CLINICAL REVIEWS

Effect of HCV Viral Dynamics onTreatment Design: Lessons Learned From HIVVincent G. Bain, M.D.Division of Gastroenterology, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada

ABSTRACTViral load measurements provide an indication of viralreplication, and thereby serve as a valuable tool to guide theinitiation of therapy and subsequent changes. Plasma humanimmunodeficiency viral load strongly predicts the rate ofdecrease in CD4� lymphocyte count, and progression toAIDS and death. Furthermore, the efficacy of antiretroviraltherapy can be assessed by monitoring changes in plasmahuman immunodeficiency viral load. Similarly, viral loadprovides valuable information about the natural history ofthe hepatitis C virus infection. Hepatitis C viral load can beused to predict the likelihood of response to standard inter-feron-� treatment and other interferon-� regimens and tomonitor treatment efficacy. Increased understanding of thenatural history of the hepatitis C virus infection and thenature of resistance to interferon-� therapy suggests thateffective treatment regimens must maintain serum levels ofinterferon-�. Ideally, interferon-� serum levels should pro-vide constant pressure on the virus and should prevent viralrebound, thereby avoiding continued viral replication andminimizing the potential for emergence of resistant quasi-species. Current regimens designed to address these pointsinclude early aggressive intervention, combination drug reg-imens, prolonged maintenance, and novel interferons. Byenabling the design and rapid assessment of new treatmentregimens, viral load measurement will revolutionize theclinical management of the hepatitis C virus infection, as ithas the HIV. (Am J Gastroenterol 2001;96:2818–2828.© 2001 by Am. Coll. of Gastroenterology)

INTRODUCTION

Sustained responses to standard interferon-� therapy in pa-tients with chronic hepatitis C infection are discouraginglylow (1), and responses to the combination of ribavirin plusstandard interferon-� average 40% (2, 3). Important ques-tions about the management of infection with the hepatitis Cvirus (HCV) and the management of infection with HIV arewhen and how aggressively to treat, and how to monitortreatment efficacy (4). Recent progress in the understandingof HIV-1 disease pathogenesis, in the ability to monitor viralload, and in antiretroviral therapies indicates the interdepen-dence of these factors in the successful treatment and man-agement of this viral disease (5). Although there are clearly

differences between the two viruses and resultant clinicalconsequences, the HIV paradigm has inspired the explora-tion for data supporting a similar interdependence in HCVinfection, and an examination of the implications of HCVviral load for treatment outcomes and the design of treat-ment regimens.

HUMAN IMMUNODEFICIENCY VIRUS

Like all retroviruses, HIV-1 is a single-stranded plus-senseRNA virus. After internalization of the virus by a CD4�T-lymphocyte, viral reverse transcriptase generates a dou-ble-stranded DNA copy of the viral RNA that is integratedinto the host chromosome (6). This integration leads to aselective and progressive depletion of CD4� helper lym-phocytes, which is the hallmark of AIDS. The clinicalconsequences are progressive deterioration of the host im-mune system, leading to increased susceptibility to oppor-tunistic infections and neoplasms and, ultimately, death (7).Recent declines in morbidity and mortality due to AIDShave been attributed to the use of intensive multidrug com-bination antiretroviral regimens, which include variouscombinations of nucleoside analog reverse transcriptase in-hibitors, protease inhibitors, and nonnucleoside reverse tran-scriptase inhibitors (8, 9). Both the International AIDS So-ciety’s United States panel and the Panel on ClinicalPractices for Treatment of HIV Infection, convened by theUnited States Department of Health and Human Services,recommend a potent protease inhibitor in combination withtwo nucleoside analog reverse transcriptase inhibitors as thepreferred initial treatment of established HIV-1 infection(9, 10).

Viral Load Monitoring and Implications for TherapyViral load monitoring by plasma HIV RNA quantificationhas provided insights into HIV viral dynamics. Plasma HIVviral load strongly predicts the rate of decrease in CD4�T-lymphocyte count, and progression to AIDS and death(11, 12).

HIV-1 viral load monitoring is useful as a therapeutic andprognostic marker, and has been shown to reflect antiretro-viral drug activity in the short term when effective antiret-roviral therapy is introduced (5). Viral load and CD4� cellcount are the primary values that should be used to guide theinitiation of antiretroviral therapy and subsequent changes

THE AMERICAN JOURNAL OF GASTROENTEROLOGY Vol. 96, No. 10, 2001© 2001 by Am. Coll. of Gastroenterology ISSN 0002-9270/01/$20.00Published by Elsevier Science Inc. PII S0002-9270(01)02796-4

in therapy (13). The goal of therapy is maximum reductionof plasma viral load for as long as possible (9), ideally tobelow the level of detection of the most sensitive test avail-able. Suppression of plasma viral load to �20 to 50 cop-ies/ml restricts the evolution of resistance and increases thedurability of response to an antiretroviral regimen (9, 10,14). The durability of response is directly related to thedepth of the nadir in the viral load (10).

Effect of Viral Dynamics onDesign of Therapeutic RegimensIt had been estimated that, on average, 109 HIV-1 virions areproduced and cleared every day from the blood, givinghalf-lives of productively infected cells and virions of ap-proximately 2 days and �6 h, respectively (15). Morerecently, using plasma apheresis to analyze changes inplasma virus concentration, it was estimated that virus pro-duction and clearance are much higher than previouslythought (approximately 1010–1011), corresponding to a half-life of only 28–110 min (16).

During antiretroviral therapy, viral load demonstrates abiphasic or multiphase response, with a rapid initial decline(corresponding to the rapid elimination of free virus andvirally infected CD4� T-lymphocytes), followed by aslower phase or phases (corresponding to a decrease inactivation of CD4 cells and/or the decay rate in longer livedinfected cell populations) (15, 17–21). During initiation ofhighly active antiretroviral therapy, the elimination half-lifeof the free virus has been reported to be 0.6 or 0.8 daysbetween days 1 and 3 of therapy, 1.7 or 1.5 days betweendays 3 and 7 of therapy, and 8 or 8.2 days between days 7and 28 of therapy (20, 21). Recent studies that demonstrateongoing low-level viral replication in patients receivinghighly active antiretroviral therapy suggest that at least 10 yrof treatment would be needed for complete eradication ofHIV-1 (22). In addition, virus elimination may remain elu-sive because of small reservoirs of latently infected CD4�T-lymphocytes that persist for years (23), macrophages thatmay express HIV-1 for prolonged periods, follicular den-dritic cells that may hold infectious HIV-1 on their surfacesfor indeterminate lengths of time, and/or viral reservoirs insites at which antiretroviral drugs cannot penetrate (4). Akey anatomical reservoir for HIV-1 appears to be the centralnervous system; eradication from this site may require sus-tained peak concentrations of antiretrovirals (24).

HEPATITIS C VIRUS

Though infected individuals may remain asymptomatic fordecades, chronic HCV infection typically manifests withepisodes of increased symptoms (which usually are accom-panied by laboratory abnormalities) separated by periods ofrelative quiescence. A sustained virological response, whichis often accompanied by histological improvement, is thecurrent standard therapeutic endpoint, having replaced theprevious emphasis on biochemical responses. However,

chronic infection may be present despite normalization ofbiochemical parameters, negative tests for antibodies toHCV, and even plasma viral load below the limit of detec-tion (because of viral sequestration in the liver and possiblyin extrahepatic sites) (25). Some evidence has suggested thatperipheral blood mononuclear cells may act as a reservoir ofHCV, but other evidence argues against this (26).

One third of patients with chronic HCV infection havepersistently normal ALT values (27). Ten percent to 20% ofpatients eventually develop cirrhosis or progressive liverfailure, and in some geographic areas, a high percentage ofpatients with primary hepatocellular carcinoma have sero-logical evidence for HCV (28). Hepatocellular carcinomadevelops in 1–5% of persons with chronic HCV infectionover a period of 20–30 yr, and may develop in as many as1–4% annually among the subset of patients with cirrhosis(29).

