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l I , NO. 2. 1991

Prevention and Therapy of Viral Hepatitis

Prevention and therapy of viral hepatitis, the ultimate clinical goals of all our efforts to study and undcrstand these agents, have evolved dramatically over the last decade. As the 1980s were ushcred in, thc dcvelopmcnt of hepatitis B vaccine and the demonstration of its efficacy in randomized. controlled trials took center stage. Remaining the focus of attention during the early part of the decade, hepatitis B vaccination has become quite routine in some circles, and the rapid advances of the early years have been replaced by the contemporary pursuit of refinements in vaccines and their implementation. As the star of hepatitis B vaccine began to fade, however. interest was killed in hepatitis A vaccine, and antiviral therapy of chronic viral hepatitis began to achieve a level of heretofore elusive legitimacy. These trends will be reviewed.

HEPATITIS B VACCINES The development, nearly a decade ago, of a safe and effective hepatitis B vaccine from the plasma of hepatitis B carriers was a promising advance in the effort to control hepatitis B.' Despite its exhaustive inactivation process, despite its excellent safety and efficacy profile, this first-generation vaccine met with limited acceptance, especially because of unfounded fears about its safety. The introduction, in 1987, of a second-generation hepatitis B vaccine derived from recombinant yeast containing the gene for hepatitis B surface antigen (HBsAg) (the S gene) helped to allay this fear about the source and safety of the original plasma-derived vaccine,' and now there are two comniercially available recombinant yeast vaccines.9oth the plasma-derived and recombinant-yeast hepatitis B vaccines are safe, immunogenic, and effective in preventing hepatitis B. Current interest has focused on a number of issues that remain to be resolved.

Failure of Vaccine Implementation Policy Despite the availability for almost a decade of a safe and effective vaccine, the incidence of hepatitis B in the

From the Ga.stroitzic..\rit~trI Unit (Mdic,trl S e r ~ ' i w s nntl ) Liwr.Bilitrry-Prrnc.rerrs Center. Mtr.s.\tr~~lzu.sett.\Genertrl Ho.\pitul trrzd the Dqxrrtrnrnt of' Metlic.int, Htrrrarrl Medic,trl School, Bo.\rorr. Mos~o(~ht[.s~ft~ Reprint requests: Dr. Dienstag, Gastrointestinal Unit, Maasachusetts General Hosp~tal,Boston, MA 021 14.

United States has increased in recent years.' In part, this can be blamed on the fact that fewer than 10% of the estimated 22 million people considered at high risk of hepatitis B virus (HBV) infection have actually been v a c ~ i n a t e d . Certainly, ~.~ adequate coverage of populations at risk can have an impact on the occurrence of hepatitis B, as was demonstrated in Switzerland7 and Taiwan.' However, in the United States high-risk populations have been difficult to reach. Moreover, approximately half of the new cases recognized each year in the United States have occurred in persons who do not fall into any recognized high-risk category, that is, they have no known risk factor for exposure to viral hepatitis. Expanded vaccination strategies are being considered, and the one gaining advocates among public health officials is a universal hepatitis B vaccination program. An analogy may be found in the expansion of the original screening program in pregnant women. When HBsAg screening was limited to women in high-risk groups for hepatitis B exposure, approximately half of the HBsAgpositive women were missed, all of whom would have been able to transmit HBV infection to their offspring." This realization led to the recommendation that all pregnant women be screened for HBsAg to identify babies to be vaccinated at birth."' An obstacle to such a policy of universal vaccination is the cost of hepatitis B vaccine, now prohibitive but potentially affordable if technologic advances, marketplace competition, innovative delivery (such as, changes in route, dose, and schedule), and economies of scale bring the price of hepatitis B vaccine down. Another issue is the timing of vaccination. Universal vaccination o f children with their other childhood vaccinations would simplify the logistics of such a policy; however, data are inadequate to determine whether vaccination so early in life and duration of protection would suffice to protect against an infection that occurs in the United States primarily in adolescence and early adulthood. An alternative strategy of initial or booster vaccination just prior to puberty might be more timely.

Duration of Protection by Vaccine Whether childhood immunization with hepatitis B vaccine will prevent hepatitis B in adulthood depends on the duration of protection after vaccination. Duration of protection is unknown, and the need for and timing of.a booster dose of hepatitis B vaccine remains uncertain. Current observations suggest that protection lasts at least as long as measurable antibody to HBsAg (anti-HBs)

Copyright 0 1991 by Thieme Medical Publibhera, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.

