1 1054 119 CLINICAL IMPLICATIONS OF T CELL EXHAUSTION FOR CANCER IMMUNOTHERAPY. IMMUNOTHERAPY HAS BEEN A REMARKABLE CLINICAL ADVANCEMENT IN THE TREATMENT OF CANCER. T CELLS ARE PIVOTAL TO THE EFFICACY OF CURRENT CANCER IMMUNOTHERAPIES, INCLUDING IMMUNE-CHECKPOINT INHIBITORS AND ADOPTIVE CELL THERAPIES. HOWEVER, CANCER IS ASSOCIATED WITH T CELL EXHAUSTION, A HYPOFUNCTIONAL STATE CHARACTERIZED BY PROGRESSIVE LOSS OF T CELL EFFECTOR FUNCTIONS AND SELF-RENEWAL CAPACITY. THE 'UN-EXHAUSTING' OF T CELLS IN THE TUMOUR MICROENVIRONMENT IS COMMONLY REGARDED AS A KEY MECHANISM OF ACTION FOR IMMUNE-CHECKPOINT INHIBITORS, AND T CELL EXHAUSTION IS CONSIDERED A PATHWAY OF RESISTANCE FOR CELLULAR IMMUNOTHERAPIES. SEVERAL ELEGANT STUDIES HAVE PROVIDED IMPORTANT INSIGHTS INTO THE TRANSCRIPTIONAL AND EPIGENETIC PROGRAMMES THAT GOVERN T CELL EXHAUSTION. IN THIS REVIEW, WE HIGHLIGHT RECENT DISCOVERIES RELATED TO THE IMMUNOBIOLOGY OF T CELL EXHAUSTION THAT OFFER A MORE NUANCED PERSPECTIVE BEYOND THIS HYPOFUNCTIONAL STATE BEING ENTIRELY UNDESIRABLE. WE REVIEW EVIDENCE THAT T CELL EXHAUSTION MIGHT BE AS MUCH A REFLECTION AS IT IS THE CAUSE OF POOR TUMOUR CONTROL. FURTHERMORE, WE HYPOTHESIZE THAT, IN CERTAIN CONTEXTS OF CHRONIC ANTIGEN STIMULATION, INTERRUPTION OF THE EXHAUSTION PROGRAMME MIGHT IMPAIR T CELL PERSISTENCE. THEREFORE, THE PRIORITIZATION OF INTERVENTIONS THAT MITIGATE THE DEVELOPMENT OF T CELL EXHAUSTION, INCLUDING ORTHOGONAL CYTOREDUCTION THERAPIES AND NOVEL CELLULAR ENGINEERING STRATEGIES, MIGHT ULTIMATELY CONFER SUPERIOR CLINICAL OUTCOMES AND THE GREATEST ADVANCES IN CANCER IMMUNOTHERAPY. 2022 2 5689 34 SILENCING HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA: THE POTENTIAL OF AN EPIGENETIC THERAPY APPROACH. GLOBAL PROPHYLACTIC VACCINATION PROGRAMMES HAVE HELPED TO CURB NEW HEPATITIS B VIRUS (HBV) INFECTIONS. HOWEVER, IT IS ESTIMATED THAT NEARLY 300 MILLION PEOPLE ARE CHRONICALLY INFECTED AND HAVE A HIGH RISK OF DEVELOPING HEPATOCELLULAR CARCINOMA. AS SUCH, HBV REMAINS A SERIOUS HEALTH PRIORITY AND THE DEVELOPMENT OF NOVEL CURATIVE THERAPEUTICS IS URGENTLY NEEDED. CHRONIC HBV INFECTION HAS BEEN ATTRIBUTED TO THE PERSISTENCE OF THE COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) WHICH ESTABLISHES ITSELF AS A MINICHROMOSOME IN THE NUCLEUS OF HEPATOCYTES. AS THE VIRAL TRANSCRIPTION INTERMEDIATE, THE CCCDNA IS RESPONSIBLE FOR PRODUCING NEW VIRIONS AND PERPETUATING INFECTION. HBV IS DEPENDENT ON VARIOUS HOST FACTORS FOR CCCDNA FORMATION AND THE MINICHROMOSOME IS AMENABLE TO EPIGENETIC MODIFICATIONS. TWO HBV PROTEINS, X (HBX) AND CORE (HBC) PROMOTE VIRAL REPLICATION BY MODULATING THE CCCDNA EPIGENOME AND REGULATING HOST CELL RESPONSES. THIS INCLUDES VIRAL AND HOST GENE EXPRESSION, CHROMATIN REMODELING, DNA METHYLATION, THE ANTIVIRAL IMMUNE RESPONSE, APOPTOSIS, AND UBIQUITINATION. ELIMINATION OF THE CCCDNA MINICHROMOSOME WOULD RESULT IN A STERILIZING CURE; HOWEVER, THIS MAY BE DIFFICULT TO ACHIEVE. EPIGENETIC THERAPIES COULD PERMANENTLY SILENCE THE CCCDNA MINICHROMOSOME AND PROMOTE A FUNCTIONAL CURE. THIS REVIEW EXPLORES THE CCCDNA EPIGENOME, HOW HOST AND VIRAL FACTORS INFLUENCE TRANSCRIPTION, AND THE RECENT EPIGENETIC THERAPIES AND EPIGENOME ENGINEERING APPROACHES THAT HAVE BEEN DESCRIBED. 2021 3 4056 36 MAPPING THE HETEROGENEITY OF HISTONE MODIFICATIONS ON HEPATITIS B VIRUS DNA USING LIVER NEEDLE BIOPSIES OBTAINED FROM CHRONICALLY INFECTED PATIENTS. COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) FORMS THE BASIS FOR REPLICATION AND PERSISTENCE OF HEPATITIS B VIRUS (HBV) IN THE CHRONICALLY INFECTED LIVER. WE HAVE PREVIOUSLY SHOWN THAT VIRAL TRANSCRIPTION IS SUBJECT TO REGULATION BY POSTTRANSLATIONAL MODIFICATIONS (PTMS) OF HISTONE PROTEINS BOUND TO CCCDNA THROUGH ANALYSIS OF DE NOVO HBV-INFECTED CELL LINES. WE NOW REPORT THE SUCCESSFUL ADAPTATION OF THIS CHROMATIN IMMUNOPRECIPITATION SEQUENCING (CHIPSEQ) APPROACH FOR ANALYSIS OF FINE-NEEDLE PATIENT LIVER BIOPSY SPECIMENS TO INVESTIGATE THE ROLE OF HISTONE PTMS IN CHRONICALLY HBV-INFECTED PATIENTS. USING 18 