1 2421 123 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 2 740 32 CANCER/TESTIS ANTIGENS: EXPRESSION, REGULATION, TUMOR INVASION, AND USE IN IMMUNOTHERAPY OF CANCERS. CANCER/TESTIS ANTIGENS (CTAS) ARE NAMED BASED ON THEIR EXPRESSION PATTERN THAT IS RESTRICTED IN A NUMBER OF NORMAL AND ABNORMAL TISSUES. TUMOR CELLS FREQUENTLY EXPRESS ANTIGENS WHOSE EXPRESSION IS TYPICALLY RESTRICTED TO GERM CELLS. THEIR UNIQUE EXPRESSION PATTERN IS GUARANTEED BY PRECISE EPIGENETIC REGULATORY MECHANISMS. BECAUSE OF THEIR TUMOR-LIMITED, HIGH IMMUNOGENICITY, AND BIASED EXPRESSION, DISCOVERY OF THESE MOLECULES PROVIDES UNPRECEDENTED OPPORTUNITIES FOR FURTHER RESEARCH AND CLINICAL DEVELOPMENT IN THE FIELD OF CANCER DIAGNOSIS AND IMMUNOTHERAPY. EVOLVING EVIDENCE REVEALS THAT A NUMBER OF CTAS STIMULATE EPITHELIAL MESENCHYMAL TRANSITION (EMT) AND GENERATION OF CANCER STEM-LIKE CELLS, INTENSIFYING METASTASIS, INVASION, AND TUMORIGENESIS. BASED ON THESE FEATURES, CTAS ATTRACT ATTENTION TO BE CONSIDERED AS IDEAL TARGETS FOR DEVELOPING SEVERAL CLINICAL TRIALS, MANY OF THEM CONCENTRATING ON CTA VACCINE THERAPY. ACCORDING TO RECENT PRACTICAL CLINICAL INTEREST, MORE CHARACTERIZATIONS OF CTA REGULATION ARE IDENTIFIED. CTA EXPRESSION HAS BEEN DEMONSTRATED IN A VARIETY OF HUMAN CANCER TISSUES, AND SOME OF THEM HAVE BEEN FOUND TO ELICIT HUMORAL AND/OR CELLULAR IMMUNE RESPONSES IN CANCER PATIENTS. CTAS ARE BRILLIANT TARGETS FOR ANTICANCER DRUG DISCOVERY, TARGETED TUMOR THERAPY, AND DIAGNOSTIC BIOMARKERS, FURTHERMORE, VALUED GENES IN THE STUDY OF IMMUNOTHERAPY, PROMOTING TUMORIGENESIS, AND MALIGNANT PROGRESSION. THIS REVIEW OUTLINES AND CATEGORIZES OUR CURRENT UNDERSTANDING OF THE COMPLEX AND BIASED PROCESS OF CTAS MRNA AND PROTEIN EXPRESSION IN CANCER, AND SUPPLIES THE MOST RECENT INFORMATION ON THEIR REGULATION AND FUNCTION. BESIDES, A CONCISE SYNOPSIS OF THE MAJOR CLINICAL TRIALS INVOLVING CTAS, AS THERAPEUTIC AVENUES, IS DISCUSSED. ABBREVIATIONS: AIRE: AUTOIMMUNE REGULATOR; CAMP: CYCLIC ADENOSINE 3',5'-CYCLIC MONOPHOSPHATE; CEA: CARCINOEMBRYONIC ANTIGEN; CML: CHRONIC MYELOID LEUKEMIA; CREB: CYCLICAMP RESPONSE ELEMENT BINDING; CSCS: CANCER STEM CELLS; CTAS: CANCER/TESTIS ANTIGENS; CTL: CYTOTOXIC T LYMPHOCYTE; DCS: DENDRITIC CELLS; EMT: EPITHELIAL-MESENCHYMAL TRANSITION; ERK: EXTRACELLULAR SIGNAL-REGULATED KINASE; ESCC: ESOPHAGEAL SQUAMOUS CELL CARCINOMA; ETS: E26 TRANSFORMATION-SPECIFIC; HIS: HISTIDINE; HLA: HUMAN LEUKOCYTE ANTIGEN; HNSCC: HEAD AND NECK SQUAMOUS CELL