1 1175 125 CONTRIBUTIONS OF AGE-RELATED THYMIC INVOLUTION TO IMMUNOSENESCENCE AND INFLAMMAGING. IMMUNE SYSTEM AGING IS CHARACTERIZED BY THE PARADOX OF IMMUNOSENESCENCE (INSUFFICIENCY) AND INFLAMMAGING (OVER-REACTION), WHICH INCORPORATE TWO SIDES OF THE SAME COIN, RESULTING IN IMMUNE DISORDER. IMMUNOSENESCENCE REFERS TO DISRUPTION IN THE STRUCTURAL ARCHITECTURE OF IMMUNE ORGANS AND DYSFUNCTION IN IMMUNE RESPONSES, RESULTING FROM BOTH AGED INNATE AND ADAPTIVE IMMUNITY. INFLAMMAGING, DESCRIBED AS A CHRONIC, STERILE, SYSTEMIC INFLAMMATORY CONDITION ASSOCIATED WITH ADVANCED AGE, IS MAINLY ATTRIBUTED TO SOMATIC CELLULAR SENESCENCE-ASSOCIATED SECRETORY PHENOTYPE (SASP) AND AGE-RELATED AUTOIMMUNE PREDISPOSITION. HOWEVER, THE INABILITY TO REDUCE SENESCENT SOMATIC CELLS (SSCS), BECAUSE OF IMMUNOSENESCENCE, EXACERBATES INFLAMMAGING. AGE-RELATED ADAPTIVE IMMUNE SYSTEM DEVIATIONS, PARTICULARLY ALTERED T CELL FUNCTION, ARE DERIVED FROM AGE-RELATED THYMIC ATROPHY OR INVOLUTION, A HALLMARK OF THYMIC AGING. RECENTLY, THERE HAVE BEEN MAJOR DEVELOPMENTS IN UNDERSTANDING HOW AGE-RELATED THYMIC INVOLUTION CONTRIBUTES TO INFLAMMAGING AND IMMUNOSENESCENCE AT THE CELLULAR AND MOLECULAR LEVELS, INCLUDING GENETIC AND EPIGENETIC REGULATION, AS WELL AS DEVELOPMENTS OF MANY POTENTIAL REJUVENATION STRATEGIES. HEREIN, WE DISCUSS THE RESEARCH PROGRESS UNCOVERING HOW AGE-RELATED THYMIC INVOLUTION CONTRIBUTES TO IMMUNOSENESCENCE AND INFLAMMAGING, AS WELL AS THEIR INTERSECTION. WE ALSO DESCRIBE HOW T CELL ADAPTIVE IMMUNITY MEDIATES INFLAMMAGING AND PLAYS A CRUCIAL ROLE IN THE PROGRESSION OF AGE-RELATED NEUROLOGICAL AND CARDIOVASCULAR DISEASES, AS WELL AS CANCER. WE THEN BRIEFLY OUTLINE THE UNDERLYING CELLULAR AND MOLECULAR MECHANISMS OF AGE-RELATED THYMIC INVOLUTION, AND FINALLY SUMMARIZE POTENTIAL REJUVENATION STRATEGIES TO RESTORE AGED THYMIC FUNCTION. 2020 2 3183 42 HALLMARKS OF T CELL AGING. THE AGED ADAPTIVE IMMUNE SYSTEM IS CHARACTERIZED BY PROGRESSIVE DYSFUNCTION AS WELL AS INCREASED AUTOIMMUNITY. THIS DECLINE IS RESPONSIBLE FOR ELEVATED SUSCEPTIBILITY TO INFECTION AND CANCER, AS WELL AS DECREASED VACCINATION EFFICACY. RECENT EVIDENCE INDICATES THAT CD4(+) T CELL-INTRINSIC ALTERATINS CONTRIBUTE TO CHRONIC INFLAMMATION AND ARE SUFFICIENT TO ACCELERATE AN ORGANISM-WIDE AGING PHENOTYPE, SUPPORTING THE IDEA THAT T CELL AGING PLAYS A MAJOR ROLE IN BODY-WIDE DETERIORATION. IN THIS REVIEW, WE PROPOSE TEN MOLECULAR HALLMARKS TO REPRESENT COMMON DENOMINATORS OF T CELL AGING. THESE HALLMARKS ARE GROUPED INTO FOUR PRIMARY HALLMARKS (THYMIC INVOLUTION, MITOCHONDRIAL DYSFUNCTION, GENETIC AND EPIGENETIC ALTERATIONS, AND LOSS OF PROTEOSTASIS) AND FOUR SECONDARY HALLMARKS (REDUCTION OF THE TCR REPERTOIRE, NAIVE-MEMORY IMBALANCE, T CELL SENESCENCE, AND LACK OF EFFECTOR PLASTICITY), AND TOGETHER THEY EXPLAIN THE MANIFESTATION OF THE TWO INTEGRATIVE HALLMARKS (IMMUNODEFICIENCY AND INFLAMMAGING). A MAJOR CHALLENGE NOW IS WEIGHING THE RELATIVE IMPACT OF THESE HALLMARKS ON T CELL AGING AND UNDERSTANDING THEIR INTERCONNECTIONS, WITH THE FINAL GOAL OF DEFINING MOLECULAR TARGETS FOR INTERVENTIONS IN THE AGING PROCESS. 