HCV genotype 1a shows a better virological response to antiviral therapy than HCV genotype 1b

Despite the promise of new antiviral drugs that can act directly on hepatitis C viral replication such as protease and polymerase inhibitors, a 48 weeks course of PEGylated interferon (PEG-INF) combined with ribavirin remains the current standard treatment for genotype 1 chronic hepatitis C (CHC) [1, 2]. Extensive research has shown that patients infected with HCV genotype 1 have a lower rate of viral response than those infected with genotype 2 or 3. In large randomized multinational trials, PEGylated interferon α-2a plus ribavirin has produced an SVR of about 50% in the more difficult-to-treat subgroup of patients infected with HCV genotype 1 [3, 4]. Furthermore, advanced fibrosis is a predictor of non response to antiviral treatment in patients with genotype 1 virus [5–7]. Very few studies have examined whether the subtype of genotype 1(1a or 1b) affects the rate of SVR [7–10].

We have performed an observational study on a large cohort of “naïve” HCV patients to evaluate the influence of HCV subtypes 1 on the response to treatment with PEG-INF plus ribavirin.

We have conducted a large observational study to assess the influence of viral subtype within HCV genotype 1 on the virological response to antiviral treatment in naïve HCV patients. Logistic regression analysis showed that HCV subtype 1a, mild liver fibrosis scored as less than S3 (Ishak score), HCV-RNA level less than 5.6 log₁₀ IU/ml, age less than 50 years, and ALT level less than 100 IU/ml were all independent predictors of SVR.

Many efforts have been made to identify predictors of SVR to antiviral treatment in the difficult-to- treat chronic hepatitis C genotype 1 patients. Liver histology and viral HCV-RNA levels seem to be particularly important predictor of response in these patients. A recent study by Cheng et al. showed that naïve genotype-1 patients with advanced fibrosis were less likely to achieve SVR than those without advanced fibrosis [5]. Bruno et al. demonstrated that age and liver fibrosis predicted the response rate to PEG-INF and ribavirin combination therapy [6]. Few studies have investigated the impact of viral subtype on SVR genotype 1 patients. A study by Legrand-Abravanel et al. showed by multivariate analysis that genotype 1 subtype 1a was associated with a lower response to HCV therapy than subtype 1b [8]. However, this was an observational study with some potential confunding factors: more than 23% of the patients were concomitantly infected with HIV or HBV; and nearly 35% were interferon experienced patients. Similarly, Nicot et al. found that genotype 1b and HCVRNA < 15IU/ml were the only independent predictors of SVR in genotype 1 patients. However the population of patients analysed in this study was not homogeneous: 23% of all patients were coinfected with HIV and 42% had not responded to previous interferon treatment [9]. Zein et al. found no difference in SVR rates between subtype 1a and 1b patients treated with standard interferon [13]. The PROBE study, which included more than 6000 HCV infected patients, showed that SVR was marginally associated with subtype 1a ( OR 1.41; 95% CI 1.0-2.03) [7]. A recent observational study with a retrospective and prospective phase conducted in Italy (AIFA study), which included naïve, relapser and no responder patients, showed that genotype 1a naive patients experienced a rate of SVR around 6% higher than that observed for genotype 1b naïve patients and comparable to that observed in genotype 4 (retrospective phase-SVR G1a versus G1b 37.1 vs 31.6% p < 0.001 and prospective phase-SVR 31.0 vs 26.5% p < 0.001) [10]. A higher rate of adverse events and in particular of anemia reported in AIFA study, could have influenced the different rate of SVR observed respect to our study. We hypothesize that, in particular, an high rate of anemia could have been responsible for ribavirin or peginterferon dose modification in the AIFA study (data not reported).

Genotype 1 subtypes 1a and 1b are the most common HCV genotypes in the United State. These subtypes are also predominant in Europe and subtype 1b is responsible for up to 73% of HCV infection in Japan. Zein et al. found that patients with HCV subtype 1b were older on average than those infected with other genotypes and that subtype 1b may have been present in some countries before the other genotypes. All patients who acquired HCV before 1955 were infected with subtype 1b. Subtype 1a was introduced in the late 1950s and then, it became the most prevalent genotype [13]. According to this model HCV subtype 1b is associated with more severe liver disease not because it is a more aggressive form of HCV but because it reflect a longer duration of infection [14]. In our study more genotype 1b than genotype 1a patients relapsed after treatment although the difference was not statistically significance. This difference could have been due to the higher percentage of slow responding patients in genotype 1b group than in genotype 1a group. Some studies have demonstrated a significant association between slow response and relapse in patients with an EVR[15, 16]. Although genotype 1a present a lower age and lower baseline HCVRNA level respect to genotype 1b patients, the logistic regression analysis and in particular Adjusted odds ratio shows the independent influence of genotype 1a on SVR without the disturbing influence of other variables. For the above- mentioned reasons subtype 1b patients may respond less favourably than subtype 1a patients to PEG-INF plus ribavirin.

While we observed in dual antiviral therapy a better SVR of genotype 1a respect to genotype 1b patients, genotype 1a presents higher virologic failure respect to genotype 1b in patients treated with triple antiviral combination therapy including protease inhibitors Boceprevir or Telaprevir. Overall, the barrier to resistance is lower in genotype 1a than in genotype 1b strains, resulting in higher breakthrough rates in the former [17].

In our study we found similar SVR in patients treated with pegylated interferon alfa-2a and alfa 2-b, this is in agreement with Ideal and AIFA study [10, 18] but it is in contrast with two italian randomized controlled studies that demonstrated higher SVR in genotype 1 patients treated with pegylated interferon alfa-2a [19, 20]. At present the superiority of one regimen over the other in terms of treatment efficacy remains unknown. The performance of the two drugs has not been explored in patients stratified by treatment modifiers such as fibrosis stage, basal viral load, insulin resistance, age and it is unlikely that future effort will extend current knowledge as we enter in the era of protease and polymerase inhibitors [21].

The interleukin-28B (IL28B) polymorphism has been reported to influence viral kinetics and SVR in genotype 1 patients [22]. We did not determine this parameter in the present study; its significance was not known at the time that the study was conducted. Therefore, we cannot exclude the possibility that our subtype 1a patients may have had a more favourable IL28B polymorphism profile than did the subtype 1b patients. IL28B polymorphism could be an additional parameter explaining the uniquely higher SVR rate for subtype 1a versus 1b observed in the Italian population.

Finally, we would like to emphasise that this study was conducted in “real- world- patients”, thus providing a representative picture of HCV treatment.

While in triple antiviral combination therapy including protease inhibitors Boceprevir or Telaprevir genotype 1a presents higher virologic failure respect to genotype 1b patients, we observed in dual antiviral therapy a better SVR of genotype 1a respect to genotype 1b patients that is independent of other factors that may favour viral clearance.