Reply to: “Understanding triphasic HCV decline during treatment in the era of IL28B polymorphisms and direct acting antiviral agents via mathematical modeling”
Authors: Charles D. Howell, Runyan Jin, Thomas C. Dowling
Journal: Journal of Hepatology (2012)

Single nucleotide polymorphism upstream of interleukin 28B associated with phase 1 and phase 2 of early viral kinetics in patients infected with HCV genotype 1Journal of HepatologyVol. 56Issue 3PreviewWe studied the relationship between IL28B gene-related SNP rs12979860 and early viral kinetics (day 0–28) during peginterferon and ribavirin treatment, in 173 African Americans (AA) and 188 Caucasian Americans (CA) with HCV genotype 1. Full-Text PDF Understanding triphasic HCV decline during treatment in the era of IL28B polymorphisms and direct acting antiviral agents via mathematical modelingJournal of HepatologyVol. 58Issue 4PreviewHowell and colleagues [1] have recently provided important insights into the relationship among viral kinetic patterns, including the triphasic pattern (Fig. 1 in [1]), ethnicity (African Americans, AA, and Caucasian Americans, CA) and IL28B genotypes (rs12979860; CC, TC and TT genotypes) during pegylated interferon-alpha-2a (PegIFNα-2a) + ribavirin (RBV) treatment. Their study strongly suggested differences in viral kinetic patterns under PegIFNα-2a ± RBV between AA and CA are associated with IL28B genotypes and elegantly showed that the difference disappears in AA or CA subjects with the same favorable allele (CC). Full-Text PDF Open Access We thank Dahari et al. for their comments on our recent manuscript investigating the relationship between IL28B SNP 12979860 and early HCV RNA kinetics in 173 African American (AA) and 188 Caucasian American (CA) patients infected with chronic HCV genotype 1, during peginterferon alfa-2a and ribavirin (PegIFN-α-2a/RBV) therapy in the VIRAHEP-C study [[1]Howell C.D. Gorden A. Ryan K.A. Thompson A.J. Ibrahim C. Fried M. et al.Single nucleotide polymorphism upstream of interleukin 28B associated with phase 1 and phase 2 of early viral kinetics in patients infected with HCV genotype 1.J Hepatol. 2012; 56: 557-563Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar]. Compared to SNP C/T and T/T genotypes, the C/C genotype was associated with greater phase 1 and faster phase 2 declines in HCV RNA in both AA and CA patients. Thus, we concluded that this SNP predicts both interferon (IFN) effectiveness at blocking HCV production (i.e., phase 1) and clearance of infected hepatocytes (i.e., phase 2), and that this could explain how the IL28B SNP 12979860 C/C genotype increases the probability of SVR (compared to non-C/C genotypes) following PegIFN-α-2a/RBV treatment for HCV genotype 1. Differences in early viral kinetics between AA and CA could be largely explained by racial differences in the frequency of the IL28B SNP C allele. Patients with IL28B SNP non-C/C genotypes were more likely to have either a static phase or an increase in serum HCV RNA (i.e., shoulder) from day 2–7. We hypothesized that the IL28B SNP-related variability in the shoulder phase was due primarily to differences in IFN effectiveness (SNP C/C > C/T and T/T), as the decline in HCV RNA from day 2–7 was more strongly correlated with the magnitude of phase 1 than the phase 2 slope. In addition, we noted that the rebound in HCV RNA was temporally related to the decline in serum peginterferon from day 2/3 to 7 between the first and second injection [[2]Howell C.D. Dowling T.C. Paul M. Wahed A.S. Terrault N.A. Taylor M. et al.Peginterferon pharmacokinetics in African American and Caucasian American patients with hepatitis C virus genotype 1 infection.Clin Gastroenterol Hepatol. 2008; 6: 575-583Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar]. Furthermore, we cited evidence that ribavirin also plays a significant role in regulating viral kinetics between day 2–7 [[3]Feld J.J. Lutchman G.A. Heller T. Hara K. Pfeiffer J.K. Leff R.D. et al.Ribavirin improves early responses to peginterferon through improved interferon signaling.Gastroenterology. 2010; 139 (e2): 154-162Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar]. It is known that ribavirin has no effect on phase 1, either when administered alone or when combined with peginterferon alfa; when combined with peginterferon, it prevents an increase (rebound) in HCV RNA from day 2–7 and accelerates the fall in HCV RNA from day 7–28 (phase 2), in patients with an adequate first phase response [[3]Feld J.J. Lutchman G.A. Heller T. Hara K. Pfeiffer J.K. Leff R.D. et al.Ribavirin improves early responses to peginterferon through improved interferon signaling.Gastroenterology. 2010; 139 (e2): 154-162Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar]. With regard to ribavirin, viral kinetics models that include ribavirin and IFN effectiveness are better able to explain early HCV RNA kinetics than models with IFN effectiveness alone [[4]Dixit N.M. Layden-Almer J.E. Layden T.J. Perelson A.S. Modelling how ribavirin improves interferon response rates in hepatitis C virus infection.Nature. 