF1, T-BET, AND TOX IN THE PROCESS. THESE DATA REVEAL A FOUR-STAGE DEVELOPMENTAL HIERARCHY FOR TEX CELLS AND DEFINE THE MOLECULAR, TRANSCRIPTIONAL, AND EPIGENETIC MECHANISMS THAT COULD PROVIDE OPPORTUNITIES TO IMPROVE CANCER IMMUNOTHERAPY. 2020 9 2421 39 EPIGENETIC SIGNATURE OF PD-1+ TCF1+ CD8 T CELLS THAT ACT AS RESOURCE CELLS DURING CHRONIC VIRAL INFECTION AND RESPOND TO PD-1 BLOCKADE. WE HAVE RECENTLY DEFINED A NOVEL POPULATION OF PD-1 (PROGRAMMED CELL DEATH 1)+ TCF1 (T CELL FACTOR 1)+ VIRUS-SPECIFIC CD8 T CELLS THAT FUNCTION AS RESOURCE CELLS DURING CHRONIC LCMV INFECTION AND PROVIDE THE PROLIFERATIVE BURST SEEN AFTER PD-1 BLOCKADE. SUCH CD8 T CELLS HAVE BEEN FOUND IN OTHER CHRONIC INFECTIONS AND ALSO IN CANCER IN MICE AND HUMANS. THESE CD8 T CELLS EXHIBIT STEM-LIKE PROPERTIES UNDERGOING SELF-RENEWAL AND ALSO DIFFERENTIATING INTO THE TERMINALLY EXHAUSTED CD8 T CELLS. HERE WE COMPARED THE EPIGENETIC SIGNATURE OF STEM-LIKE CD8 T CELLS WITH EXHAUSTED CD8 T CELLS. ATAC-SEQ ANALYSIS SHOWED THAT STEM-LIKE CD8 T CELLS HAD A UNIQUE SIGNATURE IMPLICATING ACTIVITY OF HMG (TCF) AND RHD (NF-KAPPAB) TRANSCRIPTION FACTOR FAMILY MEMBERS IN CONTRAST TO HIGHER ACCESSIBILITY TO ETS AND RUNX MOTIFS IN EXHAUSTED CD8 T CELLS. IN ADDITION, REGULATORY REGIONS OF THE TRANSCRIPTION FACTORS TCF7 AND ID3 WERE MORE ACCESSIBLE IN STEM-LIKE CELLS WHEREAS PRDM1 AND ID2 WERE MORE ACCESSIBLE IN EXHAUSTED CD8 T CELLS. WE ALSO COMPARED THE EPIGENETIC SIGNATURES OF THE 2 CD8 T CELL SUBSETS FROM CHRONICALLY INFECTED MICE WITH EFFECTOR AND MEMORY CD8 T CELLS GENERATED AFTER AN ACUTE LCMV INFECTION. BOTH CD8 T CELL SUBSETS GENERATED DURING CHRONIC INFECTION WERE STRIKINGLY DIFFERENT FROM CD8 T CELL SUBSETS FROM ACUTE INFECTION. INTERESTINGLY, THE STEM-LIKE CD8 T CELL SUBSET FROM CHRONIC INFECTION, DESPITE SHARING KEY FUNCTIONAL PROPERTIES WITH MEMORY CD8 T CELLS, HAD A VERY DISTINCT EPIGENETIC PROGRAM. THESE RESULTS SHOW THAT THE CHRONIC STEM-LIKE CD8 T CELL PROGRAM REPRESENTS A SPECIFIC ADAPTATION OF THE T CELL RESPONSE TO PERSISTENT ANTIGENIC STIMULATION. 2019 10 5704 36 SINGLE-CELL RNA-SEQ REVEALS TOX AS A KEY REGULATOR OF CD8(+) T CELL PERSISTENCE IN CHRONIC INFECTION. PROGENITOR-LIKE CD8(+) T CELLS MEDIATE LONG-TERM IMMUNITY TO CHRONIC INFECTION AND CANCER AND RESPOND POTENTLY TO IMMUNE CHECKPOINT BLOCKADE. THESE CELLS SHARE TRANSCRIPTIONAL REGULATORS WITH MEMORY PRECURSOR CELLS, INCLUDING T CELL-SPECIFIC TRANSCRIPTION FACTOR 1 (TCF1), BUT IT IS UNCLEAR WHETHER THEY ADOPT DISTINCT PROGRAMS TO ADAPT TO THE IMMUNOSUPPRESSIVE ENVIRONMENT. BY COMPARING THE SINGLE-CELL TRANSCRIPTOMES AND