Similarly to HIV-1, HCV is a single-stranded RNA virus.There are nine distinct HCV genotypes and over 30 subtypes(30). In comparison, there are two principal genetic groupsof HIV-1, designated M (main, which is highly prevalent)and O (outlier); M is further classified into 10 establishedenvelope subtypes, A through J (31). Like all RNA viruses,HCV has a high mutation rate, higher than HIV-1 by anorder of magnitude. This high mutation rate produces aheterogeneous population of closely related HCV variants,called quasispecies, within an HCV-infected individual;these quasispecies have only minor variations in the nucle-otide sequence (30). The inability of antibodies produced inresponse to one quasispecies to protect against other quasi-species may be one of the factors that enables HCV toescape from immune surveillance and allows for persistentinfection (32).

The rapid generation of viral diversity (i.e., production ofquasispecies) and the opportunity for viral escape phenom-ena from the host immune surveillance and from antiviraltherapy (mutation to resistance) are explained by two char-acteristics of HIV-1 and HCV (12, 33, 34). The first char-acteristic is the high turnover (replication) rate. The secondcharacteristic is, as for all RNA viruses, the absence ofproofreading mechanisms that preserve the genetic compo-sition of organisms with double-stranded DNA genomes.

Viral Load Monitoring and Implications for TherapyAs has been demonstrated for HIV-1 disease, viral burden isimportant to the natural history of HCV infection. Viral load(the concentration of HCV RNA in the plasma) is an indi-cator of disease activity (35), a prognostic indicator ofnatural disease course, and an indicator of the efficacy oftherapeutic regimens. As will be discussed later, pretreat-ment high viral load is associated with a poorer response tostandard interferon-�. Although no definitive data correlatehigh viral load with the subsequent development of cirrhosisor hepatic cancer, high levels of circulating HCV RNAcorrelate with advanced inflammation on liver biopsy andadvanced clinical stage of disease (e.g., end stage liver

2819AJG – October, 2001 Effect of HCV Viral Dynamics on Treatment Design

disease) (36–39) and predict worsening liver histology (40).Serum HCV RNA levels have been shown to correlate withthe HCV RNA levels in the liver and therefore reflect thehepatic viral burden (41). Viral elimination from blood andliver tissue is associated with histological improvement(42), gradual regression of liver fibrosis, and possibly even-tual resolution of early cirrhosis (43).

Quantitative assays for measuring HCV viral load havebeen developed, including a quantitative reverse transcrip-tase polymerase chain reaction assay (AMPLICOR HCVMonitor, Roche Molecular Systems, Branchburg, NJ) (44)and a branched DNA signal amplification assay (QuantiplexHCV RNA 2.0 Assay [bDNA], Bayer, Tarrytown, NY). TheAMPLICOR HCV Monitor, a quantitative assay used tomeasure viral load, should not be confused with theAMPLICOR HCV, a qualitative assay (Roche MolecularSystems) used for diagnosis and for assessing virologicalresponse (i.e., the absence of viral RNA) during both ther-apy and follow-up. Gene amplification methods, such as theAmplicor HCV Monitor assay and nucleic acid sequence-based amplification (Organon Teknika, Boxtel, The Neth-erlands), have better sensitivity than branched DNA signalamplification assays for quantification of HCV RNA inpatients with chronic HCV infection (45). Second-genera-tion Amplicor HCV Monitor assays have been developedthat provide equal amplification efficiency across all HCVgenotypes (46). Finally, preliminary studies with transcrip-tion-mediated amplification assays suggest improved sensi-tivity over existing assays with the potential to detect �50HCV RNA copies/ml (47).

Interferon-� TherapySTANDARD INTERFERON-� MONOTHERAPY. Untilrecently, when the combination of standard interferon-�plus ribavirin therapy became available, the standard of carein the United States for the treatment of chronic HCVinfection was standard interferon-� at a dosage of 3 MIUthree times weekly for 12 months (1, 29, 48). In somepatients this regimen can normalize serum aminotransferaselevels (biochemical response), improve liver histology (his-tological response), and eliminate HCV RNA from theblood (virological response) (49, 50). These responses areusually evaluated at the end of treatment and again 6 monthsor more after discontinuation of treatment. Sustained viro-logical response (defined as absence of HCV RNA through-out a 6-month follow-up period after therapy has beendiscontinued) to treatment with standard interferon-� mayalso reduce progression of chronic hepatitis to cirrhosis ordecompensation and, in some studies, was associated with adecreased incidence of hepatocellular carcinoma (49–54).

However, although induction rates (percentage of patientswho respond initially to therapy) are encouraging (30–40%), sustained responses are low, as relapse to therapy iscommon. A sustained virological response occurs in approx-imately 10–20% of patients treated for 6 months with in-terferon monotherapy (1). Patients with a sustained virolog-

ical response have approximately a 90% chance of long termremission, whereas patients with a sustained biochemicalresponse who are still positive for HCV RNA have a highprobability of relapse (48).

The disappointingly low rate of sustained responsesachieved with standard interferon-�, 3 MIU three timesweekly for 6 or 12 months, prompted investigation of al-ternate treatment regimens. Meta-analysis of 25 trials com-paring different doses and treatment schedules of standardinterferon-� revealed that higher doses increased sustainedresponses by 10% compared with standard doses. It wasevident that a dose-response relationship exists across awide range of doses and that the total dose may be moreimportant than the duration of administration (45). How-ever, the overall probability of adverse effects that resultedin discontinuation of treatment nearly doubled, increasingfrom 5.7% with standard doses to 9.2% with higher doses(p � 0.05) (48). This suggests consideration of longer termlow dose regimens or regimens that combine short term highdose therapy with prolonged low dose therapy. However,adhering to a three (or more) times weekly injection sched-ule for prolonged periods is difficult. Thus, the tolerabilityand practicality issues associated with standard interferon-�suggest the necessity for alternatives to simply increasingtotal dosage and/or duration of therapy.

STANDARD INTERFERON-� COMBINED WITHRIBAVIRIN. Combination therapy with ribavirin plusstandard interferon-�-2b (3 MIU three times weekly) is themost effective regimen currently licensed, having beenshown to be significantly superior to standard interferon-�alone in the treatment of patients with chronic HCV infec-tion (2, 3). The mechanism of action of ribavirin is un-known; it appears to have no significant effect on viral loador quasispecies distribution (55, 56). As end-of-treatmentresponses with combination therapy approximate those withinterferon-� monotherapy, it is thought that one mechanismby which ribavirin acts may be to reduce relapse duringfollow-up, and hence increase sustained responses to ther-apy. In a large (N � 912) double blind, randomized, pla-cebo-controlled study, sustained virological responses withcombination therapy were 31% (vs 6% for standard inter-feron-� monotherapy) in patients treated for 24 wk and 38%(vs 13% for standard interferon-� monotherapy) in patientstreated for 48 wk (2). An international randomized con-trolled trial using a similar protocol (but without the6-month interferon-� control arm) showed similar results inCanadian and European patients, again demonstrating thesuperiority of combination therapy over standard interfer-on-� monotherapy (3). However, higher dropout rates wereseen in the combination treatment group (as high as 19% forpatients treated for 48 wk vs only 13% for standard inter-feron-� monotherapy) (3), and the dose had to be modifiedbecause of adverse events more often (17% vs 9%) (2).

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PEGYLATED INTERFERON-� MONOTHERAPY. Short-comings of recombinant proteins include a limited half-lifeand subsequent limited clinical success. The attachment ofpolyethylene glycol (PEG) to the parent protein can result inenhanced pharmacokinetic and pharmacodynamic profiles(57). The pegylation process can be manipulated, for exam-ple, by varying the size and structure of the PEG moiety andits attachment to the parent protein to optimize these phar-macological properties.

Currently, two pegylated � interferons are under investi-gation for treatment of hepatitis C. Pegylation of interfer-on-� has created sustained levels of interferons such thatonly one dose per week would be required (compared tothree times weekly administration of unmodified, or stan-dard, interferon).