2021 3 233 27 ADAPTIVE T CELL TUNING IN IMMUNE REGULATION AND IMMUNOTHERAPY OF AUTOIMMUNE DISEASES(?). LYMPHOCYTE RECEPTORS CONFER ANTIGEN SPECIFICITY ON THE ADAPTIVE IMMUNE RESPONSE. INCREASING EVIDENCE POINTS TO THE ROLE OF ADAPTIVE TUNING PARTICULARLY AMONGST CD4(+) T CELL RESPONSES. THIS REVIEW SUMMARISES HOW T CELL TUNING IMPACTS ON CRITICALLY IMPORTANT ASPECTS OF IMMUNE REGULATION INCLUDING THYMIC SELECTION, THE IMMUNE RESPONSE TO CHRONIC ANTIGEN EXPOSURE AND ANTIGEN-SPECIFIC IMMUNOTHERAPY OF AUTOIMMUNE CONDITIONS. RECENT WORK HAS REVEALED A NOVEL MECHANISM FOR T CELL ANERGY AND REGULATORY TYPE 1 T CELL DIFFERENTIATION THROUGH A LIMITATION OF T CELL RECEPTOR MEDIATED SIGNALLING COMBINED WITH EPIGENETIC PRIMING OF TOLERANCE ASSOCIATED GENES. 2022 4 3551 44 IMMUNOSENESCENCE: MOLECULAR MECHANISMS AND DISEASES. INFECTION SUSCEPTIBILITY, POOR VACCINATION EFFICACY, AGE-RELATED DISEASE ONSET, AND NEOPLASMS ARE LINKED TO INNATE AND ADAPTIVE IMMUNE DYSFUNCTION THAT ACCOMPANIES AGING (KNOWN AS IMMUNOSENESCENCE). DURING AGING, ORGANISMS TEND TO DEVELOP A CHARACTERISTIC INFLAMMATORY STATE THAT EXPRESSES HIGH LEVELS OF PRO-INFLAMMATORY MARKERS, TERMED INFLAMMAGING. THIS CHRONIC INFLAMMATION IS A TYPICAL PHENOMENON LINKED TO IMMUNOSENESCENCE AND IT IS CONSIDERED THE MAJOR RISK FACTOR FOR AGE-RELATED DISEASES. THYMIC INVOLUTION, NAIVE/MEMORY CELL RATIO IMBALANCE, DYSREGULATED METABOLISM, AND EPIGENETIC ALTERATIONS ARE STRIKING FEATURES OF IMMUNOSENESCENCE. DISTURBED T-CELL POOLS AND CHRONIC ANTIGEN STIMULATION MEDIATE PREMATURE SENESCENCE OF IMMUNE CELLS, AND SENESCENT IMMUNE CELLS DEVELOP A PROINFLAMMATORY SENESCENCE-ASSOCIATED SECRETORY PHENOTYPE THAT EXACERBATES INFLAMMAGING. ALTHOUGH THE UNDERLYING MOLECULAR MECHANISMS REMAIN TO BE ADDRESSED, IT IS WELL DOCUMENTED THAT SENESCENT T CELLS AND INFLAMMAGING MIGHT BE MAJOR DRIVING FORCES IN IMMUNOSENESCENCE. POTENTIAL COUNTERACTIVE MEASURES WILL BE DISCUSSED, INCLUDING INTERVENTION OF CELLULAR SENESCENCE AND METABOLIC-EPIGENETIC AXES TO MITIGATE IMMUNOSENESCENCE. IN RECENT YEARS, IMMUNOSENESCENCE HAS ATTRACTED INCREASING ATTENTION FOR ITS ROLE IN TUMOR DEVELOPMENT. AS A RESULT OF THE LIMITED PARTICIPATION OF ELDERLY PATIENTS, THE IMPACT OF IMMUNOSENESCENCE ON CANCER IMMUNOTHERAPY IS UNCLEAR. DESPITE SOME SURPRISING RESULTS FROM CLINICAL TRIALS AND DRUGS, IT IS NECESSARY TO INVESTIGATE THE ROLE OF IMMUNOSENESCENCE IN CANCER AND OTHER AGE-RELATED DISEASES. 