Flying Under the Radar: The Immunobiology of Hepatitis C

Mechanisms and Consequences of Genetic Variation in Hepatitis C Virus (HCV)

Chronic infection with hepatitis C virus (HCV) is an important contributor to the global incidence of liver diseases, including liver cirrhosis and hepatocellular carcinoma. Although common for single-stranded RNA viruses, HCV displays a remarkable high level of genetic diversity, produced primarily by the error-prone viral polymerase and host immune pressure. The high genetic heterogeneity of HCV has led to the evolution of several distinct genotypes and subtypes, with important consequences for pathogenesis, and clinical outcomes. Genetic variability constitutes an evasion mechanism against immune suppression, allowing the virus to evolve epitope escape mutants that avoid immune recognition. Thus, heterogeneity and variability of the HCV genome represent a great hindrance for the development of vaccines against HCV. In addition, the high genetic plasticity of HCV allows the virus to rapidly develop antiviral resistance mutations, leading to treatment failure and potentially representing a major hindrance for the cure of chronic HCV patients. In this chapter, we will present the central role that genetic diversity has in the viral life cycle and epidemiology of HCV. Incorporation errors and recombination, both the result of HCV polymerase activity, represent the main mechanisms of HCV evolution. The molecular details of both mechanisms have been only partially clarified and will be presented in the following sections. Finally, we will discuss the major consequences of HCV genetic diversity, namely its capacity to rapidly evolve antiviral and immunological escape variants that represent an important limitation for clearance of acute HCV, for treatment of chronic hepatitis C and for broadly protective vaccines.

Diagnosis and Clinical Manifestations of Acute Hepatitis C Infection in People Living with HIV

HIV/hepatitis C virus (HCV) coinfection is a global health problem with overlapping modes of transmission. We performed a single-center retrospective case series of acute HCV infections at the Atlanta Veterans Affairs Health Care System between January 2001 and June 2020 to better characterize the presentation and clinical course of acute HCV among veterans with HIV. Cases were discovered through routine clinical care. We identified 29 cases of acute HCV: all men. Risk for HCV acquisition included men who have sex with men (MSM; 93%) and injection drug use (17%). Thirteen (45%) had a concurrent sexually transmitted infection (STI). Symptoms were seen in 76% of acute HCV cases and resulted in hospitalization in 59% of symptomatic cases. Seven (24%) presented as HCV antibody seronegative. Three never seroconverted, all with CD4 T cell counts <200. Spontaneous HCV clearance occurred in 21% (n = 6) and was more common in those who developed jaundice (p = 0.01). Time to treatment was significantly reduced in the direct-acting antivirals (DAAs) era versus the interferon era (300 vs. 1631 days, p < 0.01). Of those who did not spontaneously clear, 87% were treated (n = 20/23) and 95% (n = 19/20) achieved sustained virological response. Three patients died before HCV treatment, all in the pre-DAA period (one death was liver related). In this case series of acute HCV infection in persons with HIV, many were symptomatic MSM who had a concurrent STI, suggesting sexual HCV transmission. Some presented as HCV antibody negative, highlighting the role of enhanced HCV screening and treatment in MSM with HIV to prevent HCV transmission in sexual networks.

Hepatitis C Virus-Related Central and Peripheral Nervous System Disorders

Hepatitis C Virus (HCV), despite being a hepatotropic virus, is the causative agent of many systemic disorders, such as vasculitis, autoimmune diseases, lymphoproliferative disorders, and a broad spectrum of neurological and psychiatric manifestations. Although symptoms have been misdiagnosed or underdiagnosed, only recently, evidence of direct (inflammatory) or indirect (immune-mediated) HCV-dependent cerebral effects has been established. HCV infection can promote acute inflammatory response, pro-coagulative status and ischemic disorders, and neurodegeneration. These effects rely on cerebral HCV replication, possibly mediated by blood-brain barrier alterations. Further study is needed to better understand the HCV-related mechanisms of brain damage.

Hepatitis C Virus Glycan-Dependent Interactions and the Potential for Novel Preventative Strategies

Chronic hepatitis C virus (HCV) infections continue to be a major contributor to liver disease worldwide. HCV treatment has become highly effective, yet there are still no vaccines or prophylactic strategies available to prevent infection and allow effective management of the global HCV burden. Glycan-dependent interactions are crucial to many aspects of the highly complex HCV entry process, and also modulate immune evasion. This review provides an overview of the roles of viral and cellular glycans in HCV infection and highlights glycan-focused advances in the development of entry inhibitors and vaccines to effectively prevent HCV infection.

CD8+ T Cell Responses during HCV Infection and HCC

Chronic hepatitis C virus (cHCV) infection is a major global health burden and the leading cause of hepatocellular carcinoma (HCC) in the Western world. The course and outcome of HCV infection is centrally influenced by CD8⁺ T cell responses. Indeed, strong virus-specific CD8⁺ T cell responses are associated with spontaneous viral clearance while failure of these responses, e.g., caused by viral escape and T cell exhaustion, is associated with the development of chronic infection. Recently, heterogeneity within the exhausted HCV-specific CD8⁺ T cells has been observed with implications for immunotherapeutic approaches also for other diseases. In HCC, the presence of tumor-infiltrating and peripheral CD8⁺ T cell responses correlates with a favorable prognosis. Thus, tumor-associated and tumor-specific CD8⁺ T cells are considered suitable targets for immunotherapeutic strategies. Here, we review the current knowledge of CD8+ T cell responses in chronic HCV infection and HCC and their respective failure with the potential consequences for T cell-associated immunotherapeutic approaches.

HCV-2a NS5A downregulates viral translation predominantly through domain I

Hepatitis C virus (HCV) non-structural protein NS5A is a multifunctional protein with critical roles in viral replication and assembly. We previously showed that HCV-1b NS5A downregulates viral translation only in the presence of the poly(U/UC) tract in 3'UTR. As NS5A of different HCV genotypes may have different functions or carry out the same functions through genotype-specific mechanisms, we investigated the effect of HCV-2a NS5A on viral translation. We found that HCV-2a NS5A downregulates RNA translation of both HCV-2a and -1b, whereas the effect of HCV-1b NS5A is limited to HCV-1b only. In addition, individual regions of 3'UTR are not required for HCV-2a NS5A to downregulate viral RNA translation. We also found that HCV-2a NS5A inhibits capped mRNA translation. Mapping experiments showed that the translation downregulation by HCV-2a NS5A is predominantly mediated by domain I. Furthermore, we found that the integrity of serine-146 residue plays an important role in translation downregulation by NS5A. Our results increased our understanding on genotype-specific functions of HCV NS5A.

Interferon Response in Hepatitis C Virus-Infected Hepatocytes: Issues to Consider in the Era of Direct-Acting Antivirals

When interferons (IFNs) bind to their receptors, they upregulate numerous IFN-stimulated genes (ISGs) with antiviral and immune regulatory activities. Hepatitis C virus (HCV) is a single-stranded, positive-sense RNA virus that affects over 71 million people in the global population. Hepatocytes infected with HCV produce types I and III IFNs. These endogenous IFNs upregulate a set of ISGs that negatively impact the outcome of pegylated IFN-α and ribavirin treatments, which were previously used to treat HCV. In addition, the IFNL4 genotype was the primary polymorphism responsible for a suboptimal treatment response to pegylated IFN-α and ribavirin. However, recently developed direct-acting antivirals have demonstrated a high rate of sustained virological response without pegylated IFN-α. Herein, we review recent studies on types I and III IFN responses to in HCV-infected hepatocytes. In particular, we focused on open issues related to IFN responses in the direct-acting antiviral era.

