Single-cell atlas of the liver myeloid compartment before and after cure of chronic viral hepatitis.

BACKGROUND & AIMS: Chronic viral infections present serious public health challenges; however, direct-acting antivirals (DAAs) are now able to cure nearly all patients infected with hepatitis C virus (HCV), representing the only cure of a human chronic viral infection to date. DAAs provide a valuable opportunity to study immune pathways in the reversal of chronic immune failures in an in vivo human system. METHODS: To leverage this opportunity, we used plate-based single-cell RNA-seq to deeply profile myeloid cells from liver fine needle aspirates in patients with HCV before and after DAA treatment. We comprehensively characterised liver neutrophils, eosinophils, mast cells, conventional dendritic cells, plasmacytoid dendritic cells, classical monocytes, non-classical monocytes, and macrophages, and defined fine-grained subpopulations of several cell types. RESULTS: We discovered cell type-specific changes post-cure, including an increase in MCM7+STMN1+ proliferating CD1C+ conventional dendritic cells, which may support restoration from chronic exhaustion. We observed an expected downregulation of interferon-stimulated genes (ISGs) post-cure as well as an unexpected inverse relationship between pre-treatment viral load and post-cure ISG expression in each cell type, revealing a link between viral loads and sustained modifications of the host's immune system. We found an upregulation of PD-L1/L2 gene expression in ISG-high neutrophils and IDO1 expression in eosinophils, pinpointing cell subpopulations crucial for immune regulation. We identified three recurring gene programmes shared by multiple cell types, distilling core functions of the myeloid compartment. CONCLUSIONS: This comprehensive single-cell RNA-seq atlas of human liver myeloid cells in response to cure of chronic viral infections reveals principles of liver immunity and provides immunotherapeutic insights. CLINICAL TRIAL REGISTRATION: This study is registered at ClinicalTrials.gov (NCT02476617). IMPACT AND IMPLICATIONS: Chronic viral liver infections continue to be a major public health problem. Single-cell characterisation of liver immune cells during hepatitis C and post-cure provides unique insights into the architecture of liver immunity contributing to the resolution of the first curable chronic viral infection of humans. Multiple layers of innate immune regulation during chronic infections and persistent immune modifications after cure are revealed. Researchers and clinicians may leverage these findings to develop methods to optimise the post-cure environment for HCV and develop novel therapeutic approaches for other chronic viral infections.

Hepatitis-B virus: replication cycle, targets, and antiviral approaches.

An estimated 257 million people are chronic carriers of hepatitis-B virus (HBV) infection, which resulted in around 1 million deaths, mainly due to hepatocellular carcinoma (HCC). Long-term nucleotide analog treatment of HBV infection is associated with favorable prognosis, no disease progression, and a reduction of HCC risk, but lifelong treatments are required. A better understanding of HBV replication cycle and the host immune response will likely improve the identification of new targets for drug development. Studies are ongoing to determine if it is possible to successfully combine direct-acting antivirals (DAA) with an immunomodulatory therapy to allow increased cure rates. This review will start with summarizing the HBV replication cycle, recall current treatments, and then discuss potential targets and antiviral approaches in development to optimistically reach the HBV cure.

Differentiation of exhausted CD8+ T cells after termination of chronic antigen stimulation stops short of achieving functional T cell memory.

T cell exhaustion is associated with failure to clear chronic infections and malignant cells. Defining the molecular mechanisms of T cell exhaustion and reinvigoration is essential to improving immunotherapeutic modalities. Here we confirmed pervasive phenotypic, functional and transcriptional differences between memory and exhausted antigen-specific CD8+ T cells in human hepatitis C virus (HCV) infection before and after treatment. After viral cure, phenotypic changes in clonally stable exhausted T cell populations suggested differentiation toward a memory-like profile. However, functionally, the cells showed little improvement, and critical transcriptional regulators remained in the exhaustion state. Notably, T cells from chronic HCV infection that were exposed to antigen for less time because of viral escape mutations were functionally and transcriptionally more similar to memory T cells from spontaneously resolved HCV infection. Thus, the duration of T cell stimulation impacts exhaustion recovery, with antigen removal after long-term exhaustion being insufficient for the development of functional T cell memory.