SPECIMENS FROM PATIENTS IN DIFFERENT STAGES OF CHRONIC HBV INFECTION, OUR WORK SHOWS THAT THE PROFILE OF HISTONE PTMS IN CHRONIC INFECTION IS MORE NUANCED THAN PREVIOUSLY OBSERVED IN IN VITRO MODELS OF ACUTE INFECTION. IN LINE WITH OUR PREVIOUS FINDINGS, WE FIND THAT THE MAJORITY OF HBV-DERIVED SEQUENCES ARE ASSOCIATED WITH THE ACTIVATING HISTONE PTM H3K4ME3. HOWEVER, WE SHOW A STRIKING INTERPATIENT VARIABILITY OF ITS DEPOSITION IN THIS PATIENT COHORT CORRELATED WITH VIRAL TRANSCRIPTION AND PATIENT HBV EARLY ANTIGEN (HBEAG) STATUS. UNEXPECTEDLY, WE DETECTED DEPOSITION OF THE CLASSICAL INHIBITORY HISTONE PTM H3K9ME3 ON HBV-DNA IN AROUND HALF OF THE PATIENT BIOPSY SPECIMENS, WHICH COULD NOT BE LINKED TO REDUCED LEVELS OF VIRAL TRANSCRIPTS. OUR RESULTS SHOW THAT CURRENT IN VITRO MODELS ARE UNABLE TO FULLY RECAPITULATE THE COMPLEX EPIGENETIC LANDSCAPE OF CHRONIC HBV INFECTION OBSERVED IN VIVO AND DEMONSTRATE THAT FINE-NEEDLE LIVER BIOPSY SPECIMENS CAN PROVIDE SUFFICIENT MATERIAL TO FURTHER INVESTIGATE THE INTERACTION OF VIRAL AND HOST PROTEINS ON HBV-DNA.IMPORTANCE HEPATITIS B VIRUS (HBV) IS A MAJOR GLOBAL HEALTH CONCERN, CHRONICALLY INFECTING MILLIONS OF PATIENTS AND CONTRIBUTING TO A RISING BURDEN OF LIVER DISEASE. THE VIRAL GENOME FORMS THE BASIS FOR CHRONIC INFECTION AND HAS BEEN SHOWN TO BE SUBJECT TO REGULATION BY EPIGENETIC MECHANISMS, SUCH AS POSTTRANSLATIONAL MODIFICATION OF HISTONE PROTEINS. HERE, WE CONFIRM AND EXPAND ON PREVIOUS RESULTS BY ADAPTING A HIGH-RESOLUTION TECHNIQUE FOR ANALYSIS OF HISTONE MODIFICATIONS FOR USE WITH PATIENT-DERIVED FINE-NEEDLE LIVER BIOPSY SPECIMENS. OUR WORK HIGHLIGHTS THAT THE SITUATION IN VIVO IS MORE COMPLEX THAN PREDICTED BY CURRENT IN VITRO MODELS, FOR EXAMPLE, BY SUGGESTING A NOVEL, NONCANONICAL ROLE OF THE HISTONE MODIFICATION H3K9ME3 IN THE HBV LIFE CYCLE. IMPORTANTLY, ENABLING THE USE OF FINE-NEEDLE LIVER BIOPSY SPECIMENS FOR SUCH HIGH-RESOLUTION ANALYSES MAY FACILITATE FURTHER RESEARCH INTO THE EPIGENETIC REGULATION OF THE HBV GENOME. 2019 4 4055 29 MAPPING OF HISTONE MODIFICATIONS IN EPISOMAL HBV CCCDNA UNCOVERS AN UNUSUAL CHROMATIN ORGANIZATION AMENABLE TO EPIGENETIC MANIPULATION. CHRONIC HEPATITIS B VIRUS (HBV) INFECTION AFFECTS 240 MILLION PEOPLE WORLDWIDE AND IS A MAJOR RISK FACTOR FOR LIVER FAILURE AND HEPATOCELLULAR CARCINOMA. CURRENT ANTIVIRAL THERAPY INHIBITS CYTOPLASMIC HBV GENOMIC REPLICATION, BUT IS NOT CURATIVE BECAUSE IT DOES NOT DIRECTLY AFFECT NUCLEAR HBV CLOSED CIRCULAR DNA (CCCDNA), THE GENOMIC FORM THAT TEMPLATES VIRAL TRANSCRIPTION AND SUSTAINS VIRAL PERSISTENCE. NOVEL APPROACHES THAT DIRECTLY TARGET CCCDNA REGULATION WOULD THEREFORE BE HIGHLY DESIRABLE. CCCDNA IS ASSEMBLED WITH CELLULAR HISTONE PROTEINS INTO CHROMATIN, BUT LITTLE IS KNOWN ABOUT THE REGULATION OF HBV CHROMATIN BY HISTONE POSTTRANSLATIONAL MODIFICATIONS (PTMS). HERE, USING A NEW CCCDNA CHIP-SEQ APPROACH, WE REPORT, TO OUR KNOWLEDGE, THE FIRST GENOME-WIDE MAPS OF PTMS IN CCCDNA-CONTAINING CHROMATIN FROM DE NOVO INFECTED HEPG2 CELLS, PRIMARY HUMAN HEPATOCYTES, AND FROM HBV-INFECTED LIVER TISSUE. WE FIND HIGH LEVELS OF PTMS ASSOCIATED WITH ACTIVE TRANSCRIPTION ENRICHED AT SPECIFIC SITES WITHIN THE HBV GENOME AND, SURPRISINGLY, VERY LOW LEVELS OF PTMS LINKED TO TRANSCRIPTIONAL REPRESSION EVEN AT SILENT HBV PROMOTERS. WE SHOW THAT TRANSCRIPTION AND ACTIVE PTMS IN HBV CHROMATIN ARE REDUCED BY THE ACTIVATION OF AN INNATE IMMUNITY PATHWAY, AND THAT THIS EFFECT CAN BE RECAPITULATED WITH A SMALL MOLECULE EPIGENETIC MODIFYING AGENT, OPENING THE POSSIBILITY THAT CHROMATIN-BASED REGULATION OF CCCDNA TRANSCRIPTION COULD BE A NEW THERAPEUTIC APPROACH TO CHRONIC HBV INFECTION. 