No abstract

Resistance mutations to hepatitis C virus (HCV) nonstructural protein 3 (NS3) protease inhibitors in <1% of the viral quasispecies may still allow >1000-fold viral load reductions upon treatment, consistent with their reported reduced replicative fitness in vitro. Recently, however, an R155K protease mutation was reported as the dominant quasispecies in a treatment-naïve individual, raising concerns about possible full drug resistance. To investigate the prevalence of dominant resistance mutations against specifically targeted antiviral therapy for HCV (STAT-C) in the population, we analyzed HCV genome sequences from 507 treatment-naïve patients infected with HCV genotype 1 from the United States, Germany, and Switzerland. Phylogenetic sequence analysis and viral load data were used to identify the possible spread of replication-competent, drug-resistant viral strains in the population and to infer the consequences of these mutations upon viral replication in vivo. Mutations described to confer resistance to the protease inhibitors Telaprevir, BILN2061, ITMN-191, SCH6 and Boceprevir; the NS5B polymerase inhibitor AG-021541; and to the NS4A antagonist ACH-806 were observed mostly as sporadic, unrelated cases, at frequencies between 0.3% and 2.8% in the population, including two patients with possible multidrug resistance. Collectively, however, 8.6% of the patients infected with genotype 1a and 1.4% of those infected with genotype 1b carried at least one dominant resistance mutation. Viral loads were high in the majority of these patients, suggesting that drug-resistant viral strains might achieve replication levels comparable to nonresistant viruses in vivo. Conclusion: Naturally occurring dominant STAT-C resistance mutations are common in treatment-naïve patients infected with HCV genotype 1. Their influence on treatment outcome should further be characterized to evaluate possible benefits of drug resistance testing for individual tailoring of drug combinations when treatment options are limited due to previous nonresponse to peginterferon and ribavirin.

The immune response to viral antigens is thought to be responsible for viral clearance and disease pathogenesis during hepatitis C virus (HCV) infection. In chronically infected patients, the T-cell response to the HCV is polyclonal and multispecific, although it is not as strong as the response in acutely infected patients who display a more vigorous T-cell response. Importantly, viral clearance in acutely infected patients is associated with a strong CD4 ؉ helper T-cell response. Thus, the dominant cause of viral persistence during HCV infection may be the development of a weak antiviral immune response to the viral antigens, with corresponding inability to eradicate infected cells. The most striking feature of hepatitis C is its tendency toward chronicity. The hepatitis C virus (HCV) contains a positive-stranded RNA genome of about 10 kilobases, which contains a single uninterrupted open reading frame that encodes a protein of 3010-3011 amino acids. 1,2 The virus is classified as a Flavivirus. HCV infects an estimated 400 million people, corresponding to more than 3% of the world population. 3 Numerous partial and complete nucleotide sequences have been derived from geographically widespread HCV isolates. The data indicate substantial sequence diversity within, and especially between, each geographic area. The European and American isolates appear to be more closely related to each other than to the Japanese isolates. Based on a polymerase chain reaction-based algorithm, a classification system has been proposed by Okamoto 4 and revised by Simmonds. 5 Different viral sequences (quasispecies) have been isolated from the same patient upon sequential sampling, and multiple isolates have been reported in a single sample. 6 The degree of similarity between isolates at the amino acid level varies from genome region to region. The nucleocapsid protein (core) has the highest sequence homology among all isolates sequenced to date. In contrast, the E1 and E2/NS1 regions present the highest degree of sequence variability among different isolates; in particular, the N terminal portion of E2/NS1 contains a hypervariable region of 30 amino acids, which shows extensive variation between virtually all known isolates. 7 The major extracellular loop of CD81, a cell-surface protein widely expressed on B and T lymphocytes and other cells including hepatocytes, has been shown to bind E2. 8 The recent success of isolating a cDNA clone capable of generating infectious RNA transcripts may be an important step toward the development of a tissue culture system. 9,10 The only animal model, the chimpanzee, mirrors several features of human HCV infection. Most importantly, the frequency of persistent infection is high in both species, and virus replication occurs despite evidence of cellular and humoral immune responses. 11,12 A key difference is that necroinflammatory lesions in chronically infected chimpanzees are almost always mild, whereas in humans, the disease spectrum is very wide, ranging from mild to severe hepatitis and end-sta...