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persists in the circulation; 5 years after vaccination, almost 90% of vaccinees retain detectable antibody, and approximately 80% retain antibody levels considered protective (10 mIU1ml or higher)."-" The loss of detectable anti-HBs after vaccination, however, does not necessarily imply a loss of protection. Previously determined levels of anti-HBs considered minimally protective against infection may not correlate with a loss of immunity when antibody falls after vaccination. In vitro studies have demonstrated intact immunologic memory in B cells obtained from hepatitis B vaccine responders who had low (less than 10 mIU/ml) or undetectable antiHBs levels 7 to 8 years after immunization.'"urthermore, evidence suggests that, even in those whose anti-HBs levels have become undetectable after primary immunization, natural exposure to HBV long after primary vaccination results in an immediatc, boostcrlike, anamnestic increase in anti-HBs levels that should be sufficiently timely and intense to protect against infcction." Even 7 years after vaccination, when a large proportion of vaccinees have lost detectable anti-HBs, booster vaccination results in an anamnestic rise in antiHBs,lS suggesting that immunity to natural infection would stimulate the samc immune response. The maximal level of anti-HBs following an initial series of three vaccinations with hepatitis B vaccine is predictive of the persistence of antibody. ' ' . ' h . ' 7 The rate of anti-HBs decline appears to be similar among all vaccine recipients and is independent of the initial antibody response. In a large cohort of vaccinated homosexual men, Hadler et all' found that, among those with peak postvaccination anti-HBs levels of 100 serum radioimmunoassay units (SRU), only 7% had lost antibody after 5 years, whereas among those with an initial peak level below 50 SRU, 54% had lost detectable anti-HBs in the same period. Levels of anti-HBs fall sixfold between their 9-month peak and 18 months after vaccination, then decline more gradually thereafter. In the cohort of vaccinated homosexual men studied by Hadler et al," a small proportion experienced cvidence of HBV infection, despite vaccination, long after immunization. With the exception of a single case of detectable hepatitis B surface antigenemia and transient, modest aminotransferase elevation, all of these infections were subclinical and were recognized by the de novo appearance of antibody to hepatitis B core antigen (anti-HBc), a serologic response that indicates exposure to the entire virion (that is, infection), not just to the surface protein present in the vaccine (immunization). The risk of such subclinical seroconversions in this population highly exposed via the sexual route was inversely proportional to the peak anti-HBs level achieved after primary immunization. Despite such subclinical infections, even vaccinees with minimally or undetectable anti-HBs long after vaccination appear to be protected against clinically apparent hepatitis B, hepatitis B surface antigenemia (detectable viremia), and chronic HBV infection. In fact, these observations in an early 1980s (before the acquired immune deficiency syndrome [AIDS] cohort of sexually promiscuous homosexual men may represent the worst case and may not be applicable to other population groups with less intense exposure to HBV. A 5-year follow-up study in a cohort of immuno-

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competent health workers who received plasma-derived vaccine, no clinical or subclinical infections were encountered.'.' Based on the apparent long-term protection provided by vaccination and the absence of data demonstrating that booster immunization has an advantage over natural reexposure, the United States Public Health Service has issued no recommendations for booster vaccination, except in hemodialysis patients,'." in whom hepatitis B vaccine-induced immunity to HBV is less protective than in immunocompetent adults. Additional long-term follow-up data in vaccinees will be necessary to answer questions about the duration of protection and the need for and timing of booster doses.

Escape Mutants of Hepatitis B Virus Clinical or subclinical infection with HBV after vaccination has been attributed to either vaccine nonresponsiveness or to loss of protection over time. Recent evidcnce, however, is accumulating to suggest that under certain circumstances, evolutionary pressures may promote the emcrgcncc of mutation in the HBV gcnomc and that the resulting HBV mutants may elude protection afforded by passively or actively acquircd anti-HBs. [Mutations in the pre-coreicore region of the HBV genome may account for a population of patients who maintain high levels of HBV replication and liver injury but who lack the traditional qualitative marker of replication, hepatitis B e antigen (HBeAg). For considerations of virus mutations and the success of vaccination, however, S-gene mutants are more important.] For example, treatment of HBsAg-positive liver transplant recipients with a high-potency human-mouse hybrid monoclonal antiHBs has been shown to suppress detectable HBsAg after transplantation; however, after several months of such therapy, HBsAg that is no longer recognized by the monoclonal anti-HBs may become detectable. These emerging variants have been shown to differ from the original HBV isolate by two amino acids, including a single amino acid change from glycine to arginine at position 145 of a highly conserved, hydrophobic, antigenic domain of the HBsAgla determinant. Therefore, a change in this single amino acid appears to be sufficient to interfere with the reactivity of protective antibody." In a complementary report from Great Britain and Italy, hepatitis B infection was documented in a group of immunized contacts of hepatitis B carriers, including infants born to chronically infected mothers." All of these immunized persons acquired protective anti-HBs levels after vaccination. Sequencing of the genome from the HBV isolate of one of the infants with "breakthrough" infection revealed the same point mutation at position 587 of the genome, resulting in a single amino acid substitution, arginine for glycine at position 145 of the a determinant of HBsAg. This specific change in the highly antigenic a determinant can render the resulting escape mutant virus resistant to neutralizing antibody raised against the HBsAg carried in hepatitis B vaccine. Such viral mutations that change highly antigenic regions, but do not otherwise affect essential viral functions, could account for some HBV infections after immunization. Whether escape mutants account for cases of HBV infection in successfully immunized hemodi-

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alysis patients'hnd whether this phenomenon is common and a major concern in hepatitis B vaccination programs or a rare event with little practical clinical import remain to be seen.