CARCINOMA; IFN-GAMMA: INTERFERON-GAMMA; IHC: IMMUNOHISTOCHEMISTRY; IL-7: INTERLEUKIN7; MHC: MAJOR HISTOCOMPATIBILITY COMPLEX; MMP2: MATRIX METALLOPROTEINASE 2; MTECS: MEDULLARY THYMUS EPITHELIAL CELLS; MUC1: MUCIN 1; NSCLC: NON-SMALL CELL LUNG CANCER; PRAME: PREFERENTIALLY EXPRESSED ANTIGEN IN MELANOMA; RDA: REPRESENTATIONAL DIFFERENCE ANALYSIS; SEREX: SEROLOGICAL ANALYSIS OF CDNA EXPRESSION; SSX: SYNOVIAL SARCOMA X CHROMOSOME; TAAS: TUMOR-ASSOCIATED ANTIGENS; TCR: T-CELL RECEPTOR; TCGA: THE CANCER GENOME ATLAS; TGF-BETA: TRANSFORMING GROWTH FACTOR-BETA. 2016 3 6522 42 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 4 770 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 5 5849 23 SUBEROYLANILIDE HYDROXAMIC ACID (SAHA) AND CLADRIBINE SYNERGISTICALLY INDUCE APOPTOSIS IN NK-LGL LEUKAEMIA. NATURAL KILLER (NK) LARGE GRANULAR LYMPHOCYTE (LGL) LEUKAEMIA FEATURES A CLONAL PROLIFERATION OF CD3(-) NK CELLS THAT CAN BE CLASSIFIED INTO EITHER AGGRESSIVE OR CHRONIC CATEGORIES. THE NKL CELL LINE, DERIVED FROM AN AGGRESSIVE ASIAN NK CELL LEUKAEMIA, AND PATIENT SAMPLES FROM CHRONIC NK-LGL LEUKAEMIA WERE USED IN OUR STUDY TO PROBE FOR SYNERGISTIC EFFICACY OF THE EPIGENETIC DRUGS VORINOSTAT (SAHA) AND CLADRIBINE IN THIS DISEASE. WE DEMONSTRATE THAT HISTONE DEACETYLASES (HDACS) ARE OVER-EXPRESSED IN BOTH AGGRESSIVE AND CHRONIC NK LEUKAEMIA. ADMINISTRATION OF THE HDAC INHIBITOR SAHA REDUCES CLASS I AND II HDAC EXPRESSION AND ENHANCES HISTONE ACETYLATION IN LEUKAEMIC NK CELLS. IN VITRO COMBINATION TREATMENT WITH SAHA AND CLADRIBINE DOSE-DEPENDENTLY EXERTS SYNERGISTIC CYTOTOXIC AND APOPTOTIC EFFECTS ON LEUKAEMIC NK CELLS. EXPRESSION PROFILING OF APOPTOTIC REGULATORY GENES SUGGESTS THAT BOTH COMPOUNDS LED TO CASPASE-DEPENDENT APOPTOSIS THROUGH ACTIVATION OF INTRINSIC MITOCHONDRIAL AND EXTRINSIC DEATH RECEPTOR PATHWAYS. COLLECTIVELY, THESE DATA SHOW THAT COMBINED EPIGENETIC THERAPY, USING HDAC AND DNA METHYLTRANSFERASE INHIBITORS, MAY BE A PROMISING THERAPEUTIC APPROACH FOR NK-LGL LEUKAEMIA. 2015 6 2879 39 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 7 590 31 BET BROMODOMAIN PROTEIN INHIBITION REVERSES CHIMERIC ANTIGEN RECEPTOR EXTINCTION AND REINVIGORATES EXHAUSTED T CELLS IN CHRONIC LYMPHOCYTIC LEUKEMIA. CHIMERIC ANTIGEN RECEPTOR (CAR) T CELLS HAVE INDUCED REMARKABLE ANTITUMOR RESPONSES IN B CELL MALIGNANCIES. SOME PATIENTS DO NOT RESPOND BECAUSE OF T CELL DEFICIENCIES THAT HAMPER THE EXPANSION, PERSISTENCE, AND EFFECTOR FUNCTION OF THESE