Pegylation of interferon-�-2a with a large, 40-kd molec-ular weight, branched PEG moiety resulted in an interferon[PEG(40kd) interferon-�-2a, Pegasys, Roche, Basel, Swit-zerland] that has demonstrated a 100-fold reduction in renalclearance, a restricted volume of distribution, both rapid andsustained absorption after s.c. injection (50 h), and an in-creased terminal half-life (58–60). In combination, thesepharmacokinetic enhancements may overcome the clinicallimitations of unmodified interferon and improve efficacy toan extent that cannot be achieved simply by manipulatingthe dose of interferon.

Interferon-�-2b has also been pegylated with a smaller(12 kd) linear PEG moiety (peginterferon-�-2b, PEG-In-tron, Schering-Plough, Kenilworth, NJ). Peginterferon-�-2bis associated with a mean apparent clearance equivalent toapproximately 10% of unmodified interferon and a similarvolume of distribution and absorption when compared withunmodified interferon (61).

Several large studies have reported an overall greatersustained virological response associated with pegylatedinterferons relative to standard interferon therapy. One dose-ranging study and two large phase III multinational studieshave compared 48 wk of once weekly therapy with pegy-lated interferons with three times weekly administration ofthe unmodified interferon, in interferon-naive patients withchronic HCV. In a phase II comparative study of 155 pa-tients PEG(40kd) interferon-�-2a achieved a sustained (72wk) virological response that varied with dose, peaking at36% with a dose of 180 �g, compared with a response ofonly 5% for standard interferon-�-2a, 3 MIU three timesweekly (62). In a double blind study of 1219 patients,peginterferon-�-2b achieved a sustained (72 wk) virologicalresponse that also varied with dose, peaking at 25% with adose of 1 �g/kg, compared with a response of 12% forstandard interferon-�-2b, 3 MIU three times weekly (p �0.01 vs pegylated interferon-�-2b) (63). In a phase III mul-tinational trial, 531 patients were randomized to onceweekly administration of PEG(40kd) interferon-�-2a, 180�g for 48 wk, or to three times weekly administration of aninduction regimen of standard interferon-�-2a in a dosage of6 MIU for 12 wk and then 3 MIU for 26 wk (64). Sustained

(72 wk) virological responses were obtained in 39% ofpatients treated with PEG(40kd) interferon-�-2a and in 19%of those treated with standard interferon-�-2a.

Patients with cirrhosis are often excluded from interferontrials because of a perceived low benefit:risk ratio. In apopulation of 271 interferon-naive patients with compen-sated HCV cirrhosis or bridging fibrosis, virological sus-tained responses to 48 wk of treatment were 30% in patientsrandomized to 180 �g of PEG(40kd) interferon-�-2a onceweekly and 8% in patients randomized to unmodified inter-feron-� 3 MIU 3 times weekly (65). The virological sus-tained response in patients with genotype 1 was disappoint-ingly low at 12.5% and 2% of those treated with 180 �g ofPEG interferon-�-2a and standard interferon-�-2a, respec-tively. In addition, this study showed that PEG(40kd) inter-feron-�-2a was safe in this patient population.

In contrast to the increased incidence of adverse effectsassociated with high doses of standard interferon-�, the typeand frequency of adverse effects associated with onceweekly administration of PEG(40kd) interferon-�-2a orpeginterferon-�-2b in these clinical trials were comparableto those associated with traditional doses of standard inter-feron-�. The discontinuation rates for drug intolerance werealso similar between the pegylated interferons and theirrespective parent compounds.

PEGYLATED INTERFERON-� COMBINED WITHRIBAVIRIN. Combination therapy with ribavirin plus pe-gylated interferon has been evaluated in two open-labelphase II studies. It should be noted that the results fromthese trials are not directly comparable because of differ-ences in baseline demographic and disease characteristicsand in the analysis of the responses.

In the first study, 20 patients received s.c. PEG(40kd)interferon-�-2a (180 �g) once weekly plus oral ribavirin(1000–1200 mg) daily. Patients with HCV genotype non-1were treated for 24 wk, whereas those with HCV genotype1 received 48 wk of treatment if HCV RNA was undetect-able at 24 wk by AMPLICOR MONITOR II. The end-of-treatment and sustained virological responses for patientswith HCV genotype 1 were 60% and 38%, respectively.Those with genotype 2 had end-of-treatment and sustainedresponses of 100%. No patients required discontinuation oftherapy because of neutropenia, thrombocytopenia, or ane-mia (66).

In the second study, 72 patients were evaluated usingpegylated interferon-�-2b and ribavirin in variable dosagecombinations. Patients received pegylated interferon-�-2b(0.35, 0.7, or 1.4 �g/kg s.c. weekly) for 24 wk as mono-therapy or in combination with ribavirin (600, 800, or1000–1200 mg daily). Results showed dose-response trendsfor pegylated interferon-�-2b alone and added dose-re-sponse trends when combined with increasing daily doses ofribavirin. End-of-treatment virological response was 81% at1.4 �g/kg, and sustained virological response was 60%.Adverse events were similar in all dose categories (67).

2821AJG – October, 2001 Effect of HCV Viral Dynamics on Treatment Design

Finally, a large multicenter study was recently presentedthat compared peginterferon-�-2b (two different doses) plusribavirin to standard interferon plus ribavirin in treatment-naive patients (68). The group that received 1.5 �g/kgpegylated interferon had a superior sustained virologicalresponse (54%) relative to the standard interferon group(47%). Therefore, despite the enhanced pharmocokineticand pharmacodynamic properties afforded by pegylation,there will continue to be a subset of patients who willrequire additional therapies when available.

Retreatment. Nonresponse to an initial course of treat-ment with standard interferon-� predicts a very low likeli-hood of response to retreatment. In contrast, a patient whoresponds initially to standard interferon-� monotherapy andthen relapses has a modest chance of response to retreat-ment. Combined data from 13 studies of patients who werenonresponders or only partial responders to an initial courseof treatment with standard interferon-� revealed that sus-tained responses occurred in no patients retreated with 3MIU three times weekly for 6 months, and in only 2–3% ofpatients retreated with higher doses and/or for longer peri-ods (69). Retreatment with ribavirin plus standard interfer-on-� (3 MIU or 4.5 MIU three times weekly) for 6 monthsincreased sustained virological responses to 15–17% amonginitial nonresponders (70–72). Increasing the dose of stan-dard interferon-� to 10 MIU daily increased the sustainedvirological response to approximately 25% among initialnonresponders; the tolerability at this dose was not reported(73). Results are somewhat more encouraging with retreat-ment of relapsers: a review of data from 11 studies revealedthat sustained responses occurred in 15% of relapsers re-treated with 3 MIU three times weekly for 6 months and inapproximately 30–40% of those retreated with higher dosesor for a longer duration (69). Similar results were reportedin an additional, more recent study (74). Retreatment ofrelapsers with ribavirin plus standard interferon-� for 6months increased the sustained virological response to 33%(56) or 49% (75, 76).

PREDICTORS OF RESPONSE TO TREATMENT. Sev-eral parameters have been associated with a sustained viro-logical response to standard interferon-� therapy. Low pre-treatment viral load is one of the most frequently reportedpredictors of a sustained virological response (48, 74, 77–84). Low pretreatment viral load per liver cell has also beenshown to be an accurate predictor of sustained response tostandard interferon-� therapy (85), but pretreatment intra-hepatic viral titers were not correlated with the pattern ofresponse (86). Other factors that predict success includefemale gender, patients younger than 40 yr of age regardlessof gender (48, 74, 80, 85), absence of cirrhosis (4, 48), lowgenetic complexity in the hypervariable region 1 (83, 87),and, most importantly, HCV genotype other than type 1 (74,77, 80, 82, 85, 88, 89). In the recently published multina-tional peginterferon-�-2a trial, HCV genotype other than 1had the highest odds ratio by multiple logistic regression

analysis for the prediction of a sustained virological re-sponse (64).