EPIGENETIC PROFILES OF CD8(+) T CELLS RESPONDING TO ACUTE AND CHRONIC VIRAL INFECTIONS, WE FOUND THAT PROGENITOR-LIKE CD8(+) T CELLS BECAME DISTINCT FROM MEMORY PRECURSOR CELLS BEFORE THE PEAK OF THE T CELL RESPONSE. WE DISCOVERED A COEXPRESSION GENE MODULE CONTAINING TOX THAT EXHIBITED HIGHER TRANSCRIPTIONAL ACTIVITY ASSOCIATED WITH MORE ABUNDANT ACTIVE HISTONE MARKS IN PROGENITOR-LIKE CELLS THAN MEMORY PRECURSOR CELLS. MOREOVER, THYMOCYTE SELECTION-ASSOCIATED HIGH MOBILITY GROUP BOX PROTEIN TOX (TOX) PROMOTED THE PERSISTENCE OF ANTIVIRAL CD8(+) T CELLS AND WAS REQUIRED FOR THE PROGRAMMING OF PROGENITOR-LIKE CD8(+) T CELLS. THUS, LONG-TERM CD8(+) T CELL IMMUNITY TO CHRONIC VIRAL INFECTION REQUIRES UNIQUE TRANSCRIPTIONAL AND EPIGENETIC PROGRAMS ASSOCIATED WITH THE TRANSCRIPTION FACTOR TOX. 2019 11 6417 31 THE SWI/SNF CHROMATIN REMODELING COMPLEXES BAF AND PBAF DIFFERENTIALLY REGULATE EPIGENETIC TRANSITIONS IN EXHAUSTED CD8(+) T CELLS. CD8(+) T CELL EXHAUSTION (TEX) LIMITS DISEASE CONTROL DURING CHRONIC VIRAL INFECTIONS AND CANCER. HERE, WE INVESTIGATED THE EPIGENETIC FACTORS MEDIATING MAJOR CHROMATIN-REMODELING EVENTS IN TEX-CELL DEVELOPMENT. A PROTEIN-DOMAIN-FOCUSED IN VIVO CRISPR SCREEN IDENTIFIED DISTINCT FUNCTIONS FOR TWO VERSIONS OF THE SWI/SNF CHROMATIN-REMODELING COMPLEX IN TEX-CELL DIFFERENTIATION. DEPLETION OF THE CANONICAL SWI/SNF FORM, BAF, IMPAIRED INITIAL CD8(+) T CELL RESPONSES IN ACUTE AND CHRONIC INFECTION. IN CONTRAST, DISRUPTION OF PBAF ENHANCED TEX-CELL PROLIFERATION AND SURVIVAL. MECHANISTICALLY, PBAF REGULATED THE EPIGENETIC AND TRANSCRIPTIONAL TRANSITION FROM TCF-1(+) PROGENITOR TEX CELLS TO MORE DIFFERENTIATED TCF-1(-) TEX SUBSETS. WHEREAS PBAF ACTED TO PRESERVE TEX PROGENITOR BIOLOGY, BAF WAS REQUIRED TO GENERATE EFFECTOR-LIKE TEX CELLS, SUGGESTING THAT THE BALANCE OF THESE FACTORS COORDINATES TEX-CELL SUBSET DIFFERENTIATION. TARGETING PBAF IMPROVED TUMOR CONTROL BOTH ALONE AND IN COMBINATION WITH ANTI-PD-L1 IMMUNOTHERAPY. THUS, PBAF MAY PRESENT A THERAPEUTIC TARGET IN CANCER IMMUNOTHERAPY. 2023 12 5015 39 PERSISTENCE OF SELF-REACTIVE CD8+ T CELLS IN THE CNS REQUIRES TOX-DEPENDENT CHROMATIN REMODELING. SELF-REACTIVE CD8(+) T CELLS ARE IMPORTANT MEDIATORS OF PROGRESSIVE TISSUE DAMAGE IN AUTOIMMUNE DISEASES, BUT THE MOLECULAR PROGRAM UNDERLYING THESE CELLS' FUNCTIONAL ADAPTATION IS UNCLEAR. HERE WE CHARACTERIZE THE TRANSCRIPTIONAL AND EPIGENETIC LANDSCAPE OF SELF-REACTIVE CD8(+) T CELLS IN A MOUSE MODEL OF PROTRACTED CENTRAL NERVOUS SYSTEM (CNS) AUTOIMMUNITY AND COMPARE IT TO POPULATIONS OF CNS-RESIDENT MEMORY CD8(+) T CELLS EMERGING