CELLS. WE USED LONGITUDINAL IMMUNE PROFILING TO IDENTIFY PHENOTYPIC AND PHARMACODYNAMIC CHANGES IN CD19-DIRECTED CAR T CELLS IN PATIENTS WITH CHRONIC LYMPHOCYTIC LEUKEMIA (CLL). CAR EXPRESSION MAINTENANCE WAS ALSO INVESTIGATED BECAUSE THIS CAN AFFECT RESPONSE DURABILITY. CAR T CELL FAILURE WAS ACCOMPANIED BY PREEXISTING T CELL-INTRINSIC DEFECTS OR DYSFUNCTION ACQUIRED AFTER INFUSION. IN A SMALL SUBSET OF PATIENTS, CAR SILENCING WAS OBSERVED COINCIDENT WITH LEUKEMIA RELAPSE. USING A SMALL MOLECULE INHIBITOR, WE DEMONSTRATED THAT THE BROMODOMAIN AND EXTRA-TERMINAL (BET) FAMILY OF CHROMATIN ADAPTERS PLAYS A ROLE IN DOWNREGULATING CAR EXPRESSION. BET PROTEIN BLOCKADE ALSO AMELIORATED CAR T CELL EXHAUSTION AS MANIFESTED BY INHIBITORY RECEPTOR REDUCTION, ENHANCED METABOLIC FITNESS, INCREASED PROLIFERATIVE CAPACITY, AND ENRICHED TRANSCRIPTOMIC SIGNATURES OF T CELL REINVIGORATION. BET INHIBITION DECREASED LEVELS OF THE TET2 METHYLCYTOSINE DIOXYGENASE, AND FORCED EXPRESSION OF THE TET2 CATALYTIC DOMAIN ELIMINATED THE POTENCY-ENHANCING EFFECTS OF BET PROTEIN TARGETING IN CAR T CELLS, PROVIDING A MECHANISM LINKING BET PROTEINS AND T CELL DYSFUNCTION. THUS, MODULATING BET EPIGENETIC READERS MAY IMPROVE THE EFFICACY OF CELL-BASED IMMUNOTHERAPIES. 2021 8 6851 36 [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 9 2660 28 EPITHERAPY AND IMMUNE CHECKPOINT BLOCKADE: USING EPIGENETIC REINVIGORATION OF EXHAUSTED AND DYSFUNCTIONAL T CELLS TO REIMBURSE IMMUNOTHERAPY RESPONSE. BACKGROUND: CANCER CELLS SUBVERT NATURAL IMMUNOSUPPRESSION BY UPREGULATING THE EXPRESSION OF CHECKPOINT PROTEINS AND THEIR LIGANDS. FOR EXAMPLE, TUMOR CELLS EXPRESSING PROGRAMMED DEATH-LIGAND 1 (PD-L1) INDUCE IMMUNE CELL TOLERANCE TO CANCERS, THEREBY FACILITATING TUMOR PROGRESSION. THE RECENT CLINICAL SUCCESS OF IMMUNOTHERAPY, PARTICULARLY CHECKPOINT BLOCKADE, REPRESENTS A SIGNIFICANT ADVANCE IN CANCER THERAPY. HOWEVER, MANY CANCERS DEVELOP RESISTANCE TO IMMUNOTHERAPIES, AND THE UNDERLYING MECHANISMS AND HOW THESE MIGHT BE EXPLOITED TO OVERCOME RESISTANCE STILL NEED TO BE DETERMINED. METHODS: T CELL DYSFUNCTION, IN PART CAUSED BY CHRONIC T CELL RECEPTOR STIMULATION, DIMINISHES THE CAPACITY FOR DURABLE RESPONSES TO CHECKPOINT BLOCKADE. FURTHERMORE, T CELL POPULATIONS ARE PHENOTYPICALLY AND FUNCTIONALLY HETEROGENEOUS, RESULTING IN VARYING RESPONSES TO CHECKPOINT BLOCKADE. RECENT MOLECULAR STUDIES OF T CELL HETEROGENEITY HAVE SHOWN THAT CHECKPOINT BLOCKADE ON ITS OWN DOES NOT ALTER THE EPIGENETIC LANDSCAPE OF T CELLS, DESPITE EPIGENETIC CHANGES GOVERNING T CELL PHENOTYPE. CONCLUSION: HERE WE ARGUE THAT EPIGENETIC MODIFIERS CAN BE USED TO PRIME AND SENSITIZE T CELLS TO IMMUNOTHERAPY. ADMINISTERING EPITHERAPY IN CONJUNCTION WITH CHECKPOINT BLOCKADE COULD DECREASE T CELL EXHAUSTION AND IMMUNOTHERAPY RESISTANCE IN MANY CANCER TYPES. 