2004; 432: 922-994Crossref PubMed Scopus (314) Google Scholar]. According to this model, the requirement for ribavirin during phase 2 is inversely related to IFN effectiveness. Thus, phase 2 and SVR in patients with IL28B SNP C/C are expected to be less dependent on ribavirin than in patients with non-C/C genotypes. In their letter, Dahari et al. reviewed the prevailing concepts of the shoulder phase from day 2–7 incorporating observations from 2 studies of US and Brazilian patients who were co-infected with HCV and HIV [5Dahari H. Markatou M. Zeremski M. Haller I. Ribeiro R.M. Licholai T. et al.Early ribavirin pharmacokinetics, HCV RNA and alanine aminotransferase kinetics in HIV/HCV co-infected patients during treatment with pegylated interferon and ribavirin.J Hepatol. 2007; 47: 23-30Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar, 6de Araujo E.S. Dahari H. Cotler S.J. Layden T.J. Neumann A.U. Melo C.E. et al.Pharmacodynamics of PEG-IFN-[alpha]-2a and HCV response as a function of IL28B polymorphism in HIV/HCV-coinfected patients.J Acquir Immune Defic Syndr. 2011; 56: 95-99Crossref PubMed Scopus (21) Google Scholar]. These studies are limited by small sample sizes and inclusion of patients with HCV genotypes 2 and 3. Analogous to our study, patients in one study were stratified by IL28B SNP genotype [[6]de Araujo E.S. Dahari H. Cotler S.J. Layden T.J. Neumann A.U. Melo C.E. et al.Pharmacodynamics of PEG-IFN-[alpha]-2a and HCV response as a function of IL28B polymorphism in HIV/HCV-coinfected patients.J Acquir Immune Defic Syndr. 2011; 56: 95-99Crossref PubMed Scopus (21) Google Scholar]. In keeping with our results, HCV genotype 1, co-infected patients with SNP C/C genotypes had significantly higher first (day 0–2) and second (day 2–29) phase declines in serum HCV RNA [[6]de Araujo E.S. Dahari H. Cotler S.J. Layden T.J. Neumann A.U. Melo C.E. et al.Pharmacodynamics of PEG-IFN-[alpha]-2a and HCV response as a function of IL28B polymorphism in HIV/HCV-coinfected patients.J Acquir Immune Defic Syndr. 2011; 56: 95-99Crossref PubMed Scopus (21) Google Scholar]. In addition, the peginterferon alfa serum concentration associated with half maximum IFN effectiveness (EC50) was lower in patients with IL28B SNP C/C genotypes compared to non-C/C genotypes (p= 0.02), suggesting that patients with C/C genotype were more sensitive to peginterferon. Dahari et al. suggested that the faster declines in serum HCV RNA from day 2–7 in patients with IL28B SNP C/C in our study may be partly related to greater IFN sensitivity (peginterferon EC50) and a higher infected cell loss rate. Our results are consistent with the concept that the shoulder phase reflects both IFN effectiveness and the infected cell loss rate. The peginterferon EC50 (IFN sensitivity) hypothesis is intriguing. However, the difference in peginterferon EC50 between C/C and non-C/C genotypes was not significant in HIV-co-infected patients with HCV genotype 1 (p= 0.6), possibly due to inadequate statistical power. Studies with larger numbers of patients infected with HCV genotype 1 alone are needed to address this question and to determine if peginterferon EC50 is an independent predictor of the shoulder and second phase responses. In another study, Dahari et al. observed significantly lower ribavirin plasma concentrations during the first 2 weeks and lower ribavirin exposure or area under the concentration–time curve (AUC) levels at days 3, 7, 14, and 28 of peginterferon alfa combination treatment in HCV-HIV co-infected patients who achieved an SVR relative to those without an SVR [[5]Dahari H. Markatou M. Zeremski M. Haller I. Ribeiro R.M. Licholai T. et al.Early ribavirin pharmacokinetics, HCV RNA and alanine aminotransferase kinetics in HIV/HCV co-infected patients during treatment with pegylated interferon and ribavirin.J Hepatol. 2007; 47: 23-30Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar]. They raised the possibility that lower early ribavirin levels in patients with IL28B CC genotypes might explain the transient viral declines and shoulder phase during the first week in our report. In more recent studies, we have investigated the importance of ribavirin pharmacokinetics to the lower efficacy of peginterferon and ribavirin therapy in AA compared to CA with HCV genotype 1 [7Jin R. Fossler M.J. McHutchison J.G. Howell C.D. Dowling T.C. Population pharmacokinetics and pharmacodynamics of ribavirin in patients with chronic hepatitis C genotype 1 infection.AAPS J. 2012; 14: 571-580Crossref PubMed Scopus (17) Google Scholar, 8Jin R. Cai L. Tan M. McHutchison J.G. Dowling T.C. Howell C.D. Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1.Am J Gastroenterol. 