Nonresponsiveness to Hepatitis B Vaccine Nonresponsiveness, defined as the failure to acquire anti-HBs after vaccination, and hyporesponsiveness, defined as the failure to acquire so-called protective (10 mIU/ml or higher) levels of anti-HBs after vaccination, have been observed both in immunocompetent and immunosuppressed populations. Approximately 2.5 to 5% of immunocompetent vaccine recipients fail to acquire anti-HBs following a series of three hepatitis B vaccine injections. In such nonresponders, a second course of vaccine injections can induce an immune response in 40% of cases; however, the immune response tends to be feeble and limited in duration. In hyporesponders, revaccination is successful in inducing an immune response in almost all cases, and the immune response tends to be quantitatively adequate and ~ustained.'~In hemodialysis patients, a group immunosuppressed by their chronic renal failure, at least 40% do not respond adeq~ately,'~ and in organ transplant recipients receiving immunosuppressive therapy, 70 to 80% cannot mount adequate humoral immune responses to hepatitis B vaccine, 26.27 There are no data to suggest that revaccination is successful in these immunosuppressed patients. Investigations of immunologic nonresponsiveness to HBsAg in mice demonstrate that antibody production to this antigen is an inherited genetic trait. Strains of mice homozygous for certain major histocon~patibility complex (MHC) haplotypes do not produce adequate levels of anti-HB~.'~.'"The presence of an immune response gene accounting for anti-HBs production in humans is supported by the identification of an increased frequency of specific extended haplotypes in nonresponders to hepatitis B vaccine. A marked increase over the expected frequencies of two extended haplotypes, HLA B8, SCO1, DR3 and B44, DR7, FC3 1 , was found in nonresponders and hyporesponders who failed to improve their responsiveness even after a complete second course of vaccine injection^.^' In a follow-up study of persons who were selected for homozygosity at one of these extended haplotypes, evidence supported the existence of a dominant immune response gene in the MHC that is required for a humoral immune response to HBsAg; therefore, those who lack this gene cannot mount an adequate anti-HBs resp~nse.~"imilar or other genes may be identified in other geographic regions or ethnic populations; other hepatitis B vaccine nonresponder genotypes have been described by others.".3' Studies of genetically determined in~munologic nonresponsiveness to HBsAg in mice suggest that alterations in route of immunization, dose of immunogen, and vaccine antigen can be exploited in strategies to overcome nonre~ponsiveness.~'.'~ For example, in the murine system, immune responsiveness to HBsAg, the product of the S gene, and to the product of the pre-S regions of the HBV genome are linked to different histocompatibility loci. The fact that nonresponsiveness in mice to HBsAg can be overcome by immunization with

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the product of the pre-S plus S genes and the demonstration that immune responsiveness to HBsAg in humans is also genetically determined suggest that a similar approach might be feasible in humans. Little doubt exists over the excellent immunogenicity of hepatitis B vaccine devoid of pre-S proteins, such as the original plasmaderived vaccine and the currently available recombinant vaccines. Still, the potential remains that nonresponders to these currently available vaccines might respond to vaccines containing pre-S proteins. Vaccination of susceptible chimpanzees with a synthetic pre-S2 polypeptide was protective against challenge with hepatitis B vir ~ s , 'and ~ a stable vaccine incorporating the products of the pre-S2 plus S regions has been developed and is being tested currently in normal immunocompetent adults and in populations that have responded poorly to earlier-generation vaccines." Preliminary results show comparable levels of anti-HBs following immunization with either pre-S + S or commercially available recombinant vaccine in healthy adults." In immunocompromised persons, global immunosuppression, rather than a specific genetic defect, is the dominant factor that accounts for vaccine nonresponsiveness. Even though an increase in HLA A1 , B8, and DR3 and the extended haplotype incorporating these individual haplotypes was found by French investigators to be more common in nonresponder hemodialysis patients," relying on strategies to overcome genetic nonresponsiveness in such patients is unlikely to be successful. Instead, in these populations, a more rational strategy for overcoming vaccine nonresponsiveness is the combination of immune response modifiers with vaccine.'"reliminary reports are promising for the use of immune adjuvants, such as interleukin-2 and gamma interferon and alpha interferon given with hepatitis B vaccine to hemodialysis