HCV NS5A hyperphosphorylation is involved in viral translation modulation

Hepatitis C virus (HCV) non-structural (NS) 5A protein is a multifunctional phosphoprotein. NS5A exists as hypo- and hyper-phosphorylated forms and the dynamic transitions between these two states are involved in the functions of NS5A. Hyperphosphorylation occurs primarily at six serine residues within the low complexity sequence I of NS5A. We previously showed that NS5A downregulates viral translation. In this study, we investigated the role of NS5A hyperphosphorylation in translation modulation. By analyzing the effects of phospho-ablative and phospho-mimetic mutants of the six serine residues on translation, we showed that NS5A hyperphospho-ablative mutation at all six serine residues can no longer downregulate viral translation. We then studied the effects of phospho-mutations at each of the six serine residues on translation. We found that phosphorylation of S222, S225, S235 is not involved in translation downregulation by NS5A. In contrast, NS5A with alanine mutations at S229 or S238 can no longer downregulate translation, whereas S229D or S238D mutations have no effect. Interestingly, S232D NS5A, but not S232A, abrogates translation downregulation by NS5A. Since dimerization of NS5A plays an important role in its functions, we also studied the effects of phospho-mutants of S229, S232, and S238 on dimerization in a protein-protein interaction assay. We showed that phopho-mimetic S229D or S238D mutations enhances NS5A dimerization, whereas the phospho-ablative mutations of these two residues have no effect. Neither phospho-ablative nor phopho-mimetic mutations of S232 affect dimerization. These results indicate that phosphorylation of NS5A at S229, S232, and S238 is involved in viral translation regulation and NS5A dimerization.

HCV and flaviviruses hijack cellular mechanisms for nuclear STAT2 degradation: Up-regulation of PDLIM2 suppresses the innate immune response

Host encounters with viruses lead to an innate immune response that must be rapid and broadly targeted but also tightly regulated to avoid the detrimental effects of unregulated interferon expression. Viral stimulation of host negative regulatory mechanisms is an alternate method of suppressing the host innate immune response. We examined three key mediators of the innate immune response: NF-KB, STAT1 and STAT2 during HCV infection in order to investigate the paradoxical induction of an innate immune response by HCV despite a multitude of mechanisms combating the host response. During infection, we find that all three are repressed only in HCV infected cells but not in uninfected bystander cells, both in vivo in chimeric mouse livers and in cultured Huh7.5 cells after IFNα treatment. We show here that HCV and Flaviviruses suppress the innate immune response by upregulation of PDLIM2, independent of the host interferon response. We show PDLIM2 is an E3 ubiquitin ligase that also acts to stimulate nuclear degradation of STAT2. Interferon dependent relocalization of STAT1/2 to the nucleus leads to PDLIM2 ubiquitination of STAT2 but not STAT1 and the proteasome-dependent degradation of STAT2, predominantly within the nucleus. CRISPR/Cas9 knockout of PDLIM2 results in increased levels of STAT2 following IFNα treatment, retention of STAT2 within the nucleus of HCV infected cells after IFNα stimulation, increased interferon response, and increased resistance to infection by several flaviviruses, indicating that PDLIM2 is a global regulator of the interferon response.

The response of cells to an invading pathogen must be swift and well controlled because of the detrimental effects of chronic inflammation. However, viruses often hijack host control mechanisms. HCV and flaviviruses are known to suppress the innate immune response in cells by a variety of mechanisms. This study clarifies and expands a specific cellular mechanism for global control of the antiviral response after the induction of interferon expression. It shows how several viruses hijack this control mechanism to suppress the innate interferon response.

Hypervariable region 1 and N-linked glycans of hepatitis C regulate virion neutralization by modulating envelope conformations

About two million new cases of hepatitis C virus (HCV) infections annually underscore the urgent need for a vaccine. However, this effort has proven challenging because HCV evades neutralizing antibodies (NAbs) through molecular features of viral envelope glycoprotein E2, including hypervariable region 1 (HVR1) and N-linked glycans. Here, we observe large variation in the effects of removing individual E2 glycans across HCV strains H77(genotype 1a), J6(2a), and S52(3a) in Huh7.5 cell infections. Also, glycan-mediated effects on neutralization sensitivity were completely HVR1-dependent, and neutralization data were consistent with indirect protection of epitopes, as opposed to direct steric shielding. Indeed, the effect of removing each glycan was similar both in type (protective or sensitizing) and relative strength across four nonoverlapping neutralization epitopes. Temperature-dependent neutralization (e.g., virus breathing) assays indicated that both HVR1 and protective glycans stabilized a closed, difficult to neutralize, envelope conformation. This stabilizing effect was hierarchical as removal of HVR1 fully destabilized closed conformations, irrespective of glycan status, consistent with increased instability at acidic pH and high temperatures. Finally, we observed a strong correlation between neutralization sensitivity and scavenger receptor BI dependency during viral entry. In conclusion, our study indicates that HVR1 and glycans regulate HCV neutralization by shifting the equilibrium between open and closed envelope conformations. This regulation appears tightly linked with scavenger receptor BI dependency, suggesting a role of this receptor in transitions from closed to open conformations during entry. This importance of structural dynamics of HCV envelope glycoproteins has critical implications for vaccine development and suggests that similar phenomena could contribute to immune evasion of other viruses.

HCV-Specific T Cell Responses During and After Chronic HCV Infection

Hepatitis C virus (HCV)-specific T cell responses are closely linked to the clinical course of infection. While T cell responses in self-limiting infection are typically broad and multi-specific, they display several distinct features of functional impairment in the chronic phase. Moreover, HCV readily adapts to immune pressure by developing escape mutations within epitopes targeted by T cells. Much of our current knowledge on HCV-specific T cell responses has been gathered under the assumption that this might eventually pave the way for a therapeutic vaccine. However, with the development of highly efficient direct acting antivirals (DAAs), there is less interest in the development of a therapeutic vaccine for HCV and the scope of T cell research has shifted. Indeed, the possibility to rapidly eradicate an antigen that has persisted over years or decades, and has led to T cell exhaustion and dysfunction, provides the unique opportunity to study potential T cell recovery after antigen cessation in a human in vivo setting. Findings from such studies not only improve our basic understanding of T cell immunity but may also advance immunotherapeutic approaches in cancer or chronic hepatitis B and D infection. Moreover, in order to edge closer to the WHO goal of HCV elimination by 2030, a prophylactic vaccine is clearly required. Thus, in this review, we will summarize our current knowledge on HCV-specific T cell responses and also provide an outlook on the open questions that require answers in this field.