2015 5 5365 27 RECENT ADVANCES IN HEPATITIS B TREATMENT. HEPATITIS B VIRUS INFECTION AFFECTS OVER 250 MILLION CHRONIC CARRIERS, CAUSING MORE THAN 800,000 DEATHS ANNUALLY, ALTHOUGH A SAFE AND EFFECTIVE VACCINE IS AVAILABLE. CURRENTLY USED ANTIVIRAL AGENTS, PEGYLATED INTERFERON AND NUCLEOS(T)IDE ANALOGUES, HAVE MAJOR DRAWBACKS AND FAIL TO COMPLETELY ERADICATE THE VIRUS FROM INFECTED CELLS. THUS, ACHIEVING A "FUNCTIONAL CURE" OF THE INFECTION REMAINS A REAL CHALLENGE. RECENT FINDINGS CONCERNING THE VIRAL REPLICATION CYCLE HAVE LED TO DEVELOPMENT OF NOVEL THERAPEUTIC APPROACHES INCLUDING VIRAL ENTRY INHIBITORS, EPIGENETIC CONTROL OF CCCDNA, IMMUNE MODULATORS, RNA INTERFERENCE TECHNIQUES, RIBONUCLEASE H INHIBITORS, AND CAPSID ASSEMBLY MODULATORS. PROMISING PRECLINICAL RESULTS HAVE BEEN OBTAINED, AND THE LEADING MOLECULES UNDER DEVELOPMENT HAVE ENTERED CLINICAL EVALUATION. THIS REVIEW SUMMARIZES THE KEY STEPS OF THE HBV LIFE CYCLE, EXAMINES THE CURRENTLY APPROVED ANTI-HBV DRUGS, AND ANALYZES NOVEL HBV TREATMENT REGIMENS. 2021 6 5368 26 RECENT ADVANCES IN THE STUDY OF HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA. CHRONIC HEPATITIS B INFECTION IS CAUSED BY HEPATITIS B VIRUS (HBV) AND A TOTAL CURE IS YET TO BE ACHIEVED. THE VIRAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IS THE KEY TO ESTABLISH A PERSISTENT INFECTION WITHIN HEPATOCYTES. CURRENT ANTIVIRAL STRATEGIES HAVE NO EFFECT ON THE PRE-EXISTING CCCDNA RESERVOIR. THEREFORE, THE STUDY OF THE MOLECULAR MECHANISM OF CCCDNA FORMATION IS BECOMING A MAJOR FOCUS OF HBV RESEARCH. THIS REVIEW SUMMARIZES THE CURRENT ADVANCES IN CCCDNA MOLECULAR BIOLOGY AND THE LATEST STUDIES ON THE ELIMINATION OR INACTIVATION OF CCCDNA, INCLUDING THREE MAJOR AREAS: (1) EPIGENETIC REGULATION OF CCCDNA BY HBV X PROTEIN, (2) IMMUNE-MEDIATED DEGRADATION, AND (3) GENOME-EDITING NUCLEASES. ALL THESE ASPECTS PROVIDE CLUES ON HOW TO FINALLY ATTAIN A CURE FOR CHRONIC HEPATITIS B INFECTION. 2017 7 2915 34 GENE THERAPY FOR CHRONIC HBV-CAN WE ELIMINATE CCCDNA? CHRONIC INFECTION WITH THE HEPATITIS B VIRUS (HBV) IS A GLOBAL HEALTH CONCERN AND ACCOUNTS FOR APPROXIMATELY 1 MILLION DEATHS ANNUALLY. AMONGST OTHER LIMITATIONS OF CURRENT ANTI-HBV TREATMENT, FAILURE TO ELIMINATE THE VIRAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) AND EMERGENCE OF RESISTANCE REMAIN THE MOST WORRISOME. VIRAL REBOUND FROM LATENT EPISOMAL CCCDNA RESERVOIRS OCCURS FOLLOWING CESSATION OF THERAPY, PATIENT NON-COMPLIANCE, OR THE DEVELOPMENT OF ESCAPE MUTANTS. SIMULTANEOUS VIRAL CO-INFECTIONS, SUCH AS BY HIV-1, FURTHER COMPLICATE THERAPEUTIC INTERVENTIONS. THESE CHALLENGES HAVE PROMPTED DEVELOPMENT OF NOVEL TARGETED HEPATITIS B THERAPIES. GIVEN THE EASE WITH WHICH HIGHLY SPECIFIC AND POTENT NUCLEIC ACID THERAPEUTICS CAN BE RATIONALLY DESIGNED, GENE THERAPY HAS GENERATED INTEREST FOR ANTIVIRAL APPLICATION. GENE THERAPY STRATEGIES DEVELOPED FOR HBV INCLUDE GENE SILENCING BY HARNESSING RNA INTERFERENCE, TRANSCRIPTIONAL INHIBITION THROUGH EPIGENETIC MODIFICATION OF TARGET DNA, GENOME EDITING BY DESIGNER NUCLEASES, AND IMMUNE MODULATION WITH CYTOKINES. DNA-BINDING DOMAINS AND EFFECTORS BASED ON THE ZINC FINGER (ZF), TRANSCRIPTION ACTIVATOR-LIKE EFFECTOR (TALE), AND CLUSTERED REGULARLY INTERSPACED SHORT PALINDROMIC REPEAT (CRISPR) SYSTEMS ARE REMARKABLY WELL SUITED TO TARGETING EPISOMAL CCCDNA. THIS REVIEW DISCUSSES RECENT DEVELOPMENTS AND CHALLENGES FACING THE FIELD OF ANTI-HBV GENE THERAPY, ITS POTENTIAL CURATIVE SIGNIFICANCE AND THE PROGRESS TOWARDS CLINICAL APPLICATION. 2018 8 5936 22 TARGETING HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA AND HEPATITIS B VIRUS X PROTEIN: RECENT ADVANCES AND NEW APPROACHES. CHRONIC HEPATITIS B VIRUS (HBV) INFECTION REMAINS A WORLDWIDE CONCERN AND PUBLIC HEALTH PROBLEM. TWO KEY ASPECTS OF THE HBV LIFE CYCLE ARE ESSENTIAL FOR VIRAL REPLICATION AND THUS THE DEVELOPMENT OF CHRONIC INFECTIONS: THE ESTABLISHMENT OF THE VIRAL MINICHROMOSOME, COVALENTLY CLOSED CIRCULAR (CCC) DNA, WITHIN THE NUCLEUS OF INFECTED HEPATOCYTES AND THE EXPRESSION OF THE REGULATORY HEPATITIS B VIRUS X PROTEIN (HBX). INTERESTINGLY, NUCLEAR HBX REDIRECTS HOST EPIGENETIC MACHINERY TO ACTIVATE CCCDNA TRANSCRIPTION. IN THIS PERSPECTIVE, WE PROVIDE AN OVERVIEW OF RECENT ADVANCES IN UNDERSTANDING THE REGULATION OF CCCDNA AND THE MECHANISTIC AND FUNCTIONAL ROLES OF HBX. WE ALSO DESCRIBE THE PROGRESS TOWARD TARGETING BOTH CCCDNA AND HBX FOR