2023 5 5543 42 ROLE OF ENDOGENOUS GLUCOCORTICOIDS IN CANCER IN THE ELDERLY. ALTHOUGH NOT A DISEASE ITSELF, AGING REPRESENTS A RISK FACTOR FOR MANY AGING-RELATED ILLNESSES, INCLUDING CANCER. NUMEROUS CAUSES UNDERLIE THE INCREASED INCIDENCE OF MALIGNANCIES IN THE ELDERLY, FOR EXAMPLE, GENOMIC INSTABILITY AND EPIGENETIC ALTERATIONS THAT OCCUR AT CELLULAR LEVEL, WHICH ALSO INVOLVE THE IMMUNE CELLS. THE PROGRESSIVE DECLINE OF THE IMMUNE SYSTEM FUNCTIONS THAT OCCURS IN AGING DEFINES IMMUNOSENESCENCE, AND INCLUDES BOTH INNATE AND ADAPTIVE IMMUNITY; THE LATTER UNDERGOES MAJOR ALTERATIONS. AGING AND CHRONIC STRESS SHARE THE ABNORMAL HYPOTHALAMIC(-)PITUITARY(-)ADRENAL AXIS ACTIVATION, WHERE ALTERED PERIPHERAL GLUCOCORTICOIDS (GC) LEVELS AND CHRONIC STRESS HAVE BEEN ASSOCIATED WITH ACCELERATED CELLULAR AGING, PREMATURE IMMUNOSENESCENCE, AND AGING-RELATED DISEASES. CONSEQUENTLY, CHANGES IN GC LEVELS AND SENSITIVITY CONTRIBUTE TO THE SIGNS OF IMMUNOSENESCENCE, NAMELY FEWER NAIVE T CELLS, POOR IMMUNE RESPONSE TO NEW ANTIGENS, DECREASED CELL-MEDIATED IMMUNITY, AND THYMIC INVOLUTION. GC SIGNALING ALTERATIONS ALSO INVOLVE EPIGENETIC ALTERATIONS IN DNA METHYLATION, WITH TRANSCRIPTION MODIFICATIONS THAT MAY CONTRIBUTE TO IMMUNOSENESCENCE. IMMUNE CELL AGING LEADS TO DECREASED LEVELS OF IMMUNOSURVEILLANCE, THEREBY PROVIDING TUMOR CELLS ONE MORE ROUTE FOR IMMUNE SYSTEM ESCAPE. HERE, THE CONTRIBUTION OF GC SECRETION AND SIGNALING DYSREGULATION TO THE INCREASED INCIDENCE OF TUMORIGENESIS IN THE ELDERLY IS REVIEWED. 2018 6 438 22 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 7 660 27 BLOOD LEVELS OF T-CELL RECEPTOR EXCISION CIRCLES (TRECS) PROVIDE AN INDEX OF EXPOSURE TO TRAUMATIC STRESS IN MICE AND HUMANS. EXPOSURE TO STRESS TRIGGERS BIOLOGICAL CHANGES THROUGHOUT THE BODY. ACCUMULATING EVIDENCE INDICATES THAT ALTERATIONS IN IMMUNE SYSTEM FUNCTION ARE ASSOCIATED WITH THE DEVELOPMENT OF STRESS-ASSOCIATED ILLNESSES SUCH AS MAJOR DEPRESSIVE DISORDER AND POST-TRAUMATIC STRESS DISORDER, INCREASING INTEREST IN IDENTIFYING IMMUNE MARKERS THAT PROVIDE INSIGHT INTO MENTAL HEALTH. RECOMBINATION EVENTS DURING T-CELL RECEPTOR REARRANGEMENT AND T-CELL MATURATION IN THE THYMUS PRODUCE CIRCULAR DNA FRAGMENTS CALLED T-CELL RECEPTOR EXCISION CIRCLES (TRECS) THAT CAN BE UTILIZED AS INDICATORS OF THYMIC FUNCTION AND NUMBERS OF NEWLY EMIGRATING T-CELLS. GIVEN DATA SUGGESTING THAT STRESS AFFECTS THYMUS FUNCTION, WE EXAMINED WHETHER BLOOD LEVELS OF TRECS MIGHT SERVE AS A QUANTITATIVE PERIPHERAL INDEX OF CUMULATIVE STRESS EXPOSURE AND ITS PHYSIOLOGICAL CORRELATES. WE HYPOTHESIZED THAT CHRONIC STRESS EXPOSURE WOULD COMPROMISE THYMUS FUNCTION AND PRODUCE CORRESPONDING DECREASES IN LEVELS OF TRECS. IN MALE MICE, EXPOSURE TO CHRONIC SOCIAL DEFEAT STRESS (CSDS) PRODUCED THYMIC INVOLUTION, ADRENAL HYPERTROPHY, AND DECREASED LEVELS OF TRECS IN BLOOD. EXTENDING