Selection of hepatitis C virus quasispecies during interferon treatment

Quasispecies of genotype 4 of hepatitis C virus genomes in Saudi patients managed with interferon alfa and ribavirin therapy

BACKGROUND AND OBJECTIVES

Many patients with hepatitis C virus (HCV) infection do not respond to antiviral treatment, possibly due to viral quasispecies. We aimed to investigate whether the quasispecies population could be used as a predictor of response to therapy in our patients.

METHODS

The quasispecies of HCV genotype 4 (HCV-4) were studied in 25 naïve Saudi patients at zero, three, and six months following interferon alfa and ribavirin combination therapy. Hypervariable region 1 within the E2/NS1 gene of the virus was analyzed by the single-strand conformation polymorphism (SSCP) technique after amplification.

RESULTS

Pretreatment DNA bands by SSCP (2-7 bands) were detected in all patients. In those who achieved a complete virological response within six months (viral load P=.53). Two of the four patients with pretreatment high viral load and the same or decreased composition of quasispecies bands responded to the therapy.

CONCLUSION

Quasispecies in our studied patients cannot be used to predict responsiveness to treatment, but may offer an explanation for failure of most HCV-4 patients to respond to interferon alfa and ribavirin therapy.

Replicative homeostasis: a fundamental mechanism mediating selective viral replication and escape mutation

Hepatitis C (HCV), hepatitis B (HBV), the human immunodeficiency viruses (HIV), and other viruses that replicate via RNA intermediaries, cause an enormous burden of disease and premature death worldwide. These viruses circulate within infected hosts as vast populations of closely related, but genetically diverse, molecules known as "quasispecies". The mechanism(s) by which this extreme genetic and antigenic diversity is stably maintained are unclear, but are fundamental to understanding viral persistence and pathobiology. The persistence of HCV, an RNA virus, is especially problematic and HCV stability, maintained despite rapid genomic mutation, is highly paradoxical. This paper presents the hypothesis, and evidence, that viruses capable of persistent infection autoregulate replication and the likely mechanism mediating autoregulation - Replicative Homeostasis - is described. Replicative homeostasis causes formation of stable, but highly reactive, equilibria that drive quasispecies expansion and generates escape mutation. Replicative homeostasis explains both viral kinetics and the enigma of RNA quasispecies stability and provides a rational, mechanistic basis for all observed viral behaviours and host responses. More importantly, this paradigm has specific therapeutic implication and defines, precisely, new approaches to antiviral therapy. Replicative homeostasis may also modulate cellular gene expression.

Significance of pretreatment analysis of hepatitis C virus genotype 1b hypervariable region 1 sequences to predict antiviral outcome

The heterogeneity of hypervariable region 1 (HVR1), located at the amino terminus of the E2 envelope, may be involved in resistance to alpha interferon (IFN-alpha) treatment. We investigated whether peculiar HVR1 domain profiles before treatment were associated with the maintenance of sensitivity or the appearance of resistance to treatment. Fifteen patients infected with hepatitis C virus genotype 1b and treated with IFN with or without ribavirin were selected. Ten responded to treatment (groups R1 and R2) and five did not (group NR). The amino acid sequences of 150 naturally occurring HVR1 variants present in the serum before therapy were compared in relation to treatment outcome. HVR1 variants from the NR group contained a constant nonantigenic amino acid segment that was not found in HVR1 variants from the R groups.

Hepatitis C virus. The importance of viral heterogeneity

Although recent evidence indicates that the quasispecies nature of HCV constitutes a critical strategy for the virus to survive in the host, the mechanisms of viral persistence remain unknown. Similarly, the correlates of immune protection in a limited proportion of individuals who succeed in clearing HCV are still largely undefined. Understanding the mechanisms of sterilizing immunity is essential for devising preventive measures against HCV and unraveling how the virus eludes such immunity. As in other viral infections, the complex interactions between the virus and the host early in the course of HCV infection probably determine the outcome of the disease (i.e., resolution or persistence). The evidence now accumulated on HCV and other models of viral infection is compatible with the hypothesis that both cellular and humoral components are needed for definitive viral clearance. Nevertheless, detailed studies of the specific cellular and humoral immune responses during the incubation period and the acute phase of hepatitis C, in relation to the viral quasispecies evolution and the clinical outcome, are still lacking both in humans and in the chimpanzee model. Until such studies are performed, most ideas of viral clearance mechanisms remain hypothetical, and the immunologic basis of HCV clearance will continue to be inferred from associations rather than from causal relationships.

[Characteristics of the hepatitis C virus and viral predictors of therapeutic response]

NATURAL HISTORY OF HEPATITIS C-INFECTION AND VIRAL CHARACTERISTICS: Hepatitis C-virus (HCV) infection is a major cause of non-A, non-B-hepatitis and, additionally, is associated with liver cirrhosis and hepato-cellular carcinoma. The high degree of chronificity of HCV-infection is reasonable due to antigenic variability of neutralizing epitopes leading to incomplete immunoresponse with subsequent virus persistence. Besides genetic variants of HCV within a virus population (quasispecies nature of HCV), different genotypes are classified being genetically and phenotypically distinct, and geographically restricted in part. Genotyping of HCV is not only important for phylogenetic and epidemiological studies, but also a predictive marker for pathogenesis and therapy. VIRAL PREDICTORS OF HCV THERAPY: In a meta-analysis of 18 therapeutical studies of chronical HCV infections, genotype 1 and high levels of viremia determined markedly the response to interferon therapy. In this context, clinical trials have proven the effect of a combined therapy with interferon and ribavirin. Especially patients with HCV genotype 1 or high levels of viremia had a real benefit from combined antiviral therapy in comparison to monotherapy with interferon. CONCLUSION AND FUTURE CONCEPTS: Besides recent concepts improving the therapeutical response to HCV infection, further effort is necessary to develop more successful strategies for eradication of hepatitis C virus. In this context, variations of interferon therapy should be evaluated (e.g. higher and daily doses, longer duration of interferon therapy, "retarded" interferon (PEG-IFN). In addition, new therapeutical concepts should be performed including a combination of interferon with other known antiviral agents (amantadine), a combination with immunomodulators (GM-CSF, thymosin alpha 1), the development of new antiviral agents (inhibitors of viral proteases, helicases and polymerases) and the exploration of anti-viral, molecular strategies (specific ribozymes, antisense oligonucleotides and DNA-vaccination). Nevertheless, the development of an effective vaccination should be the most important challenge for the future.