Epigenetic scars of CD8+ T cell exhaustion persist after cure of chronic infection in humans.

T cell exhaustion is an induced state of dysfunction that arises in response to chronic infection and cancer. Exhausted CD8+ T cells acquire a distinct epigenetic state, but it is not known whether that chromatin landscape is fixed or plastic following the resolution of a chronic infection. Here we show that the epigenetic state of exhaustion is largely irreversible, even after curative therapy. Analysis of chromatin accessibility in HCV- and HIV-specific responses identifies a core epigenetic program of exhaustion in CD8+ T cells, which undergoes only limited remodeling before and after resolution of infection. Moreover, canonical features of exhaustion, including super-enhancers near the genes TOX and HIF1A, remain 'epigenetically scarred.' T cell exhaustion is therefore a conserved epigenetic state that becomes fixed and persists independent of chronic antigen stimulation and inflammation. Therapeutic efforts to reverse T cell exhaustion may require new approaches that increase the epigenetic plasticity of exhausted T cells.

Differentiation of exhausted CD8 T cells after termination of chronic antigen stimulation stops short of achieving functional T cell memory

T cell exhaustion is associated with failure to clear chronic infections and malignant cells. Defining the molecular mechanisms of T cell exhaustion and reinvigoration is essential to improving immunotherapeutic modalities. Analysis of antigen-specific CD8+ T cells before and after antigen removal in human hepatitis C virus (HCV) infection confirmed pervasive phenotypic, functional, and transcriptional differences between exhausted and memory CD8+ T cells. After viral cure, we observed broad phenotypic and transcriptional changes in clonally stable exhausted T-cell populations suggesting differentiation towards a memory-like profile. However, functionally, the cells showed little improvement and critical transcriptional regulators remained in the exhaustion state. Notably, T cells from chronic HCV infection that were exposed to antigen for shorter periods of time because of viral escape mutations were functionally and transcriptionally more similar to memory T cells from spontaneously resolved acute HCV infection. Thus, duration of T cell stimulation impacts the ability to recover from exhaustion, as antigen removal after long-term T cell exhaustion is insufficient for the development of key T cell memory characteristics.

Evolution of the innate and adaptive immune response in women with acute Zika virus infection.

Zika virus (ZIKV) is a flavivirus that is closely related to other human pathogens, such as dengue virus (DENV)1. Primary transmission usually involves Aedes aegypti, which has expanded its distribution range considerably2, although rarer infection routes, including mother-to-fetus transmission, sexual contact and blood transfusion, have also been observed3-7. Primary ZIKV infection is usually asymptomatic or mild in adults, with quickly resolved blood viraemia, but ZIKV might persist for months in saliva, urine, semen, breast milk and the central nervous system8-12. During a recent ZIKV outbreak in South America, substantial numbers of neurological complications, such as Guillain-Barré syndrome, were reported13,14 together with cases of microcephaly and associated developmental problems in infants born to women infected with ZIKV during pregnancy15-20, highlighting the clinical importance of this infection. Analyses of the human immune response to ZIKV are lacking21-28, but the recent outbreak has provided an opportunity to assess ZIKV immunity using current immunological methods. Here, we comprehensively assess the acute innate and adaptive immune response to ZIKV infection in ten women who were recruited during early infection and followed through reconvalescence. We define a cascade of events that lead to immunological control of ZIKV, with previous exposure to DENV impacting some, but not all, mediators of antiviral immunity.

Dynamic changes in innate immune responses during direct-acting antiviral therapy for HCV infection.