THERAPEUTIC PURPOSES. FINALLY, WE OUTLINE STANDING QUESTIONS IN THE FIELD AND PROPOSE COMPLEMENTARY CHEMICAL BIOLOGY APPROACHES TO ADDRESS THEM. 2019 9 5952 39 TARGETING VIRAL CCCDNA FOR CURE OF CHRONIC HEPATITIS B. PURPOSE OF REVIEW: CHRONIC HEPATITIS B (CHB), CAUSED BY HEPATITIS B VIRUS (HBV), IS A MAJOR CAUSE OF ADVANCED LIVER DISEASE AND HEPATOCELLULAR CARCINOMA (HCC) WORLDWIDE. HBV REPLICATION IS CHARACTERIZED BY THE SYNTHESIS OF COVALENTLY CLOSED CIRCULAR (CCC) DNA WHICH IS NOT TARGETED BY ANTIVIRAL NUCLEOS(T)IDE ANALOGUES (NUCS) THE KEY MODALITY OF STANDARD OF CARE. WHILE HBV REPLICATION IS SUCCESSFULLY SUPPRESSED IN TREATED PATIENTS, THEY REMAIN AT RISK FOR DEVELOPING HCC. WHILE FUNCTIONAL CURE, CHARACTERIZED BY LOSS OF HBSAG, IS THE FIRST GOAL OF NOVEL ANTIVIRAL THERAPIES, CURATIVE TREATMENTS ELIMINATING CCCDNA REMAIN THE ULTIMATE GOAL. THIS REVIEW SUMMARIZES RECENT ADVANCES IN THE DISCOVERY AND DEVELOPMENT OF NOVEL THERAPEUTIC STRATEGIES AND THEIR IMPACT ON CCCDNA BIOLOGY. RECENT FINDINGS: WITHIN THE LAST DECADE, SUBSTANTIAL PROGRESS HAS BEEN MADE IN THE UNDERSTANDING OF CCCDNA BIOLOGY INCLUDING THE DISCOVERY OF HOST DEPENDENCY FACTORS, EPIGENETIC REGULATION OF CCCDNA TRANSCRIPTION AND IMMUNE-MEDIATED DEGRADATION. SEVERAL APPROACHES TARGETING CCCDNA EITHER IN A DIRECT OR INDIRECT MANNER ARE CURRENTLY AT THE STAGE OF DISCOVERY, PRECLINICAL OR EARLY CLINICAL DEVELOPMENT. EXAMPLES INCLUDE GENOME-EDITING APPROACHES, STRATEGIES TARGETING HOST DEPENDENCY FACTORS OR EPIGENETIC GENE REGULATION, NUCLEOCAPSID MODULATORS AND IMMUNE-MEDIATED DEGRADATION. SUMMARY: WHILE DIRECT-TARGETING CCCDNA STRATEGIES ARE STILL LARGELY AT THE PRECLINICAL STAGE OF DEVELOPMENT, CAPSID ASSEMBLY MODULATORS AND IMMUNE-BASED APPROACHES HAVE REACHED THE CLINICAL PHASE. CLINICAL TRIALS ARE ONGOING TO ASSESS THEIR EFFICACY AND SAFETY IN PATIENTS INCLUDING THEIR IMPACT ON VIRAL CCCDNA. COMBINATION THERAPIES PROVIDE ADDITIONAL OPPORTUNITIES TO OVERCOME CURRENT LIMITATIONS OF INDIVIDUAL APPROACHES. 2020 10 3185 24 HBC BINDS TO THE CPG ISLANDS OF HBV CCCDNA AND PROMOTES AN EPIGENETIC PERMISSIVE STATE. HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IS THE TEMPLATE FOR THE TRANSCRIPTION OF HBV. HBV CORE PROTEIN (HBC) IS A MAIN COMPONENT OF THE HBV CCCDNA MINICHROMOSOME. HOWEVER, THE FUNCTION OF HBC IN CCCDNA IS NOT FULLY UNDERSTOOD. IN LIGHT OF RECENT FINDINGS THAT HBV CCCDNA MAY BE REGULATED EPIGENETICALLY, WE ANALYZED THE BINDING OF HBC TO CCCDNA AND THE IMPACT OF HBC ON CCCDNA EPIGENETIC PROFILE IN THE LIVER BIOPSY SAMPLES OF 22 PATIENTS WITH CHRONIC HEPATITIS B (CHB). WE FOUND THAT HBC BINDING TO HBV CCCDNA OCCURRED PREFERENTIALLY AT CPG ISLAND 2, AN IMPORTANT REGION FOR THE REGULATION OF HBV TRANSCRIPTION. FURTHERMORE, THE RELATIVE ABUNDANCES OF HBC BINDING TO CPG ISLAND 2 WERE POSITIVELY CORRELATED WITH THE RATIOS OF RELAXED CIRCULAR DNA TO CCCDNA AND THE LEVELS OF SERUM HBV DNA IN THOSE PATIENTS. INTERESTINGLY, THE RELATIVE ABUNDANCES OF HBC BINDING TO CPG ISLAND 2 WERE ASSOCIATED WITH THE BINDING OF CREB BINDING PROTEIN (CBP) AND WITH HYPOMETHYLATION IN CPG ISLAND 2 OF HBV CCCDNA MINICHROMOSOMES. HOWEVER, RELATIVELY HIGHER AMOUNTS OF HBC BINDING TO CPG ISLAND 2 OF CCCDNA WERE ACCOMPANIED BY LOWER AMOUNTS OF HDAC1 BINDING. MULTIVARIATE ANALYSIS REVEALED THAT THE ABUNDANCES OF HBC BINDING TO CPG ISLAND 2 OF CCCDNA AND POSITIVE HBEAG WERE INDEPENDENT FACTORS ASSOCIATED WITH THE REPLICATION OF HBV (P = 0.001 FOR BOTH). APPARENTLY, HBC IS A POSITIVE REGULATOR OF HBV TRANSCRIPTION AND REPLICATION, MAINTAINING THE PERMISSIVE EPIGENETIC STATE IN THE CRITICAL REGION OF THE HBV CCCDNA MINICHROMOSOMES. 