In several studies, the strongest predictor of a sustainedvirological response to standard interferon-� therapy wasthe early (within 2–4 wk) loss of or substantial (3 log)decrease in detectable HCV RNA in the blood (44, 90–100).Some investigators have found that HCV RNA levels asearly as 2 wk after start of treatment can be used as prog-nostic markers of response to therapy (84, 99, 101). Thepredictive value of the early (within 4 wk) loss of viremiafor a sustained virological response has also been demon-strated for patients treated with standard interferon-� plusribavirin (102). The overall sensitivity and specificity ofHCV RNA testing after 4 wk of therapy, as a prognosticindicator of sustained virological response, was significantlybetter than testing of ALT at week 4, 8, or 12 (p � 0.001 foreach testing time) (102).

For pegylated interferon, HCV genotype other than type1, pretreatment ALT quotient � 3, low pretreatment viralload, body surface area � 2, lack of cirrhosis or bridgingfibrosis, and age younger than 40 have been identified asfavorable indicators for a sustained virological response (64).

VIRAL DYNAMICS: LESSONS TO BE LEARNED

Minimum virus production and clearance in patients withchronic HCV infection has been reported to be 6.7 � 1010

virions/day (33), 1.3 � 1012 virions/day (101), 1.8 � 1011

virions/day (56), and 3.7 � 1011 virions/day (34). Thesevalues suggest that, like HIV-1, HCV has a high rate of viralinfection, replication, and turnover (3).

The response of HCV viremia to interferon-� therapyparallels the case of HIV-1 viremia in response to antiret-roviral therapy. HCV viremia declines rapidly and in abiphasic manner after administration of standard interfer-on-� (Table 1) (103, 104). Results from preliminary studiesindicate that PEG(40kd) interferon-�-2a enhances virionclearance, reinforces the death rate of infected cells, and hasa rapid viral response and reduced breakthrough rate duringtreatment (105, 106). Addition of ribavirin to standard in-terferon-� does not significantly affect the half-life of viralclearance (56). However, the vastly different immune re-sponse to HIV-1 and HCV infection complicate the abilityto draw parallels between HIV-1 and HCV viral dynamics,and the respective response of viral dynamics to treatment.Specifically, HIV-1 infection is characterized by widespreadimmunosuppression, whereas HCV infection challenges butdoes not destroy the immune system; indeed, under thepressure of ongoing immune surveillance against HCV, thedominant viral subtype may evolve (28). Also, in contrast tothe antiretroviral treatments for HIV infection, which haveonly direct antiviral mechanisms, interferons have compleximmunomodulatory and antiviral effects. Interferon-� isinstrumental in the development of T helper immune re-sponses, and appears to be the major cytokine responsiblefor the amplification of the CD8� T-cell response and

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resistance to viral infections (107). Interferons stimulatenuclear factors to inhibit viral replication, inhibit viral bud-ding, and indirectly inhibit viral replication by stimulatingcellular phosphorylating activity (108). A pre-existing im-mune response to HCV-infected hepatocytes (109), a high invitro response capacity of mononuclear cells to interferon-�(110), and interferon-�–enhanced NS3, helicase, and NS4antigen–specific T helper cell responses (111) may be im-portant components of early viral clearance and eventualsustained virological response. The host immune responsemediated by CD8� cytotoxic T-lymphocyte activity may bea particularly important determinant of the outcome of in-terferon-� therapy of chronic HCV infection (112). Thus,although a rapid and early fall in viral load in response totreatment is an important prognostic factor in both HIV andHCV infections, the mechanisms by which this is achievedmay be quite different.

Early Aggressive Intervention andMaintenance of Antiviral PressureThe rapid first phase of HCV elimination in response tostandard interferon-� therapy represents the rate of clear-ance of virus from the serum. This rate was positivelycorrelated with dosage (34, 74), suggesting the value ofearly aggressive intervention. Also, viral loads rapidly re-bounded in the absence of continued antiviral pressure (34).For example, after a single dose of standard interferon-� (3,5, or 10 MIU), viral load monitoring showed mean percent-age serum virus reductions of 41.4%, 63.7%, and 85.5%,respectively, from baseline after 24 h, and of 22.9%, 61.9%,and 74.3%, respectively, from baseline after 48 h (34).Although, curiously, the 5-MIU results showed little re-bound in viral load, the rapid viral rebound with the othertwo doses suggests the value of the maintenance of antiviralpressure with adequate trough concentrations.

Experimental evidence suggests that, for HIV-1 infec-tion, maintenance of serum concentrations of antiretro-viral drugs that result in sustained antiviral activity invivo delays the emergence of highly resistant variants(113). Similarly, maintenance of antiviral pressure should

minimize the potential for continued HCV infectionand/or production and the possibility of viral resistanceemergence.

The nonstructural 5A gene has been proposed as theinterferon-� sensitivity determining region of HCV (114,115), although this remains controversial (116, 117). Asproposed by Pawlotsky et al. (118), high quasispecies nu-cleotide sequence entropy of the interferon-� sensitivitydetermining region and high replication rates are central tothe development of resistance of HCV to interferon-�.Therefore, resistance may develop if the interferon-� dosedoes not sufficiently suppress replication, allowing interfer-on-resistant mutants to emerge. However, maintenance ofsustained concentrations of interferon-� is difficult withstandard interferon-� because of its rapid clearance from thecirculation. Standard interferon-� is cleared in a biexponen-tial manner, with a terminal elimination half-life that rangesfrom 4 to 16 h (119, 120). Thus, three times weekly (or evenonce daily) administration of standard interferon-� is un-likely to achieve the sustained concentrations of interfer-on-� that are required to provide constant antiviral pressure.In contrast, PEG(40kd) interferon-�-2a maintains constantand sustained concentrations of interferon-� with onceweekly injection; the peak-to-trough ratio after multipledosing is about 1.3–2.0 (121).

Long Term TreatmentAlthough elimination of HIV-1 may remain impossible be-cause of the putative existence of small reservoirs of virus,a significant proportion of HCV-infected patients experi-ence a sustained virological response to treatment withstandard interferon-�. This difference may be a direct resultof the retention of immune function during HCV infectionand the immune component of the mechanism of action ofinterferon-�.

Some patients completely clear HCV from the serumduring the first 24 h after administration of standard inter-feron-� (34, 103, 104). Others, who do not initially clear thevirus, show no further significant viral clearance with con-tinuation of treatment for up to 6 months (122). However,

Table 1. Elimination of HCV After Administration of Standard Interferon-�

Dosage (Sampling Duration)

Half-Life

ReferencePhase I Phase II

3 MIU three times a week (8 wk) 0.7 � 0.4 days 2.7 � 1.3 days Zeuzem et al. (33)3 vs 6 MIU three times a week 0.67 � 0.36 vs 0.23 � 0.15 days 2.3 � 1.2 vs 2.5 � 2.1 days Zeuzem et al. (56)

(8 wk) (p � 0.004)6 MIU every day (8 days) 7.2 � 3.1 h �100 h Yasui et al. (104)10 MIU � one dose (48 h) �0.3 days Lam et al. (34)10 MIU every day � 1 wk,

then three times a week (4 wk)6.7 h 400 h* Bekkering et al. (103)

5, 10, or 15 MIU every day(14 days)

2.7 h 1.7–70 days† Neumann et al. (101)

* Calculated for four of six patients. No phase II half-life could be calculated for two patients; one became HCV RNA negative after 24 h and had a sustained response, andone showed a slight rise in viral load between day 2 and day 28.

† Range of half-lives of infected cell death rates.

2823AJG – October, 2001 Effect of HCV Viral Dynamics on Treatment Design

many patients with chronic HCV infection who are treatedwith standard interferon-� do demonstrate a second, slowerphase of elimination. For example, among 12 patients ad-ministered standard interferon-� (6 MIU) daily for 2 wk,and then three times weekly for an additional 22 wk, sevenpatients demonstrated a decrease of viremia to below thedetection limit during the first 2 days, and maintained anegative viral load thereafter (104). HCV genotype repre-sentation for this pattern was approximately equally dividedbetween HCV genotypes 1 and 2. In the five remainingpatients, the initial rapid decrease of viremia was followedduring days 1 to 8 with a slower decrease characterized bya half-life of approximately 100 h; 80% (4/5) of the patientsdemonstrating this biphasic pattern were infected with HCVgenotype 1.