THESE STUDIES TO HUMANS REVEALED ROBUST INVERSE CORRELATIONS BETWEEN LEVELS OF CIRCULATING TRECS AND CHILDHOOD EMOTIONAL AND PHYSICAL ABUSE. CELL-TYPE SPECIFIC ANALYSES ALSO REVEALED ASSOCIATIONS BETWEEN TREC LEVELS AND BLOOD CELL COMPOSITION, AS WELL AS CELL-TYPE SPECIFIC METHYLATION CHANGES IN CD4T + AND CD8T + CELLS. ADDITIONALLY, TREC LEVELS CORRELATED WITH EPIGENETIC AGE ACCELERATION, A COMMON BIOMARKER OF STRESS EXPOSURE. OUR FINDINGS DEMONSTRATE ALIGNMENT BETWEEN FINDINGS IN MICE AND HUMANS AND SUGGEST THAT BLOOD-BORNE TRECS ARE A TRANSLATIONALLY-RELEVANT BIOMARKER THAT CORRELATES WITH, AND PROVIDES INSIGHT INTO, THE CUMULATIVE PHYSIOLOGICAL AND IMMUNE-RELATED IMPACTS OF STRESS EXPOSURE IN MAMMALS. 2022 8 4178 25 MEMORY T-CELL HETEROGENEITY AND TERMINOLOGY. IMMUNOLOGICAL MEMORY AND EXHAUSTION ARE FUNDAMENTAL FEATURES OF ADAPTIVE IMMUNITY. RECENT ADVANCES REVEAL INCREASING HETEROGENEITY AND DIVERSITY AMONG CD8 T-CELL SUBSETS, RESULTING IN NEW SUBSETS TO ANNOTATE AND UNDERSTAND. HERE, WE REVIEW OUR CURRENT KNOWLEDGE OF DIFFERENTIATION AND MAINTENANCE OF MEMORY AND EXHAUSTED CD8 T CELLS, INCLUDING PHENOTYPIC CLASSIFICATION, DEVELOPMENTAL PATHS, TRANSCRIPTIONAL AND EPIGENETIC FEATURES, AND CELL INTRINSIC AND EXTRINSIC FACTORS. ADDITIONALLY, WE USE THIS OUTLINE TO DISCUSS THE NOMENCLATURE OF EFFECTOR, MEMORY, AND EXHAUSTED CD8 T CELLS. FINALLY, WE DISCUSS HOW NEW FINDINGS ABOUT THESE CELL TYPES MAY IMPACT THE THERAPEUTIC EFFICACY AND DEVELOPMENT OF IMMUNOTHERAPIES TARGETING EFFECTOR, MEMORY, AND/OR EXHAUSTED CD8 T CELLS IN CHRONIC INFECTIONS AND CANCER. 2021 9 4186 28 METABOLIC AND EPIGENETIC REGULATION OF T-CELL EXHAUSTION. CURRENT IMMUNOTHERAPIES YIELD REMARKABLE CLINICAL OUTCOMES BY BOOSTING THE POWER OF HOST IMMUNITY IN CANCER CELL ELIMINATION AND VIRAL CLEARANCE. HOWEVER, AFTER PROLONGED ANTIGEN EXPOSURE, CD8(+) T CELLS DIFFERENTIATE INTO A SPECIAL DIFFERENTIATION STATE KNOWN AS T-CELL EXHAUSTION, WHICH POSES ONE OF THE MAJOR HURDLES TO ANTIVIRAL AND ANTITUMOR IMMUNITY DURING CHRONIC VIRAL INFECTION AND TUMOUR DEVELOPMENT. GROWING EVIDENCE INDICATES THAT EXHAUSTED T CELLS UNDERGO METABOLIC INSUFFICIENCY WITH ALTERED SIGNALLING CASCADES AND EPIGENETIC LANDSCAPES, WHICH DAMPEN EFFECTOR IMMUNITY AND CAUSE POOR RESPONSIVENESS TO IMMUNE-CHECKPOINT-BLOCKADE THERAPIES. HOW METABOLIC STRESS AFFECTS T-CELL EXHAUSTION REMAINS UNCLEAR; THEREFORE, IN THIS REVIEW, WE SUMMARIZE CURRENT KNOWLEDGE OF HOW T-CELL EXHAUSTION OCCURS, AND DISCUSS HOW METABOLIC INSUFFICIENCY AND PROLONGED STRESS RESPONSES MAY AFFECT SIGNALLING CASCADES AND EPIGENETIC REPROGRAMMING, THUS LOCKING T CELLS INTO AN EXHAUSTED STATE VIA SPECIALIZED DIFFERENTIATION PROGRAMMING. 