Innate and Adaptive Immune Responses in Chronic HCV Infection

Hepatitis C virus (HCV) remains a public health problem of global importance, even in the era of potent directly-acting antiviral drugs. In this chapter, I discuss immune responses to acute and chronic HCV infection. The outcome of HCV infection is influenced by viral strategies that limit or delay the initiation of innate antiviral responses. This delay may enable HCV to establish widespread infection long before the host mounts effective T and B cell responses. HCV's genetic agility, resulting from its high rate of replication and its error prone replication mechanism, enables it to evade immune recognition. Adaptive immune responses fail to keep up with changing viral epitopes. Neutralizing antibody epitopes may be hidden by decoy structures, glycans, and lipoproteins. T cell responses fail due to changing epitope sequences and due to exhaustion, a phenomenon that may have evolved to limit immune-mediated pathology. Despite these difficulties, innate and adaptive immune mechanisms do impact HCV replication. Immune-mediated clearance of infection is possible, occurring in 20-50% of people who contract the disease. New developments raise hopes for effective immunological interventions to prevent or treat HCV infection.

Ultrastructural Localization and Molecular Associations of HCV Capsid Protein in Jurkat T Cells

Hepatitis C virus core protein is a highly basic viral protein that multimerizes with itself to form the viral capsid. When expressed in CD4⁺ T lymphocytes, it can induce modifications in several essential cellular and biological networks. To shed light on the mechanisms underlying the alterations caused by the viral protein, we have analyzed HCV-core subcellular localization and its associations with host proteins in Jurkat T cells. In order to investigate the intracellular localization of Hepatitis C virus core protein, we have used a lentiviral system to transduce Jurkat T cells and subsequently localize the protein using immunoelectron microscopy techniques. We found that in Jurkat T cells, Hepatitis C virus core protein mostly localizes in the nucleus and specifically in the nucleolus. In addition, we performed pull-down assays combined with Mass Spectrometry Analysis, to identify proteins that associate with Hepatitis C virus core in Jurkat T cells. We found proteins such as NOLC1, PP1γ, ILF3, and C1QBP implicated in localization and/or traffic to the nucleolus. HCV-core associated proteins are implicated in RNA processing and RNA virus infection as well as in functions previously shown to be altered in Hepatitis C virus core expressing CD4⁺ T cells, such as cell cycle delay, decreased proliferation, and induction of a regulatory phenotype. Thus, in the current work, we show the ultrastructural localization of Hepatitis C virus core and the first profile of HCV core associated proteins in T cells, and we discuss the functions and interconnections of these proteins in molecular networks where relevant biological modifications have been described upon the expression of Hepatitis C virus core protein. Thereby, the current work constitutes a necessary step toward understanding the mechanisms underlying HCV core mediated alterations that had been described in relevant biological processes in CD4⁺ T cells.

Hepatocyte-derived exosomes promote T follicular regulatory cell expansion during hepatitis C virus infection

Hepatitis C virus (HCV) is a global health concern that can cause severe liver disease, such as cirrhosis and hepatocellular carcinoma. Control of HCV requires vigorous T-cell responses, yet CD4⁺ T cells in chronic HCV patients are dysfunctional. T follicular regulatory (Tfr) cells are a subset of regulatory T cells that suppress T follicular helper (Tfh) cells and the generation of high affinity antibody-producing B cells. In this study, we examined the accumulation of Tfr cells in the liver compartment during chronic HCV infection and defined the cellular and molecular mechanisms underlying their expansion. Our analysis revealed a substantial population of Tfr cells in livers of chronic HCV patients that is absent in liver tissues from nonviral hepatitis or healthy subjects. Coculture of PBMCs from healthy subjects with HCV-infected hepatoma cells resulted in preferential expansion of circulating Tfr cells, leading to suppression of Tfh cells. Additionally, coculture of tonsillar cells with infected hepatoma cells lead to an expansion of germinal center Tfr. Notably, expansion was mediated by transforming growth factor beta (TGF-β)-containing exosomes released from HCV-infected hepatocytes given that blockade of exosome-associated TGF-β or inhibition of exosome release abrogated Tfr expansion.

CONCLUSION

These results show that liver-derived exosomes play a pivotal role in the accumulation of Tfr cells, likely leading to suppression of Tfh responses in HCV-infected patients. Our study identifies a novel pathway in which HCV infection in hepatocytes exacerbates Tfr cell responses to subvert antiviral immunity. (Hepatology 2018;67:71-85).

Immune Evasion Strategies during Chronic Hepatitis B and C Virus Infection

Both hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are a major global healthcare problem with more than 240 million and 70 million infected, respectively. Both viruses persist within the liver and result in progressive liver disease, resulting in liver fibrosis, cirrhosis and hepatocellular carcinoma. Strikingly, this pathogenesis is largely driven by immune responses, unable to clear an established infection, rather than by the viral pathogens themselves. Even though disease progression is very similar in both infections, HBV and HCV have evolved distinct mechanisms, by which they ensure persistence within the host. Whereas HCV utilizes a cloak-and-dagger approach, disguising itself as a lipid-like particle and immediately crippling essential pattern-recognition pathways, HBV has long been considered a "stealth" virus, due to the complete absence of innate immune responses during infection. Recent developments and access to improved model systems, however, revealed that even though it is among the smallest human-tropic viruses, HBV may, in addition to evading host responses, employ subtle immune evasion mechanisms directed at ensuring viral persistence in the absence of host responses. In this review, we compare the different strategies of both viruses to ensure viral persistence by actively interfering with viral recognition and innate immune responses.

Quinolinate Phosphoribosyltransferase is an Antiviral Host Factor Against Hepatitis C Virus Infection

HCV infection can decrease NAD⁺/NADH ratio, which could convert lipid metabolism to favor HCV replication. In hepatocytes, quinolinate phosphoribosyl transferase (QPRT) catabolizes quinolinic acid (QA) to nicotinic acid mononucleotide (NAMN) for de novo NAD synthesis. However, whether and how HCV modulates QPRT hence the lipogenesis is unknown. In this work, we found QPRT was reduced significantly in livers of patients or humanized C/O^Tg mice with persistent HCV infection. Mechanistic studies indicated that HCV NS3/4A promoted proteasomal degradation of QPRT through Smurf2, an E3 ubiquitin-protein ligase, in Huh7.5.1 cells. Furthermore, QPRT enzymatic activity involved in suppression of HCV replication in cells. Activation of QPRT with clofibrate (CLO) or addition of QPRT catabolite NAD both inhibited HCV replication in cells, probably through NAD⁺-dependent Sirt1 inhibition of cellular lipogenesis. More importantly, administration of CLO, a hypolipidemic drug used in clinics, could significantly reduce the viral load in HCV infected C/O^Tg mice. Take together, these results suggested that HCV infection triggered proteasomal degradation of QPRT and consequently reduced de novo NAD synthesis and lipogenesis, in favor of HCV replication. Hepatic QPRT thus likely served as a cellular factor that dampened productive HCV replication.

Hepatitis C virus in vitro replication is efficiently inhibited by acridone Fac4

Hepatitis C virus (HCV) affects about 170 million people worldwide. The current treatment has a high cost and variable response rates according to the virus genotype. Acridones, a group of compounds extracted from natural sources, showed potential antiviral actions against HCV. Thus, this study aimed to evaluate the effect of a panel of 14 synthetic acridones on the HCV life cycle. The compounds were screened using an Huh7.5 cell line stably harbouring the HCV genotype 2a subgenomic replicon SGR-Feo-JFH-1. Cells were incubated in the presence or absence of compounds for 72 h and cell viability and replication levels were assessed by MTT and luciferase assays, respectively. At a concentration of 5 µM the acridone Fac4 exhibited a >90 % inhibition of HCV replication with no effect on cell viability. The effects of Fac4 on virus replication, entry and release steps were evaluated in Huh7.5 cells infected with the JFH-1 isolate of HCV (HCVcc). Fac4 inhibited JFH-1 replication to approximately 70 %, while no effect was observed on virus entry. The antiviral activity of Fac4 was also observed on viral release, with almost 80 % of inhibition. No inhibitory effect was observed against genotype 3 replication. Fac4 was able to intercalate into dsRNA, however did not inhibit NS5B polymerase activity or translation driven by the HCV IRES. Although its mode of action is partly understood, Fac4 presents significant inhibition of HCV replication and can therefore be considered as a candidate for the development of a future anti-HCV treatment.