Other studies have also demonstrated the biphasic declineof viremia (34, 101, 103). The slope of the elimination rateof phase II was found to be inversely correlated with base-line viral load and positively correlated with baseline ALTlevel (101). There was a large interpatient variation in thephase II half-life (1.7–70 days); shorter half-lives predicteda virological response at 3 months and showed a nonsignif-icant trend to association with high doses of standard inter-feron-� (101).

Phase II of the biphasic decline has been proposed torepresent either clearance of virus that is slowly releasedfrom infected cells, with interferon-� preventing new cellinfection (56), or the rate of killing of infected cells by theimmune system, with interferon-� preventing the produc-tion and release of virions (34, 101). The different dynamicsof virus elimination between patients treated with standardinterferon-� may reflect interpatient differences in the abil-ity of the immune system to eliminate the virus, probablyfrom sites of sequestration. The biphasic elimination ofHCV by standard interferon-� suggests the possible value oflong term treatment with interferon-�, in combination withhigh dose induction and sustained pressure, for some pa-tients infected with HCV. Prolonged maintenance therapyafter early aggressive intervention could provide the inter-feron-�–stimulated immune system more time to mount anefficient response to escape variants selected during the firstmonths of therapy or to clear the virus from sites of seques-tration.

The once weekly administration schedule of pegylatedinterferons should have a positive effect on complianceduring long term administration, and has shown a markedincrease in self-rated quality of life relative to standardinterferon-� as measured by the standardized 36-questionshort form Health Survey. Forty-eight percent of patientstreated with PEG(40kd) interferon-�-2a reported feelingbetter or much better after completion of therapy, as com-pared with only 26% of patients treated with standard in-terferon-�. Therapeutic responders were more likely to re-port improved health-related quality of life thannonresponders (123).

DISCUSSION

Plasma HIV-1 load strongly predicts the rate of decrease inCD4� lymphocyte count and progression to AIDS anddeath; viral load monitoring should be used to guide theinitiation of antiretroviral therapy and subsequent changesin therapy. Similarly, viral load provides valuable informa-tion about the natural history of HCV infection; the abilityto determine viral load enables prediction of the likelihoodof response to treatment, as well as a way to assess treatmentefficacy.

Viral load monitoring and molecular genetic analyseshave greatly advanced our understanding of the naturalhistory of chronic HCV and the genetic basis of resistanceto interferon-� therapy. Data collected with these techniquessuggest why the standard interferon-� regimen has lim-ited efficacy and point to potentially more effective ap-proaches for treating HCV infection. Sustained responsesassociated with standard interferon-� monotherapy aredisappointingly low at 10 –20%, and are 30 – 47% withthe combination of ribavirin plus standard interferon-� intreatment-naive patients. Early aggressive interventionand the maintenance of antiviral pressure to prevent viralrebound are essential to halting continuing cell infectionand viral replication, minimizing the potential for emer-gence of resistant quasispecies. Prolonged maintenancetherapy may be necessary to provide the interferon-�–stimulated immune system sufficient time to mount anefficient response to escape variants selected during thefirst months of therapy.

The rapid absorption and removal from the circulation ofstandard interferon-� precludes the maintenance of sus-tained serum interferon-� concentrations throughout a threetimes weekly or even a daily dosage interval. High doseregimens are not a practical approach for producing higherserum concentrations because they are associated with agreatly increased incidence of adverse effects. The pegy-lated interferons provide the sustained serum concentrationsnecessary for constant antiviral pressure with only onceweekly administration, and may be a clinically more effec-tive alternative to aggressive regimens of standard interfer-on-�. Preliminary data suggest that pegylated interferonplus ribavirin will further enhance sustained virologicalresponses. Thus, pegylated interferon may prove to be cen-tral to the three-part therapeutic goal of early aggressiveintervention, maintenance of antiviral pressure, and pro-longed maintenance therapy in the treatment of chronicHCV infection.

ACKNOWLEDGMENT

Grants and other financial support came from F. Hoff-mann-La Roche Ltd. (Basel, Switzerland).

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Reprint requests and correspondence: Vincent G. Bain, M.D.,University of Alberta, Department of Medicine, Division of Gas-troenterology, 8440 112 Street, 2E1.14 WMC, Edmonton, AlbertaT6G 2R7 Canada.

Received Mar. 22, 2000; accepted June 20, 2001.

REFERENCES

1. National Institutes of Health. Management of hepatitis C.NIH Consensus Statement 1997;15(3):1–41.

2. McHutchison JG, Gordon SC, Schiff ER, et al. Interferonalfa-2b alone or in combination with ribavirin as initial treat-ment for chronic hepatitis C. N Engl J Med 1998;339:1485–92.

3. Poynard T, Marcellin P, Lee SS, et al. Randomised trial ofinterferon alpha 2b plus ribavirin for 48 weeks or for 24weeks versus interferon alpha 2b plus placebo for 48 weeksfor treatment of chronic infection with hepatitis C virus.Lancet 1998;352:1426–32.

4. de Jong MD, Boucher CAB, Danner SA, et al. Summary ofthe international consensus symposium on management ofHIV, CMV and hepatitis virus infection. Antiviral Res 1998;37:1–16.

5. Hammer SM. Advances in antiretroviral therapy and viralload monitoring. AIDS 1996;10(suppl 3):S1–11.

6. Shaw GM. Biology of human immunodeficiency viruses. In:Bennet JC, Plum F, eds. Cecil textbook of medicine, 20th ed.Vol. 2. Philadelphia: Saunders, 1996:1841–6.

7. Walker BD. Immunology related to AIDS. In: Bennet JC,Plum F, eds. Cecil textbook of medicine, 20th ed. Vol. 2.Philadelphia: Saunders, 1996:1837–41.

8. Palella FJ Jr, Delaney KM, Moorman AC, et al. Decliningmorbidity and mortality among patients with advanced hu-man immunodeficiency virus infection. N Engl J Med 1998;338:853–60.

9. Carpenter CCJ, Fischi MA, Hammer SM, et al. Antiretroviraltherapy for HIV infection in 1998. JAMA 1998;279:78–86.

10. Gulick RM. HIV treatment strategies: Planning for the longterm. JAMA 1998;279:957–8.

11. Mellors JW, Rinaldo CR Jr, Gupta P, et al. Prognosis inHIV-1 infection predicted by the quantity of virus in plasma.Science 1996;272:1167–70.

12. Mellors JW, Munoz A, Giorgi JV, et al. Plasma viral load andCD4� lymphocytes as prognostic markers of HIV-1 infec-tion. Ann Intern Med 1997;126:946–54.

13. Hirsch MS, Conway B, D’Aquila RT, et al. Antiretroviraldrug resistance testing in adults with HIV infection. JAMA1998;279:1984–91.

14. Raboud JM, Montaner JSG, Conway B, et al. Suppression ofplasma viral load below 20 copies/ml is required to achievea long-term response to therapy. AIDS 1998;12:1619–24.

15. Perelson AS, Neumann AU, Markowitz M, et al. HIV-1dynamics in vivo: Virion clearance rate, infected cell life-span, and viral generation time. Science 1996;271:1582–6.

16. Ramratnam B, Bonhoeffer S, Binley J, et al. Rapid produc-tion and clearance of HIV-1 and hepatitis C virus assessed bylarge volume plasma apheresis. Lancet 1999;354:1782–5.

17. Perelson AS, Essunger P, Cao Y, et al. Decay characteristicsof HIV-1-infected compartments during combination ther-apy. Nature 1997;387:188–91.

18. Ho DD, Neumann AU, Perelson AS, et al. Rapid turnover ofplasma virions and CD4 lymphocytes in HIV-1 infection.Nature 1995;373:123–6.

