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.

Hepatitis C virus-specific CD4+ T cell phenotype and function in different infection outcomes.

CD4+ T cell failure is a hallmark of chronic hepatitis C virus (HCV) infection. However, the mechanisms underlying the impairment and loss of virus-specific CD4+ T cells in persisting HCV infection remain unclear. Here we examined HCV-specific CD4+ T cells longitudinally during acute infection with different infection outcomes. We found that HCV-specific CD4+ T cells are characterized by expression of a narrower range of T cell inhibitory receptors compared with CD8+ T cells, with initially high expression levels of PD-1 and CTLA-4 that were associated with negative regulation of proliferation in all patients, irrespective of outcome. In addition, HCV-specific CD4+ T cells were phenotypically similar during early resolving and persistent infection and secreted similar levels of cytokines. However, upon viral control, CD4+ T cells quickly downregulated inhibitory receptors and differentiated into long-lived memory cells. In contrast, persisting viremia continued to drive T cell activation and PD-1 and CTLA-4 expression, and blocked T cell differentiation, until the cells quickly disappeared from the circulation. Our data support an important and physiological role for inhibitory receptor-mediated regulation of CD4+ T cells in early HCV infection, irrespective of outcome, with persistent HCV viremia leading to sustained upregulation of PD-1 and CTLA-4.

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.

Hepatitis C Virus as a Unique Human Model Disease to Define Differences in the Transcriptional Landscape of T Cells in Acute versus Chronic Infection.

The hepatitis C virus is unique among chronic viral infections in that an acute outcome with complete viral elimination is observed in a minority of infected patients. This unique feature allows direct comparison of successful immune responses with those that fail in the setting of the same human infection. Here we review how this scenario can be used to achieve better understanding of transcriptional regulation of T-cell differentiation. Specifically, we discuss results from a study comparing transcriptional profiles of hepatitis C virus (HCV)-specific CD8 T-cells during early HCV infection between patients that do and do not control and eliminate HCV. Identification of early gene expression differences in key T-cell differentiation molecules as well as clearly distinct transcriptional networks related to cell metabolism and nucleosomal regulation reveal novel insights into the development of exhausted and memory T-cells. With additional transcriptional studies of HCV-specific CD4 and CD8 T-cells in different stages of infection currently underway, we expect HCV infection to become a valuable model disease to study human immunity to viruses.

Simultaneous Analysis of HCV-Specific CD4+ and CD8+ T Cells by Multicolor Flow Cytometry.

CD4 T cell responses are key to effective control of HCV infection. However, their precise mechanisms of action and the molecular programs leading to effective T help versus CD4 T cell failure remain elusive. Direct visualization of HCV-specific CD4 T cells using HLA class II tetramers holds the promise to better define the function and phenotype of these cells and to isolate them for further molecular analysis. Here we describe how to utilize peptide-MHC (pMHC) class II tetramers in multicolor flow cytometry to define the expression of molecules on the surface and within HCV-specific CD4 T cells, how to analyze HCV-specific CD4 and CD8 T cells in the same tube, and how to sort live HCV-specific CD4 T cells as single cells or T cell populations for further analysis by RNAseq or other methods.

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.

CD39 Expression Identifies Terminally Exhausted CD8+ T Cells.

Exhausted T cells express multiple co-inhibitory molecules that impair their function and limit immunity to chronic viral infection. Defining novel markers of exhaustion is important both for identifying and potentially reversing T cell exhaustion. Herein, we show that the ectonucleotidse CD39 is a marker of exhausted CD8+ T cells. CD8+ T cells specific for HCV or HIV express high levels of CD39, but those specific for EBV and CMV do not. CD39 expressed by CD8+ T cells in chronic infection is enzymatically active, co-expressed with PD-1, marks cells with a transcriptional signature of T cell exhaustion and correlates with viral load in HIV and HCV. In the mouse model of chronic Lymphocytic Choriomeningitis Virus infection, virus-specific CD8+ T cells contain a population of CD39high CD8+ T cells that is absent in functional memory cells elicited by acute infection. This CD39high CD8+ T cell population is enriched for cells with the phenotypic and functional profile of terminal exhaustion. These findings provide a new marker of T cell exhaustion, and implicate the purinergic pathway in the regulation of T cell exhaustion.

Bystander chronic infection negatively impacts development of CD8(+) T cell memory.