2020 10 6522 30 TRANSCRIPTIONAL AND EPIGENETIC REGULATION OF T CELL HYPORESPONSIVENESS. NAIVE CD8(+) T CELLS DIFFERENTIATE INTO EFFECTOR AND MEMORY CYTOLYTIC T CELLS (CTLS) DURING AN ACUTE INFECTION. IN CONTRAST, IN SCENARIOS OF PERSISTENT ANTIGEN STIMULATION, SUCH AS CHRONIC INFECTIONS AND CANCER, ANTIGEN-SPECIFIC CTLS SHOW A GRADUAL DECREASE IN EFFECTOR FUNCTION, A PHENOMENON THAT HAS BEEN TERMED CD8(+) T CELL "EXHAUSTION" OR "DYSFUNCTION." ANOTHER HYPORESPONSIVE STATE, TERMED "ANERGY", IS OBSERVED WHEN T CELLS ARE ACTIVATED IN THE ABSENCE OF POSITIVE COSTIMULATORY SIGNALS. AMONG THE MANY NEGATIVE REGULATORS INDUCED IN HYPORESPONSIVE T CELLS ARE INHIBITORY CELL-SURFACE RECEPTORS, SUCH AS PD-1, LAG-3, CTLA-4, AND TIM-3; "CHECKPOINT BLOCKADE" THERAPIES THAT INVOLVE TREATMENT OF PATIENTS WITH CANCER WITH BLOCKING ANTIBODIES TO THOSE RECEPTORS SHOW CONSIDERABLE PROMISE IN THE CLINIC BECAUSE THE BLOCKING ANTIBODIES CAN MITIGATE HYPORESPONSIVENESS AND PROMOTE TUMOR REJECTION. IN THIS REVIEW, WE DESCRIBE RECENT ADVANCES IN OUR MOLECULAR UNDERSTANDING OF THESE HYPORESPONSIVE STATES. WE REVIEW EVIDENCE FOR THE INVOLVEMENT OF DIVERSE TRANSCRIPTION FACTORS, METABOLIC PROGRAMS, AND CHROMATIN ACCESSIBILITY CHANGES IN HYPORESPONSIVE T CELLS, AND WE DISCUSS HOW CHECKPOINT BLOCKADE THERAPIES AFFECT THE MOLECULAR PROGRAM OF CD8(+) T CELL EXHAUSTION. 2017 11 4196 27 METABOLIC PLASTICITY AND REGULATION OF T CELL EXHAUSTION. THE METABOLIC REPROGRAMMING DURING T CELL ACTIVATION AND DIFFERENTIATION AFFECTS T CELL FATE AND IMMUNE RESPONSES. CELL METABOLISM MAY SERVE AS THE DRIVING FORCE THAT INDUCES EPIGENETIC MODIFICATIONS, CONTRIBUTING TO REGULATING T CELL DIFFERENTIATION. PERSISTENT PATHOGEN INFECTION LEADS TO T CELL EXHAUSTION, WHICH IS COMPOSED OF TWO MAIN SUBSETS AND WITH DISTINCT METABOLIC CHARACTERISTICS. THE PROGENITOR EXHAUSTED T CELLS UTILIZE MITOCHONDRIAL FATTY ACID OXIDATION (FAO) AND OXIDATIVE PHOSPHORYLATION (OXPHOS) FOR ENERGY, WHILE TERMINALLY EXHAUSTED T CELLS MAINLY RELY ON GLYCOLYTIC METABOLISM WITH IMPAIRED GLYCOLYSIS AND OXPHOS. HERE, WE COMPILED THE LATEST RESEARCH ON HOW T CELL METABOLISM DEFINES DIFFERENTIATION, FOCUSING ON T CELL EXHAUSTION DURING CHRONIC INFECTIONS. IN ADDITION, METABOLIC-RELATED FACTORS INCLUDING ANTIGEN STIMULATION SIGNALS STRENGTH, CYTOKINES AND EPIGENETICS AFFECTING T CELL EXHAUSTION WERE ALSO REVIEWED. FURTHERMORE, THE INTERVENTION STRATEGIES ON METABOLISM AND EPIGENETICS TO REVERSE T CELL EXHAUSTION WERE DISCUSSED IN DETAIL, WHICH MAY CONTRIBUTE TO ACHIEVING THE GOAL OF PREVENTION AND TREATMENT OF T CELL EXHAUSTION. 