19. Wei X, Ghosh SK, Taylor ME, et al. Viral dynamics in

human immunodeficiency virus type 1 infection. Nature1995;373:117–22.

20. Neumann AU, Mallet A, Calvez V, et al. Modeling thesources for persistent HIV load in patients receivingHAART—evidence for a drug sanctuary compartment. IntConf AIDS 1998;12:12–3.

21. Neumann AU, Calvez V, Li TS, et al. Initial viral load isnegatively correlated with rapid HIV decline during HAARTand positively correlated with HIV rebound at its interrup-tion. Presented at the 6th Conference on Retroviruses andOpportunistic Infections; January 31–February 4, 1999; Chi-cago, IL.

22. Dornadula G, Zhang H, VanUitert B, et al. Residual HIV-1RNA in blood plasma of patients taking suppressive highlyactive antiretroviral therapy. JAMA 1999;282:1627–32.

23. Finzi D, Blankson J, Siliciano JD, et al. Latent infection ofCD4� T cells provides a mechanism for lifelong persistenceof HIV-a, even in patients on effective combination therapy.Nat Med 1999;5:512–7.

24. Schrager LK, D’Souza P. Cellular and anatomical reservoirsof HIV-1 in patients receiving potent antiretroviral combina-tion therapy. JAMA 1998;280:67–71.

25. Ockner RK. Acute viral hepatitis. In: Bennet JC, Plum F, eds.Cecil textbook of medicine, 20th ed. Vol. 2. Philadelphia:Saunders, 1996:762–72.

26. Moonka DK, Henzel BS, Gutekunst K, et al. Quantitativeassessment of hepatitis C virus RNA in peripheral bloodmononuclear cells during therapy with interferon-� 2a. JViral Hepat 1998;5:27–33.

27. Conry-Cantilena C, Vanraden M, Gibble J, et al. Routes ofinfection, viremia, and liver disease in blood donors found tohave hepatitis C virus infection. N Engl J Med 1996;334:1691–6.

28. Ockner RK. Chronic hepatitis. In: Bennet JC, Plum F, eds.Cecil textbook of medicine, 20th ed. Vol. 2. Philadelphia:Saunders, 1996:776–81.

29. Recommendations for prevention and control of hepatitis Cvirus (HCV) infection and HCV-related chronic disease.Centers for Disease Control and Prevention. MMWR MorbMortal Wkly Rep 1998;47(RR-19):1–40.

30. Bukh J, Miller RH, Purcell RH. Genetic heterogeneity ofhepatitis C virus: Quasispecies and genotypes. Semin LiverDis 1995;15:41–63.

31. Leitner T. Genetic subtypes of HIV-1. In: Myers G, Foley B,Mellors JW, et al, eds. Human retroviruses and AIDS. The-oretical biology and biophysics. Los Alamos, NM: LosAlamos National Laboratory, 1996:III28–40.

32. Weiner AJ, Geysen HM, Christopherson C, et al. Evidencefor immune selection of hepatitis C virus (HCV) putativeenvelope glycoprotein variants: potential role in chronicHCV infections. Proc Natl Acad Sci U S A 1992;89:3468–72.

33. Zeuzem S, Schmidt JM, Lee J-H, et al. Effect of interferonalfa on the dynamics of hepatitis C virus turnover in vivo.Hepatology 1996;23:366–71.

34. Lam NP, Neumann AU, Gretch DR, et al. Dose-dependentacute clearance of hepatitis C genotype 1 virus with inter-feron alfa. Hepatology 1997;26:226–31.

35. Pontisso P, Bellati G, Brunetto M, et al. Hepatitis C virusRNA profiles in chronically infected individuals: Do theyrelate to disease activity. Hepatology 1999;29:585–9.

36. Gretch D, Corey L, Wilson J, et al. Assessment of hepatitisC virus RNA levels by quantitative competitive RNA poly-merase chain reaction: High-titer viremia correlates withadvanced stage of disease. J Infect Dis 1994;169:1219–25.

37. Gretch DR, Polyak SJ, Willson RA, et al. Treatment of

2825AJG – October, 2001 Effect of HCV Viral Dynamics on Treatment Design

chronic hepatitis C virus infection: A clinical and virologicalperspective. Antiviral Chem Chemother 1996;4:207–25.

38. Lau JYN, Davis GL, Kniffen J, et al. Significance of serumhepatitis C virus RNA levels in chronic hepatitis C. Lancet1993;341:1501–4.

39. Kato N, Yokosuka O, Hosoda K, et al. Quantification ofhepatitis C virus by competitive reverse transcription-poly-merase chain reaction: Increase of the virus in advanced liverdisease. Hepatology 1993;18:16–20.

40. Iuliano R, Pizzigallo AM, Alecci A, et al. Quantitation ofHCV viraemia by branched DNA signal amplification inpatients treated with �-interferon—a longitudinal study. In-fection 1996;24:292–6.

41. Adinolfi LE, Andreana R, Utili R, et al. HCV RNA levels inserum, liver, and peripheral blood mononuclear cells ofchronic hepatitis C patients, and their relationship to liverinjury. Am J Gastroenterol 1998;93:2162–6.

42. Teramura K, Fukuda A, Kobayashi H, et al. Virus elimina-tion and histologic improvement in patients with chronichepatitis C treated with interferon alpha. J Clin Gastroenterol1997;25:346–51.

43. Shiratori Y. Histological improvement of fibrosis in hepatitisC patients with sustained response (SR) to interferon (IFN)therapy—long-term follow-up study using paired biopsysamples. Presented at Digestive Disease Week ScientificSessions; May 16–19, 1999; Orlando, FL.

44. Colucci G, Gutekunst K. Development of a quantitative PCRassay for monitoring HCV viraemia levels in patients withchronic hepatitis C. J Viral Hepat 1997;4(suppl 1):75–8.

45. Lunel F, Cresta P, Vitour D, et al. Comparative evaluation ofhepatitis C virus RNA quantitation by branched DNA,NASBA, and monitor assays. Hepatology 1999;29:528–35.

46. Doglio A, Laffont C, Caroli-Bosc FX, et al. Second gener-ation of the automated Cobas Amplicor HCV assay improvessensitivity of hepatitis C virus RNA detection and yieldsresults that are more clinically relevant. J Clin Microbiol1999;37:1567–9.

47. Sarrazin C, Teuber G, Kokka R, et al. Detection of residualhepatitis C virus RNA by transcription-mediated amplifica-tion in patients with complete virologic response according topolymerase chain reaction-based assays. Hepatology 2000;32:818–23.

48. Camma C, Giunta M, Pinzello G, et al. Chronic hepatitis Cand interferon alpha: Conventional and cumulative meta-analyses of randomized controlled trials. Am J Gastroenterol1999;94:581–95.

49. Hayashi J, Kashiwagi S. Hepatitis C virus infection in theelderly: Epidemiology, prophylaxis and optimal treatment.Drug Aging 1997;11:296–308.

50. Mazzella G, Accogli E, Sottili S, et al. Alpha interferontreatment may prevent hepatocellular carcinoma in HCV-related liver cirrhosis. J Hepatol 1996;24:141–7.

51. Yoshida H. How long will the virological sustained respond-ers to IFN remain at risk of developing hepatocellular carci-noma? Presented at Digestive Disease Week ScientificSessions; May 16–19, 1999; Orlando, FL.

52. Realdi G. Interferon therapy of HCV cirrhosis reduces theincidence of HCC, and decompensation, and significantlyimproves survival: A 5 year comparative trial. Presented atDigestive Disease Week Scientific Sessions; May 16–19,1999; Orlando, FL.

53. Kasahara A, Hayashi N, Mochizuki K, et al. Risk factors forhepatocellular carcinoma and its incidence after interferontreatment in patients with chronic hepatitis C. Hepatology1998;27:1394–402.

54. Serfaty L, Aumaitre H, Chazouilleres O, et al. Determinants

of outcome of compensated hepatitis C virus-related cirrho-sis. Hepatology 1998;27:1435–40.