FROM ACUTE VIRAL INFECTION. WE FIND THAT AUTOIMMUNE CD8(+) T CELLS PERSISTING AT SITES OF SELF-ANTIGEN EXHIBIT CHARACTERISTIC TRANSCRIPTIONAL REGULATION TOGETHER WITH DISTINCT EPIGENETIC REMODELING. THIS SELF-REACTIVE CD8(+) T CELL FATE DEPENDS ON THE TRANSCRIPTIONAL REGULATION BY THE DNA-BINDING HMG-BOX PROTEIN TOX WHICH REMODELS MORE THAN 400 GENOMIC REGIONS INCLUDING LOCI SUCH AS TCF7, WHICH IS CENTRAL TO STEMNESS OF CD8(+) T CELLS. CONTINUOUS EXPOSURE TO CNS SELF-ANTIGEN SUSTAINS TOX LEVELS IN SELF-REACTIVE CD8(+) T CELLS, WHEREAS GENETIC ABLATION OF TOX IN CD8(+) T CELLS RESULTS IN SHORTENED PERSISTENCE OF SELF-REACTIVE CD8(+) T CELLS IN THE INFLAMED CNS. OUR STUDY ESTABLISHES AND CHARACTERIZES THE GENETIC DIFFERENTIATION PROGRAM ENABLING CHRONIC T CELL-DRIVEN IMMUNOPATHOLOGY IN CNS AUTOIMMUNITY. 2021 13 5593 38 ROLE, FUNCTION AND REGULATION OF THE THYMOCYTE SELECTION-ASSOCIATED HIGH MOBILITY GROUP BOX PROTEIN IN CD8(+) T CELL EXHAUSTION. THYMOCYTE SELECTION-ASSOCIATED HIGH MOBILITY GROUP BOX PROTEIN (TOX), A MEMBER OF THE HIGH-MOTILITY GROUP BOX (HMG) PROTEIN SUPERFAMILY, IS AN EVOLUTIONARILY CONSERVED DNA-BINDING PROTEIN. IT FUNCTIONS AS A TRANSCRIPTION FACTOR THAT MODULATES TRANSCRIPTIONAL PROGRAMS BY BINDING TO DNA IN A STRUCTURE-DEPENDENT MANNER. IT HAS BEEN WELL ESTABLISHED THAT TOX IS REQUIRED FOR THE DEVELOPMENT OF CD4(+) T CELLS, NATURAL KILLER (NK) CELLS AND INNATE LYMPHOID CELLS (ILCS), AS WELL AS THE AUTOIMMUNITY MEDIATED BY CD8(+) T CELLS. RECENTLY, EMERGING EVIDENCE SUPPORTS AN ESSENTIAL ROLE FOR TOX IN THE INDUCTION OF T CELL EXHAUSTION IN THE SETTING OF TUMOR OR CHRONIC VIRAL INFECTION BY MEDIATING TRANSCRIPTIONAL AND EPIGENETIC CHANGES, WHICH ARE CARDINAL HALLMARKS OF EXHAUSTED T CELLS. MOREOVER, TOX PLAYS A KEY ROLE IN THE PERSISTENCE OF ANTIGEN-SPECIFIC T CELLS AND IN THE MITIGATION OF TISSUE DAMAGE CAUSED BY IMMUNOPATHOLOGY OVER THE COURSE OF TUMORIGENESIS AND CHRONIC INFECTION. ADDITIONALLY, TOX CONTRIBUTES TO THE HIGH LEVEL OF PROGRAMMED CELL DEATH PROTEIN 1 (PD-1) ON THE CELL SURFACE BY PARTICIPATING IN THE PROCESS OF ENDOCYTIC RECYCLING OF PD-1. IN THIS REVIEW, WE SUMMARIZE THE MOST RECENT INFORMATION ABOUT THE ROLE OF TOX IN THE PROCESS OF T CELL EXHAUSTION, WHICH ENRICHES OUR UNDERSTANDING OF THE MOLECULAR MECHANISMS OF CD8(+) T CELL EXHAUSTION UPON CHRONIC ANTIGEN STIMULATION AND REVEALS PROMISING THERAPEUTIC TARGETS FOR PERSISTING INFECTION AND CANCER. 