2020 10 3373 31 HISTONE MODULATION BLOCKS TREG-INDUCED FOXP3 BINDING TO THE IL-2 PROMOTER OF VIRUS-SPECIFIC CD8(+) T CELLS FROM FELINE IMMUNODEFICIENCY VIRUS-INFECTED CATS. CD8(+) T CELLS ARE CRITICAL FOR CONTROLLING HIV INFECTION. DURING THE CHRONIC PHASE OF LENTIVIRAL INFECTION, CD8(+) T CELLS LOSE THEIR PROLIFERATIVE CAPACITY AND EXHIBIT IMPAIRED ANTIVIRAL FUNCTION. THIS LOSS OF CD8(+) T CELL FUNCTION IS DUE, IN PART, TO CD4(+)CD25(+) T REGULATORY (TREG) CELL-MEDIATED SUPPRESSION. OUR RESEARCH GROUP HAS DEMONSTRATED THAT LENTIVIRUS-ACTIVATED CD4(+)CD25(+) TREG CELLS INDUCE THE REPRESSIVE TRANSCRIPTION FACTOR FORKHEAD BOX P3 (FOXP3) IN AUTOLOGOUS CD8(+) T CELLS FOLLOWING CO-CULTURE. WE HAVE RECENTLY REPORTED THAT TREG-INDUCED FOXP3 BINDS THE INTERLEUKIN-2 (IL-2), INTERFERON-GAMMA (IFN- GAMMA), AND TUMOR NECROSIS FACTOR-ALPHA (TNF-ALPHA) PROMOTERS IN VIRUS-SPECIFIC CD8(+) T CELLS. THESE DATA SUGGEST AN IMPORTANT ROLE OF FOXP3-MEDIATED CD8(+) T CELL DYSFUNCTION IN LENTIVIRAL INFECTION. TO ELUCIDATE THE MECHANISM OF THIS SUPPRESSION, WE PREVIOUSLY REPORTED THAT DECREASED METHYLATION FACILITATES FOXP3 BINDING IN MITOGEN-ACTIVATED CD8(+) T CELLS FROM FELINE IMMUNODEFICIENCY VIRUS (FIV)-INFECTED CATS. WE DEMONSTRATED THE REDUCED BINDING OF FOXP3 TO THE IL-2 PROMOTER BY INCREASING METHYLATION OF CD8(+) T CELLS. IN THE STUDIES PRESENTED HERE, WE ASK IF ANOTHER FORM OF EPIGENETIC MODULATION MIGHT ALLEVIATE FOXP3-MEDIATED SUPPRESSION IN CD8(+) T CELLS. WE HYPOTHESIZED THAT DECREASING HISTONE ACETYLATION IN VIRUS-SPECIFIC CD8(+) T CELLS WOULD DECREASE TREG-INDUCED FOXP3 BINDING TO THE IL-2 PROMOTER. INDEED, USING ANACARDIC ACID (AA), A KNOWN HISTONE ACETYL TRANSFERASE (HAT) INHIBITOR, WE DEMONSTRATE A REDUCTION IN FOXP3 BINDING TO THE IL-2 PROMOTER IN VIRUS-SPECIFIC CD8(+) T CELLS CO-CULTURED WITH AUTOLOGOUS TREG CELLS. THESE DATA IDENTIFY A NOVEL MECHANISM OF FOXP3-MEDIATED CD8(+) T CELL DYSFUNCTION DURING LENTIVIRAL INFECTION. 