2011 11 2240 25 EPIGENETIC MODULATION IN CHRONIC HEPATITIS B VIRUS INFECTION. THE HUMAN HEPATITIS B VIRUS (HBV) IS A SMALL-ENVELOPED DNA VIRUS CAUSING ACUTE AND CHRONIC HEPATITIS. DESPITE THE EXISTENCE OF AN EFFECTIVE PROPHYLACTIC VACCINE AND THE STRONG CAPACITY OF APPROVED ANTIVIRAL DRUGS TO SUPPRESS VIRAL REPLICATION, CHRONIC HBV INFECTION (CHB) CONTINUES TO BE A MAJOR HEALTH BURDEN WORLDWIDE. BOTH THE INABILITY OF THE IMMUNE SYSTEM TO RESOLVE CHB AND THE UNIQUE REPLICATION STRATEGY EMPLOYED BY HBV, WHICH FORMS A STABLE VIRAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) MINICHROMOSOME IN THE HEPATOCYTE NUCLEUS, ENABLE INFECTION PERSISTENCE. KNOWLEDGE OF THE COMPLEX NETWORK OF INTERACTIONS THAT HBV ENGAGES WITH ITS HOST IS STILL LIMITED BUT ACCUMULATING EVIDENCE INDICATES THAT EPIGENETIC MODIFICATIONS OCCURRING BOTH ON THE CCCDNA AND ON THE HOST GENOME IN THE COURSE OF INFECTION ARE ESSENTIAL TO MODULATE VIRAL ACTIVITY AND LIKELY CONTRIBUTE TO PATHOGENESIS AND CANCER DEVELOPMENT. THUS, A DEEPER UNDERSTANDING OF EPIGENETIC REGULATORY PROCESSES MAY OPEN NEW VENUES TO CONTROL AND EVENTUALLY CURE CHB. THIS REVIEW SUMMARIZES MAJOR FINDINGS IN HBV EPIGENETIC RESEARCH, FOCUSING ON THE EPIGENETIC MECHANISMS REGULATING CCCDNA ACTIVITY AND THE MODIFICATIONS DETERMINED IN INFECTED HOST CELLS AND TUMOR LIVER TISSUES. 2020 12 3288 41 HIERARCHICAL TRANSCRIPTIONAL NETWORK GOVERNING HETEROGENEOUS T CELL EXHAUSTION AND ITS IMPLICATIONS FOR IMMUNE CHECKPOINT BLOCKADE. THE FUNDAMENTAL PRINCIPLE OF IMMUNE CHECKPOINT BLOCKADE (ICB) IS TO PROTECT TUMOR-INFILTRATING T CELLS FROM BEING EXHAUSTED. DESPITE THE REMARKABLE SUCCESS ACHIEVED BY ICB TREATMENT, ONLY A SMALL GROUP OF PATIENTS BENEFIT FROM IT. CHARACTERIZED BY A HYPOFUNCTIONAL STATE WITH THE EXPRESSION OF MULTIPLE INHIBITORY RECEPTORS, EXHAUSTED T (TEX) CELLS ARE A MAJOR OBSTACLE IN IMPROVING ICB. T CELL EXHAUSTION IS A PROGRESSIVE PROCESS WHICH ADAPTS TO PERSISTENT ANTIGEN STIMULATION IN CHRONIC INFECTIONS AND CANCERS. IN THIS REVIEW, WE ELUCIDATE THE HETEROGENEITY OF TEX CELLS AND OFFER NEW INSIGHTS INTO THE HIERARCHICAL TRANSCRIPTIONAL REGULATION OF T CELL EXHAUSTION. FACTORS AND SIGNALING PATHWAYS THAT INDUCE AND PROMOTE EXHAUSTION ARE ALSO SUMMARIZED. MOREOVER, WE REVIEW THE EPIGENETIC AND METABOLIC ALTERATIONS OF TEX CELLS AND DISCUSS HOW PD-1 SIGNALING AFFECTS THE BALANCE BETWEEN T CELL ACTIVATION AND EXHAUSTION, AIMING TO PROVIDE MORE THERAPEUTIC TARGETS FOR APPLICATIONS OF COMBINATIONAL IMMUNOTHERAPIES. 2023 13 2324 24 EPIGENETIC REGULATION OF HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA: IMPLICATIONS FOR EPIGENETIC THERAPY AGAINST CHRONIC HEPATITIS B. HEPATITIS B VIRUS (HBV) INFECTION REPRESENTS A SIGNIFICANT PUBLIC HEALTH BURDEN WORLDWIDE. ALTHOUGH CURRENT THERAPEUTICS MANAGE TO CONTROL THE DISEASE PROGRESSION, LIFELONG TREATMENT AND SURVEILLANCE ARE REQUIRED BECAUSE DRUG RESISTANCE DEVELOPS DURING TREATMENT AND REACTIVATIONS FREQUENTLY OCCUR FOLLOWING MEDICATION CESSATION. THUS, THE OCCURRENCE OF HEPATOCELLULAR CARCINOMA IS DECREASED, BUT NOT ELIMINATED. ONE MAJOR REASON FOR FAILURE OF HBV TREATMENT IS THE INABILITY TO ERADICATE OR INACTIVATE THE VIRAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA), WHICH IS A STABLE EPISOMAL FORM OF THE VIRAL GENOME DECORATED WITH HOST HISTONES AND NONHISTONE PROTEINS. ACCUMULATING EVIDENCE SUGGESTS THAT EPIGENETIC MODIFICATIONS OF CCCDNA CONTRIBUTE TO VIRAL REPLICATION AND THE OUTCOME OF CHRONIC HBV INFECTION. HERE, WE SUMMARIZE CURRENT PROGRESS ON HBV EPIGENETICS RESEARCH AND THE THERAPEUTIC IMPLICATIONS FOR CHRONIC HBV INFECTION BY LEARNING FROM THE EPIGENETIC THERAPIES FOR CANCER AND OTHER VIRAL DISEASES, WHICH MAY OPEN A NEW VENUE TO CURE CHRONIC HEPATITIS B. (HEPATOLOGY 2017;66:2066-2077). 2017 14 6479 47 TOWARD A NEW ERA OF HEPATITIS B VIRUS THERAPEUTICS: THE PURSUIT OF A FUNCTIONAL CURE. HEPATITIS B VIRUS (HBV) INFECTION, ALTHOUGH PREVENTABLE BY VACCINATION, REMAINS A GLOBAL HEALTH PROBLEM AND A MAJOR CAUSE OF CHRONIC LIVER DISEASE. ALTHOUGH CURRENT TREATMENT STRATEGIES SUPPRESS VIRAL REPLICATION VERY EFFICIENTLY, THE OPTIMAL ENDPOINT OF HEPATITIS B SURFACE ANTIGEN (HBSAG) CLEARANCE IS RARELY ACHIEVED. MOREOVER, THE THORNY PROBLEMS OF PERSISTENT CHROMATIN-LIKE COVALENTLY CLOSED CIRCULAR DNA AND THE PRESENCE OF INTEGRATED HBV DNA IN THE HOST GENOME ARE IGNORED. THEREFORE, THE SCIENTIFIC COMMUNITY HAS FOCUSED ON DEVELOPING INNOVATIVE THERAPEUTIC