2022 12 5896 36 T CELLS IN HEALTH AND DISEASE. T CELLS ARE CRUCIAL FOR IMMUNE FUNCTIONS TO MAINTAIN HEALTH AND PREVENT DISEASE. T CELL DEVELOPMENT OCCURS IN A STEPWISE PROCESS IN THE THYMUS AND MAINLY GENERATES CD4(+) AND CD8(+) T CELL SUBSETS. UPON ANTIGEN STIMULATION, NAIVE T CELLS DIFFERENTIATE INTO CD4(+) HELPER AND CD8(+) CYTOTOXIC EFFECTOR AND MEMORY CELLS, MEDIATING DIRECT KILLING, DIVERSE IMMUNE REGULATORY FUNCTION, AND LONG-TERM PROTECTION. IN RESPONSE TO ACUTE AND CHRONIC INFECTIONS AND TUMORS, T CELLS ADOPT DISTINCT DIFFERENTIATION TRAJECTORIES AND DEVELOP INTO A RANGE OF HETEROGENEOUS POPULATIONS WITH VARIOUS PHENOTYPE, DIFFERENTIATION POTENTIAL, AND FUNCTIONALITY UNDER PRECISE AND ELABORATE REGULATIONS OF TRANSCRIPTIONAL AND EPIGENETIC PROGRAMS. ABNORMAL T-CELL IMMUNITY CAN INITIATE AND PROMOTE THE PATHOGENESIS OF AUTOIMMUNE DISEASES. IN THIS REVIEW, WE SUMMARIZE THE CURRENT UNDERSTANDING OF T CELL DEVELOPMENT, CD4(+) AND CD8(+) T CELL CLASSIFICATION, AND DIFFERENTIATION IN PHYSIOLOGICAL SETTINGS. WE FURTHER ELABORATE THE HETEROGENEITY, DIFFERENTIATION, FUNCTIONALITY, AND REGULATION NETWORK OF CD4(+) AND CD8(+) T CELLS IN INFECTIOUS DISEASE, CHRONIC INFECTION AND TUMOR, AND AUTOIMMUNE DISEASE, HIGHLIGHTING THE EXHAUSTED CD8(+) T CELL DIFFERENTIATION TRAJECTORY, CD4(+) T CELL HELPER FUNCTION, T CELL CONTRIBUTIONS TO IMMUNOTHERAPY AND AUTOIMMUNE PATHOGENESIS. WE ALSO DISCUSS THE DEVELOPMENT AND FUNCTION OF GAMMADELTA T CELLS IN TISSUE SURVEILLANCE, INFECTION, AND TUMOR IMMUNITY. FINALLY, WE SUMMARIZED CURRENT T-CELL-BASED IMMUNOTHERAPIES IN BOTH CANCER AND AUTOIMMUNE DISEASES, WITH AN EMPHASIS ON THEIR CLINICAL APPLICATIONS. A BETTER UNDERSTANDING OF T CELL IMMUNITY PROVIDES INSIGHT INTO DEVELOPING NOVEL PROPHYLACTIC AND THERAPEUTIC STRATEGIES IN HUMAN DISEASES. 2023 13 770 27 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 14 771 32 CD8(+) T CELL EXHAUSTION. CD8(+) T CELLS ARE IMPORTANT FOR THE PROTECTIVE IMMUNITY AGAINST INTRACELLULAR PATHOGENS AND TUMOR. IN THE CASE OF CHRONIC INFECTION OR CANCER, CD8(+) T CELLS ARE EXPOSED TO PERSISTENT ANTIGEN AND/OR INFLAMMATORY SIGNALS. THIS EXCESSIVE AMOUNT OF SIGNALS OFTEN LEADS CD8(+) T CELLS TO GRADUAL DETERIORATION OF T CELL FUNCTION, A STATE CALLED "EXHAUSTION." EXHAUSTED T CELLS ARE CHARACTERIZED BY PROGRESSIVE LOSS OF EFFECTOR FUNCTIONS (CYTOKINE PRODUCTION AND KILLING FUNCTION), EXPRESSION OF MULTIPLE INHIBITORY RECEPTORS (SUCH AS PD-1 AND LAG3), DYSREGULATED METABOLISM, POOR MEMORY RECALL RESPONSE, AND HOMEOSTATIC PROLIFERATION. THESE ALTERED FUNCTIONS ARE CLOSELY RELATED WITH ALTERED TRANSCRIPTIONAL PROGRAM AND EPIGENETIC LANDSCAPE THAT CLEARLY DISTINGUISH EXHAUSTED T CELLS FROM NORMAL EFFECTOR AND MEMORY T CELLS. T CELL EXHAUSTION IS OFTEN ASSOCIATED WITH INEFFICIENT CONTROL OF PERSISTING INFECTIONS AND CANCERS, BUT RE-INVIGORATION OF EXHAUSTED T CELLS WITH INHIBITORY RECEPTOR BLOCKADE CAN PROMOTE IMPROVED IMMUNITY AND DISEASE OUTCOME. ACCUMULATING EVIDENCES SUPPORT THE THERAPEUTIC POTENTIAL OF TARGETING EXHAUSTED T CELLS. HOWEVER, EXHAUSTED T CELLS COMPRISE HETEROGENOUS CELL POPULATION WITH DISTINCT RESPONSIVENESS TO INTERVENTION. UNDERSTANDING MOLECULAR MECHANISM OF T CELL EXHAUSTION IS ESSENTIAL TO ESTABLISH RATIONAL IMMUNOTHERAPEUTIC INTERVENTIONS. 