Decreased pro-inflammatory immune responses during recurrent acute HCV infections in HIV co-infected patients

Patients in high-risk groups continue to transmit the hepatitis C virus (HCV) and frequently experience reinfections. Since little is known regarding the immune response to HCV during reinfection, we compared primary and consecutive acute HCV infections in patients with an HIV infection, and focused on the cytokine bridging innate to adaptive immunity. We observed that the serum levels of IL-12p40, MIP-1β, MIG and IP-10 increased during primary acute HCV infection, but not during subsequent secondary acute reinfections. The weaker pro-inflammatory cytokine responses observed during HCV reinfections suggest more limited secondary acute immune responses, which may prevent damage to the infected liver.

Immune modulation by the hepatitis C virus core protein

Hepatitis C virus (HCV) infection is currently the most important cause of chronic viral hepatitis in the world and one of the most frequent indications for liver transplantation. HCV uses different strategies to evade the innate and adaptive immune response, and this evasion plays a key role in determining viral persistence. Several HCV viral proteins have been described as immune modulators. In this review, we will focus on the effect of HCV nucleocapsid core protein in the function of immune cells and its correlation with the findings observed in HCV chronically infected patients. Effects on immune cell function related to both extracellular and intracellular HCV core localization will be considered. This review provides an updated perspective on the mechanisms involved in HCV evasion related to one single HCV protein, which could become a key tool in the development of new antiviral strategies able to control and/or eradicate HCV infection.

Regulatory T Cells in Hepatitis B and C Virus Infections

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are hepatotropic viruses that establish chronic persistent infection by effectively escaping the host immune response and can cause immune-mediated liver injury. It has recently become apparent that regulatory T (Treg) cells, specifically CD4+CD25+Foxp3+ Treg cells, modulate viral diseases by suppressing antiviral immune responses and regulating inflammatory host injury. The roles of Treg cells in HBV and HCV infections range from suppressing antiviral T cell responses to protecting the liver from immune-mediated damage. This review describes Treg cells and subpopulations and focuses on the roles of these cells in HBV and HCV infections.

Characterisation of liver pathogenesis, human immune responses and drug testing in a humanised mouse model of HCV infection

OBJECTIVE

HCV infection affects millions of people worldwide, and many patients develop chronic infection leading to liver cancers. For decades, the lack of a small animal model that can recapitulate HCV infection, its immunopathogenesis and disease progression has impeded the development of an effective vaccine and therapeutics. We aim to provide a humanised mouse model for the understanding of HCV-specific human immune responses and HCV-associated disease pathologies.

DESIGN

Recently, we have established human liver cells with a matched human immune system in NOD-scid Il2rg(-/-) (NSG) mice (HIL mice). These mice are infected with HCV by intravenous injection, and the pathologies are investigated.

RESULTS

In this study, we demonstrate that HIL mouse is capable of supporting HCV infection and can present some of the clinical symptoms found in HCV-infected patients including hepatitis, robust virus-specific human immune cell and cytokine responses as well as liver fibrosis and cirrhosis. Similar to results obtained from the analysis of patient samples, the human immune cells, particularly T cells and macrophages, play critical roles during the HCV-associated liver disease development in the HIL mice. Furthermore, our model is demonstrated to be able to reproduce the therapeutic effects of human interferon alpha 2a antiviral treatment.

CONCLUSIONS

The HIL mouse provides a model for the understanding of HCV-specific human immune responses and HCV-associated disease pathologies. It could also serve as a platform for antifibrosis and immune-modulatory drug testing.

Treatment of Hepatitis C in Patients Undergoing Immunosuppressive Drug Therapy

With 185 million people chronically infected globally, hepatitis C is a leading bloodborne infection. All-oral regimens of direct acting agents have superior efficacy compared to the historical interferon-based regimens and are significantly more tolerable. However, trials of both types of regimens have often excluded patients on immunosuppressive medications for reasons other than organ transplantation. Yet, these patients-most often suffering from malignancy or autoimmune diseases-could stand to benefit from these treatments. In this study, we systematically review the literature on the treatment of hepatitis C in these neglected populations. Research on patients with organ transplants is more robust and this literature is reviewed here non-systematically. Our systematic review produced 2273 unique works, of which 56 met our inclusion criteria and were used in our review. The quality of data was low; only 3 of the 56 studies were randomized controlled trials. Sustained virologic response was reported sporadically. Interferon-containing regimens achieved this end-point at rates comparable to that in immunocompetent individuals. Severe adverse effects and death were rare. Data on all-oral regimens were sparse, but in the most robust study, rates of sustained virologic response were again comparable to immunocompetent individuals (40/41). Efficacy and safety of interferon-containing regimens and all-oral regimens were similar to rates in immunocompetent individuals; however, there were few interventional trials. The large number of case reports and case series makes conclusions vulnerable to publication bias. While firm conclusions are challenging, given the dearth of high-quality studies, our results demonstrate that antiviral therapy can be safe and effective. The advent of all-oral regimens offers patients and clinicians greatly increased chances of cure and fewer side effects. Preliminary data reveal that these regimens may confer such benefits in immunosuppressed individuals as well. More prospective interventional trials would greatly benefit the many patients with chronic hepatitis C on immunosuppressive therapies.

M. tuberculosis T Cell Epitope Analysis Reveals Paucity of Antigenic Variation and Identifies Rare Variable TB Antigens

Pathogens that evade adaptive immunity typically exhibit antigenic variation. By contrast, it appears that although the chronic human tuberculosis (TB)-causing pathogen Mycobacterium tuberculosis needs to counter host T cell responses, its T cell epitopes are hyperconserved. Here we present an extensive analysis of the T cell epitopes of M. tuberculosis. We combined population genomics with experimental immunology to determine the number and identity of T cell epitope sequence variants in 216 phylogenetically diverse strains of M. tuberculosis. Antigen conservation is indeed a hallmark of M. tuberculosis. However, our analysis revealed a set of seven variable antigens that were immunogenic in subjects with active TB. These findings suggest that M. tuberculosis uses mechanisms other than antigenic variation to evade T cells. T cell epitopes that exhibit sequence variation may not be subject to the same evasion mechanisms, and hence vaccines that include such variable epitopes may be more efficacious.

The therapeutic potential of new investigational hepatitis C virus translation inhibitors

INTRODUCTION

Hepatitis C virus (HCV) infection is a leading cause of liver cirrhosis, hepatocellular carcinoma and liver-related death worldwide. Currently, the anti-HCV armamentarium encompasses several direct-acting antivirals (DAA) that achieve very high response rates and have an excellent tolerability profile. However, they do not represent a final solution for HCV global eradication for at least these two reasons: i) some patients harbour resistant strains to DAAs and cannot benefit from currently available treatments; ii) the cost of these drugs remains very high.