2012; 107: 1675-1683Crossref PubMed Scopus (11) Google Scholar]. The results suggest that ribavirin drug exposure is a key factor determining HCV RNA dynamics during the shoulder (day 2–7) in patients with HCV genotype 1 regardless of IL28B SNP genotype. We studied 75 AA and 75 CA who were more than 90% adherent to PegIFN-α-2a and weight-based ribavirin during the first 24 weeks of therapy in the VIRAHEP-C, based on electronic drug monitoring [7Jin R. Fossler M.J. McHutchison J.G. Howell C.D. Dowling T.C. Population pharmacokinetics and pharmacodynamics of ribavirin in patients with chronic hepatitis C genotype 1 infection.AAPS J. 2012; 14: 571-580Crossref PubMed Scopus (17) Google Scholar, 8Jin R. Cai L. Tan M. McHutchison J.G. Dowling T.C. Howell C.D. Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1.Am J Gastroenterol. 2012; 107: 1675-1683Crossref PubMed Scopus (11) Google Scholar]. Compared to CA, AA had lower plasma ribavirin concentrations at weeks 1, 2, and 4, and lower ribavirin exposure (AUC) from week 1–12 that were explained by a 50% higher volume of ribavirin distribution [7Jin R. Fossler M.J. McHutchison J.G. Howell C.D. Dowling T.C. Population pharmacokinetics and pharmacodynamics of ribavirin in patients with chronic hepatitis C genotype 1 infection.AAPS J. 2012; 14: 571-580Crossref PubMed Scopus (17) Google Scholar, 8Jin R. Cai L. Tan M. McHutchison J.G. Dowling T.C. Howell C.D. Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1.Am J Gastroenterol. 2012; 107: 1675-1683Crossref PubMed Scopus (11) Google Scholar]. Ribavirin exposure (AUC) during the first week (AUC0–7), IL28B SNP genotype, age, and platelet count were independent predictors of response (undetected serum HCV RNA) at week 24 (WK24VR) and week 72 (SVR), in a multivariable regression model [[8]Jin R. Cai L. Tan M. McHutchison J.G. Dowling T.C. Howell C.D. Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1.Am J Gastroenterol. 2012; 107: 1675-1683Crossref PubMed Scopus (11) Google Scholar]. Among AA, ribavirin AUC0–7 levels were higher in responders at weeks 24 and 72. Ribavirin AUC0–7 cut-offs or thresholds that best distinguished WK24VR (⩾4095 ng/ml d) and SVR (⩾4480 ng/ml d) from non-responders were identified using receiver operating characteristics curve analysis [[8]Jin R. Cai L. Tan M. McHutchison J.G. Dowling T.C. Howell C.D. Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1.Am J Gastroenterol. 2012; 107: 1675-1683Crossref PubMed Scopus (11) Google Scholar]. Fewer AA (49% and 44%) achieved the respective AUC0–7 thresholds than did CA (70% and 64%). In addition, WK24VR and SVR rates were higher in patients with threshold compared to subthreshold ribavirin AUC0–7 levels. Yet, there were no differences in WK24VR and SVR between AA and CA with threshold ribavirin AUC0–7 levels, providing strong evidence that optimum ribavirin drug exposure during the first week can overcome the racial disparity in WK24VR and SVR. It is worth noting that WK24VR and SVR to peginterferon and ribavirin did not vary by ribavirin exposure category in patients with the IL28B SNP C/C genotype [[8]Jin R. Cai L. Tan M. McHutchison J.G. Dowling T.C. Howell C.D. Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1.Am J Gastroenterol. 2012; 107: 1675-1683Crossref PubMed Scopus (11) Google Scholar]. In contrast, patients with IL28B SNP non-C/C and threshold ribavirin AUC0–7 levels had significantly higher WK24VR and SVR rates than those with subthreshold levels. The importance of ribavirin exposure on treatment outcomes in this study was reflected in the early HCV RNA kinetics. Compared to CA, AA had a shoulder in serum HCV RNA from day 2–7 and smaller declines in HCV RNA on days 7, 14, and 28 [[8]Jin R. Cai L. Tan M. McHutchison J.G. Dowling T.C. Howell C.D. Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1.Am J Gastroenterol. 2012; 107: 1675-1683Crossref PubMed Scopus (11) Google Scholar]. The shoulder phase was observed in AA with subthreshold, but not in those with threshold ribavirin AUC0–7. HCV RNA kinetics from day 0 to 28 did not differ between AA and CA with threshold ribavirin AUC0–7. Regardless of IL28B SNP genotype, patients with subthreshold ribavirin AUC0–7 experienced a shoulder phase from day 2–7. However, phase 2 did not vary by ribavirin AUC0–7 category in patients with IL28B SNP C/C. In contrast, declines in HCV RNA from day 2–7 and day 7–28 (phase 2) were greater in non-C/C patients with threshold compared to subthreshold ribavirin AUC0–7 levels. Serum peginterferon and ribavirin levels did not vary by IL28B SNP genotype. These results indicate that suboptimum ribavirin exposure was responsible for the shoulder in HCV RNA from day 2–7 during peginterferon combination treatment, and are consistent with the concept that due to higher IFN effectiveness and infected cell loss rates, the phase 2 (day 7–28) decline rate is less dependent on threshold ribavirin exposure in patients with HCV genotype 1 who carry the IL28B SNP C/C genotype. C.H. serves on the Roche-Genentech Pegasys Advisory Board.