2018 11 991 35 CHRONIC STIMULATION DRIVES HUMAN NK CELL DYSFUNCTION AND EPIGENETIC REPROGRAMING. A POPULATION OF NATURAL KILLER (NK) CELLS EXPRESSING THE ACTIVATING RECEPTOR NKG2C AND THE MATURATION MARKER CD57 EXPANDS IN RESPONSE TO HUMAN CYTOMEGALOVIRUS (HCMV) INFECTION. CD3-CD56DIMCD57+NKG2C+ NK CELLS ARE SIMILAR TO CD8+ MEMORY T CELLS WITH RAPID AND ROBUST EFFECTOR FUNCTION UPON RE-STIMULATION, PERSISTENCE, AND EPIGENETIC REMODELING OF THE IFNG LOCUS. CHRONIC ANTIGEN STIMULATION DRIVES CD8+ MEMORY T CELL PROLIFERATION WHILE ALSO INDUCING GENOME-WIDE EPIGENETIC REPROGRAMING AND DYSFUNCTION. WE HYPOTHESIZED THAT CHRONIC STIMULATION COULD SIMILARLY INDUCE EPIGENETIC REPROGRAMING AND DYSFUNCTION IN NK CELLS. HERE WE SHOW THAT CHRONIC STIMULATION OF ADAPTIVE NK CELLS THROUGH NKG2C USING PLATE-BOUND AGONISTIC ANTIBODIES IN COMBINATION WITH IL-15 DROVE ROBUST PROLIFERATION AND ACTIVATION OF CD3-CD56DIMCD57+NKG2C+ NK CELLS WHILE SIMULTANEOUSLY INDUCING HIGH EXPRESSION OF THE CHECKPOINT INHIBITORY RECEPTORS LAG-3 AND PD-1. MARKED INDUCTION OF CHECKPOINT INHIBITORY RECEPTORS WAS ALSO OBSERVED ON THE SURFACE OF ADAPTIVE NK CELLS CO-CULTURED WITH HCMV-INFECTED ENDOTHELIAL CELLS. CHRONICALLY STIMULATED ADAPTIVE NK CELLS WERE DYSFUNCTIONAL WHEN CHALLENGED WITH TUMOR TARGETS. THESE CELLS EXHIBITED A PATTERN OF EPIGENETIC REPROGRAMING, WITH GENOME-WIDE ALTERATIONS IN DNA METHYLATION. OUR STUDY HAS IMPORTANT IMPLICATIONS FOR CANCER IMMUNOTHERAPY AND SUGGEST THAT EXHAUSTED NK CELLS COULD BE TARGETED WITH INHIBITORY CHECKPOINT RECEPTOR BLOCKADE. 2019 12 5704 40 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 13 6481 42 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 14 1711 38 DYSFUNCTIONAL STATE OF T CELLS OR EXHAUSTION DURING CHRONIC VIRAL INFECTIONS AND COVID-19: A REVIEW. CORONAVIRUS DISEASE 2019 (COVID-19) CONTINUOUSLY AFFECTING THE LIVES OF MILLIONS OF PEOPLE. THE VIRUS IS SPREAD THROUGH THE RESPIRATORY ROUTE TO AN UNINFECTED PERSON, CAUSING MILD-TO-MODERATE RESPIRATORY DISEASE-LIKE SYMPTOMS THAT SOMETIMES PROGRESS TO SEVERE FORM AND CAN BE FATAL. WHEN THE HOST IS INFECTED WITH THE VIRUS, BOTH INNATE AND ADAPTIVE IMMUNITY COMES INTO PLAY. THE EFFECTOR T CELLS ACT AS THE MASTER PLAYER OF ADAPTIVE IMMUNE RESPONSE IN ERADICATING THE VIRUS FROM THE SYSTEM. BUT DURING CANCER AND CHRONIC VIRAL INFECTIONS, THE FATE OF AN EFFECTOR T CELL IS ALTERED, AND THE T CELL MAY ENTERS A STATE OF EXHAUSTION, WHICH IS MARKED BY LOSS OF EFFECTOR FUNCTION, DEPLETED PROLIFERATIVE CAPACITY AND CYTOTOXIC EFFECT ACCOMPLISHED BY AN INCREASED EXPRESSION OF NUMEROUS INHIBITORY RECEPTORS SUCH AS PROGRAMMED CELL DEATH PROTEIN 1 (PD-1), LYMPHOCYTE-ACTIVATION