HEPATITIS A VACCINE Over the last several decades, the incidence of hepatitis A virus (HAV) infection has been decreasing in developed countries, and infection in early childhood, the period during which subclinical infections are almost universal in developing countries, is growing less common. As a result, a population of susceptible adolescents and adults, in whom hepatitis A can be more severe, is emerging. Paradoxically, then, as the frequency of HAV infection declines, the likelihood of clinically severe cases of hepatitis A in adults increases. Until now. we relied for protection against HAV infection on passive immunization with serum immune globulin (IG); however, the duration of protection is limited following an appropriate dose of IG, and ongoing exposure requires repeat dosing with IG on a regular basis. Clearly, a strategy for longer duration protection, such as that afforded by active immunization with vaccine, is required. Despite minor genomic differences among HAV isolates, only one serotype has been identified, and HAV can be cultivated in cell culture. Therefore a hepatitis A vaccine effective against isolates in all parts of the world should be practical. Moreover, the loss of HAV virulence

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PREVENTION A N D THERAPY O F HEPATITIS-KATKOV.

in cell culture allows the development of a live-attenuated vaccine, and the characterization and cloning of the entire HAV genome allows the development of a recombinant complementary DNA vaccine for this RNA virus (reviewed by Ticehurst"). Although HAV can be attenuated by serial subpassage in tissue culture, finding an ideal strain that retains immunogenicity but that lacks pathogenicity has been difficult. The largest experience so far has been accumulated with a highly pathogenic strain of HAV that has been attenuated in tissue culture but then killed with formalin, that is, a killed wholevirus vaccine." Nearly 100% of healthy adults receiving this vaccine have acquired detectable antibody to HAV (anti-HAV) following three vaccine injection over 6 months. Levels of anti-HAV after vaccination are comparable to those observed in natural infection and significantly higher than those achieved with IG. Trials to establish the safety, immunogenicity, and efficacy of hepatitis A vaccines are underway: however, currently, such vaccines arc not available commercially.

TREATMENT OF VIRAL HEPATITIS: ROLE OF INTERFERON Recently published authoritative reports describing controlled trials of alpha interferon for the treatment of chronic viral hepatitis provide a foundation for the rational use of antiviral therapy for chronic hepatitis B and C. A detailed summary of interferon therapy for chronic viral hepatitis appeared in a recent issue of Srminurs in Liver Disea.se,"" to which the reader is referred. Because of the importance of and advances in this area of viral hepatitis research, however, the editors thought that a brief overview should round out this issue of Srtnitlurs devoted to viral hepatitis.

Antiviral Therapy of Chronic Hepatitis B Interferons are endogenous, naturally occurring glycoproteins with antiviral, antiproliferative, and immunomodulatory activities. Interferon alpha, derived from leukocytes, and interferon beta, derived from fibroblasts, are very similar molecules and occupy the same receptor on their cell targets. Interferon gamma, the product of T cells, is a different lymphokine and occupies a different cell receptor. To date, most studies have been done with interferon alpha, although evidence suggests that a stable interferon beta (an elusive goal until the advent of recombinant preparations) could be just as effective. On the other hand, despite limited data suggesting that interferon gamma might enhance the activity of other interferons against hepatitis B , the consensus is that interferon gamma is not an effective agent for treating chronic hepatitis B. The pathogenesis of liver injury in chronic hepatitis B is not characterized completely, but a reasonable hypothesis is that cytolytic T lymphocyte (CTL) activity is impaired. There may be an intrinsic CTL defect or inadequate expression of host self-proteins on the hepatocyte membrane, a requirement for adequate recognition of virus-infected cells by CTL. Interferon has properties that have an impact both on virus