APPROACHES TO ACHIEVE A FUNCTIONAL CURE OF HBV, DEFINED AS UNDETECTABLE HBV DNA AND HBSAG LOSS OVER A LIMITED TREATMENT PERIOD. A DEEPER UNDERSTANDING OF THE HBV LIFE CYCLE HAS LED TO THE INTRODUCTION OF NOVEL DIRECT-ACTING ANTIVIRALS THAT EXERT THEIR FUNCTION THROUGH MULTIPLE MECHANISMS, INCLUDING INHIBITION OF VIRAL ENTRY, TRANSCRIPTIONAL SILENCING, EPIGENETIC MANIPULATION, INTERFERENCE WITH CAPSID ASSEMBLY, AND DISRUPTION OF HBSAG RELEASE. IN PARALLEL, ANOTHER CATEGORY OF NEW DRUGS AIMS TO RESTORE DYSREGULATED IMMUNE FUNCTION IN CHRONIC HEPATITIS B ACCOMPANIED BY LETHARGIC CELLULAR AND HUMORAL RESPONSES. STIMULATION OF INNATE IMMUNITY BY PATTERN-RECOGNITION RECEPTOR AGONISTS LEADS TO UPREGULATION OF ANTIVIRAL CYTOKINE EXPRESSION AND APPEARS TO CONTRIBUTE TO HBV CONTAINMENT. IMMUNE CHECKPOINT INHIBITORS AND ADOPTIVE TRANSFER OF GENETICALLY ENGINEERED T CELLS ARE BREAKTHROUGH TECHNOLOGIES CURRENTLY BEING EXPLORED THAT MAY ELICIT POTENT HBV-SPECIFIC T-CELL RESPONSES. IN ADDITION, SEVERAL CLINICAL TRIALS ARE ATTEMPTING TO CLARIFY THE ROLE OF THERAPEUTIC VACCINATION IN THIS SETTING. ULTIMATELY, IT IS INCREASINGLY RECOGNIZED THAT ELIMINATION OF HBV REQUIRES A TREATMENT REGIMEN BASED ON A COMBINATION OF MULTIPLE DRUGS. THIS REVIEW DESCRIBES THE RATIONALE FOR PROGRESSIVE THERAPEUTIC INTERVENTIONS AND DISCUSSES THE LATEST FINDINGS IN THE FIELD OF HBV THERAPEUTICS. 2021 15 1178 24 CONTROL OF CCCDNA FUNCTION IN HEPATITIS B VIRUS INFECTION. THE TEMPLATE OF HEPATITIS B VIRUS (HBV) TRANSCRIPTION, THE COVALENTLY CLOSED CIRCULAR DNA (CCCDNA), PLAYS A KEY ROLE IN THE LIFE CYCLE OF THE VIRUS AND PERMITS THE PERSISTENCE OF INFECTION. NOVEL MOLECULAR TECHNIQUES HAVE OPENED NEW POSSIBILITIES TO INVESTIGATE THE ORGANIZATION AND THE ACTIVITY OF THE CCCDNA MINICHROMOSOME IN VIVO, AND RECENT ADVANCES HAVE STARTED TO SHED LIGHT ON THE COMPLEXITY OF THE MECHANISMS CONTROLLING CCCDNA FUNCTION. NUCLEAR CCCDNA ACCUMULATES IN HEPATOCYTE NUCLEI AS A STABLE MINICHROMOSOME ORGANIZED BY HISTONE AND NON-HISTONE VIRAL AND CELLULAR PROTEINS. IDENTIFICATION OF THE MOLECULAR MECHANISMS REGULATING CCCDNA STABILITY AND ITS TRANSCRIPTIONAL ACTIVITY AT THE RNA, DNA AND EPIGENETIC LEVELS IN THE COURSE OF CHRONIC HEPATITIS B (CH-B) INFECTION MAY REVEAL NEW POTENTIAL THERAPEUTIC TARGETS FOR ANTI-HBV DRUGS AND HENCE ASSIST IN THE DESIGN OF STRATEGIES AIMED AT SILENCING AND EVENTUALLY DEPLETING THE CCCDNA RESERVOIR. 2009 16 1052 31 CLINICAL IMPLICATIONS OF HEPATITIS B VIRUS RNA AND COVALENTLY CLOSED CIRCULAR DNA IN MONITORING PATIENTS WITH CHRONIC HEPATITIS B TODAY WITH A GAZE INTO THE FUTURE: THE FIELD IS UNPREPARED FOR A STERILIZING CURE. . CHRONIC HEPATITIS B VIRUS (HBV) INFECTION HAS LONG REMAINED A CRITICAL GLOBAL HEALTH ISSUE. COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IS A PERSISTENT FORM OF THE HBV GENOME THAT MAINTAINS HBV CHRONICITY. DECADES OF EXTENSIVE RESEARCH RESULTED IN THE TWO THERAPEUTIC OPTIONS CURRENTLY AVAILABLE: NUCLEOT(S)IDE ANALOGS AND INTERFERON (IFN) THERAPY. A PLETHORA OF RELIABLE MARKERS TO MONITOR HBV PATIENTS HAS BEEN ESTABLISHED, INCLUDING THE RECENTLY DISCOVERED ENCAPSIDATED PREGENOMIC RNA IN SERUM, WHICH CAN BE USED TO DETERMINE TREATMENT END-POINTS AND TO PREDICT THE SUSCEPTIBILITY OF PATIENTS TO IFN. ADDITIONALLY, HBV RNA SPLICE VARIANTS AND CCCDNA AND ITS EPIGENETIC MODIFICATIONS ARE ASSOCIATED WITH THE CLINICAL COURSE AND RISKS OF HEPATOCELLULAR CARCINOMA (HCC) AND LIVER FIBROSIS. HOWEVER, NEW ANTIVIRALS, INCLUDING CRISPR/CAS9, APOBEC-MEDIATED DEGRADATION OF CCCDNA, AND T-CELL THERAPIES AIM AT COMPLETELY ELIMINATING HBV, AND IT IS CLEAR THAT THE DIAGNOSTIC ARSENAL FOR DEFINING THE LONG-AWAITED STERILIZING CURE IS MISSING. IN THIS REVIEW, WE DISCUSS THE CURRENTLY AVAILABLE TOOLS FOR DETECTING AND MEASURING HBV RNAS AND CCCDNA, AS WELL AS THE STATE-OF-THE-ART IN CLINICAL IMPLICATIONS OF THESE MARKERS, AND DEBATE NEEDS AND GOALS WITHIN THE CONTEXT OF THE STERILIZING CURE THAT IS SOON TO COME. 2018 17 3186 26 HBV COVALENTLY CLOSED CIRCULAR DNA MINICHROMOSOMES IN DISTINCT