PROTEIN 3 (LAG-3), AND CYTOTOXIC T LYMPHOCYTE-ASSOCIATED ANTIGEN 4 (CTLA-4) ON THEIR SURFACE. VARIOUS OTHER TRANSCRIPTIONAL AND EPIGENETIC CHANGES TAKE PLACE INSIDE THE T CELL WHEN IT ENTERS INTO AN EXHAUSTED STATE. LATEST STUDIES POINT TOWARD THE INDUCTION OF AN ABNORMAL IMMUNE RESPONSE SUCH AS LYMPHOPENIA, CYTOKINE STORM, AND T CELL EXHAUSTION DURING SARS-COV-2 (SEVERE ACUTE RESPIRATORY SYNDROME CORONAVIRUS 2) INFECTION. THIS REVIEW SHEDS LIGHT ON THE DYSFUNCTIONAL STATE OF T CELLS DURING CHRONIC VIRAL INFECTION AND COVID-19. UNDERSTANDING THE CAUSE AND THE EFFECT OF T CELL EXHAUSTION OBSERVED DURING COVID-19 MAY HELP RESOLVE NEW THERAPEUTIC POTENTIALS FOR TREATING CHRONIC INFECTIONS AND OTHER DISEASES. 2022 15 771 33 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 16 1313 35 DELETING DNMT3A IN CAR T CELLS PREVENTS EXHAUSTION AND ENHANCES ANTITUMOR ACTIVITY. CHIMERIC ANTIGEN RECEPTOR (CAR) T CELL THERAPY IS REVOLUTIONIZING CANCER IMMUNOTHERAPY FOR PATIENTS WITH B CELL MALIGNANCIES AND IS NOW BEING DEVELOPED FOR SOLID TUMORS AND CHRONIC VIRAL INFECTIONS. ALTHOUGH CLINICAL TRIALS HAVE DEMONSTRATED THE CURATIVE POTENTIAL OF CAR T CELL THERAPY, A SUBSTANTIAL AND WELL-ESTABLISHED LIMITATION IS THE HEIGHTENED CONTRACTION AND TRANSIENT PERSISTENCE OF CAR T CELLS DURING PROLONGED ANTIGEN EXPOSURE. THE UNDERLYING MECHANISM(S) FOR THIS DYSFUNCTIONAL STATE, OFTEN TERMED CAR T CELL EXHAUSTION, REMAINS POORLY DEFINED. HERE, WE REPORT THAT EXHAUSTION OF HUMAN CAR T CELLS OCCURS THROUGH AN EPIGENETIC REPRESSION OF THE T CELL'S MULTIPOTENT DEVELOPMENTAL POTENTIAL. DELETION OF THE DE NOVO DNA METHYLTRANSFERASE 3 ALPHA (DNMT3A) IN T CELLS EXPRESSING FIRST- OR SECOND-GENERATION CARS UNIVERSALLY PRESERVED THE CELLS' ABILITY TO PROLIFERATE AND MOUNT AN ANTITUMOR RESPONSE DURING PROLONGED TUMOR EXPOSURE. THE INCREASED FUNCTIONALITY OF THE EXHAUSTION-RESISTANT DNMT3A KNOCKOUT CAR T CELLS WAS COUPLED TO AN UP-REGULATION OF INTERLEUKIN-10, AND GENOME-WIDE DNA METHYLATION PROFILING DEFINED AN ATLAS OF GENES TARGETED FOR EPIGENETIC SILENCING. THIS ATLAS PROVIDES A MOLECULAR DEFINITION OF CAR T CELL EXHAUSTION, WHICH INCLUDES MANY TRANSCRIPTIONAL REGULATORS THAT LIMIT THE "STEMNESS" OF IMMUNE CELLS, INCLUDING CD28, CCR7, TCF7, AND LEF1. LAST, WE DEMONSTRATE THAT THIS EPIGENETICALLY REGULATED MULTIPOTENCY PROGRAM IS FIRMLY COUPLED TO THE CLINICAL OUTCOME OF PRIOR CAR T CELL THERAPIES. THESE DATA DOCUMENT THE CRITICAL ROLE EPIGENETIC MECHANISMS PLAY IN LIMITING THE FATE POTENTIAL OF HUMAN T CELLS AND PROVIDE A ROAD MAP FOR LEVERAGING THIS INFORMATION FOR IMPROVING CAR T CELL EFFICACY. 