55. Lee J-H, von Wagner M, Roth WK, et al. Effect of ribavirinon virus load and quasispecies distribution in patients in-fected with hepatitis C virus. J Hepatol 1998;29:29–35.

56. Zeuzem X, Schmidt JM, Lee J-H, et al. Hepatitis C virusdynamics in vivo. Effect of ribavirin and interferon alfa onviral turnover. Hepatology 1998;28:245–52.

57. Monfardini C, Schiavon O, Caliceti P, et al. A branchedmonomethoxypoly (ethylene glycol) for protein modifica-tion. Bioconjugate Chem 1995;6:62–9.

58. Neiforth KA, Nadeau R, Patel IH, et al. Use of an indirectpharmacodynamic stimulation model of MX protein induc-tion to compare in vivo activity of interferon alfa-2a and apolyethylene glycol-modified derivative in healthy subjects.Clin Pharmacol Ther 1996;59:636–46.

59. Algranati NE, Sy S, Modi MW. A branched methoxy 40 kDapolyethylene glycol (PEG) moiety optimizes the pharmaco-kinetics (PK) of peginterferon �-2a (PEG-IFN) and mayexplain its enhanced efficacy in chronic hepatitis C (CHC).Hepatology 1999;30(suppl):190A.

60. Xu Z-X, Patel I, Joubert P. Single-dose safety/tolerability andpharmacokinetic/pharmacodynamics (PK/PD) following ad-ministration of ascending subcutaneous doses of pegylated-interferon (PEG-IFN) and interferon �-2a (IFN �-2a) tohealthy subjects. Hepatology 1998;28(suppl):702.

61. Glue P, Fang J, Sabo R, et al. Peg-interferon-�2B. Pharma-cokinetics, pharmacodynamics, safety and preliminary effi-cacy data. Hepatology 1999;30(suppl):189A.

62. Shiffman M, Pockros PJ, Reddy RK, et al. A controlled,randomized, multicenter, descending dose phase II trial ofpegylated interferon alfa-2a (PEG) vs standard interferonalfa-2a (IFN) for treatment of chronic hepatitis C. Gastroen-terology 1999;116(suppl):Part 2.

63. Trepo C, Lindsay K, Niederau C, et al. Pegylated interferonalfa-2b (Peg-Intron) monotherapy is superior to interferonalfa-2b (Intron A) for the treatment of chronic hepatitis C.J Hepatol 2000;32(suppl 2):29.

64. Zeuzem S, Feinman SV, Rasenack J, et al. Peginterferonalfa-2A in patients with hepatitis C. N Engl J Med 2000;343:1666–72.

65. Heathcote EJ, Shiffman ML, Cooksley G, et al. Peginterferon�-2a (PEG-IFN) in patients with chronic hepatitis C, andcirrhosis. N Engl J Med 2000;343:1673–80.

66. Sulkowski MS, Reindollar R, Yu J. Pegylated interferonalfa-2A (PEGASYS TM) and ribavirin combination therapyfor chronic hepatitis C: A phase II open-label study. Gastro-enterology 2000;118(suppl 2):950.

67. Glue P, Rouzier-Panis R, Raffanel C, et al. A dose-rangingstudy of pegylated interferon alfa-2b and ribavirin in chronichepatitis C. Hepatology 2000;32:647–53.

68. Manns MP, McHutchison JG, Gordon S, et al. Peginterferonalfa-2B plus ribavirin compared to interferon alfa-2B plusribavirin for the treatment of chronic hepatitis C. Hepatology2000;32:297A.

69. Alberti A, Chemello L, Noventa F, et al. Therapy of hepatitisC: Re-treatment with alpha interferon. Hepatology 1997;26(suppl 1):137S–42S.

70. Sostegni R, Ghisetti V, Pittaluga F, et al. Sequential versusconcomitant administration of ribavirin and interferonalfa-n3 in patients with chronic hepatitis C not responding tointerferon alone: results of a randomized, controlled trial.Hepatology 1998;28:341–6.

71. Bell H, Hellum K, Harthug S, et al. Treatment with interfer-on-alpha 2a alone or interferon-alpha 2a plus ribavirin inpatients with chronic hepatitis C previously treated withinterferon-alpha 2a. Scand J Gastroenterol 1999;34:194–8.

2826 Bain AJG – Vol. 96, No. 10, 2001

72. Barbaro G, Di Lorenzo G, Soldini M, et al. Interferon-alpha-2B and ribavirin in combination for chronic hepatitis Cpatients not responding to interferon-alpha alone: An Italianmulticenter, randomized, controlled, clinical study. Am JGastroenterol 1998;93:2445–51.

73. Bekkering FC, Brouwer JT, Leroux-Roels G, et al. Ultrarapid hepatitis C virus clearance by daily high-dose inter-feron in non-responders to standard therapy. J Hepatol 1998;28:960–4.

74. Payen J-L, Izopet J, Galindo-Migeot V, et al. Better efficacyof a 12-month interferon alfa-2b retreatment in patients withchronic hepatitis C relapsing after a 6-month treatment: Amulticenter, controlled, randomized trial. Hepatology 1998;28:1680–6.

75. Davis GL, Esteban-Mur R, Rustgi V, et al. Interferon alfa-2balone or in combination with ribavirin for the treatment ofrelapse of chronic hepatitis C. N Engl J Med 1998;339:1493–9.

76. Davis GL. Combination therapy with interferon alfa andribavirin as retreatment of interferon relapse in chronic hep-atitis C. Semin Liver Dis 1999;19(suppl 1):49–55.

77. Knolle PA, Kremp S, Hohler T, et al. Viral and host factorsin the prediction of response to interferon-� therapy inchronic hepatitis C after long-term follow-up. J Viral Hepat1998;5:399–406.

78. Reichard O, Norkrans G, Fryden A, et al. Comparison of 3quantitative HCV RNA assays—accuracy of baseline viralload to predict treatment outcome in chronic hepatitis C.Scand J Infect Dis 1998;30:441–6.

79. Soffredini R, Rumi MG, Del Ninno E, et al. Serum levels ofhepatitis C virus RNA predict non-response to interferontherapy: Comparison of two commercial assays. J ViralHepat 1999;6:65–71.

80. Bell H, Hellum K, Harthug S, et al. Genotype, viral load, andage as independent predictors of treatment outcome of inter-feron-�2a treatment in patients with chronic hepatitis C.Scand J Infect Dis 1997;29:17–22.

81. Takagi H, Takehara K, Shimoda R, et al. Prediction of effectof interferon on chronic hepatitis C. Dig Dis Sci 1997;42:2270–6.

82. Shiratori Y, Kato N, Yokosuka O, et al. Predictors of theefficacy of interferon therapy in chronic hepatitis C infection.Gastroenterology 1997;113:558–66.

83. Nomura H, Tsuchiya Y, Kimura Y, et al. Clinical efficacy ofinterferon therapy for chronic hepatitis C in the Kita-Kyushudistrict of Japan. Fukuoka Acta Med 1997;88:253–60.

84. Nomura H, Kimura Y, Rikimaru N, et al. Usefulness ofHCV-RNA assays in efficacy evaluation of interferon treat-ment for chronic hepatitis C: AmplicorTM HCV assay andbranched DNA probe assay. J Infect 1997;34:249–55.

85. Schlaak JF, Trippler M, Ernst I, et al. Chronic hepatitis C:The viral load per liver cell before treatment as a new markerto predict long-term response to IFN � therapy. J Hepatol1997;27:917–21.

86. Negro F, Krawczynski K, Quadri R, et al. Detection ofgenomic- and minus-strand of hepatitis C virus RNA in theliver of chronic hepatitis C patients by strand-specific semi-quantitative reverse-transcriptase polymerase chain reaction.Hepatology 1999;29:536–42.

87. Pawlotsky J-M, Pellerin M, Bouvier M, et al. Genetic com-plexity of the hypervariable region 1 (HVR1) of hepatitis Cvirus (HCV): Influence on the characteristics of the infectionand responses to interferon alfa therapy in patients withchronic hepatitis C. J Med Virol 1998;54:256–64.

