Understanding triphasic HCV decline during treatment in the era of IL28B polymorphisms and direct acting antiviral agents via mathematical modeling
Authors: Harel Dahari, Scott J. Cotler, Thomas J. Layden, Alan S. Perelson
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 Reply to: "Understanding triphasic HCV decline during treatment in the era of IL28B polymorphisms and direct acting antiviral agents via mathematical modeling"Journal of HepatologyVol. 58Issue 4PreviewWe 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]. 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. Full-Text PDF Open Access Howell and colleagues [[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] have recently provided important insights into the relationship among viral kinetic patterns, including the triphasic pattern (Fig. 1 in [[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]), 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). Interestingly, Howell et al. described subjects in whom a static or increasing viral phase (termed here a shoulder) was observed during days 2–7 after treatment initiation (Fig. 1 in [[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]). While the nature of the shoulder phase is still not known, Howell et al. [[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] related this phase to "a delay in the pharmacologic activity of ribavirin" or "lower PegIFNα-2a effectiveness". We sought here to clarify the current theory behind the nature of the shoulder phase and provide further insights into the subject.A transient viral decline was observed in some HCV-monoinfected subjects during the first week of RBV monotherapy [[2]Pawlotsky J.M. Dahari H. Neumann A.U. Hezode C. Germanidis G. Lonjon I. et al.Antiviral action of ribavirin in chronic hepatitis C.Gastroenterology. 2004; 126: 703-714Abstract Full Text Full Text PDF PubMed Scopus (221) Google Scholar]. In a recent study, in which subjects were treated with RBV alone for 4 weeks, there was no association between HCV RNA kinetics measured weekly and IL28B genotypes (submitted). In HIV/HCV co-infected subjects treated with PegIFNα-2b and RBV, median RBV area under the curve levels were lower in sustained viral responders (SVRs) compared with non-SVRs at days 3 and 7 and were associated with a continued viral decline during days 3–7 (in SVRs) compared to a shoulder in non-SVRs (Fig. 2C in [[3]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]). Unfortunately, data on IL28B genotypes is not yet available to be linked to our previous studies [2Pawlotsky J.M. Dahari H. Neumann A.U. Hezode C. Germanidis G. Lonjon I. et al.Antiviral action of ribavirin in chronic hepatitis C.Gastroenterology. 2004; 126: 703-714Abstract Full Text Full Text PDF PubMed Scopus (221) Google Scholar, 3Dahari 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], but if indeed subjects with IL28B CC genotypes in Howell et al. are associated with early lower RBV levels and/or transient viral decline during the first week, then it could, partly, explain their findings.A more evident cause of the viral shoulder phase is the known pharmacokinetics of PegIFNα which peaks and then declines during the first week of treatment [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 5Talal A.H. Ribeiro R.M. Powers K.A. Grace M. Cullen C. Hussain M. et al.Pharmacodynamics of PEG-IFN alpha differentiate HIV/HCV coinfected sustained virological responders from nonresponders.Hepatology. 2006; 43: 943-953Crossref PubMed Scopus (71) Google Scholar]. To explain the shoulder phase with the standard model [[6]Neumann A.U. Lam N.P. Dahari H. Gretch D.R. Wiley T.E. Layden T.J. et al.Hepatitis C viral dynamics in vivo and the antiviral efficacy of interferon-alpha therapy.Science. 1998; 282: 103-107Crossref PubMed Scopus (1889) Google Scholar], the PegIFNα concentration in serum, C(t), was coupled with its effectiveness, ε(t), in blocking viral production/release [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 5Talal A.H. Ribeiro R.M. Powers K.A. Grace M. Cullen C. Hussain M. et al.Pharmacodynamics of PEG-IFN alpha differentiate HIV/HCV coinfected sustained virological responders from nonresponders.Hepatology. 2006; 43: 943-953Crossref PubMed Scopus (71) Google Scholar] (see Fig. 1 for equations and parameters definition). Using this theory, the observed viral kinetic patterns from Howell et al. can be predicted (Fig. 1). Interestingly, we recently showed, in HIV/HCV (genotype 1/3) co-infected subjects treated with PegIFNα-2a + RBV, that the significantly higher effectiveness in subjects with CC genotype was associated with significantly lower EC50 (median 1.3) compared to TC/TT subjects (median 3.3) [[7]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 second phase of viral decline was faster and the infected cell loss rate, δ, was larger in CC than in TC/CC subjects (δ = 0.25 vs. 0.13 d−1) [[7]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]. Accordingly, the higher PegIFNα-2a effectiveness and the continued viral decline between days 2 and 7 in subjects with a CC genotype from Howell et al. may be partly related to lower EC50 and higher δ, compared to TC/TT patients (Fig. 1; black vs. grey/blue lines). Model simulations suggest that the shoulder phase in CT/TT genotype patients is not necessarily due to low PegIFNα-2a effectiveness, but may also be due to lower δ. Clearly, further studies that combine PegIFNα-2a and RBV pharmacokinetics/pharmacodynamics with frequent viral kinetics during the first week of treatment are necessary to pinpoint the causes of the shoulder phase observed in TC/TT subjects.While individual viral kinetics were not shown by Howell et al., it might be true that some patients experienced a longer (up to day 28) shoulder phase as previously documented [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 8Herrmann E. Lee J.H. Marinos G. Modi M. Zeuzem S. Effect of ribavirin on hepatitis C viral kinetics in patients treated with pegylated interferon.Hepatology. 