The role of the endogenous interferon (IFN) system has been well characterized during IFN-based therapy for chronic hepatitis C virus (HCV) infection; less is known for direct-acting antivirals (DAAs). In this phase 3b open-label study, we assessed changes in IFN-stimulated genes (ISGs) in non-cirrhotic treatment-naïve or pegIFN/RBV-experienced HCV-GT1a-infected patients receiving paritaprevir/ritonavir/ombitasvir + dasabuvir + ribavirin (PrOD + R) for 12 weeks. ISG expression was quantified from peripheral blood mononuclear cells at baseline, treatment weeks (TW)2, TW4, TW8, end of treatment (EOT) and at post-treatment week 12. Paired sera were used to assess IFN-α/IFN-related chemokines/cytokines. Twenty-five patients were enrolled. Overall sustained virologic response (SVR)12 was 92% (no virologic failure [VF]) and 100% for those completing the study protocol. Two patients were excluded from the ISG analysis due to lack of post-treatment samples. The majority of ISGs were downregulated at TW2-TW4 (nadir TW4); however, a relative increase was observed at TW8-EOT, although levels were lower than baseline. This downregulation was accompanied by increases in IFN-α/IFN-related chemokines, a finding not observed with TH 1/2-related cytokines. Following SVR, ISG expression returned to TW2 levels. In conclusion, PrOD + R for 12 weeks was well-tolerated with no VF. Our data demonstrate dynamic alterations in innate immune profiles during highly potent IFN-free DAA therapy. The downregulation of ISG post-therapy suggests reversal of the "exhausted" ISG phenotype following SVR, and the rise in ISGs and IFN-α/IFN-responsive chemokines late during therapy suggests resetting of IFN responsiveness that may be relevant in determining duration of or immunological sequelae from DAA therapy, including HBV reactivation.

Phenotype and function of HBV-specific T cells is determined by the targeted epitope in addition to the stage of infection.

OBJECTIVE: Chronic HBV infection affects more than 250 million people worldwide and remains a global healthcare problem in part because we lack curative treatment. Sustained viral control requires HBV-specific T cells, but these become functionally impaired in chronic infection. Clinical evidence indicates that functional cure of HBV infection by the host immune response is feasible. Developing T cell-based therapies able to achieve functional cure will require identification of the requirements for a successful T cell response against HBV and the relative contribution of individual T cell specificities to HBV control. DESIGN: The phenotype and function of HBV-specific T cells were studied directly ex vivo using fluorochrome-labelled multimers. We studied multiple HBV-specific T cell specificities targeting different HBV proteins in individuals with either an acute self-limiting or chronic HBV infection. RESULTS: We detected strong T cell responses targeting multiple HBV viral proteins in acute self-limiting and low-frequency core and polymerase-specific T cells in chronic infection. Expression of the T cell inhibitory receptor PD-1, as well as T cell differentiation, T cell function and T cell regulation differed by stages and outcomes of infection. In addition, these features differed significantly between T cells targeting different HBV specificities. CONCLUSION: HBV-specific T cells with different target specificities are characterised by distinct phenotypical and functional profiles. These results have direct implications for the design of immunological studies in HBV infection, and are potentially relevant for informing immunotherapeutic approaches to induce functional cure.

Early Transcriptional Divergence Marks Virus-Specific Primary Human CD8+ T Cells in Chronic versus Acute Infection.

Distinct molecular pathways govern the differentiation of CD8+ effector T cells into memory or exhausted T cells during acute and chronic viral infection, but these are not well studied in humans. Here, we employed an integrative systems immunology approach to identify transcriptional commonalities and differences between virus-specific CD8+ T cells from patients with persistent and spontaneously resolving hepatitis C virus (HCV) infection during the acute phase. We observed dysregulation of metabolic processes during early persistent infection that was linked to changes in expression of genes related to nucleosomal regulation of transcription, T cell differentiation, and the inflammatory response and correlated with subject age, sex, and the presence of HCV-specific CD4+ T cell populations. These early changes in HCV-specific CD8+ T cell transcription preceded the overt establishment of T cell exhaustion, making this signature a prime target in the search for the regulatory origins of T cell dysfunction in chronic viral infection.

Maintenance of macrophage transcriptional programs and intestinal homeostasis by epigenetic reader SP140.