2021 17 6060 33 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 18 1759 33 EARLY PRECURSOR T CELLS ESTABLISH AND PROPAGATE T CELL EXHAUSTION IN CHRONIC INFECTION. CD8(+) T CELLS RESPONDING TO CHRONIC INFECTIONS OR TUMORS ACQUIRE AN 'EXHAUSTED' STATE ASSOCIATED WITH ELEVATED EXPRESSION OF INHIBITORY RECEPTORS, INCLUDING PD-1, AND IMPAIRED CYTOKINE PRODUCTION. EXHAUSTED T CELLS ARE CONTINUOUSLY REPLENISHED BY T CELLS WITH PRECURSOR CHARACTERISTICS THAT SELF-RENEW AND DEPEND ON THE TRANSCRIPTION FACTOR TCF1; HOWEVER, THEIR DEVELOPMENTAL REQUIREMENTS ARE POORLY UNDERSTOOD. IN THE PRESENT STUDY, WE DEMONSTRATE THAT HIGH ANTIGEN LOAD PROMOTED THE DIFFERENTIATION OF PRECURSOR T CELLS, WHICH ACQUIRED HALLMARKS OF EXHAUSTION WITHIN DAYS OF INFECTION, WHEREAS EARLY EFFECTOR CELLS RETAINED POLYFUNCTIONAL FEATURES. EARLY PRECURSOR T CELLS SHOWED EPIGENETIC IMPRINTING CHARACTERISTIC OF T CELL RECEPTOR-DEPENDENT TRANSCRIPTION FACTOR BINDING AND WERE RESTRICTED TO THE GENERATION OF CELLS DISPLAYING EXHAUSTION CHARACTERISTICS. TRANSCRIPTION FACTORS BACH2 AND BATF WERE KEY REGULATORS WITH OPPOSING FUNCTIONS IN THE GENERATION OF EARLY PRECURSOR T CELLS. OVERALL, WE DEMONSTRATE THAT EXHAUSTION MANIFESTS FIRST IN TCF1(+) PRECURSOR T CELLS AND IS PROPAGATED SUBSEQUENTLY TO THE POOL OF ANTIGEN-SPECIFIC T CELLS. 2020 19 6590 22 TUMOR SUPPRESSOR INACTIVATION IN THE PATHOGENESIS OF ADULT T-CELL LEUKEMIA. TUMOR SUPPRESSOR FUNCTIONS ARE ESSENTIAL TO CONTROL CELLULAR PROLIFERATION, TO ACTIVATE THE APOPTOSIS OR SENESCENCE PATHWAY TO ELIMINATE UNWANTED CELLS, TO LINK DNA DAMAGE SIGNALS TO CELL CYCLE ARREST CHECKPOINTS, TO ACTIVATE APPROPRIATE DNA REPAIR PATHWAYS, AND TO PREVENT THE LOSS OF ADHESION TO INHIBIT INITIATION OF METASTASES. THEREFORE, TUMOR SUPPRESSOR GENES ARE INDISPENSABLE TO MAINTAINING GENETIC AND GENOMIC INTEGRITY. CONSEQUENTLY, INACTIVATION OF TUMOR SUPPRESSORS BY SOMATIC MUTATIONS OR EPIGENETIC MECHANISMS IS FREQUENTLY ASSOCIATED WITH TUMOR INITIATION AND DEVELOPMENT. IN CONTRAST, REACTIVATION OF TUMOR SUPPRESSOR FUNCTIONS CAN EFFECTIVELY REVERSE THE TRANSFORMED PHENOTYPE AND LEAD TO CELL CYCLE ARREST OR DEATH OF CANCEROUS CELLS AND BE USED AS A THERAPEUTIC STRATEGY. ADULT T-CELL LEUKEMIA/LYMPHOMA (ATLL) IS AN AGGRESSIVE LYMPHOPROLIFERATIVE DISEASE ASSOCIATED WITH INFECTION OF CD4 T CELLS BY THE HUMAN T-CELL LEUKEMIA