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replication and on host HLA class I expression. Whether these properties underlie the success of interferon in treating chronic hepatitis B is unknown; however, as will be disiussed later, observations suggest that both the antiviral and immunomodulatorv effects of interferon are necessary for effective antiviral therapy of chronic hepatitis B. The report in 1976 from Stanford4' that buffy-coatderived leukocyte interferon could lower the titer of viral antigens and depress HBV DNA polymerase, a marker of HBV replication, to undetectable levels, and the demonstration of biochemical and histologic improvement after successful interferon therapyJhprovided the impetus to pursue antiviral therapy for this chronic viral disease. The early studies of the-decade that followed were limited by inadequate quantities of relatively unstable interferons, they were often uncontrolled. and they included vcry small numbers of patients. The fact that the spontaneous seroconversion rate from replicative (HBeAgpositive, HBV DNA-positive) to nonreplicative (antiHBe-positive. HBV DNA-negative) HBV infection was 10 to 15% interfered with the interpretation of many of these small, uncontrolled trials. An analysis of several of the more important small trials of the late 1970s and early 1980s by Davis and Hoofnagle" showed that 43 patients treated with interferon for a month or shorter had a response rate of only 8%, indistinguishable from that expected spontaneously, whereas 59 patients treated for 3 to 4 months with interferon had a response rate of 31%. A lesson gleaned from thcsc early trials was that long-term low-dose therapy was more effective and associated with fewer side cffects than short-duration, high-dose therapy." Also during this same 10-year period, a number of other antiviral drugs were tried in the treatment of chronic hepatitis B. 1ntr&enouslY administered adenine arabinoside (ArA-A) and its water-soluble. intramuscularly administered monophosphate derivative, ArA-AMP, are more potent inhibitors of HBV replication than interferon; however, they have not been shown to have an impact on the natural history of HBV infection," and ArA-AMP has been associated with an unacceptably high rate of painful, disabling sensory neuropathy, which can outlast therapy by many months. Even when combined with interferon, ArA-AMP is not effective in chronic hepatitis B." Acyclovir, in high doses, may have some antiviral effect against HBV,'o.5' but, in and of itself, it is not considered a practical or effective agent. Development of large quantities of cell-derived or recombinant alpha interferons made large-scale application of antiviral therapy a realistic goal. Several small pivotal trials were conducted in the mid-1980s. Two small studies, one at the National Institutes of Health (NIH) in the United States," the other at King's College Hospital (KCH) in England,53 involved 45 and 46 patients, respectively. In the NIH study patients were randomized to receive 4 months of recombinant interferon alpha-2b therapy, either 5 million U daily or I0 million U every other day, or no therapy. The two interferon groups responded similarly-although the group receiving 10 million U every other day had more side effectsand were combined for analysis. In the 31 treated patients, 10 (32%) experienced a sustained loss of de-

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tectable HBV DNA and HBeAg versus only one of 14 in the untreated control group. Although the numbers were too small to be statistically significant, the trend was clear-cut. In addition, all those who lost detectable HBeAg experienced improvements in liver biochemical indicators of intlammation, and liver histologic appearance was improved in nine of the In the KCH study. patients were randomized to receive 6 months of treatment with lymphoblastoid interferon or no treatment. Treated patients received 10 mUlrn' by intramuscular injection for 5 days, followed by a maintenance dose given three times a week and scaled down because of side effects to 3 to 4 mUlmL;therapy was continued for a maximum of 6 months. Six (26%) of the 23 treated patients lost detectable HBV DNA and HBeAg and acquired antiHBe, and five of the six (22% of the 23 treated patients) lost HBsAg. These losses of replication and infection were sustained for the 18 months of follow-up observation. In contrast, losses of HBV replication did not occur in any of the 23 untreated control patients (p < 0.05).'" In these studies. the loss of HBeAg occurred between 6 and 10 weeks (in the NIH study) or between 8 and 12 weeks (in the KCH study) of interferon therapy, and seroconversion from replicative to nonreplicative HBV infection was accompanied by an acute hepatitis-like elevation in aminotransferase activity. The observation that responses to interferon were more likely in patients with pretreatment elevations in ALT and the f x t that a period of hepatic inflammation accompanied successful responses are taken as circumstantial evidence that a response to interferon is effected not only by the antiviral activities of interferon but also by its immunomodulatory properties. Presumably. the acute hepatitis-like elevation represents enhanced cytolytic T-cell activity against virus-infected hepatocytes. Another seminal pilot study was conducted at Washington University by Perrillo and colleague^.'^ Although data had been accumulating since the late 1970s to show that corticosteroids were ineffective, and perhaps even deleterious, in patients with chronic active hepatitis B, the potential existed that corticosteroid-associated interactions between HBV and the host could be exploited beneficially. During steroid therapy, the level of HBV DNA increases, presumably as a result of activation of a corticosteroid-responsive element of the HBV genome, which is upstream of the promoter region. Presumably, this is associated also with an increase in hepatocyte membrane expression of HBV antigen or antigens. Corticosteroids are inflammatory and immunosuppressive; the anti-inflammatory effect would account for the reduction in aminotransferase activity associated with steroid therapy, and the immunosuppressive effect would be expected to suppress CTL activity. When steroids are withdrawn, however, all these trends are reversed. The level of HBV DNA falls as the stimulus for enhanced replication is removed, and the resulting level of HBV DNA tends to be lower than the baseline, pretreatment level. As corticosteroid immunosuppression is withdrawn, CTL activity is restored, and CTL would be expected to encounter hepatocytes in which membrane HBV antigen expression had been enhanced by the period of steroid exposure. This would lead to a burst of CTL activity against virus-infected he-