2019 15 3735 25 INNATE IMMUNE MEMORY: IMPLICATIONS FOR DEVELOPMENT OF PEDIATRIC IMMUNOMODULATORY AGENTS AND ADJUVANTED VACCINES. UNIQUE FEATURES OF IMMUNITY EARLY IN LIFE INCLUDE A DISTINCT IMMUNE SYSTEM PARTICULARLY RELIANT ON INNATE IMMUNITY, WITH WEAK T HELPER (TH)1-POLARIZING IMMUNE RESPONSES, AND IMPAIRED RESPONSES TO CERTAIN VACCINES LEADING TO A HEIGHTENED SUSCEPTIBILITY TO INFECTION. TO THESE IMPORTANT ASPECTS, WE NOW ADD AN INCREASINGLY APPRECIATED CONCEPT THAT THE INNATE IMMUNE SYSTEM DISPLAYS EPIGENETIC MEMORY OF AN EARLIER INFECTION OR VACCINATION, A PHENOMENON THAT HAS BEEN NAMED "TRAINED IMMUNITY." EXPOSURE OF NEONATAL LEUKOCYTES IN VITRO OR NEONATAL ANIMALS OR HUMANS IN VIVO TO SPECIFIC INNATE IMMUNE STIMULI RESULTS IN AN ALTERED INNATE IMMUNE SET POINT. GIVEN THE PARTICULAR IMPORTANCE OF INNATE IMMUNITY EARLY IN LIFE, TRAINED IMMUNITY TO EARLY LIFE INFECTION AND/OR IMMUNIZATION MAY PLAY AN IMPORTANT ROLE IN MODULATING BOTH ACUTE AND CHRONIC DISEASES. 2014 16 1208 35 COVID-19 INFECTION AND RESPONSE TO VACCINATION IN CHRONIC KIDNEY DISEASE AND RENAL TRANSPLANTATION: A BRIEF PRESENTATION. CHRONIC KIDNEY DISEASE (CKD) IS ASSOCIATED WITH PHENOTYPIC AND FUNCTIONAL CHANGES IN THE IMMUNE SYSTEM, FOLLOWED BY DETRIMENTAL CLINICAL CONSEQUENCES, SUCH AS SEVERE INFECTIONS AND DEFECTIVE RESPONSE TO VACCINATION. TWO YEARS OF THE PANDEMIC, DUE TO SEVERE ACUTE RESPIRATORY SYNDROME CORONAVIRUS 2 (SARS-COV-2), HAVE UNDOUBTEDLY CHANGED THE WORLD; HOWEVER, ALL EFFORTS TO CONFRONT INFECTION AND PROVIDE NEW GENERATION VACCINES TREMENDOUSLY IMPROVED OUR UNDERSTANDING OF THE MECHANISMS OF THE IMMUNE RESPONSE AGAINST INFECTIONS AND AFTER VACCINATION. HUMORAL AND CELLULAR RESPONSES TO VACCINES, INCLUDING MRNA VACCINES, ARE APPARENTLY AFFECTED IN CKD PATIENTS, AS ELIMINATION OF RECENT THYMIC EMIGRANT AND NAIVE LYMPHOCYTES AND REGULATORY T-CELLS, TOGETHER WITH CONTRACTION OF T-CELL REPERTOIRE AND HOMEOSTATIC PROLIFERATION RATE, WHICH CHARACTERIZED CKD PATIENTS ARE RESPONSIBLE FOR IMPAIRED IMMUNE ACTIVATION. SUCCESSFUL RENAL TRANSPLANTATION WILL RESTORE SOME OF THESE CHANGES, ALTHOUGH SEVERAL EPIGENETIC CHANGES ARE IRREVERSIBLE AND EVEN ACCELERATED BY THE INDUCTION OF IMMUNOSUPPRESSION. RESPONSE TO VACCINATION IS DEFINITELY IMPAIRED AMONG BOTH CKD AND RT PATIENTS. IN THE PRESENT REVIEW, WE ANALYZED THE DIFFERENCES IN IMMUNE RESPONSE AFTER VACCINATION BETWEEN THESE PATIENTS AND HEALTHY INDIVIDUALS AND DEPICTED SPECIFIC PARAMETERS, SUCH AS ALTERATIONS IN THE IMMUNE SYSTEM, PREDISPOSING TO THIS DEFICIENT RESPONSE. 