EPIGENETIC TRANSCRIPTIONAL STATES DIFFER IN THEIR VULNERABILITY TO DAMAGE. BACKGROUND AND AIMS: HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IS A MAJOR OBSTACLE FOR A CURE OF CHRONIC HEPATITIS B. ACCUMULATING EVIDENCE SUGGESTS THAT EPIGENETIC MODIFICATIONS REGULATE THE TRANSCRIPTIONAL ACTIVITY OF CCCDNA MINICHROMOSOMES. HOWEVER, IT REMAINS UNCLEAR HOW THE EPIGENETIC STATE OF CCCDNA AFFECTS ITS STABILITY. APPROACHES AND RESULTS: BY USING HBV INFECTION CELL MODELS AND IN VITRO AND IN VIVO RECOMBINANT CCCDNA (RCCCDNA) AND HBVCIRCLE MODELS, THE REDUCTION RATE OF HBV CCCDNA AND THE EFFICACY OF APOLIPOPROTEIN B MRNA EDITING ENZYME CATALYTIC SUBUNIT 3A (APOBEC3A)-MEDIATED AND CRISPR/CRISPR-ASSOCIATED 9 (CAS9)-MEDIATED CCCDNA TARGETING WERE COMPARED BETWEEN CCCDNAS WITH DISTINCT TRANSCRIPTIONAL ACTIVITIES. INTERFERON-ALPHA TREATMENT AND HEPATITIS B X PROTEIN (HBX) DELETION WERE APPLIED AS TWO STRATEGIES FOR CCCDNA REPRESSION. CHROMATIN IMMUNOPRECIPITATION AND MICROCOCCAL NUCLEASE ASSAYS WERE PERFORMED TO DETERMINE THE EPIGENETIC PATTERN OF CCCDNA. HBV CCCDNA LEVELS REMAINED STABLE IN NONDIVIDING HEPATOCYTES; HOWEVER, THEY WERE SIGNIFICANTLY REDUCED DURING CELL DIVISION, AND THE REDUCTION RATE WAS SIMILAR BETWEEN CCCDNAS IN TRANSCRIPTIONALLY ACTIVE AND TRANSCRIPTIONALLY REPRESSED STATES. STRIKINGLY, HBV RCCCDNA WITHOUT HBX EXPRESSION EXHIBITED A SIGNIFICANTLY LONGER PERSISTENCE IN MICE. THE CCCDNA WITH LOW TRANSCRIPTIONAL ACTIVITY EXHIBITED AN EPIGENETICALLY INACTIVE PATTERN AND WAS MORE DIFFICULT TO ACCESS BY APOBEC3A AND ENGINEERED CRISPR-CAS9. THE EPIGENETIC REGULATOR ACTIVATING CCCDNA INCREASED ITS VULNERABILITY TO APOBEC3A. CONCLUSIONS: HBV CCCDNA MINICHROMOSOMES IN DISTINCT EPIGENETIC TRANSCRIPTIONAL STATES SHOWED A SIMILAR REDUCTION RATE DURING CELL DIVISION BUT SIGNIFICANTLY DIFFERED IN THEIR ACCESSIBILITY AND VULNERABILITY TO TARGETED NUCLEASES AND ANTIVIRAL AGENTS. EPIGENETIC SENSITIZATION OF CCCDNA MAKES IT MORE SUSCEPTIBLE TO DAMAGE AND MAY POTENTIALLY CONTRIBUTE TO AN HBV CURE. 2022 18 3794 34 INTERLEUKIN-33 MEDIATES BOTH IMMUNE-RELATED AND NON-IMMUNE-RELATED INHIBITORY EFFECTS AGAINST HEPATITIS B VIRUS. CHRONIC INFECTION BY HEPATITIS B VIRUS (HBV) IS ASSOCIATED WITH HIGH RISKS OF LIVER FIBROSIS, CIRRHOSIS AND HEPATOCELLULAR CARCINOMA. HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IN THE NUCLEUS OF INFECTED HEPATOCYTE SERVES AS TRANSCRIPTION TEMPLATE. NEITHER NATURAL RESOLUTION OF ACUTE INFECTION NOR CURRENT TREATMENT OPTIONS FOR CHRONIC INFECTION ARE BELIEVED TO CAUSE CCCDNA CLEARANCE. WE PREVIOUSLY SHOWED THAT INJECTION OF IL-33-EXPRESSING PLASMID FACILITATED CLEARANCE OF INTRAHEPATIC HBV DNA IN A MOUSE MODEL OF HBV PERSISTENCE. IN THIS WORK, HBV-TARGETING THERAPEUTIC EFFECTS OF IL-33 WERE FURTHER EXPLORED. MURINE IL-33 DELIVERED BY RECOMBINANT ADENO-ASSOCIATED VIRUS (AAV-MIL-33) INDUCED CLEARANCE OF BOTH SERUM HBV MARKERS AND INTRAHEPATIC HBV DNA IN TWO MOUSE MODELS OF HBV PERSISTENCE BASED ON REPLICON PLASMID AND RECOMBINANT CCCDNA (RCCCDNA) RESPECTIVELY. CLEARANCE WAS ASSOCIATED WITH SERUM ALT ELEVATIONS AND LIVER INFILTRATIONS BY CD4(+) AND CD8(+) T CELLS, INDICATING IL-33-INDUCED CELLULAR IMMUNE RESPONSES AGAINST HBV-HARBORING CELLS. ADOPTIVE TRANSFER OF SPLENOCYTES FROM AAV-MIL-33-CURED MICE WAS INDEED SUFFICIENT TO ENGENDER SIMILAR CLEARANCE IN RECIPIENT MICE. IN VITRO, INTRACELLULAR, INSTEAD OF EXTRACELLULAR, IL-33 WAS MAINLY RESPONSIBLE FOR REPRESSING VIRAL TRANSCRIPTION, PROTEIN PRODUCTION AND GENOME REPLICATION IN HUH7 CELLS TRANSFECTED WITH HBV REPLICON OR RCCCDNA. IL-33 WAS SHOWN TO BE RECRUITED ONTO RCCCDNA MINICHROMOSOME ACCOMPANIED BY LOSS OF TRANSCRIPTIONAL ACTIVATION EPIGENETIC MARKS. FINALLY, TRANSFECTION OF IL-33 INTO HBV-INFECTED HEPG2/NTCP CELLS RESULTED IN REDUCED TRANSCRIPTION, ANTIGEN EXPRESSION AND GENOME REPLICATION, SUGGESTING REPRESSION OF CANONICAL CCCDNA. THESE DATA DEMONSTRATED DIVERSE INHIBITORY EFFECTS ON HBV AND HBV-INFECTED CELLS MEDIATED BY IL-33, AND SUGGEST IL-33 AS AN INTERESTING THERAPEUTIC CANDIDATE. 