The HLA class I-restricted cytotoxic T Iymphocyte (CTL) response is a major defense mechanism in viral infections. It has been suggested that the CTL response may contribute to viral clearance and liver cell injury during hepatitis C virus (HCV) infection. To test this hypothesis requires an understanding of the characteristics of HCV-specific cytotoxic effector cells and identification of the target antigens to which they respond. To begin this process we stimulated peripheral blood mononuclear cells (PBMC) from a group of HLA-A2 positive patients with chronic hepatitis C with a panel of 130 HCV-derived peptides containing the HLA-A2 binding motif. Effector cells were tested for their capacity to lyse HLA-A2-matched target cells that were either sensitized with peptide or infected with a vaccinia virus construct containing HCV sequences. Using this approach we have identified nine immunogenic peptides in HCV, three of which are derived from the putative core protein, three from the nonstructural (NS) 3 domain, two from NS4 and one from NS5. Selected responses were shown to be HLA-A2 restricted, mediated by CD8+ T cells and to recognize endogenously synthesized viral antigen. Unexpectedly, peptide-specific CTL responses could also be induced in seronegative individuals, suggesting in vitro activation of naive CTL precursors. The precursor frequency of peptide-specific CTL was 10 to 100-fold higher in infected patients compared to uninfected controls, and the responses were greatly diminished by removal of CD45 RO + (memory) T cells. Further quantitative studies are clearly required to establish whether a correlation exists between the HCVspecific CTL response and the clinical course of this disease. Definition of the molecular targets of the human CTL response to HCV creates this opportunity, and may also contribute to the development of a T cell-based HCV vaccine.(J. Clin. Invest. 1995. 95:521-530.)

Cellular immune responses are likely to play a key role in determining the clinical outcome in acute infection with hepatitis C virus (HCV), but the dynamics of such responses and their relationship to viral clearance are poorly understood. In a previous study we have shown highly activated, multispecific cytotoxic T lymphocyte responses arising early and persisting in an individual who subsequently cleared the virus. In this study the HCV‐specific CD8+ lymphocytes response has been similarly analyzed, using peptide‐HLA class I tetramers, in a further nine individuals with documented acute HCV infection, six of whom failed to clear the virus. Significant populations of virus‐specific CD8+ lymphocytes were detected at the peak of acute hepatic illness (maximally 3.5 % of CD8+ lymphocytes). Frequencies were commonly lower than those seen previously and were generally not sustained. Early HCV‐specific CD8+ lymphocytes showed an activated phenotype in all patients (CD38+ and HLA class II+), but this activation was short‐lived. Failure to sustain sufficient numbers of activated virus‐specific CD8+ lymphocytes may contribute to persistence of HCV.

CD8+ T lymphocytes play a major role in antiviral immune defense. Their significance for acute hepatitis C is unclear. Our aim was to correlate the CD8+ T cell response with the outcome of infection. Eighteen patients with acute hepatitis C and 19 normal donors were studied. Hepatitis C virus (HCV)-specific CD8+ T cells were identified in the enzyme-linked immunospot assay by their interferon-gamma (IFN-gamma) production after specific stimulation. The highest numbers of IFN-gamma-producing HCV-specific CD8+ T cells were found in patients with acute hepatitis C and a self-limited course of disease during the first 6 months after onset of disease, but these numbers dropped thereafter to undetectable levels. The differences in responsiveness between patients with self-limited disease versus patients with a chronic course were statistically significant (P<.001). Our data show that the number of IFN-gamma-producing HCV-specific CD8+ T cells during the first 6 months after onset of disease is associated with eradication of the HCV infection.

No abstract

A new polymorphism near the IL28B locus negatively affects induction of IL28B and exhibits strong predictive value for HCV treatment response and spontaneous resolution.