Epidemiological evidence suggests that chronic infections impair immune responses to unrelated pathogens and vaccines. The underlying mechanisms, however, are unclear and distinguishing effects on priming versus development of immunological memory has been challenging. We investigated whether bystander chronic infections impact differentiation of memory CD8(+) T cells, the hallmark of protective immunity against intracellular pathogens. Chronic bystander infections impaired development of memory CD8(+) T cells in several mouse models and humans. These effects were independent of initial priming and were associated with chronic inflammatory signatures. Chronic inflammation negatively impacted the number of bystander CD8(+) T cells and their memory development. Distinct underlying mechanisms of altered survival and differentiation were revealed with the latter regulated by the transcription factors T-bet and Blimp-1. Thus, exposure to prolonged bystander inflammation impairs the effector to memory transition. These data have relevance for immunity and vaccination during persisting infections and chronic inflammation.

Kinetic differences in the induction of interferon stimulated genes by interferon-α and interleukin 28B are altered by infection with hepatitis C virus.

UNLABELLED: Several genome-wide association studies (GWAS) have identified a genetic polymorphism associated with the gene locus for interleukin 28B (IL28B), a type III interferon (IFN), as a major predictor of clinical outcome in hepatitis C. Antiviral effects of the type III IFN family have previously been shown against several viruses, including hepatitis C virus (HCV), and resemble the function of type I IFN including utilization of the intracellular Janus kinase signal transducer and activator of transcription (JAK-STAT) pathway. Effects unique to IL28B that would distinguish it from IFN-α are not well defined. By analyzing the transcriptomes of primary human hepatocytes (PHH) treated with IFN-α or IL28B, we sought to identify functional differences between IFN-α and IL28B to better understand the roles of these cytokines in the innate immune response. Although our data did not reveal distinct gene signatures, we detected striking kinetic differences between IFN-α and IL28B stimulation for interferon stimulated genes (ISGs). While gene induction was rapid and peaked at 8 hours of stimulation with IFN-α in PHH, IL28B produced a slower, but more sustained increase in gene expression. We confirmed these findings in the human hepatoma cell line Huh7.5.1. Interestingly, in HCV-infected cells the rapid response after stimulation with IFN-α was blunted, and the induction pattern resembled that caused by IL28B. CONCLUSION: The kinetics of gene induction are fundamentally different for stimulations with either IFN-α or IL28B in hepatocytes, suggesting distinct roles of these cytokines within the immune response. Furthermore, the observed differences are substantially altered by infection with HCV.

Liver environment and HCV replication affect human T-cell phenotype and expression of inhibitory receptors.

BACKGROUND & AIMS: There is an unclear relationship between inhibitory receptor expression on T cells and their ability to control viral infections. Studies of human immune cells have been mostly limited to T cells from blood, which is often not the site of infection. We investigated the relationship between T-cell location, expression of inhibitory receptors, maturation, and viral control using blood and liver T cells from patients with hepatitis C virus (HCV) and other viral infections. METHODS: We analyzed 36 liver samples from HCV antibody-positive patients (30 from patients with chronic HCV infection, 5 from patients with sustained virological responses to treatment, and 1 from a patient with spontaneous clearance) with 19 paired blood samples and 51 liver samples from HCV-negative patients with 17 paired blood samples. Intrahepatic and circulating lymphocytes were extracted; T-cell markers and inhibitory receptors were quantified for total and virus-specific T cells by flow cytometry. RESULTS: Levels of the markers PD-1 and 2B4 (but not CD160, TIM-3, or LAG-3) were increased on intrahepatic T cells from healthy and diseased liver tissues compared with T cells from blood. HCV-specific intrahepatic CD8(+) T cells from patients with chronic HCV infection were distinct in that they expressed TIM-3 along with PD-1 and 2B4. In comparison, HCV-specific CD8(+) T cells from patients with sustained virological responses and T cells that recognized cytomegalovirus lacked TIM-3 but expressed higher levels of LAG-3; these cells also had different memory phenotypes and proliferative capacity. CONCLUSIONS: T cells from liver express different inhibitory receptors than T cells from blood, independent of liver disease. HCV-specific and cytomegalovirus-specific CD8(+) T cells can be differentiated based on their expression of inhibitory receptors; these correlate with their memory phenotype and levels of proliferation and viral control.