AREAS COVERED

This review summarizes pre-clinical and clinical data regarding HCV translation inhibitors, a new class of drugs currently in the pipeline with novel mechanisms of action.

EXPERT OPINION

The availability of DAAs resolved most issues related to HCV treatment compared with the previous interferon-based therapies. However, there are some patients that cannot achieve a viral clearance with currently available treatments. Therefore, there is still room for new drugs in this setting, providing that they demonstrate an advantage in terms of efficacy, safety, cost or or simplicity of use. Based on preliminary results, at least for some promising molecules (e.g. miravirsen and RG-101), studies on safety and efficacy on this intriguing class of drugs are needed.

Immune responses and immunopathology in acute and chronic viral hepatitis

Hepatitis A virus (HAV), hepatitis B virus (HBV) and hepatitis C virus (HCV) are responsible for most cases of viral hepatitis. Infection by each type of virus results in a different typical natural disease course and clinical outcome that are determined by virological and immunological factors. HCV tends to establish a chronic persistent infection, whereas HAV does not. HBV is effectively controlled in adults, although it persists for a lifetime after neonatal infection. In this Review, we discuss the similarities and differences in immune responses to and immunopathogenesis of HAV, HBV and HCV infections, which may explain the distinct courses and outcomes of each hepatitis virus infection.

Natural killer cells in highly exposed hepatitis C-seronegative injecting drug users

Injecting drug use remains the major risk factor for hepatitis C (HCV) transmission. A minority of long-term injecting drug users remain seronegative and aviraemic, despite prolonged exposure to HCV - termed highly exposed seronegative subjects. Natural killer (NK) cells have been implicated in this apparent protection. A longitudinal nested, three group case-control series of subjects was selected from a prospective cohort of seronegative injecting drug users who became incident cases (n = 11), remained seronegative (n = 11) or reported transient high-risk behaviour and remained uninfected (n = 11). The groups were matched by age, sex and initial risk behaviour characteristics. Stored peripheral blood mononuclear cells were assayed in multicolour flow cytometry to enumerate natural killer cell subpopulations and to assess functional activity using Toll-like receptor ligands before measurement of activation, cytokine production and natural cytotoxicity receptor expression. Principal components were derived to describe the detailed phenotypic characteristics of the major NK subpopulations (based on CD56 and CD16 co-expression), before logistic regression analysis to identify associations with exposed, seronegative individuals. The CD56(dim) CD16(+) (P = 0.05, OR 6.92) and CD56(dim) CD16(-) (P = 0.05, OR 6.07) principal components differed between exposed, seronegative individuals and pre-infection samples of the other two groups. These included CD56(dim) CD16(+) and CD56(dim) CD16(-) subsets with CD56(dim) CD16(+) IFN-γ and TNF-α on unstimulated cells, and CD56(dim) CD16(-) CD69(+) , CD107a(+) , IFN-γ and TNF-α following TLR stimulation. The cytotoxic CD56(dim) NK subset thus distinguished highly exposed, seronegative subjects, suggesting NK cytotoxicity may contribute to protection from HCV acquisition. Further investigation of the determinants of this association and prospective assessment of protection against HCV infection are warranted.

Immunological changes in different patient populations with chronic hepatitis C virus infection

AIM: To investigate killer inhibitory and activating receptor expression by natural killer (NK), natural killer T-like (NKT-like) and CD8+ T lymphocytes in patients with chronic hepatitis C virus (HCV) infection with elevated and with persistently normal alanine aminotransferase (PNALT).

METHODS: The percentage of peripheral blood Treg cells, KIR2DL3, ILT-2, KIR3DL1, CD160, NKG2D, NKG2C expressing NK, T and NKT-like cells, cytokine production and NK cytotoxicity were determined by flow cytometry. Twenty-one patients with chronic HCV infection with elevated alanine aminotransferase, 11 HCV carriers with persistently normal alanine aminotransferase and 15 healthy volunteers were enrolled.

RESULTS: No significant differences were observed in the percentage of total T, NK or NKT-like cells between study groups. Comparing the activating and inhibitory receptor expression by NK cells obtained from HCV carriers with PNALT and chronic HCV hepatitis patients with elevated alanine aminotransferase, NKG2D activating receptor expression was the only receptor showing a significant difference. NKG2D expression of NK cells was significantly lower in patients with elevated alanine aminotransferase. The expression of CD160, NKG2D and NKG2C activating receptor by CD8+ T cells were significantly lower in patients with chronic HCV hepatitis than in healthy controls and in HCV carriers with PNALT. Plasma TGF-β1 levels inversely correlated with NKG2D expression by NK cells. In vitroTGF-β1 treatment inhibited NK cells cytotoxic activity and downregulated NKG2D expression. CD8+ T cells from HCV carriers with PNALT showed significantly elevated expression of CD160, NKG2D and NKG2C activating receptors compared to chronic HCV patients with elevated alanine aminotransferase. Enhanced expression of inhibitory KIR2DL3 receptor, and decreased ILT-2 expression on NK cells were also found in chronic hepatitis C patients compared to healthy controls.

CONCLUSION: Our study demonstrated a complex dysregulation of activating and inhibitory receptor expression, such as decreased NKG2D and CD160 activating receptor expression and increased KIR2DL3 inhibitory receptor expression by NK and cytotoxic T cells and may provide further mechanism contributing to defective cellular immune functions in chronic hepatitis C. Increased NKG2D receptor expression in HCV patients with persistently normal ALT suggests an important pathway for sustaining NK and CD8 T cell function and a protective role against disease progression.

New combination antiviral for the treatment of hepatitis C

PURPOSE

The pharmacology, pharmacokinetics, clinical efficacy, and safety of Viekira, as well as its place in hepatitis C virus (HCV) therapy, are reviewed.

SUMMARY

Ombitasvir 25 mg-paritaprevir 150 mg-ritonavir 100 mg plus dasabuvir 250 mg (Viekira) is approved in the United States as a combination direct-acting antiviral agent for treatment-naive or treatment-experienced patients with HCV genotype 1 infection, including those with compensated cirrhosis. It is the first coformulated direct-acting antiviral that targets different stages of the virus's life cycle. Viekira is administered as an oral, interferon-free regimen. Phase III clinical trials demonstrated that Viekira administered with or without ribavirin can achieve sustained virological response rates of ≥90%. These results are notable because they show that high virological cure rates can be achieved without peginterferon and ribavirin. Viekira is also effective for special patient populations, such as individuals coinfected with HIV, liver transplant recipients, and those with advanced renal disease. The most frequently reported adverse effects among patients associated with Viekira without ribavirin were nausea, pruritus, and insomnia. During clinical trials, the most common adverse effects among patients receiving Viekira with ribavirin were fatigue, nausea, pruritus, insomnia, and weakness.

CONCLUSION

Viekira, the first coformulated direct-acting antiviral that targets different stages of the HCV life cycle, is an interferon-free treatment for HCV genotype 1 infection. It is associated with a virological cure rate of ≥90% and treatment durations of 12 and 24 weeks. Viekira is also effective and safe for patients who have undergone liver transplantation, are coinfected with HIV, or have advanced kidney disease.