VIRUS TYPE 1 (HTLV-I). HTLV-I-ASSOCIATED T-CELL TRANSFORMATION IS THE RESULT OF A MULTISTEP ONCOGENIC PROCESS IN WHICH THE VIRUS INITIALLY INDUCES CHRONIC T-CELL PROLIFERATION AND ALTERS CELLULAR PATHWAYS RESULTING IN THE ACCUMULATION OF GENETIC DEFECTS AND THE DEREGULATED GROWTH OF VIRALLY INFECTED CELLS. THIS REVIEW WILL FOCUS ON THE CURRENT KNOWLEDGE OF THE GENETIC AND EPIGENETIC MECHANISMS REGULATING THE INACTIVATION OF TUMOR SUPPRESSORS IN THE PATHOGENESIS OF HTLV-I. 2015 20 835 27 CHEMICAL CARCINOGEN MECHANISMS OF ACTION AND IMPLICATIONS FOR TESTING METHODOLOGY. CHEMICAL CARCINOGENS ARE OF TWO DISTINCT TYPES, DNA-REACTIVE AND EPIGENETIC. TESTING METHODOLOGY CAN BE DIRECTED TOWARD DETECTING EFFECTS OF BOTH TYPES OF CARCINOGEN. CARCINOGENS OF THE DNA-REACTIVE TYPE ARE DEFINED BY THE FORMATION OF COVALENTLY BOUND DNA ADDUCTS. THESE CHEMICALS HAVE STRUCTURES THAT YIELD ELECTROPHILIC REACTANTS EITHER DIRECTLY OR AFTER BIOACTIVATION. THESE AGENTS CAUSE GENOMIC ALTERATION IN THE STRUCTURE OR FUNCTION OF DNA IN THE TARGET CELL. IN ADDITION, THESE COMPOUNDS CAN EXERT OTHER CELLULAR AND TISSUE EPIGENETIC EFFECTS, SUCH AS CELL PROLIFERATION AND GROWTH PROMOTION. CARCINOGENS OF THE EPIGENETIC (PARAGENETIC) TYPE, IN CONTRAST, DO NOT REACT WITH DNA, BUT RATHER DISPLAY CELLULAR EFFECTS SUCH AS NEOPLASM GROWTH PROMOTION, CYTOTOXICITY, INHIBITION OF TISSUE GROWTH REGULATION, PEROXISOME PROLIFERATION, ENDOCRINE MODIFICATION, IMMUNOSUPPRESSION AND/OR SUSTAINED TISSUE ISCHEMIA THAT CAN BE THE BASIS FOR INCREASES IN NEOPLASIA. THEIR CHEMICAL STRUCTURE IS SUCH THAT THEY DO NOT GIVE RISE TO A REACTIVE ELECTROPHILE. THE TESTING METHODOLOGIES TO IDENTIFY EITHER TYPE FOLLOW A DECISION POINT APPROACH DESIGNED TO IDENTIFY POTENTIAL CARCINOGENICITY AND YIELD MECHANISTIC INFORMATION ON THE PRODUCTION OF EFFECTS THAT UNDERLIE CARCINOGENICITY. IT HAS 5 STAGES FOCUSING ON THE CHEMICAL STRUCTURE, DNA-REACTIVITY, EPIGENETIC EFFECTS, LIMITED BIOASSAYS AND FINALLY THE APPLICATION OF THE ACCELERATED BIOASSAY (ABA). ABA REQUIRES 40 WEEKS AND APPLIES THE USE OF SENSITIVE MARKERS FOR INDUCTION OF NEOPLASIA IN COMPARISON TO POSITIVE CONTROL COMPOUNDS FOR IMPORTANT ORGANS IN HUMAN CARCINOGENESIS. IT ENABLES DATA ACQUISITION OF THE ENTIRE CARCINOGENIC PROCESS DIRECTED TOWARD DEVELOPING MECHANISTIC INFORMATION. THE ABA HAS THE POTENTIAL TO REPLACE THE CHRONIC BIOASSAY IN RODENTS IN SOME CIRCUMSTANCES AND CAN SERVE AS AN ALTERNATIVE TO A CHRONIC BIOASSAY IN A SECOND SPECIES. 1996