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patocytes, which would be recognized clinically by an acute he~atitis-likeexacerbation in aminotransferase activity. In fact, this effect of a brief course of corticosteroid therapy followed by abrupt withdrawal appears to resemble the events that accompany successful interferon therapy, and spontaneous HBeAg-to-anti-HBe seroconversions are also accompanied by a similar acute hepatitis-like exacerbation. Therefore, a period of corticosteroid therapy and withdrawal had been advocated in and of itself i s an antiviral approach to chronic hepatitis B. Abandoned as a lone approach because of earlier trials that either failed to demonstrate its efficacy or that were associated with severe decompensation of chronic ~' withdrawal was believed to be liver d i s e a ~ e , ' ~ -steroid a potentially useful approach to combine with an antiviral agent, and several anecdotal reports of such successful combination approaches led Perrillo and his colleagues to undertake a controlled trial.'4 Thirty-nine patients with chronic replicative hepatitis B were randomized to receive no treatment or td receive 6 weeks of prednisone, in decremental doses (from 60 mglday for 2 weeks, to 40 mglday for 2 weeks, to 20 rngiday for 2 weeks), followed, after a 2-week rest period, by daily injections for 3 months of 5 million U of recombinant interferon alpha-2b. Among the 18 treated patients, a sustained loss of HBV DNA occurred in nine (50%), of HBeAg occurred in eight (44%), of HBsAg occurred in four (22%), ALT returned to normal in nine (50%), and an improvement in histologic features was documented in I I of 15 with follow-up biopsies. In contrast, among the 21 untreated control patients, loss of HBV DNA occurred in only three (14%) (p = 0.035), of HBeAg in only four (19%) (not significant), of HBsAg in none (p = 0.037), and normalization of ALT in only three (14%) ( p = 0.035). This preliminary trial suggested that interferon following prednisone withdrawal might be even more effective than interferon alone. These pilot studies paved the way for a numerically and statisticallv definitive. multicenter. randomized, controlled trial in which the best strategies derived from smaller clinical trials could be compared head to head." In this study, 169 patients with well-compensated chronic replicative hepatitis B with at least minor elevations (1.3 or more times the normal cutoff) in ALT were randomized to one of four groups: ( 1 ) 43 patients were untreated controls, (2) 44 patients receivkd a 6week tapered course of prednisone prior to 16 weeks of 5 million U of interferon alpha-2b daily, (3) 41 patients received a 6-week course of oral placebo prior to 16 weeks of 5 million U of interferon daily (interferon alone at 5 million U a day), and (4) 41 patients received oral placebo followed by I million U of interferon daily for 16 weeks (interferon alone at 1 million U a day). A sustained loss of HBV replication (loss of HBeAg and HBV DNA) occurred in 36% of patients in the prednisone withdrawal15 million U interferon group, in an indistinguishable 37% of the 5 million U interferon-alone group (p < 0.001) compared to controls), but in only 17% of the 1 million U interferon-daily group (not statistically better than controls), and in only 7% of the untreated control group. A loss of HBsAg was recorded in 1 1 % of -

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the prednisone withdrawal15 million U interferon group and in 12% of the 5 million U interferon-alone group, that is, in approximately one quarter of responders. Only one of the group receiving I million U of interferon and none of the untreated control patients lost HBsAg. Aminotransferase levels returned to normal in 87% of responders (43% and 44%, respectively, of those in the groups receiving 5 million U of interferon, with or without prednisone withdrawal. 27% of those receiving I million U of interferon, and 19% of those in the untreated control group). In addition, an improvement in histologic evidence of periportal necrosis was observed in treated patients. Reactivation of HBV replication after a response to interferon was very rare, occurring in only two patients. The fact that the response rate in patients treated with 5 million U of interferon following prednisone withdrawal was not better than that in patients treated with 5 million U of interferon alone was unexpected; however, analysis of pretreatment characteristics that predicted responsiveness provided a potential explanation. If the pretreatment ALT level was elevated more than 200 Uiliter, the response rates between the two groups were similar, 40% for the prednisone-withdrawal group and 50% for the intcrfcron-alone group. In contrast, if the pretreatment ALT level was less than 100 Ul liter, then a dramatic difference between the two groups emerged. In the prednisone-pretreatment group, the expected 44% response rate occurred; however, in the interferon-alone group, the response rate was only 17%. This dichotomy suggests that patients who are already primed to destroy virus-infected hepatocytes. presumably via CTL and as reflected by elevated ALT levels, can mount an interferon response without the help of prednisone pretreatment. On the other hand, in the absence of active necroinflammatory activity in the liver. prednisone pretreatment provides the necessary milieu, the cell-mediated immunologic priming necessary for a response to interferon. Although this observation relies on a small number of patients, whcn interferon is approved for use in chronic hepatitis B, a preliminary period of prednisone therapy and withdrawal is likely to be recommended for patients with minimal to modest ALT elevations, not for those with substantial elevations. In addition to pretreatment ALT, and even more predictive of outcome. was the pretreatment HBV DNA level. Among patients with HBV DNA levels less than 100 pgiml, approximately 50% responded to 5 million U of interferon, compared to approximately 7% of those with HBV DNA levels more than 200 pgllnml (p < 0.0001). The other pretreatment variable that had an effect on outcome was the duration of chronic hepatitis B. Those who lost HBsAg were likely to have had recognized disease for a shorter time (mean approximately I '/z years) compared to those who did not lose HBsAg (mean approximately 3 to 3Y2 years). In summary, approximately 40% of patients with chronic replicative hepatitis B respond to therapy with 5 million U of interferon alpha-2b daily for 16 weeks with a loss of HBV DNA and HBeAg. Response is more likely if the initial HBV DNA level is less than 100 pgl ml and the pretreatment ALT is more than 200 Uiliter.