Influence of cytokine and cytokine receptor gene polymorphisms on the degree of liver damage in patients with chronic hepatitis C

Hepatic fibrosis may be the result of repetitive injury to hepatocytes caused by HCV infection and the immune response to it. Cytokines regulate the inflammatory response to injury and modulate hepatic fibrogenesis. Single nucleotide polymorphisms (SNPs) located in cytokine genes may influence the cytokine expression and secretion that may contribute to hepatic fibrogenesis in HCV infection. The aim of this study was to determine the genotype of 22 SNPs found in the genes of 13 cytokines/cytokine receptors to assess the influence of polymorphic variants on the stage of liver damage in Brazilian patients chronically infected with HCV genotype 1 only. 141 unrelated patients were grouped according to their stage of fibrosis: absence of fibrosis or patients in the initial stages of fibrosis (F0-F2, n = 84), patients with advanced stages of fibrosis or cirrhosis (F3-F4, n = 57), without cirrhosis (F0-F3, n = 103), and with cirrhosis (F4, n = 38). The comparison of frequencies in each sub-sample was performed by 2 × 2 contingency tables using the chi-square or Fisher's exact test. Stepwise logistic regression was also used to assess independent associations between cirrhosis or fibrosis with polymorphic variants. The TNFA-308G:A genotype conferred increased risk of fibrosis and cirrhosis. The TNFA-238G:G genotype was associated with protection from cirrhosis. The IL10-819C:T genotype conferred protection from fibrosis and the IL1B-511C:T genotype conferred increased risk of cirrhosis. Some of these genotypes showed results on the borderline of statistical significance in the bivariate analysis. We conclude that gene variants of cytokines/receptors may influence liver damage in patients chronically infected by HCV genotype 1.

Natural killer cells in hepatitis C: Current progress

Patients infected with the hepatitis C virus (HCV) are characterized by a high incidence of chronic infection, which results in chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. The functional impairment of HCV-specific T cells is associated with the evolution of an acute infection to chronic hepatitis. While T cells are the important effector cells in adaptive immunity, natural killer (NK) cells are the critical effector cells in innate immunity to virus infections. The findings of recent studies on NK cells in hepatitis C suggest that NK cell responses are indeed important in each phase of HCV infection. In the early phase, NK cells are involved in protective immunity to HCV. The immune evasion strategies used by HCV may target NK cells and might contribute to the progression to chronic hepatitis C. NK cells may control HCV replication and modulate hepatic fibrosis in the chronic phase. Further investigations are, however, needed, because a considerable number of studies observed functional impairment of NK cells in chronic HCV infection. Interestingly, the enhanced NK cell responses during interferon-α-based therapy of chronic hepatitis C indicate successful treatment. In spite of the advances in research on NK cells in hepatitis C, establishment of more physiological HCV infection model systems is needed to settle unsolved controversies over the role and functional status of NK cells in HCV infection.

Hepatitis C virus regulates the production of monocytic myeloid-derived suppressor cells from peripheral blood mononuclear cells through PI3K pathway and autocrine signaling

Hepatitis C virus (HCV) infection is a major liver disease that ultimately develops into chronic hepatitis. Consequently, such patients are predisposed to serious complications, such as hepatocellular carcinoma. In HCV-infected patients, impaired T-cell responses are associated with persistent infection. Myeloid-derived suppressor cells (MDSCs) play a pivotal role in suppressing T-cell responses. In this study, we investigated the capacity and mechanism through which HCV transforms CD14+ monocytes into monocytic (Mo)-MDSCs. We showed that HCV core protein promotes CD14+ monocytes to develop a CD14+HLA-DR/low phenotype with upregulated indoleamine 2,3-dioxygenase (IDO) expression and suppressed T-cell proliferation. Importantly, HCV-induced Mo-MDSC production was attributed to the PI3K pathway via induction of IL-10 and TNF-α secretion. This process could be reversed by polyinosinic:polycytidylic acid (polyI:C) treatment. In conclusion, our results suggest that HCV regulates Mo-MDSC production from monocytes through the PI3K pathway and autocrine cytokines. The latter can serve as effective targets for novel HCV therapies.

Peripheral lymphocyte subsets in chronic hepatitis C: Effects of 12 weeks of antiviral treatment with interferon-alpha plus ribavirin

Chronic infection with hepatitis C virus (HCV) causes a quantitative and functional alteration in innate and adaptative immunity. In the present work, we determined by flow-cytometry the profile of blood lymphocyte of untreated HCV patients and in subjects of this group that achieved or not an early virologic response at 12-weeks of treatment with interferon-α plus ribavirin. Twenty-six untreated HCV patients and 20 control healthy individuals were enrolled in the study. Untreated HCV patients had a higher proportion of B cell and a lower proportion of CD8(+) T cell and NK cells than healthy individuals did, but the proportions of CD4(+) T cells and Treg cells (CD4(+)CD25(+)Foxp3(+)) were similar in these patients and controls. Untreated HCV patients presenting cryoglobulinemia had a lower proportion of Treg cells and a lower Treg/NK cell ratio when compared with those without cryoglobulins. Nineteen out of 26 untreated HCV patients remained in the study and were treated with Interferon-α plus ribavirin. At 12-weeks of treatment, 10 of them achieved early virologic response (EVR), whereas 9 were non-responders (NR). EVR patients differed from NR patients in the increase of their proportion of NK cells at 12 weeks of treatment. In conclusion, untreated HCV patients exhibit an altered profile of blood lymphocyte subsets, including a reduction in the proportion of CD4(+)CD25(+)FoxP3(+)T regulatory cells in patients that present cryoglobulinemia. An early virological response at 12-weeks of treatment with IFN-α plus ribavirin seems to be associated a significant improvement in the proportion of NK cells of HCV treated patients.

A systematic analysis of a broadly neutralizing antibody AR3C epitopes on Hepatitis C virus E2 envelope glycoprotein and their cross-reactivity

Background

Hepatitis C virus (HCV) belongs to Flaviviridae family of viruses. HCV represents a major challenge to public health since its estimated global prevalence is 2.8% of the world's human population. The design and development of HCV vaccine has been hampered by rapid evolution of viral quasispecies resulting in antibody escape variants. HCV envelope glycoprotein E1 and E2 that mediate fusion and entry of the virus into host cells are primary targets of the host immune responses.

Results

Structural characterization of E2 core protein and a broadly neutralizing antibody AR3C together with E1E2 sequence information enabled the analysis of B-cell epitope variability. The E2 binding site by AR3C and its surrounding area were identified from the crystal structure of E2c-AR3C complex. We clustered HCV strains using the concept of "discontinuous motif/peptide" and classified B-cell epitopes based on their similarity.

Conclusions

The assessment of antibody neutralizing coverage provides insights into potential cross-reactivity of the AR3C neutralizing antibody across a large number of HCV variants.

Novel human anti-claudin 1 mAbs inhibit hepatitis C virus infection and may synergize with anti-SRB1 mAb

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and liver carcinoma and new therapies based on novel targets are needed. The tight junction protein claudin 1 (CLDN-1) is essential for HCV cell entry and spread, and anti-CLDN-1 rat and mouse mAbs are safe and effective in preventing and treating HCV infection in a human liver chimeric mouse model. To accelerate translation of these observations into a novel approach to treat HCV infection and disease in humans, we screened a phage display library of human single-chain antibody fragments by using a panel of CLDN-1-positive and -negative cell lines and identified phage specifically binding to CLDN-1. The 12 clones showing the highest levels of binding were converted into human IgG4. Some of these mAbs displayed low-nanomolar affinity, and inhibited infection of human hepatoma Huh7.5 cells by different HCV isolates in a dose-dependent manner. Cross-competition experiments identified six inhibitory mAbs that recognized distinct epitopes. Combination of the human anti-SRB1 mAb C-1671 with these anti-CLDN-1 mAbs could either increase or reduce inhibition of cell culture-derived HCV infection in vitro. These novel human anti-CLDN-1 mAbs are potentially useful to develop a new strategy for anti-HCV therapy and lend support to the combined use of antibodies targeting the HCV receptors CLDN-1 and SRB1, but indicate that care must be taken in selecting the proper combination.

