Viral kinetic and Pharmacodynamic Parameters and IL28B Polymorphism
The maximum PEG-IFN effectiveness during the first week of therapy, ε7max, the average PEG-IFN effectiveness during the first week of therapy, ε7average, and the maximum PEG-IFN effectiveness from week 4 to week 12 of therapy, εmax, were significantly (P = 0.008, 0.008, and 0.044, respectively) higher in genotype-CC [median (IQR) 94% (11%), 92% (13%), and 96% (6%), respectively] than in patients with genotype-TC/TT [81% (45%), 77% (45%), and 87% (33%), respectively; Table 1]. The PEG-IFN concentration at which the PEG-IFN-α-2a effectiveness in blocking viral production is half its maximum, EC50, was significantly (P = 0.02) lower in genotype-CC [median (IQR) 1.3(1.8)] than in genotype-TC or TT [3.3(11.5)]. When the analysis was confined to HCV genotype-1 cases, EC50 was lower (but not significant, P = 0.6) in genotype-CC, but there was a trend toward a correlation between genotype-CC and both ε7average and δ (P = 0.11, Table 1). In contrast, in HCV-genotype-3 patients, there were trends toward higher ε7average and lower EC50 (P = 0.1) with genotype-CC, whereas an association was less evident for δ (P = 0.7, Table 1) among IL28B genotypes.
A detailed HCV kinetic analysis provided new and important information regarding the impact of IL28B genotype on response to PEG-IFN plus RBV in HIV/HCV-coinfected patients. Overall, the CC-genotype was most strongly associated with a higher first-phase viral decline and maximum PEG-IFN effectiveness during the first week of therapy, ε7max. These findings indicate that PEG-IFN has greater efficacy in blocking HCV production/release in patients with the favorable IL28B CC-genotype. Our results are in agreement with recent findings in HCV-monoinfected patients.14,15 The PEG-IFN-α-2a EC50 was lower in genotype-CC compared with genotype-TC/TT, providing further evidence that the CC-genotype confers a higher sensitivity to IFN treatment. Thus far, the mechanism of action of the IL28B polymorphism has not been identified. The location of the genetic polymorphism upstream of the IFN-λ gene18,19 raises the possibility that the IL28B genotype mediates endogenous production of IFN-λ, which contributes to the first-phase response by stimulating IFN signaling.
The second-phase viral decline slope also was associated with genotype-CC in genotype 1 patients (Table 1). The overall correlation between the CC-genotype and the infection death/loss rate, δ, was less prominent (trend, P = 0.11). This discrepancy could be explained by the fact that 6 of 21 of patients who finished 48 weeks of therapy in our study17 had a triphasic viral decline pattern consisting of a first phase (1-2 days) with a rapid virus load decline followed by a “shoulder phase” (8-28 days), in which virus levels decay slowly or remain constant, and a third phase of renewed viral decay.20,21 Calculating the slower phase slope from the measured data includes the “shoulder phase” in these triphasic patients. In contrast, by using a mathematical model that includes hepatocytes proliferation, estimated δ reflects the final slope and excludes the shoulder phase.22 Interestingly, 5 of the 6 triphasic patients had genotype-TT/TC and only 1 had genotype-CC (not shown). In addition, we recently showed that drug effectiveness, ε, can significantly affect the serum second-phase slope decline,22 and that when ε∼1 the slower phase slope is close to δ. Indeed, when the analysis was performed only in patients with first-phase decline >1 log (ie, ε > 90%), the association between IL28B genotype-CC and the slower phase slope was lost (P = 0.5, not shown), in agreement with recent results in HCV-monoinfected patients.15 Thus, although the slower phase slope, and as a consequence RVR rates, are correlated with the IL28B genotype, the driving effect is the difference in the IFN antiviral effectiveness in blocking virion production (first-phase decline). The data suggest that the IL28B polymorphism has less of an effect on the infected-cell-loss rate that has been attributed to immune mediated clearance of infected cells.23
Among viral response parameters, we found that RVR and cEVR rates are significantly associated with genotype-CC (see Table 1, Supplemental Digital Content 1, http://links.lww.com/QAI/A112), in agreement with recent results in HCV (genotypes 1/2/3)-monoinfected patients.15,24 Among HCV genotype-1 subjects in our study, 10 subjects (of 11) who had genotype CT/TT failed to achieve an SVR in agreement with the strong association recently shown in larger HIV/HCV-coinfected cohorts by Rallon et al25 and Pineda et al.26 However, the weak association between genotype-CC and SVR (P = 0.3; see Table 1, Supplemental Digital Content 1, http://links.lww.com/QAI/A112) in HCV genotype-1-infected subjects in our study may be related to the small sample size and to the discontinuation of 5 patients at week 12 of therapy as previously explained.17 The faster first and second-phase viral declines observed in IL28B genotype-1-CC patients and the higher first-phase viral decline in genotype-3-CC patients provide evidence that the IL28B genotype favorably impacts on viral kinetics.