2003; 37: 1351-1358Crossref PubMed Scopus (226) Google Scholar], and with a higher proportion in subjects with TT/TC genotypes compared to CC, as recently observed by de Araujo et al. in HIV/HCV co-infected subjects [[7]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]. This longer shoulder phase is explained by other mechanisms that are not related to PegIFNα-2a pharmacokinetics/pharmacodynamics as described in [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 8Herrmann E. Lee J.H. Marinos G. Modi M. Zeuzem S. Effect of ribavirin on hepatitis C viral kinetics in patients treated with pegylated interferon.Hepatology. 2003; 37: 1351-1358Crossref PubMed Scopus (226) Google Scholar, 9Dahari H. Ribeiro R.M. Perelson A.S. Triphasic decline of hepatitis C virus RNA during antiviral therapy.Hepatology. 2007; 46: 16-21Crossref PubMed Scopus (100) Google Scholar].In the era of direct-acting antiviral agents (DAAs) against HCV, it is important to note that the aforementioned shoulder phase is not commonly seen (e.g., one case in supplementary material of [[10]Rong L. Dahari H. Ribeiro R.M. Perelson A.S. Rapid emergence of protease inhibitor resistance in hepatitis C virus.Sci Transl Med. 2010; 2: 30-32Crossref Scopus (312) Google Scholar]). This may be attributed to the ability of DAAs not only to reduce the synthesis of new intracellular HCV RNA, vRNA, but also to enhance the degradation of vRNA. Based on this theory, the shoulder phase is not observed as intracellular vRNA continuously declines and thus, the overall production of virions declines as well, even if the DAA is combined with PegIFNα-2a and its effectiveness declines during the first week of treatment. However, PegIFNα + RBV is still the backbone of the current standard of care and is also used as a lead-in in some protocols, the existence of the shoulder phase is still relevant and should be further explored in order to better optimize the standard of care.Financial supportU.S. Department of Energy under contract DE-AC52-06NA25396, NIH grants P20-RR018754, R56/R01-AI078881, OD011095, AI028433, and AI065256 and the University of Illinois Walter Payton Liver Center GUILD.Conflict of interestThe authors declare that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. Howell and colleagues [[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] have recently provided important insights into the relationship among viral kinetic patterns, including the triphasic pattern (Fig. 1 in [[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]), 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). Interestingly, Howell et al. described subjects in whom a static or increasing viral phase (termed here a shoulder) was observed during days 2–7 after treatment initiation (Fig. 1 in [[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]). While the nature of the shoulder phase is still not known, Howell et al. [[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] related this phase to "a delay in the pharmacologic activity of ribavirin" or "lower PegIFNα-2a effectiveness". We sought here to clarify the current theory behind the nature of the shoulder phase and provide further insights into the subject. A transient viral decline was observed in some HCV-monoinfected subjects during the first week of RBV monotherapy [[2]Pawlotsky J.M. Dahari H. Neumann A.U. Hezode C. Germanidis G. Lonjon I. et al.Antiviral action of ribavirin in chronic hepatitis C.Gastroenterology. 2004; 126: 703-714Abstract Full Text Full Text PDF PubMed Scopus (221) Google Scholar]. In a recent study, in which subjects were treated with RBV alone for 4 weeks, there was no association between HCV RNA kinetics measured weekly and IL28B genotypes (submitted). In HIV/HCV co-infected subjects treated with PegIFNα-2b and RBV, median RBV area under the curve levels were lower in sustained viral responders (SVRs) compared with non-SVRs at days 3 and 7 and were associated with a continued viral decline during days 3–7 (in SVRs) compared to a shoulder in non-SVRs (Fig. 2C in [[3]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]). Unfortunately, data on IL28B genotypes is not yet available to be linked to our previous studies [2Pawlotsky J.M. Dahari H. Neumann A.U. Hezode C. Germanidis G. Lonjon I. et al.Antiviral action of ribavirin in chronic hepatitis C.Gastroenterology. 2004; 126: 703-714Abstract Full Text Full Text PDF PubMed Scopus (221) Google Scholar, 3Dahari 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], but if indeed subjects with IL28B CC genotypes in Howell et al. are associated with early lower RBV levels and/or transient viral decline during the first week, then it could, partly, explain their findings. A more evident cause of the viral shoulder phase is the known pharmacokinetics of PegIFNα which peaks and then declines during the first week of treatment [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 5Talal A.H. Ribeiro R.M. Powers K.A. Grace M. Cullen C. Hussain M. et al.Pharmacodynamics of PEG-IFN alpha differentiate HIV/HCV coinfected sustained virological responders from nonresponders.Hepatology. 