Programmed death-1/programmed death-L1 signaling pathway and its blockade in hepatitis C virus immunotherapy

Chronic hepatitis C virus (HCV) infection is a public health issue that often progresses to life-threatening complications, including liver cirrhosis, fibrosis, and hepatocellular carcinoma. Impaired immune responses to HCV are key features of chronic HCV infection. Therefore, intervention strategies usually involve enhancing the immune responses against HCV. Cytotoxic CD8⁺ T lymphocytes (CTLs) play a critical role in the control of HCV infection. However, their cytolytic function can be impaired by the expression of co-inhibitory molecules. Programmed death-1 (PD-1) receptor and its ligand PD-L1 function in a T cell co-inhibitory pathway, which either blocks the function of CTLs or the differentiation of CD8⁺ T cells. During chronic HCV infection, the immune inhibitory receptor PD-1 is upregulated on dysfunctional HCV-specific CD8⁺ T cells. As such, blockade of the PD-1/PD-L1 pathway in these CD8⁺ T cells might restore their functional capabilities. Indeed, clinical trials using therapies to block this pathway have shown promise in the fostering of anti-HCV immunity. Understanding how chronic HCV infection induces upregulation of PD-1 on HCV specific T cells and how the PD-1/PD-L1 interaction develops HCV specific T cell dysfunction will accelerate the development of an efficacious prophylactic and therapeutic vaccination against chronic HCV infections, which will significantly improve HCV treatments and patient survival. In this review, we discuss the relationship between PD-1 expression and clinical responses and the potential use of PD-1 blockade for anti-HCV therapy.

Gene therapies for hepatitis C virus

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis and infects approximately three to four million people per year, about 170 million infected people in total, making it one of the major global health problems. In a minority of cases HCV is cleared spontaneously, but in most of the infected individuals infection progresses to a chronic state associated with high risk to develop liver cirrhosis, hepatocellular cancer, or liver failure. The treatment of HCV infection has evolved over the years. Interferon (IFN)-α in combination with ribavirin has been used for decades as standard therapy. More recently, a new standard-of-care treatment has been approved based on a triple combination with either HCV protease inhibitor telaprevir or boceprevir. In addition, various options for all-oral, IFN-free regimens are currently being evaluated. Despite substantial improvement of sustained virological response rates, some intrinsic limitations of these new direct-acting antivirals, including serious side effects, the risk of resistance development and high cost, urge the development of alternative or additional therapeutic strategies. Gene therapy represents a feasible alternative treatment. Small RNA technology, including RNA interference (RNAi) techniques and antisense approaches, is one of the potentially promising ways to investigate viral and host cell factors that are involved in HCV infection and replication. With this, newly developed gene therapy regimens will be provided to treat HCV. In this chapter, a comprehensive overview guides you through the current developments and applications of RNAi and microRNA-based gene therapy strategies in HCV treatment.

HCV core protein and virus assembly: what we know without structures

Chronic hepatitis C virus (HCV) infection results in a progressive disease that may end in cirrhosis and, eventually, in hepatocellular carcinoma. In the last several years, tremendous progress has been made in understanding the HCV life cycle and in the development of small molecule compounds for the treatment of chronic hepatitis C. Nevertheless, the complete understanding of HCV assembly and particle release as well as the detailed characterization and structure of HCV particles is still missing. One of the most important events in the HCV assembly is the nucleocapsid formation which is driven by the core protein, that can oligomerize upon interaction with viral RNA, and is orchestrated by viral and host proteins. Despite a growing number of new factors involved in HCV assembly process, we do not know the three-dimensional structure of the core protein or its topology in the nucleocapsid. Since the core protein contains a hydrophobic C-terminal domain responsible for the binding to cellular membranes, the assembly pathway of HCV virions might proceed via coassembly at endoplasmic reticulum membranes. Recently, new mechanisms involving viral proteins and host factors in HCV particle formation and egress have been described. The present review aims to summarize the advances in our understanding of HCV assembly with an emphasis on the core protein as a structural component of virus particles that possesses the ability to interact with a variety of cellular components and is potentially an attractive target for the development of a novel class of anti-HCV agents.

Downregulation of viral RNA translation by hepatitis C virus non-structural protein NS5A requires the poly(U/UC) sequence in the 3' UTR

Hepatitis C virus (HCV) non-structural protein 5A (NS5A) is essential for viral replication; however, its effect on HCV RNA translation remains controversial partially due to the use of reporters lacking the 3' UTR, where NS5A binds to the poly(U/UC) sequence. We investigated the role of NS5A in HCV translation using a monocistronic RNA containing a Renilla luciferase gene flanked by the HCV UTRs. We found that NS5A downregulated viral RNA translation in a dose-dependent manner. This downregulation required both the 5' and 3' UTRs of HCV because substitution of either sequence with the 5' and 3' UTRs of enterovirus 71 or a cap structure at the 5' end eliminated the effects of NS5A on translation. Translation of the HCV genomic RNA was also downregulated by NS5A. The inhibition of HCV translation by NS5A required the poly(U/UC) sequence in the 3' UTR as NS5A did not affect translation when it was deleted. In addition, we showed that, whilst the amphipathic α-helix of NS5A has no effect on viral translation, the three domains of NS5A can inhibit translation independently, also dependent on the presence of the poly(U/UC) sequence in the 3' UTR. These results suggested that NS5A downregulated HCV RNA translation through a mechanism involving the poly(U/UC) sequence in the 3' UTR.

Reversal of B-cell hyperactivation and functional impairment is associated with HBsAg seroconversion in chronic hepatitis B patients

B cells play an important role in the clearance of hepatitis B virus (HBV) and protection against reinfection. However, the functional characteristics of these cells that are associated with the outcome of chronic HBV infection remain unknown. We comprehensively investigated the frequency, phenotype, and function of peripheral B-cell subsets from CHB patients in different phases: immune tolerance (IT), immune activation (IA), immune clearance (IC), responders with HBsAg seroconversion (resolved patients, RP), and healthy controls (HC). IA patients displayed lower percentages of peripheral blood memory B cells compared with the other groups. Overall polyclonal activation of B cells, indicated by higher levels of activation markers and secretion of IgG and IgM, was observed in IA patients. This B-cell hyperactivation could be induced by increased IFN-α and soluble CD40 ligands in IA patients. Notably, the expression of the co-stimulator molecule CD80 and serum HBsAb and the frequency of HBsAg-specific B cells were significantly decreased in IT, IA, and IC patients compared with HC subjects. More importantly, the B-cell hyperactivation, co-stimulatory molecule downregulation and HBsAg-specific B-cell impairment were reversed in RP patients. The reversal of B-cell hyperactivation and functional impairment is associated with HBsAg seroconversion in chronic hepatitis B patients.

