Although the recent approval of Direct Antiviral Agents (DAA) for treatment of CH-C will change the treatment course of CH-C patients, over the past decade, the combination of PEG-INF/RBV has been the standard treatment for CH-C with 47% to 54% SVR rates . Recently, the discovery of IL28B, as a strong predictor of SVR, has brought a great deal of enthusiasm. Multiple studies have shown that CH-C patients carrying the C/C genotype have a two-fold greater chance of SVR than patients with the T* genotype (8, 10, 11). Our results are consistent with these data, showing that SVR rates are 2-3 times higher in CH-C patients with IL28B CC genotype.
Additional research has shown that IL28B T* genotype is more common in African American patients with CH-C [8, 9] who typically don't respond favorably to PEG-IFN/RBV . Consistent with these data, our study showed a higher prevalence of the T* allele in African American patients with CH-C (Table 1). These data confirm the role of IL28B genotypes in SVR and provide evidence for validation of our data [26, 27].
Despite the strong association between IL28B CC genotype and SVR, the underlying mechanism of IL28 B in determining SVR remains unknown. It is postulated that interferon lambda may produce a better immunologic profile that could favor viral clearance . Recent study by Honda and co-authors demonstrated that the expression of hepatic interferon-stimulated genes is strongly associated with both treatment response and genetic variation of IL28B . In our study, we assessed the impact of PEG-IFN/RBV on the gene expression profiles in PBMCs of patients with CH-C during treatment and analyzed these data according to their IL28B genotype status as well as their SVR outcome. We used previously collected gene expression data from a cohort of CH-C patients who were undergoing treatment with PEG-IFN/RBV  and analyzed the gene expression profile of these patients according to these patients' IL28B genotype status. Furthermore, this gene expression analysis was coupled with pathway analyses offering a novel approach to the interpretation of gene expression data . This approach provided us with further advancement over previously published time course studies of IFN-inducible genes in PBMCs of HCV patients treated with PEG-IFN/RBV [30, 31].
Our approach was validated by the fact that the most commonly activated pathway in our analysis was the Hepatitis C Pathway itself [Figure 1] Analysis of this pathway revealed two interesting observations. First, CH-C patients with IL28B T* genotype seem to have baseline activation of the Hepatitis C Pathway, via the increased expression of the IKBKE gene known to be essential for regulating antiviral signaling, whereas the CH-C patients with the IL28B C/C genotype showed activation in this pathway only after the initiation of treatment (Day 7). Second, we observed that IL28B C/C genotype patients with CH-C maintained a sustained involvement of this pathway throughout the entire 56 days of treatment with PEG-IFN/RBV; The IL28B T* patients, on the other hand, showed activation at baseline, with minimal involvement past day 7 after the initiation of treatment (Table 3).
Our study also highlighted the Chemokine Signaling as a pathway of interest. In fact, patients with CH-C IL28B CC genotype showed a clear treatment induced involvement of this pathway, whereas IL28B T* genotype failed to show any treatment induced activation of this pathway (Table 4).
It should be noted that IL28B polymorphisms has not been as strongly associated with treatment outcomes for patients with chronic hepatitis B or human immunodeficiency virus to date [32, 33]. However, it is possible that HCV shares its regulatory pathways with other types of viruses. In this context, our observation that the pathway related to measles infection is especially intriguing [Figure 2]. In fact, it has been recently shown that the V protein of the measles virus is a potent inhibitor of IFN-lambda which is encoded by the IL28B gene . It may be interesting to assess any potential association of IL28B and SVR in CH-C patients according to their previous exposure to measles virus or MMR vaccine.
To gain additional insights into the mechanisms of genotype-specific treatment-failure, we compared the lists of genes which were differentially expressed in patients who could not achieve SVR, irrespective of their Il28B genotype status. Remarkably, when gene expression patterns were compared at baseline, IRF2 and SOCS1 genes were independently identified as being down-regulated in all CH-C patients who failed treatment, regardless of their IL28B genotypes. Interestingly, transcriptional silencing of the SOCS1 gene in the liver has been suggested as a potential reason for treatment failure in CH-C patients as well as in the mouse model of chronic HCV infection . In both instances, silencing of SOCS1 led to permanent activation of the JAK-STAT signaling pathway . Additionally, hepatocytes lacking SOCS-1 exhibit a prolonged response to IFNγ . Conversely, when SOCS1 was over-expressed, the propagation of the signal through hepatic interferon-dependent pathways is abrogated [36, 37]. In fact, this interferon pathway shutdown also influences IFN-λ . Our data collected using PBMCs indicate that the action of SOCS1 is independent of IL28B genotype. Furthermore, our data suggest that CH-C patients who do not have the SOCS1 gene silenced have a better chance of achieving SVR. This hypothesis is supported by our previous observation that the lack of SOCS1 suppression in PBMCs could serve as a predictor of SVR, independent of the viral genotype or treatment status .
This study has two major limitations, an enrollment of patients infected by different HCV genotypes and of different ethnicity and evaluation of peripheral blood samples instead of hepatic tissue. However, it is important to note that we carried out our gene expression pathway analyses with all HCV genotypes and then analyzed the data separately for HCV genotype 1 patients. This was done to assess the impact of HCV genotype- specific response according to IL28B alleles. Nevertheless, the results of our pathway analyses for both HCV genotype groups were very similar, confirming that IL28B acts independent of HCV genotype.