Epigenetic "readers" that recognize defined posttranslational modifications on histones have become desirable therapeutic targets for cancer and inflammation. SP140 is one such bromodomain- and plant homeodomain (PHD)-containing reader with immune-restricted expression, and single-nucleotide polymorphisms (SNPs) within SP140 associate with Crohn's disease (CD). However, the function of SP140 and the consequences of disease-associated SP140 SNPs have remained unclear. We show that SP140 is critical for transcriptional programs that uphold the macrophage state. SP140 preferentially occupies promoters of silenced, lineage-inappropriate genes bearing the histone modification H3K27me3, such as the HOXA cluster in human macrophages, and ensures their repression. Depletion of SP140 in mouse or human macrophages resulted in severely compromised microbe-induced activation. We reveal that peripheral blood mononuclear cells (PBMCs) or B cells from individuals carrying CD-associated SNPs within SP140 have defective SP140 messenger RNA splicing and diminished SP140 protein levels. Moreover, CD patients carrying SP140 SNPs displayed suppressed innate immune gene signatures in a mixed population of PBMCs that stratified them from other CD patients. Hematopoietic-specific knockdown of Sp140 in mice resulted in exacerbated dextran sulfate sodium (DSS)-induced colitis, and low SP140 levels in human CD intestinal biopsies correlated with relatively lower intestinal innate cytokine levels and improved response to anti-tumor necrosis factor (TNF) therapy. Thus, the epigenetic reader SP140 is a key regulator of macrophage transcriptional programs for cellular state, and a loss of SP140 due to genetic variation contributes to a molecularly defined subset of CD characterized by ineffective innate immunity, normally critical for intestinal homeostasis.

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.

Alternative Splice Transcripts for MHC Class I-like MICA Encode Novel NKG2D Ligands with Agonist or Antagonist Functions.

MHC class I chain-related proteins A and B (MICA and MICB) and UL16-binding proteins are ligands of the activating NKG2D receptor involved in cancer and immune surveillance of infection. Structurally, MICA/B proteins contain an α3 domain, whereas UL16-binding proteins do not. We identified novel alternative splice transcripts for MICA encoding five novel MICA isoforms: MICA-A, -B1, -B2, -C, and -D. Alternative splicing associates with MICA*015 and *017 and results from a point deletion (G) in the 5' splice donor site of MICA intron 4 leading to exon 3 and exon 4 skipping and/or deletions. These changes delete the α3 domain in all isoforms, and the α2 domain in the majority of isoforms (A, B1, C, and D). Endothelial and hematopoietic cells contained endogenous alternative splice transcripts and isoforms. MICA-B1, -B2, and -D bound NKG2D by surface plasmon resonance and were expressed at the cell surface. Functionally, MICA-B2 contains two extracellular domains (α1 and α2) and is a novel potent agonist ligand for NKG2D. We found that MICA-D is a new truncated form of MICA with weak affinity for NKG2D despite lacking α2 and α3 domains. MICA-D may functionally impair NKG2D activation by competing with full-length MICA or MICA-B2 for NKG2D engagement. Our study established NKG2D binding for recombinant MICA-B1 but found no function for this isoform. New truncated MICA isoforms exhibit a range of functions that may drive unexpected immune mechanisms and provide new tools for immunotherapy.

MICA Mutant A5.1 Influences BK Polyomavirus Reactivation and Associated Nephropathy After Kidney Transplantation.

BACKGROUND: BK polyomavirus (BKPyV) frequently reactivates in kidney transplant recipients during immunosuppressive therapy and triggers BKPyV-associated nephropathy and graft rejection. Determining effective risk factors for BKPyV reactivation is required to achieve efficient prevention. METHODS: This study investigated the role of major histocompatibility complex (MHC) class I-related chain A (MICA) in BKPyV reactivation in a cohort of 144 transplant donor/recipient pairs, including recipients with no reactivation (controllers) and those with mild (virurics) or severe (viremics) BKPyV reactivation after graft receipt. RESULTS: We show that, in the kidney, MICA is predominantly expressed in tubule epithelial cells, the natural targets of BKPyV, questioning a role for MICA in the immune control of BKPyV infection. Focusing on MICA genotype, we found a lower incidence of BKPyV reactivation in recipients of a renal graft from a donor carrying the MICA A5.1 mutant, which encodes a truncated nonconventional MICA. We established that a mismatch for MICA A5.1 between transplant donor and recipient is critical for BKPyV reactivation and BKPyV-associated nephropathy. Functionally, we found that a low prevalence of BKPyV reactivation was associated with elevated anti-MICA sensitization and reduced plasma level of soluble MICA in recipients, 2 potential effector mechanisms. DISCUSSIONS: These findings identify the MHC-related MICA as an immunogenetic factor that may functionally influence anti-BKPyV immune responses and infection outcomes.