Within-host stochastic emergence dynamics of immune-escape mutants

Predicting the emergence of new pathogenic strains is a key goal of evolutionary epidemiology. However, the majority of existing studies have focussed on emergence at the population level, and not within a host. In particular, the coexistence of pre-existing and mutated strains triggers a heightened immune response due to the larger total pathogen population; this feedback can smother mutated strains before they reach an ample size and establish. Here, we extend previous work for measuring emergence probabilities in non-equilibrium populations, to within-host models of acute infections. We create a mathematical model to investigate the emergence probability of a fitter strain if it mutates from a self-limiting strain that is guaranteed to go extinct in the long-term. We show that ongoing immune cell proliferation during the initial stages of infection causes a drastic reduction in the probability of emergence of mutated strains; we further outline how this effect can be accurately measured. Further analysis of the model shows that, in the short-term, mutant strains that enlarge their replication rate due to evolving an increased growth rate are more favoured than strains that suffer a lower immune-mediated death rate (‘immune tolerance’), as the latter does not completely evade ongoing immune proliferation due to inter-parasitic competition. We end by discussing the model in relation to within-host evolution of human pathogens (including HIV, hepatitis C virus, and cancer), and how ongoing immune growth can affect their evolutionary dynamics.

The ongoing evolution of infectious diseases provides a constant health threat. This evolution can either result in the production of new pathogens, or new strains of existing pathogens that escape prevailing drug treatments or immune responses. The latter process, also known as immune escape, is a predominant reason for the persistence of several viruses, including HIV and hepatitis C virus (HCV), in their human host. As a consequence, the within-host emergence of new strains has been the intense focus of modelling studies. However, existing models have neglected important feedbacks that affects this emergence probability. Specifically, once a mutated pathogen arises that spreads more quickly than the initial (resident) strain, it potentially triggers a heightened immune response that can eliminate the mutated strain before it spreads. Our study outlines novel mathematical modelling techniques that accurately quantify how ongoing immune growth reduces the emergence probability of mutated pathogenic strains over the course of an infection. Analysis of this model suggests that, in order to enlarge its emergence probability, it is evolutionary beneficial for a mutated strain to increase its growth rate rather than tolerate immunity by having a lower immune-mediated death-rate. Our model can be readily applied to existing within-host data, as demonstrated with application to HIV, HCV, and cancer dynamics.

Transmitted/Founder Viruses Rapidly Escape from CD8+ T Cell Responses in Acute Hepatitis C Virus Infection

The interaction between hepatitis C virus (HCV) and cellular immune responses during very early infection is critical for disease outcome. To date, the impact of antigen-specific cellular immune responses on the evolution of the viral population establishing infection and on potential escape has not been studied. Understanding these early host-virus dynamics is important for the development of a preventative vaccine. Three subjects who were followed longitudinally from the detection of viremia preseroconversion until disease outcome were analyzed. The evolution of transmitted/founder (T/F) viruses was undertaken using deep sequencing. CD8(+) T cell responses were measured via enzyme-linked immunosorbent spot (ELISpot) assay using HLA class I-restricted T/F epitopes. T/F viruses were rapidly extinguished in all subjects associated with either viral clearance (n = 1) or replacement with viral variants leading to establishment of chronic infection (n = 2). CD8(+) T cell responses against 11 T/F epitopes were detectable by 33 to 44 days postinfection, and 5 of these epitopes had not previously been reported. These responses declined rapidly in those who became chronically infected and were maintained in the subject who cleared infection. Higher-magnitude CD8(+) T cell responses were associated with rapid development of immune escape variants at a rate of up to 0.1 per day. Rapid escape from CD8(+) T cell responses has been quantified for the first time in the early phase of primary HCV infection. These rapid escape dynamics were associated with higher-magnitude CD8(+) T cell responses. These findings raise questions regarding optimal selection of immunogens for HCV vaccine development and suggest that detailed analysis of individual epitopes may be required.

IMPORTANCE

A major limitation in our detailed understanding of the role of immune response in HCV clearance has been the lack of data on very early primary infection when the transmitted viral variants successfully establish the acute infection. This study was made possible through the availability of specimens from a unique cohort of asymptomatic primary infection cases in whom the first available viremic samples were collected approximately 3 weeks postinfection and at regular intervals thereafter. The study included detailed examination of both the evolution of the viral population and the host cellular immune responses against the T/F viruses. The findings here provide the first evidence of host cellular responses targeting T/F variants and imposing a strong selective force toward viral escape. The results of this study provide useful insight on how virus escapes the host response and consequently on future analysis of vaccine-induced immunity.

Distinct plasma immune signatures in ME/CFS are present early in the course of illness

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is an unexplained incapacitating illness that may affect up to 4 million people in the United States alone. There are no validated laboratory tests for diagnosis or management despite global efforts to find biomarkers of disease. We considered the possibility that inability to identify such biomarkers reflected variations in diagnostic criteria and laboratory methods as well as the timing of sample collection during the course of the illness. Accordingly, we leveraged two large, multicenter cohort studies of ME/CFS to assess the relationship of immune signatures with diagnosis, illness duration, and other clinical variables. Controls were frequency-matched on key variables known to affect immune status, including season of sampling and geographic site, in addition to age and sex. We report here distinct alterations in plasma immune signatures early in the course of ME/CFS (n = 52) relative to healthy controls (n = 348) that are not present in subjects with longer duration of illness (n = 246). Analyses based on disease duration revealed that early ME/CFS cases had a prominent activation of both pro- and anti-inflammatory cytokines as well as dissociation of intercytokine regulatory networks. We found a stronger correlation of cytokine alterations with illness duration than with measures of illness severity, suggesting that the immunopathology of ME/CFS is not static. These findings have critical implications for discovery of interventional strategies and early diagnosis of ME/CFS.

An Hepatitis C Virus (HCV)/HIV Co-Infected Patient who Developed Severe Hepatitis during Chronic HCV Infection: Sustained Viral Response with Simeprevir Plus Peginterferon-Alpha and Ribavirin

We herein describe the case of a 42-year-old man who developed severe hepatitis caused by hepatitis C virus (HCV) infection at 14 years after the start of human immunodeficiency virus (HIV) treatment. Surprisingly, the levels of alanine aminotransferase (ALT) fluctuated, reaching a peak higher than 1,000 IU/L during chronic HCV infection, and the hepatic histology showed advanced liver fibrosis at 3 years after the primary HCV infection. He was treated with simeprevir, peginterferon-alpha, and ribavirin with a sustained viral response. We conclude that HCV/HIV co-infected patients need to commence anti-HCV therapy when the levels of ALT fluctuate severely under successful HIV control.

The Humoral Immune Response to HCV: Understanding is Key to Vaccine Development

Hepatitis C virus (HCV) remains a global problem, despite advances in treatment. The low cost and high benefit of vaccines have made them the backbone of modern public health strategies, and the fight against HCV will not be won without an effective vaccine. Achievement of this goal will benefit from a robust understanding of virus-host interactions and protective immunity in HCV infection. In this review, we summarize recent findings on HCV-specific antibody responses associated with chronic and spontaneously resolving human infection. In addition, we discuss specific epitopes within HCV's envelope glycoproteins that are targeted by neutralizing antibodies. Understanding what prompts or prevents a successful immune response leading to viral clearance or persistence is essential to designing a successful vaccine.