2006; 43: 943-953Crossref PubMed Scopus (71) Google Scholar]. To explain the shoulder phase with the standard model [[6]Neumann A.U. Lam N.P. Dahari H. Gretch D.R. Wiley T.E. Layden T.J. et al.Hepatitis C viral dynamics in vivo and the antiviral efficacy of interferon-alpha therapy.Science. 1998; 282: 103-107Crossref PubMed Scopus (1889) Google Scholar], the PegIFNα concentration in serum, C(t), was coupled with its effectiveness, ε(t), in blocking viral production/release [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 5Talal A.H. Ribeiro R.M. Powers K.A. Grace M. Cullen C. Hussain M. et al.Pharmacodynamics of PEG-IFN alpha differentiate HIV/HCV coinfected sustained virological responders from nonresponders.Hepatology. 2006; 43: 943-953Crossref PubMed Scopus (71) Google Scholar] (see Fig. 1 for equations and parameters definition). Using this theory, the observed viral kinetic patterns from Howell et al. can be predicted (Fig. 1). Interestingly, we recently showed, in HIV/HCV (genotype 1/3) co-infected subjects treated with PegIFNα-2a + RBV, that the significantly higher effectiveness in subjects with CC genotype was associated with significantly lower EC50 (median 1.3) compared to TC/TT subjects (median 3.3) [[7]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 second phase of viral decline was faster and the infected cell loss rate, δ, was larger in CC than in TC/CC subjects (δ = 0.25 vs. 0.13 d−1) [[7]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]. Accordingly, the higher PegIFNα-2a effectiveness and the continued viral decline between days 2 and 7 in subjects with a CC genotype from Howell et al. may be partly related to lower EC50 and higher δ, compared to TC/TT patients (Fig. 1; black vs. grey/blue lines). Model simulations suggest that the shoulder phase in CT/TT genotype patients is not necessarily due to low PegIFNα-2a effectiveness, but may also be due to lower δ. Clearly, further studies that combine PegIFNα-2a and RBV pharmacokinetics/pharmacodynamics with frequent viral kinetics during the first week of treatment are necessary to pinpoint the causes of the shoulder phase observed in TC/TT subjects. While individual viral kinetics were not shown by Howell et al., it might be true that some patients experienced a longer (up to day 28) shoulder phase as previously documented [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 8Herrmann E. Lee J.H. Marinos G. Modi M. Zeuzem S. Effect of ribavirin on hepatitis C viral kinetics in patients treated with pegylated interferon.Hepatology. 2003; 37: 1351-1358Crossref PubMed Scopus (226) Google Scholar], and with a higher proportion in subjects with TT/TC genotypes compared to CC, as recently observed by de Araujo et al. in HIV/HCV co-infected subjects [[7]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]. This longer shoulder phase is explained by other mechanisms that are not related to PegIFNα-2a pharmacokinetics/pharmacodynamics as described in [4Dahari H. Affonso de Araujo E.S. Haagmans B.L. Layden T.J. Cotler S.J. Barone A.A. et al.Pharmacodynamics of PEG-IFN-alpha-2a in HIV/HCV co-infected patients: implications for treatment outcomes.J Hepatol. 2010; 53: 460-467Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 8Herrmann E. Lee J.H. Marinos G. Modi M. Zeuzem S. Effect of ribavirin on hepatitis C viral kinetics in patients treated with pegylated interferon.Hepatology. 2003; 37: 1351-1358Crossref PubMed Scopus (226) Google Scholar, 9Dahari H. Ribeiro R.M. Perelson A.S. Triphasic decline of hepatitis C virus RNA during antiviral therapy.Hepatology. 2007; 46: 16-21Crossref PubMed Scopus (100) Google Scholar]. In the era of direct-acting antiviral agents (DAAs) against HCV, it is important to note that the aforementioned shoulder phase is not commonly seen (e.g., one case in supplementary material of [[10]Rong L. Dahari H. Ribeiro R.M. Perelson A.S. Rapid emergence of protease inhibitor resistance in hepatitis C virus.Sci Transl Med. 2010; 2: 30-32Crossref Scopus (312) Google Scholar]). This may be attributed to the ability of DAAs not only to reduce the synthesis of new intracellular HCV RNA, vRNA, but also to enhance the degradation of vRNA. Based on this theory, the shoulder phase is not observed as intracellular vRNA continuously declines and thus, the overall production of virions declines as well, even if the DAA is combined with PegIFNα-2a and its effectiveness declines during the first week of treatment. However, PegIFNα + RBV is still the backbone of the current standard of care and is also used as a lead-in in some protocols, the existence of the shoulder phase is still relevant and should be further explored in order to better optimize the standard of care. Financial supportU.S. Department of Energy under contract DE-AC52-06NA25396, NIH grants P20-RR018754, R56/R01-AI078881, OD011095, AI028433, and AI065256 and the University of Illinois Walter Payton Liver Center GUILD. U.S. Department of Energy under contract DE-AC52-06NA25396, NIH grants P20-RR018754, R56/R01-AI078881, OD011095, AI028433, and AI065256 and the University of Illinois Walter Payton Liver Center GUILD. Conflict of interestThe authors declare that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. The authors declare that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.