2022 17 790 29 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 18 4386 28 MITOCHONDRIAL STRESS INDUCED BY CONTINUOUS STIMULATION UNDER HYPOXIA RAPIDLY DRIVES T CELL EXHAUSTION. CANCER AND CHRONIC INFECTIONS INDUCE T CELL EXHAUSTION, A HYPOFUNCTIONAL FATE CARRYING DISTINCT EPIGENETIC, TRANSCRIPTOMIC AND METABOLIC CHARACTERISTICS. HOWEVER, DRIVERS OF EXHAUSTION REMAIN POORLY UNDERSTOOD. AS INTRATUMORAL EXHAUSTED T CELLS EXPERIENCE SEVERE HYPOXIA, WE HYPOTHESIZED THAT METABOLIC STRESS ALTERS THEIR RESPONSES TO OTHER SIGNALS, SPECIFICALLY, PERSISTENT ANTIGENIC STIMULATION. IN VITRO, ALTHOUGH CD8(+) T CELLS EXPERIENCING CONTINUOUS STIMULATION OR HYPOXIA ALONE DIFFERENTIATED INTO FUNCTIONAL EFFECTORS, THE COMBINATION RAPIDLY DROVE T CELL DYSFUNCTION CONSISTENT WITH EXHAUSTION. CONTINUOUS STIMULATION PROMOTED BLIMP-1-MEDIATED REPRESSION OF PGC-1ALPHA-DEPENDENT MITOCHONDRIAL REPROGRAMMING, RENDERING CELLS POORLY RESPONSIVE TO HYPOXIA. LOSS OF MITOCHONDRIAL FUNCTION GENERATED INTOLERABLE LEVELS OF REACTIVE OXYGEN SPECIES (ROS), SUFFICIENT TO PROMOTE EXHAUSTED-LIKE STATES, IN PART THROUGH PHOSPHATASE INHIBITION AND THE CONSEQUENT ACTIVITY OF NUCLEAR FACTOR OF ACTIVATED T CELLS. REDUCING T CELL-INTRINSIC ROS AND LOWERING TUMOR HYPOXIA LIMITED T CELL EXHAUSTION, SYNERGIZING WITH IMMUNOTHERAPY. THUS, IMMUNOLOGIC AND METABOLIC SIGNALING ARE INTRINSICALLY LINKED: THROUGH MITIGATION OF METABOLIC STRESS, T CELL DIFFERENTIATION CAN BE ALTERED TO PROMOTE MORE FUNCTIONAL CELLULAR FATES. 2021 19 4177 38 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 20 6851 32 [MOLECULAR PROFILES OF EXHAUSTED T CELLS AND THEIR IMPACT ON RESPONSE TO IMMUNE CHECKPOINT BLOCKADE]. T CELL EXHAUSTION IS INDUCED IN THE CONTEXT OF CHRONIC VIRUS INFECTION AND TUMOR MICROENVIRONMENT, IN WHICH CYTOTOXIC T CELLS ARE REPEATEDLY EXPOSED TO THE TARGET ANTIGEN AND DEPRIVED OF THEIR EFFECTOR FUNCTIONS. MULTIPLE STUDIES HAVE ALREADY SHOWN THE SIGNIFICANT IMPACT OF IMMUNE CHECKPOINT MOLECULES SUCH AS PD1 ON FUNCTIONAL PROPERTIES OF EXHAUSTED T CELLS. IN ADDITION TO THESE SIGNALS, EXHAUSTED T CELLS POSSESS DISTINCT TRANSCRIPTIONAL AND EPIGENETIC PROFILES COMPARED WITH CONVENTIONAL EFFECTOR AND MEMORY T CELLS. IMPORTANTLY, MOST OF THESE FEATURES ARE NOT AFFECTED BY IMMUNE CHECKPOINT BLOCKADE, SUGGESTING THAT GENETIC AND EPIGENETIC REMODELING OF T CELLS IS AN UNDERLYING MOLECULAR MECHANISM ESSENTIAL FOR T CELL EXHAUSTION. MOREOVER, IT HAS NOW BEEN EVIDENT THAT EXHAUSTED T CELLS ARE A HETEROGENEOUS CELL POPULATION COMPOSED OF DISTINCT T CELL SUBSETS, AND THESE FUNCTIONAL DIFFERENCES PROFOUNDLY AFFECT THERAPEUTIC EFFICACY OF CANCER IMMUNOTHERAPY. IN THIS REVIEW, I WILL DISCUSS RECENT STUDIES INVESTIGATING MOLECULAR MECHANISMS OF T CELL EXHAUSTION, INCLUDING NOVEL KEY MOLECULES ESSENTIALLY ASSOCIATED WITH T CELL EXHAUSTION. THESE FINDINGS ARE POTENTIALLY APPLICABLE TO REINVIGORATE EFFECTOR FUNCTIONS OF EXHAUSTED T CELLS. 2022