88. Kanai K, Kako M, Aikawa T, et al. Clearance of serumhepatitis C virus RNA after interferon therapy in relation tovirus genotype. Liver 1995;15:185–8.

89. Thavarungkul P, Toriyama K, Kusuda M, et al. Clinico-pathological predictive factors of response to interferon ther-apy in chronic hepatitis C. Southeast Asian J Trop MedPublic Health 1996;27:85–90.

90. Izopet J, Payen JL, Alric L, et al. Baseline level and earlysuppression of serum HCV RNA for predicting sustainedcomplete response to alpha-interferon therapy. J Med Virol1998;54:86–91.

91. Kagawa T, Hosi K, Takashimizu S, et al. Comparison of twointerferon alfa treatment regimens characterized by an earlyvirological response in patients with chronic hepatitis C.Am J Gastroenterol 1998;93:192–6.

92. Zeuzem S, Lee J-H, Frankel A, et al. Quantification of theinitial decline of serum hepatitis C virus RNA and responseto interferon alfa. Hepatology 1998;27:1149–56.

93. Gavier B, Martinez-Gonzalez M-A, Riezu-Boj J-I, et al.Viremia after one month of interferon therapy predicts treat-ment outcome in patients with chronic hepatitis C. Gastro-enterology 1997;113:1647–63.

94. Kakumu S, Aiyama T, Okumura A, et al. Earlier loss ofhepatitis C virus RNA in interferon therapy can predict a longterm response in chronic hepatitis C. J Gastroenterol Hepatol1997;12:468–72.

95. Orito E, Mizokami M, Suzuki K, et al. Loss of serum HCVRNA at week 4 of interferon-� therapy is associated withmore favorable long-term response in patients with chronichepatitis C. J Med Virol 1995;46:109–15.

96. Hino K, Okuda M, Konishi T, et al. Serial assay of hepatitisC virus RNA in serum for predicting response to interferon-�therapy. Dig Dis Sci 1995;40:14–20.

97. Karino Y, Toyota J, Sugawara M, et al. Early loss of serumhepatitis C virus RNA can predict a sustained response tointerferon therapy in patients with chronic hepatitis C. Am JGastroenterol 1997;92:61–5.

98. Wada M, Kang KB, Nishigami T, et al. Importance of pre-treatment viral load and monitoring of serum hepatitis Cvirus RNA in predicting responses to interferon-�2a treat-ment of chronic hepatitis C. J Interferon Cytokine Res 1997;17:707–12.

99. Yamaji K, Hayashi J, Kawakami Y, et al. Hepatitis C viralRNA status at two weeks of therapy predicts the eventualresponse. J Clin Gastroenterol 1998;26:193–9.

100. Yamakawa Y, Sata M, Suzuki H, et al. Monitoring of serumlevels of HCV RNA in early phase of IFN therapy; as apredictive marker of subsequent response. Hepatogastroen-terology 1998;45:133–6.

101. Neumann AU, Lam NP, Dahari H, et al. Hepatitis C viraldynamics in vivo, and the antiviral efficacy of interferon-�therapy. Science 1998;282:103–7.

102. Brouwer JT, Hansen BE, Niesters HGM, et al. Early predic-tion of response in interferon monotherapy and in interferon-ribavirin combination therapy for chronic hepatitis C: HCVRNA at 4 weeks versus ALT. J Hepatol 1999;30:192–8.

103. Bekkering FC, Brouwer JT, Schalm SW, et al. Hepatitis C:Viral kinetics. Hepatology 1997;26:1691–2 (letter).

104. Yasui K, Okanoue T, Murakami Y, et al. Dynamics ofhepatitis C viremia following interferon-� administration.J Infect Dis 1998;177:1475–9.

105. Zeuzem S, Herrmann E, Lee J-H, et al. Hepatitis C viruskinetics in chronically infected patients treated with pegy-lated interferon-alpha. Hepatology 1999;30(suppl):309.

106. Neumann A, Zeuzem S, Brunda MJ, et al. Rapid viral re-sponse to treatment with pegylated (40kDa) interferonalfa-2a (PEGASYS) is strongly predictive of sustained viro-logical response in patients with chronic hepatitis C (CHC).Hepatology 2000;32(suppl):318A.

107. Tompkins WA. Immunomodulation and therapeutic effects

2827AJG – October, 2001 Effect of HCV Viral Dynamics on Treatment Design

of the oral use of interferon-alpha: Mechanism of action.J Interferon Cytokine Res 1999;19:817–28.

108. Gazzard BG. Viral diseases. In: Speight RM, Holford NHG,eds. Avery’s drug treatment, 4th ed. Auckland: Adis Inter-national, 1997:1515–43.

109. Mika B. Pretreatment histology activity index (HAI) is anindicator of early HCV viral clearance with IFN therapy.Presented at Digestive Disease Week Scientific Sessions;May 16–19, 1999; Orlando, FL.

110. Podevin P, Guechot J, Serfaty L, et al. Evidence for a defi-ciency of interferon response in mononuclear cells fromhepatitis C viremic patients. J Hepatol 1997;27:265–71.

111. Lohr H, Gerken G, Roth M, et al. The cellular immuneresponses induced in the follow-up of interferon-alphatreated patients with chronic hepatitis C may determine thetherapy outcome. J Hepatol 1998;29:524–32.

112. Nelson DR, Marousis CG, Ohno T, et al. Intrahepatic hepa-titis C virus-specific cytotoxic T lymphocyte activity andresponse to interferon alfa therapy in chronic hepatitis C.Hepatology 1998;28:225–30.

113. Winslow DL, Garber S, Reid C, et al. Selection conditionsaffect the evolution of specific mutations in the reverse tran-scriptase gene associated with resistance to DMP 266. AIDS1996;10:1205–9.

114. Enomoto N, Sato C. Hepatitis C virus quasispecies popula-tions during chronic hepatitis C infection. Trends Microbiol1995;3:445–6.

115. Saiz JC, Lopez-Labrador FX, Ampurdanes S, et al. Theprognostic relevance of the nonstructural 5A gene interferonsensitivity determining region is different in infections with

genotype 1b and 3a isolates of hepatitis C virus. J Infect Dis1998;177:839–47.

116. Odeberg J, Yun Z, Sonnerborg A, et al. Variation in thehepatitis C virus NS5a region in relation to hypervariableregion 1 heterogeneity during interferon treatment. J MedVirol 1998;56:3–38.

117. Squadrito G, Leone F, Sartori M, et al. Mutations in thenonstructural 5A region of hepatitic C virus and response ofchronic hepatitis C to interferon alfa. Gastroenterology 1997;113:567–72.

118. Pawlotsky J-M, Germanidis G, Neumann AU, et al. Inter-feron resistance of hepatitis C virus genotype 1b: Relation-ship to nonstructural 5A gene quasispecies mutations. J Virol1998;72:2795–805.

119. Wills RJ, Dennis S, Spiegel HE, et al. Interferon kinetics andadverse reactions after intravenous, intramuscular, and sub-cutaneous injection. Clin Pharmacol Ther 1984;35:722–7.

120. Wills RJ. Clinical pharmacokinetics of interferons. ClinPharmacokinet 1990;19:390–9.

121. Heathcote EJ, Pockros PJ, Fried MW, et al. The pharmaco-kinetics of pegylated-40 kDa, branched interferon alfa-2a(PEG-IFN) in chronic hepatitis C (CHC) patients with cir-rhosis. Gastroenterology 1999;116(suppl).

122. Lam N, Neumann AU, Perelson AS, et al. Hepatitis C: Viralkinetics. Hepatology 1997;26:1692–3 (letter).

123. Cooksley G, Foster G, Green J, et al. The effect of successfulanti-viral therapy on health-related quality of life for patientswith chronic hepatitis C and cirrhosis. Gastroenterology2000;118(suppl 2):951.

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