2021 14 568 34 BATF REGULATES PROGENITOR TO CYTOLYTIC EFFECTOR CD8(+) T CELL TRANSITION DURING CHRONIC VIRAL INFECTION. DURING CHRONIC VIRAL INFECTION, CD8(+) T CELLS DEVELOP INTO THREE MAJOR PHENOTYPICALLY AND FUNCTIONALLY DISTINCT SUBSETS: LY108(+)TCF-1(+) PROGENITORS, LY108(-)CX(3)CR1(-) TERMINALLY EXHAUSTED CELLS AND THE RECENTLY IDENTIFIED CX(3)CR1(+) CYTOTOXIC EFFECTOR CELLS. NEVERTHELESS, HOW CX(3)CR1(+) EFFECTOR CELL DIFFERENTIATION IS TRANSCRIPTIONALLY AND EPIGENETICALLY REGULATED REMAINS ELUSIVE. HERE, WE IDENTIFY DISTINCT GENE REGULATORY NETWORKS AND EPIGENETIC LANDSCAPES UNDERPINNING THE FORMATION OF THESE SUBSETS. NOTABLY, OUR DATA DEMONSTRATE THAT CX(3)CR1(+) EFFECTOR CELLS BEAR A STRIKING SIMILARITY TO SHORT-LIVED EFFECTOR CELLS DURING ACUTE INFECTION. GENETIC DELETION OF TBX21 SIGNIFICANTLY DIMINISHED FORMATION OF THE CX(3)CR1(+) SUBSET. IMPORTANTLY, WE FURTHER IDENTIFY A PREVIOUSLY UNAPPRECIATED ROLE FOR THE TRANSCRIPTION FACTOR BATF IN MAINTAINING A PERMISSIVE CHROMATIN STRUCTURE THAT ALLOWS THE TRANSITION FROM TCF-1(+) PROGENITORS TO CX(3)CR1(+) EFFECTOR CELLS. BATF DIRECTLY BOUND TO REGULATORY REGIONS NEAR TBX21 AND KLF2, MODULATING THEIR ENHANCER ACCESSIBILITY TO FACILITATE THE TRANSITION. THESE MECHANISTIC INSIGHTS CAN POTENTIALLY BE HARNESSED TO OVERCOME T CELL EXHAUSTION DURING CHRONIC INFECTION AND CANCER. 2021 15 1278 29 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 16 1262 29 CUTTING EDGE: PROLONGED EXPOSURE TO HIV REINFORCES A POISED EPIGENETIC PROGRAM FOR PD-1 EXPRESSION IN VIRUS-SPECIFIC CD8 T CELLS. AG-SPECIFIC CD8 T CELLS PLAY A CRITICAL ROLE IN CONTROLLING HIV INFECTION BUT EVENTUALLY LOSE ANTIVIRAL FUNCTIONS IN PART BECAUSE OF EXPRESSION AND SIGNALING THROUGH THE INHIBITORY PROGRAMMED DEATH-1 (PD-1) RECEPTOR. TO BETTER UNDERSTAND THE IMPACT OF PROLONGED TCR LIGATION ON REGULATION OF PD-1 EXPRESSION IN HIV-SPECIFIC CD8 T CELLS, WE INVESTIGATED THE CAPACITY OF VIRUS-SPECIFIC CD8 T CELLS TO MODIFY THE PD-1 EPIGENETIC PROGRAM AFTER REDUCTION IN VIRAL LOAD. WE OBSERVED THAT THE TRANSCRIPTIONAL REGULATORY REGION WAS UNMETHYLATED IN THE PD-1(HI) HIV-SPECIFIC CD8 T CELLS, WHEREAS IT REMAINED METHYLATED IN DONOR-MATCHED NAIVE CELLS AT ACUTE AND CHRONIC STAGES OF INFECTION. SURPRISINGLY, THE PD-1 PROMOTER REMAINED UNMETHYLATED IN HIV-SPECIFIC CD8 T CELLS FROM SUBJECTS WITH A VIRAL LOAD CONTROLLED BY ANTIVIRAL THERAPY FOR >2 Y OR FROM ELITE CONTROLLERS. TOGETHER, THESE DATA DEMONSTRATE THAT THE EPIGENETIC PROGRAM AT THE PD-1 LOCUS BECOMES FIXED AFTER PROLONGED EXPOSURE TO HIV VIRUS. 