Evaluation of baseline characteristics showed genotype-CC subjects had a higher body weight. Larger studies are needed to evaluate whether genotype CC might overcome the deleterious impact of higher body weight on SVR. In addition, there was a significantly higher proportion of IL28B genotype-CC in patients infected with HCV-genotype 3 than in patients infected with HCV-genotype 1 (see Table 1, Supplemental Digital Content 1, http://links.lww.com/QAI/A112), in agreement with recent studies that include HIV/HCV-coinfected25 and HCV-monoinfected individuals.27 We previously reported higher first and faster second-phase viral declines in genotype-3 compared with genotype-1 HIV/HCV-coinfected patients.16 In the current study, we identified a higher prevalence of IL28B CC-genotype in HCV genotype-3 cases, but no association between IL28B genotype and the second-phase viral decline or the loss rate of HCV-infected cells, δ in HCV genotype-3. Because the second slope phase and/or δ correlate with the outcome of therapy,23 these findings suggest that the relatively rapid second-phase viral decline in genotype-3 patients is related to factors other than the genetic polymorphism. Our observations might explain the lack of association between IL28B genotype and SVR in genotype-3 patients recently reported by Rallon et al.25 In contrast, higher ε7average and δ were associated (trend, P = 0.1) with CC-genotype in HCV genotype-1-infected patients. The trends observed in genotype-1 patients may reflect the small sample size and is anticipated to be significant in larger studies.
Previous studies of HCV-monoinfected patients conducted in the United States reported a higher proportion of IL28B genotype-TC/TT in African Americans than in non-Hispanic white.10,14 In contrast, we did not identify a significant (P = 0.5) difference in IL28B genotype frequencies between African Americans and white patients from Brazil (Table 1). The lack of an association between race and IL28B genotype in our South American patient population might partly explain the lack of association between race/ethnicity and viral kinetic parameters or viral response patterns in our recent reports.16,17 Indeed, preliminary results indicate that ∼80% (of 500) of HCV-monoinfected individuals in Brazil are TC or TT with a similar distribution of CC/TC/TT genotypes between African Americans and whites.28 Larger studies are needed to provide a comprehensive evaluation of IL28B genotypes and viral kinetics by race/ethnicity in South America, where patient ancestry may differ from that in the United States.
In conclusion, in HIV/HCV-coinfected patients, the IL28B-CC genotype was most strongly associated with a higher first-phase viral decline and greater average PEG-IFN effectiveness during the first week of therapy, ε7max. Pharmacodynamic analysis showed that genotype-CC conferred increased sensitivity to PEG-IFN, as shown by a lower PEG-IFN-α-2a EC50. These kinetic findings raise the possibility that the IL28B CC-genotype favorably affects viral response by augmenting IFN-λ-mediated activation of the IFN signaling cascade, leading to increased effectiveness in blocking virion production/release. Notably, as we approach a new era of combination therapy with PEG-IFN and direct antiviral agents, a better understanding of factors associated with PEG-IFN-related viral kinetics will provide the basis to develop optimal treatment strategies for HCV.29,30 Larger and more detailed studies are needed to confirm these new observations in HIV/HCV-coinfected patients.
The authors thank Steve Young from Tricore Reference Laboratories for performing HIV and HCV load tests; LIM-47 team for excellent technical assistance; Fernando F. Tatsch and Lorin Brisbin from Roche for supplying drugs and tests; and the patients and their family members for the trust and participation.
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Keywords:© 2011 Lippincott Williams & Wilkins, Inc.
Mathematical modeling; viral kinetics; pharmacodynamics; HCV; HIV; IL28B; pegylated interferon alpha-2a