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For those patients with an initial ALT less than 100 U/ liter, pretreatment with a 6-week tapered course of prednisone may be beneficial. A few additional comments about interferon and chronic hepatitis B are warranted. Because successful interferon therapy. especially after prednisone withdrawal, may be associated with an acute exacerbation of hepatitis, this combination therapy should not be used in patients with decompensated cirrhosis. In such cases. the acute exacerbation may exhaust what little marginal reserve remains and cause liver failure." On the other hand, limited experience is being gained in the use of very low doses of alpha interferon for patients with decompensated hepatitis B. If the decompensation is mild, some benefit may accrue; however, a high rate of lifethreatening adverse effects has been observed.'" If these patients are to be treated, they should be referred to special centers with experience in treating such cases, where trials are in progress. Another question that has been raised about therapy is whether interferon-induced seroconversions from replicative to nonreplicativc HBV infection are accompanied by the incorporation of HBV D N A into the host genome, as is known to occur in patients with spontaneous seroconversions. Limited data exist to address this issue; however, they show that interferon-induced seroconversions are not associated with integration of HBV DNA into the host genome. Certainly, this question remains to be pursued more thoroughly. Another problem encountered in trials of antiviral therapy for chronic hepatitis B is that, in the parts of the world, such as the Orient, in which chronic hepatitis B is a much larger problem, interferon therapy appears not to be successful.'' Perhaps most such patients have had the disease too long before therapy is introduced for successful intervention. Even children from the Orient do not appear to respond to interferon; perhaps infection that is established at birth induces a level of immunologic tolcrancc that is not amenable to reversal by antiviral therapy, at least with the antiviral drugs and strategies available today. Interferon therapy appears to offer no benefit in patients with fulminant hepatitis B," but preliminary observations in small numbers of patients with immune complex disease associated with chronic hepatitis B, for example, glomerulonephritis. suggest that interferon may be effective in this setting." Based on the apparent need in effective interferon therapy for an immunomodulatory effect, we can predict that inlmunosuppressed patients will not experience a sustained remission in HBV replication or a change in the natural history of chronic hepatitis B. Observations in patients with anti-HIV and depressed CD4 cell counts and in organ transplant recipients support this predictlon. Finally, observations based on the studies described above suggest that immunologic manipulation has a role to play in the treatment of chronic hepatitis B. Among the approaches tried in the past has been the use of thymosin. Disappointing results in an early trialh4have been supplanted by promising results of recent pilot trials in seven patients with chronic replicative hepatitis BhSand six woodchucks with chronic hepatitis virus infection." Additional studies are in progress.

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Antiviral Therapy of Chronic Hepatitis D Experience with interferon therapy in patients with chronic hepatitis D is limited. Initial observations showed that ALT activity and HDV RNA levels decline during therapy but return to baseline levels after therapy is discontinued. These studies involved small numbers of patients treated with doses of 3 to 5 mU/m2 for period ~~ concluranging from 3 to 12 m ~ n t h s . ~A' . reasonable sion based on these studies in that interferon has no impact on the natural history of hepatitis D. More recently. however, another study has been completed in which higher doses of therapy met with success. A regimen of 9 million U three times a week for 12 months was associated with a sustained biochemical remission in 7 (50%) of 14 patients as well as an inhibitition of HDV RNA and an improvement in liver histologic finding^.^' Additional details of this study and more comprehensive follow-up trials are anticipated.