2013 17 6121 32 THE EPIGENETIC LANDSCAPE OF T CELL EXHAUSTION. EXHAUSTED T CELLS IN CANCER AND CHRONIC VIRAL INFECTION EXPRESS DISTINCTIVE PATTERNS OF GENES, INCLUDING SUSTAINED EXPRESSION OF PROGRAMMED CELL DEATH PROTEIN 1 (PD-1). HOWEVER, THE REGULATION OF GENE EXPRESSION IN EXHAUSTED T CELLS IS POORLY UNDERSTOOD. HERE, WE DEFINE THE ACCESSIBLE CHROMATIN LANDSCAPE IN EXHAUSTED CD8(+) T CELLS AND SHOW THAT IT IS DISTINCT FROM FUNCTIONAL MEMORY CD8(+) T CELLS. EXHAUSTED CD8(+) T CELLS IN HUMANS AND A MOUSE MODEL OF CHRONIC VIRAL INFECTION ACQUIRE A STATE-SPECIFIC EPIGENETIC LANDSCAPE ORGANIZED INTO FUNCTIONAL MODULES OF ENHANCERS. GENOME EDITING SHOWS THAT PD-1 EXPRESSION IS REGULATED IN PART BY AN EXHAUSTION-SPECIFIC ENHANCER THAT CONTAINS ESSENTIAL RAR, T-BET, AND SOX3 MOTIFS. FUNCTIONAL ENHANCER MAPS MAY OFFER TARGETS FOR GENOME EDITING THAT ALTER GENE EXPRESSION PREFERENTIALLY IN EXHAUSTED CD8(+) T CELLS. 2016 18 5358 30 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 19 1108 22 COMMENTARY ON SOME RECENT THESES RELEVANT TO COMBATING AGING: JUNE 2021. THESES REVIEWED IN THIS ISSUE INCLUDE "ENGINEERING PROTEIN DISAGGREGASES TO COUNTER ALPHA-SYNUCLEIN AND AMYLOID-BETA NEUROTOXICITY," "HYPERGLYCAEMIA INDUCED IMMUNOMODULATION OF MACROPHAGES IN DIABETIC VASCULAR DISEASE," "MICROVASCULATURE-ON-A-CHIP SYSTEMS FOR HUMAN DISEASE MODELING," "SENESCENCE SURVEILLANCE: THE INTERPLAY BETWEEN THE IMMUNE SYSTEM AND SENESCENT CELLS," "THE HMG TRANSCRIPTION FACTOR TOX INDUCES A TRANSCRIPTIONAL AND EPIGENETIC PROGRAM OF CD8(+) T CELL EXHAUSTION IN CHRONIC INFECTION AND CANCER," AND "ZERO TO ONE-TRANSLATIONAL ADVANCEMENTS IN THE FIELD OF XENOTRANSPLANTATION." 2021 20 438 32 ANTIGEN-DRIVEN EGR2 EXPRESSION IS REQUIRED FOR EXHAUSTED CD8(+) T CELL STABILITY AND MAINTENANCE. CHRONIC STIMULATION OF CD8(+) T CELLS TRIGGERS EXHAUSTION, A DISTINCT DIFFERENTIATION STATE WITH DIMINISHED EFFECTOR FUNCTION. EXHAUSTED CELLS EXIST IN MULTIPLE DIFFERENTIATION STATES, FROM STEM-LIKE PROGENITORS THAT ARE THE KEY MEDIATORS OF THE RESPONSE TO CHECKPOINT BLOCKADE, THROUGH TO TERMINALLY EXHAUSTED CELLS. DUE TO ITS CLINICAL RELEVANCE, THERE IS SUBSTANTIAL INTEREST IN DEFINING THE PATHWAYS THAT CONTROL DIFFERENTIATION AND MAINTENANCE OF THESE SUBSETS. HERE, WE SHOW THAT CHRONIC ANTIGEN INDUCES THE ANERGY-ASSOCIATED TRANSCRIPTION FACTOR EGR2 SELECTIVELY WITHIN PROGENITOR EXHAUSTED CELLS IN BOTH CHRONIC LCMV AND TUMOURS. EGR2 ENABLES TERMINAL EXHAUSTION AND STABILIZES THE EXHAUSTED TRANSCRIPTIONAL STATE BY BOTH DIRECT EGR2-DEPENDENT CONTROL OF KEY EXHAUSTION-ASSOCIATED GENES, AND INDIRECT MAINTENANCE OF THE EXHAUSTED EPIGENETIC STATE. WE SHOW THAT EGR2 IS A REGULATOR OF EXHAUSTION THAT EPIGENETICALLY AND TRANSCRIPTIONALLY MAINTAINS THE DIFFERENTIATION COMPETENCY OF PROGENITOR EXHAUSTED CELLS. 2021