Measurement of serum HCV RNA level is absolutely imperative for the treatment of chronic HCV infection, because this is an effective predictive and indicative factor for the response of IFN therapy and duration of therapy [7
]. A more useful analysis is the time to first undetectability and its relation to the end of treatment response, relapse rate and SVR [12
]. Therefore, an advanced technique for detecting serum HCV RNA during the antiviral treatment needs a high degree of accuracy. The ideal molecular analysis for HCV RNA level has to be sensitive, accurate and have a broad dynamic range to monitor viral load changes during antiviral therapy. TaqMan assay is useful for simultaneously analyzing qualitative and quantitative HCV RNA level in serum [14
]. The present study included only patients infected with chronic HCV genotype 1, who received a full of 48-week treatment of PEG-IFN plus RBV combination with target dosages of both drugs (PEG-IFN alpha-2b 80% or over and RBV 60% or over of the above prescribed dosage). We believed that analyzing the exact response factors for antiviral treatment should be considered only under this enough dosage of the combined treatment [16
]. The present study showed the superiority of TaqMan assay over Amplicor assay for analyzing the early prediction of virologic response to antiviral therapy.
TaqMan assay, the performance of a fully automated system based on the real-time PCR technology, was evaluated for nucleic acid extraction from plasma. This results in enhanced user convenience, a great reduction in labor requirements minimizing hands-on time and a decrease the risk of sample contaminations. TaqMan assay was extremely sensitive with a linear dynamic range up to 6.6 log IU/mL (0.015-69,000 kIU/mL: 1.2-7.8 log IU/mL) [14
]. Otherwise, Amplicor 10-fold method assay had a narrower linear dynamic range up to 3.0 log IU/mL (5-5,000 kIU/mL: 3.7-6.7 log IU/mL) than TaqMan assay and qualitative Amplicor assay, the lower limit of detection was 50 IU/mL (1.7 log IU/mL) [17
]. These different ranges can explain significant differences in the pretreatment HCV RNA levels and the reduction rates of HCV RNA levels during an antiviral treatment between TaqMan and Amplicor assays.
Previous studies demonstrated that PEG-IFN plus RBV treatment dramatically increased SVR rate in patients with HCV infection and thus are currently the gold standard of treatment [3
]. The most significant predictors of SVR to IFN treatment for patients with chronic HCV infection are absence of severe fibrosis or cirrhosis, non-genotype 1 and pretreatment serum low HCV RNA level [7
]. With regard to virological factor after the start of antiviral treatment, early clearance of HCV RNA, or rapid decline of HCV RNA level during the early treatment duration is predictive of SVR among patients treated with IFN treatment [10
]. For monitoring of the antiviral response to IFN treatment, both reverse-transcription PCR and branched DNA have been developed and have become available for clinical use [18
]. These assays are especially useful because the early monitoring of favorable viral kinetics has a direct bearing on the possibility of a sustained response by IFN treatment. Actually, our findings showed that pretreatment HCV RNA by TaqMan assay may be a predictive factor for SVR, but not by Amplicor 10-fold method assay, and that TaqMan assay is more useful than qualitative Amplicor assay in analysis of the early stage (at the initial 4 and 8 weeks) of HCV dynamics, which is most related with SVR. Early prediction of early virologic response to IFN based treatment can help identify patients who are unlikely to have SVR and allow clinicians to discontinuation of treatment, saving patients the drug-induced adverse events and cost of additional treatment.
Our results suggested that the reduction rates of HCV RNA levels were significantly higher than those in non-SVR patients both in TaqMan and Amplicor 10-fold method assays for patients having achieved SVR. However, in our analysis, significant differences of the initial 4 and 8 week PPV for SVR were found between Amplicor and TaqMan assays. PPV for SVR at 4 and 8 week was 100% and 100% respectively in TaqMan assay, otherwise PPV for SVR was 80.0% and 69.6% respectively in qualitative Amplicor assay. In addition to EVR, within the initial 12 weeks undetectability of HCV RNA of the antiviral treatment, the critical role of rapid virological response (RVR), within the initial 4 weeks undetectability, on the SVR patients with genotype 1 and non-1 infection has been recently emphasized [7
]. In fact, our findings showed more advantage using TaqMan assay on the PPV for SVR, especially at weeks 4 and 8, than Amplicor assay. Apparently, TaqMan assay is more accurate than Amplicor assay in analysis of the early stage (within 8 weeks) of HCV dynamics. PEG-IFN plus RBV treatment contributed to improve rates of SVR, but this rate is still lower for patients with HCV genotype 1 infection. Especially, most of Japanese patients with chronic hepatitis C who are candidate for antiviral treatment are relatively older than other countries. As a result, a relapse rate with EVR was a little high regardless of adequate treatment. Therefore, analysis of HCV dynamics after the antiviral treatment, especially for these patients, is very important.
The present study showed that 21.3% of the patients with undetectable HCV RNA by qualitative Amplicor assay were positive for TaqMan assay within the initial 12 weeks during PEG-IFN plus RBV treatment. It is possible that qualitative Amplicor assay reveals late responders by the combined treatment in comparison with TaqMan assay. Berg and colleagues suggested extended treatment duration was recommended for patients with SVR as HCV RNA positive at week 12 but negative at week 24 [25
]. About such patients, we need to extend the duration of the combination treatment of PEG-IFN alpha-2b plus RBV from 48 weeks to 72 weeks by an appearance of TaqMan assay.