Antiviral Therapy of Chronic Hepatitis C The identification. in 1988, of the causative agent of most cases of non-A, non-B (NANB) hepatitis (hepatitis C virus, HCV) and the development of an assay for an antibody to this agent represent major advances in the understanding of this often progressive d i ~ e a s e . ' " .Even ~' before HCV was identified, efforts began to pursue antiviral therapy for chronic NANB hepatitis. Early, uncontrolled, pilot trials of relatively low-dose interferon for chronic NANB hepatitis showed marked reductions in ALT lcvels and improvement in liver histology in 50 to 80% of treated patients.7?.7%lthough responders often experienced a return of ALT lcvels to pretreatment values when interferon was stopped, retreatment often resulted in a return to normal values. These reports provided the foundation and impetus for two larger, randomized, controlled trials of interferon alpha-2b for chronic NANB hepatitis. One was a single-site study at the NIH,74 and the other was a large multicenter trial involving approximately a dozen centers throughout the United state^.'^ In the multicenter 166 patients, with primarily transfusion-associated chronic NANB hepatitis, were randomly assigned to one of three groups: an untreated control group, a group treated with I million U of interferon alpha-2b given by subcutaneous injection three times a week for 24 weeks, and a group treated with 3 million U of interferon three times a week for 24 weeks. A response to interferon, defined as either complete normalization of ALT (complete response) or a reduction in ALT by at least 50% and to within 1.5 times the normal cutoff (near-complete response), occurred in 46% of those treated with 3 million U (p < 0.001 (85% of which were complete responses), 28% of those treated with 1 million U (p, 0.02) (56% of which were complete responses), but in only 8%) of untreated control patients. Moreover, histologic improvement, primarily in lobular and periportal inflammation, was documented for the group receiving 3 million U (even in some who failed to fulfill criteria for biochemical responsiveness), but not in the group receiving 1 million U. Almost all (85%)

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responses were achieved within the first 12 weeks of therapy, and responses occurred without the acute hepatitis-like exacerbation in ALT activity characteristic of responses in patients with hepatitis B. Regardless of dose, relapses occurred within 6 months (94% within 3 months) in approximately 50% of responding patients when therapy was discontinued. Retreatment of relapses were almost universally associated with a prompt response again. Approximately a third of those with sustained responses did experience a transient "flare" in ALT activity at a median of 4 (range, 2 to 20) weeks after discontinuation of therapy; therefore, a rebound in ALT activity may be transient and should not prompt immediate reinstitution of therapy. These patients were tested retrospectively for antibody to hepatitis C (anti-HCV), which was detected in 86% of participants; the response rate was similar in antiHCV-positive and anti-HCV-negative patients. Similarly, the responsc was similar in patients with cirrhosis and in patients without cirrhosis. A number of other observations were made in this study population. Biochemical indicators were not predictive of histologic features,'hnd, despite the fact that these patients were selected to be well compensated, approximately half had ' baseline clinical histologic evidence of c i r r h ~ s i s . ~No variables predicted the likelihood of response" or of relapse." 41 patients were randomized to In the NIH receive either 2 million U of interferon alpha-2b or placebo three times a week by subcutaneous injection for 6 months. A complete response occurred in 10 (48%) of 2 1 treated patients; near-complete responses occurred in an additional three patients, for a total of 62% responsiveness in treated patients. Relapses occurred in 90% of responders within 6 to 12 months after discontinuation of therapy. A follow-up report from this group showed that HCV RNA activity fell to undetectable levels in biochemical responders, but loss of detectable HCV RNA did not preclude subsequent relapse.7y In summary, treatment of chronic hepatitis C with low-dose interferon alpha-2b (2 to 3 million U) three times a week for 24 weeks induces a biochemical response in approximately 50% of patients; however, among responders, relapse is common. Still, this approach represents an important first step and one that is associated with sustained remissions in a quarter of treated patients. Additional trials are underway now to determine whether higher doses of interferon or a longer duration of therapy will increase the frequency of responsiveness or decrease the frequency of relapse.

Side Effects of Interferon Therapy An entire article devoted to side effects of interferon appeared in a recent issue of Seminars in Liver Disease,'" to which the reader is referred. For convenience, the side effects can be divided into a number of broad categories: systemic flulike symptoms, bone marrow suppression, autoimmune phenomena (such as the appearance of asymptomatic autoantibodies or the occurrence of autoimmune thyroiditis), infections (which can be life-threatening, especially in patients with hepatic

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decompensation, and probably related to granulocytopenia), and psychiatric.

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THE FUTURE OF ANTIVIRAL THERAPY The discipline of antiviral therapy has reached a new plateau. Until very recently, we had very little to show for more than a decade of work, most of the early trials were too limited to answer questions definitely, we had no reliable data on predictors of responsiveness, and little enthusiasm was generated after a litany of inconclusive reports. Now, however, we have unlimited supplies of stable interferons, we have data from welldesigned, meaningful, randomized. controlled trials proving that antiviral therapy does, in fact, work and is better than no treatment, and new trials are underway to answer residual questions. We certainly have much to learn about interferon in particular and antivirals in general, for instance, about optimal candidates for therapy and about the impact of antiviral therapy on the natural history of chronic viral hepatitis. On the other hand. little doubt remains that interferon can be effective and that the demonstration of its efficacy represents a giant leap forward, from which there is no turning back. For patients with chronic viral hepatitis, the 1990s will usher in the antiviral era.

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1 1 , NUMBER 2, 1991