Selection of genetic variants of the 5' noncoding region of hepatitis C virus occurs only in patients responding to interferon alpha therapy

Interferon alpha (IFN alpha) can suppress the replication of hepatitis C virus (HCV) in chronically infected patients. However, HCV persists in a significant number of patients despite the normalization of alanine transaminase (ALT) during IFN alpha therapy. In this study, HCV variants in patients under IFN alpha therapy were characterized to examine their role in viral persistence during the therapy. Sixteen patients selected for this study were infected with HCV genotype 1b and remained HCV RNA positive for at least 1 month after onset of therapy. Nine patients responded to the therapy in terms of normalization of ALT (responders), whereas seven patients did not show a significant decrease of ALT level (nonresponders). To examine HCV populations in these patients, the HCV 5' noncoding region (5' NCR) was analyzed by polymerase chain reaction amplification and sequencing. Newly emerging variants of the HCV 5' NCR replaced predominant variants present prior to IFN alpha therapy in six of nine responders. Most predominant HCV variants during IFN alpha therapy carried a nucleotide substitution G to A at nt 231 within the 5' NCR. An analysis of the HCV quasispecies population in one responder revealed that a preexisting variant became predominant under IFN alpha therapy. These results emphasized the importance of the genetic heterogeneity of the HCV genome for viral resistance to IFN alpha. Five of seven HCV isolates from nonresponders were identical to those found in responders with regard to the nucleotide sequence of the 5' NCR. However, no selection of variants of the HCV 5' NCR occurred in nonresponders during the course of therapy. We conclude that IFN alpha treatment leads to the selection of variants of the HCV 5' NCR only in responders and may act differently in nonresponders. Our results suggest that the HCV 5' NCR may be a target of anti-HCV actions of IFN alpha.

The "interferon sensitivity determining region" of hepatitis C virus is a stable sequence element

BACKGROUND/AIMS

A sequence of 40 amino acids within the nonstructural protein 5A of hepatitis C virus (HCV) has been suggested to be an interferon sensitivity determining region (ISDR). The variations in the ISDR after 12-14 years of chronic infection and the correlation between ISDR and interferon response were studied in patients who were infected by the same HCV isolate.

METHODS

We determined the HCV-ISDRs of 13 chronically infected patients by direct sequencing of polymerase chain reaction products. All patients were infected by isolate HCV-AD78, but differed with respect to their sensitivity to interferon. Four patients were complete responders, two patients were non-responders, and seven showed a partial response.

RESULTS

The ISDR of HCV-AD78 differed from a prototypical HCV-1b sequence in one amino acid and was therefore classified as an intermediate type. Direct sequencing of the HCV-ISDRs of the patients 12-14 years after infection, but before interferon therapy, revealed a rate of 2.2x10(-3) nucleotide substitutions per site per year, resulting in only single intermediate type amino acid exchanges. All sequences ranked with the intermediate type. Moreover, during interferon treatment no selection to a wild type ISDR was observed in five partial responders.

CONCLUSIONS

Within the homogeneous patient group examined here, no correlation was found between the ISDR and the interferon response. Recent studies found only a small number of mutant type ISDRs in Europe. Additionally, our results indicate that the ISDR is a stable sequence element. This provides an explanation for the divergent data relating to the importance of the ISDR in different geographical regions.

Role of anti-interferon antibodies in breakthrough occurrence during alpha 2a and 2b therapy in patients with chronic hepatitis C

BACKGROUND/AIMS

Alpha interferon induces aminotransferase normalization in about 50% of patients with chronic viral hepatitis C. However, some patients who initially respond experience a relapse during the treatment period (breakthrough phenomenon). The aim of this study was to evaluate the prevalence of breakthrough and its relationship with the emergence of neutralizing anti-interferon antibodies.

METHODS

We studied 172 patients with histologically proven chronic hepatitis C, treated with interferon alpha 2a or 2b 3 mega units three times a week for 6 months. For each patient, HCV RNA level (polymerase chain reaction and bDNA) and anti-interferon antibodies dosage were determined during therapy.

RESULTS

Among 84 patients with initial response, 13 (15.5%) experienced breakthrough. The kinetics of alanine aminotransferase and HCV RNA levels were strongly correlated, suggesting that breakthrough is not due to a random alanine aminotransferase fluctuation during treatment, but to the reappearance of viral replication. Neutralizing anti-interferon antibodies emergence was observed in 38.5% in patients with breakthrough, as compared to 9.0% and 2.8% of non-responder and complete-responder patients, respectively (p<0.0005). By multivariate analysis, the only factor predictive of breakthrough was the emergence of neutralizing anti-interferon antibodies 3 months after the onset of therapy.

CONCLUSION

Our results suggest that the emergence of neutralizing anti-interferon antibodies during treatment may explain breakthrough in about one third of cases. Other causes may also be responsible for this phenomenon and they remain to be determined.