Expression of MHC class I-related molecules MICA, HLA-E and EPCR shape endothelial cells with unique functions in innate and adaptive immunity.

Endothelial cells (ECs) located at the interface of blood and tissues display regulatory activities toward coagulation, inflammation and vascular homeostasis. By expressing MHC class I and II antigens, ECs also contribute to immune responses. In transplantation, graft ECs are both trigger and target of alloimmune responses. ECs express a set of MHC class I-like or structural related molecules such as HLA-E, MHC class I related chain A (MICA) and the endothelial protein C receptor (EPCR) that provide multiple and unique functions to ECs. HLA-E is a low polymorphic ligand for the CD94/NKG2A/C receptors, and triggers HLA-E-restricted CD8+αßT cell responses against viral and bacterial peptides. MICA is a highly polymorphic ligand for NKG2D activating NK and costimulating CD8+T cells and a ligand for tissue-resident Vδ1 γδ T subsets. More intriguing is the role of EPCR, a key regulator of coagulation, as a ligand for a circulating subset of Vδ2- γδ T cells. Coexpression of this set of MHC class I-related molecules that allow ECs to activate a subtle array of immune responses upon stress and infection may also influence transplant outcome. Here, the respective structure, expression, and functions of HLA-E, MICA and EPCR as well as the impact of their polymorphism are reviewed.

Advanced glycation inhibition and protection against endothelial dysfunction induced by coumarins and procyanidins from Mammea neurophylla.

Advanced glycation end-products (AGEs) are associated with many pathogenic disorders such as pathogenesis of diabetes or endothelial dysfunction leading to cardiovascular events. Therefore, the identification of new anti-AGE molecules or extracts aims at preventing such pathologies. Many Clusiaceae and Calophyllaceae species are used in traditional medicines to treat arterial hypertension as well as diabetes. Focusing on these plant families, an anti-AGE plant screening allowed us to select Mammea neurophylla for further phytochemical and biological studies. Indeed, both DCM and MeOH stem bark extracts demonstrated in vitro their ability to prevent inflammation in endothelial cells and to reduce vasoconstriction. A bioguided fractionation of these extracts allowed us to point out 4-phenyl- and 4-(1-acetoxypropyl)coumarins and procyanidins as potent inhibitors of AGE formation, potentially preventing endothelial dysfunction. The fractionation steps also led to the isolation of two new compounds, namely neurophyllols A and B from the DCM bark extract together with thirteen known mammea A and E coumarins (mammea A/AA, mammea A/AB, mammea A/BA, mammea A/BB, mammea A/AA cycloD, mammea A/AB cycloD, disparinol B, mammea A/AB cycloE, ochrocarpin A, mammea A/AA cycloF, mammea A/AB cycloF, mammea E/BA, mammea E/BB) as well as δ-tocotrienol, xanthones (1-hydroxy-7-methoxyxanthone, 2-hydroxyxanthone) and triterpenes (friedelin and betulinic acid). During this study, R,S-asperphenamate, previously described from fungal origin was also purified.

Endothelial cell activation and proliferation modulate NKG2D activity by regulating MICA expression and shedding.