2022 19 4815 31 OCCULT HEPATITIS B INFECTION AND HEPATOCELLULAR CARCINOMA: EPIDEMIOLOGY, VIROLOGY, HEPATOCARCINOGENESIS AND CLINICAL SIGNIFICANCE. OCCULT HEPATITIS B INFECTION (OBI) REFERS TO A CONDITION WHERE REPLICATION-COMPETENT HBV DNA IS PRESENT IN THE LIVER, WITH OR WITHOUT HBV DNA IN THE BLOOD, IN INDIVIDUALS WITH SERUM HBSAG NEGATIVITY ASSESSED BY CURRENTLY AVAILABLE ASSAYS. THE EPISOMAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IN OBI IS IN A LOW REPLICATIVE STATE. VIRAL GENE EXPRESSION IS MEDIATED BY EPIGENETIC CONTROL OF HBV TRANSCRIPTION, INCLUDING THE HBV CPG ISLAND METHYLATION PATHWAY AND POST-TRANSLATIONAL MODIFICATION OF CCCDNA-BOUND HISTONE, WITH A DIFFERENT PATTERN FROM PATIENTS WITH CHRONIC HBV INFECTION. THE PREVALENCE OF OBI VARIES TREMENDOUSLY ACROSS PATIENT POPULATIONS OWING TO NUMEROUS FACTORS, SUCH AS GEOGRAPHIC LOCATION, ASSAY CHARACTERISTICS, HOST IMMUNE RESPONSE, COINFECTION WITH OTHER VIRUSES, AND VACCINATION STATUS. APART FROM THE RISK OF VIRAL REACTIVATION UPON IMMUNOSUPPRESSION AND THE RISK OF TRANSMISSION OF HBV, OBI HAS BEEN IMPLICATED IN HEPATOCELLULAR CARCINOMA (HCC) DEVELOPMENT IN PATIENTS WITH CHRONIC HCV INFECTION, THOSE WITH CRYPTOGENIC OR KNOWN LIVER DISEASE, AND IN PATIENTS WITH HBSAG SEROCLEARANCE AFTER CHRONIC HBV INFECTION. AN INCREASING NUMBER OF PROSPECTIVE STUDIES AND META-ANALYSES HAVE REPORTED A HIGHER INCIDENCE OF HCC IN PATIENTS WITH HCV AND OBI, AS WELL AS MORE ADVANCED TUMOUR HISTOLOGICAL GRADES AND EARLIER AGE OF HCC DIAGNOSIS, COMPARED WITH PATIENTS WITHOUT OBI. THE PROPOSED PATHOGENETIC MECHANISMS OF OBI-RELATED HCC INCLUDE THE INFLUENCE OF HBV DNA INTEGRATION ON THE HEPATOCYTE CELL CYCLE, THE PRODUCTION OF PRO-ONCOGENIC PROTEINS (HBX PROTEIN AND MUTATED SURFACE PROTEINS), AND PERSISTENT LOW-GRADE NECROINFLAMMATION (CONTRIBUTING TO THE DEVELOPMENT OF FIBROSIS AND CIRRHOSIS). THERE REMAIN UNCERTAINTIES ABOUT EXACTLY HOW, AND IN WHAT ORDER, THESE MECHANISMS DRIVE THE DEVELOPMENT OF TUMOURS IN PATIENTS WITH OBI. 2020 20 3806 36 INTRACELLULAR INTERFERON SIGNALLING PATHWAYS AS POTENTIAL REGULATORS OF COVALENTLY CLOSED CIRCULAR DNA IN THE TREATMENT OF CHRONIC HEPATITIS B. INFECTION WITH THE HEPATITIS B VIRUS (HBV) IS STILL A MAJOR GLOBAL HEALTH THREAT AS 250 MILLION PEOPLE WORLDWIDE CONTINUE TO BE CHRONICALLY INFECTED WITH THE VIRUS. WHILE PATIENTS MAY BE TREATED WITH NUCLEOSIDE/NUCLEOTIDE ANALOGUES, THIS ONLY SUPPRESSES HBV TITRE TO SUB-DETECTION LEVELS WITHOUT ELIMINATING THE PERSISTENT HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) GENOME. AS A RESULT, HBV INFECTION CANNOT BE CURED, AND THE VIRUS REACTIVATES WHEN CONDITIONS ARE FAVORABLE. INTERFERONS (IFNS) ARE CYTOKINES KNOWN TO INDUCE POWERFUL ANTIVIRAL MECHANISMS THAT CLEAR VIRUSES FROM INFECTED CELLS. THEY HAVE BEEN SHOWN TO INDUCE CCCDNA CLEARANCE, BUT THEIR USE IN THE TREATMENT OF HBV INFECTION IS LIMITED AS HBV-TARGETING IMMUNE CELLS ARE EXHAUSTED AND HBV HAS EVOLVED MULTIPLE MECHANISMS TO EVADE AND SUPPRESS IFN SIGNALLING. THUS, TO FULLY UTILIZE IFN-MEDIATED INTRACELLULAR MECHANISMS TO EFFECTIVELY ELIMINATE HBV, INSTEAD OF DIRECT IFN ADMINISTRATION, NOVEL STRATEGIES TO SUSTAIN IFN-MEDIATED ANTI-CCCDNA AND ANTIVIRAL MECHANISMS NEED TO BE DEVELOPED. THIS REVIEW WILL CONSOLIDATE WHAT IS KNOWN ABOUT HOW IFNS ACT TO ACHIEVE ITS INTRACELLULAR ANTIVIRAL EFFECTS AND HIGHLIGHT THE CRITICAL INTERFERON-STIMULATED GENE TARGETS AND EFFECTOR MECHANISMS WITH POTENT ANTI-CCCDNA FUNCTIONS. THESE INCLUDE CCCDNA DEGRADATION BY APOBECS AND CCCDNA SILENCING AND TRANSCRIPTION REPRESSION BY EPIGENETIC MODIFICATIONS. IN ADDITION, THE MECHANISMS THAT HBV EMPLOYS TO DISRUPT IFN SIGNALLING WILL BE DISCUSSED. DRUGS THAT HAVE BEEN DEVELOPED OR ARE IN THE PIPELINE FOR COMPONENTS OF THE IFN SIGNALLING PATHWAY AND HBV TARGETS THAT DETRACT IFN SIGNALLING MECHANISMS WILL ALSO BE IDENTIFIED AND DISCUSSED FOR UTILITY IN THE TREATMENT OF HBV INFECTIONS. TOGETHER, THESE WILL PROVIDE USEFUL INSIGHTS INTO DESIGN STRATEGIES THAT SPECIFICALLY TARGET CCCDNA FOR THE ERADICATION OF HBV. 2021