MICA are major histocompatibility complex class I-related molecules, expressed by endothelial cells (ECs), that may be targets for alloantibodies and NKG2D-expressing natural killer (NK) and T effector cells in organ allografts. This study shows that basal levels of MICA expressed on vascular ECs is sufficient to functionally modulate the expression and activity of the immunoreceptor NKG2D in allogeneic NK cells. We found that MICA expression is differentially regulated at the EC surface in response to cytokines. TNFα upregulates MICA while IFNγ significantly decreases MICA at the EC surface. Both cytokines induce the release of soluble MICA by ECs. Modulation of NKG2D correlates with the MICA level on the EC surface. Glycosylation and metalloproteinase activities account for major post-transcriptional mechanisms controlling MICA level and the function in ECs. Our results indicate that, in addition to the NFκB pathway, the mitogen-activated protein kinase pathways JNK, ERK1/2 and p38 are key signaling pathways in the control of MICA by the cytokines. Finally, we show that EC proliferation mediated by FGF-2 or wound healing increases the MICA level. Together, our data suggest that inflammation and proliferation regulate endothelial MICA expression and shedding, enabling ECs to modulate NKG2D activity on effector NK and T cells, and provide further evidence of a role for ECs in immunoregulation.

MICA variant promotes allosensitization after kidney transplantation.

MHC class I-related chain A (MICA) antigens are surface glycoproteins strongly implicated in innate immunity, and the MICA gene is highly polymorphic. Clinical observations suggest a role for donor MICA antigens expressed on transplant endothelial cells in the alloimmune response, but the effect of MICA genotype is not well understood. Here, we investigated the immunologic effect of the A5.1 mutation, related to the common MICA*008 allele. Compared with wild-type endothelial cells (ECs), homozygosity for MICA A5.1 associated with an endothelial phenotype characterized by 7- to 10-fold higher levels of MICA mRNA and MICA proteins at the cell surface, as well as exclusive release in exosomes instead of enzymatic cleavage. Mechanistically, we did not detect quantitative changes in regulatory microRNAs. Functionally, A5.1 ECs enhanced NKG2D interaction and natural killer cell activation, promoting NKG2D-dependent lysis of ECs. In kidney transplant recipients, polyreactive anti-MICA sera bound preferentially to ECs from MICA A5.1 donors, suggesting that MICA*008(A5.1) molecules are the preferential antigenic determinants on ECs of grafts. Furthermore, the incidence of MICA A5.1 mismatch revealed a statistically significant association between donor MICA A5.1 and both anti-MICA sensitization and increased proteinuria in kidney recipients. Taken together, these results identify the A5.1 mutation as an immunodominant factor and a potential risk factor for transplant survival.

HLA-E-restricted cross-recognition of allogeneic endothelial cells by CMV-associated CD8 T cells: a potential risk factor following transplantation.

Although association between CMV infection and allograft rejection is well admitted, the precise mechanisms involved remain uncertain. Here, we report the characterization of an alloreactive HLA-E-restricted CD8 T cell population that was detected in the PBL of a kidney transplant patient after its CMV conversion. This monoclonal CD8 T cell population represents a sizable fraction in the blood (3% of PBL) and is characterized by an effector-memory phenotype and the expression of multiple NK receptors. Interestingly, these unconventional T cells display HLA-E-dependent reactivity against peptides derived from the leader sequences of both various HCMV-UL40 and allogeneic classical HLA-I molecules. Consequently, while HLA-E-restricted CD8 T cells have potential to contribute to the control of CMV infection in vivo, they may also directly mediate graft rejection through recognition of peptides derived from allogeneic HLA-I molecules on graft cells. Therefore, as HLA-E expression in nonlymphoid organs is mainly restricted to endothelial cells, we investigated the reactivity of this HLA-E-restricted T cell population towards allogeneic endothelial cells. We clearly demonstrated that CMV-associated HLA-E-restricted T cells efficiently recognized and killed allogeneic endothelial cells in vitro. Moreover, our data indicate that this alloreactivity is tightly regulated by NK receptors, especially by inhibitory KIR2DL2 that strongly prevents TCR-induced activation through recognition of HLA-C molecules. Hence, a better evaluation of the role of CMV-associated HLA-E-restricted T cells in transplantation and of the impact of HLA-genotype, especially HLA-C, on their alloreactivity may determine whether they indeed represent a risk factor following organ transplantation.