Effect of immune globulin on the prevention of experimental hepatitis C virus infection

Immunizations with Chimeric Hepatitis B Virus-Like Particles to Induce Potential Anti-Hepatitis C Virus Neutralizing Antibodies

Background

Virus-like particles (VLPs) are highly immunogenic and proven to induce protective immunity. The small surface antigen (HBsAg-S) of hepatitis B virus (HBV) self-assembles into VLPs and its use as a vaccine results in protective antiviral immunity against HBV infections. Chimeric HBsAg-S proteins carrying foreign epitopes allow particle formation and have the ability to induce anti-foreign humoral and cellular immune responses.

Methods/results

The insertion of the hypervariable region 1 (HVR1) sequence derived from the envelope protein 2 (E2) of hepatitis C virus (HCV) into the major antigenic site of HBsAg-S (‘a’-determinant) resulted in the formation of highly immunogenic VLPs that retained the antigenicity of the inserted HVR1 sequence. BALB/c mice were immunized with chimeric VLPs, which resulted in antisera with anti-HCV activity. The antisera were able to immunoprecipitate native HCV envelope complexes (E1E2) containing homologous or heterologous HVR1 sequences. HCV E1E2 pseudotyped HIV-1 particles (HCVpp) were used to measure entry into HuH-7 target cells in the presence or absence of antisera that were raised against chimeric VLPs. Anti-HVR1 VLP sera interfered with entry of entry-competent HCVpps containing either homologous or heterologous HVR1 sequences. Also, immunizations with chimeric VLPs induced anti-surface antigen (HBsAg) antibodies, indicating that HBV-specific antigenicity and immunogenicity of the ‘a’-determinant region is retained.

Conclusions

A multivalent vaccine against different pathogens based on the HBsAg delivery platform should be possible. We hypothesize that custom design of VLPs with an appropriate set of HCV-neutralizing epitopes will induce antibodies that would serve to decrease the viral load at the initial infecting inoculum.

Infectivity of hepatitis C virus in plasma after drying and storing at room temperature

OBJECTIVE

To determine effect of environmental exposure on the survival and infectivity of hepatitis C virus (HCV).

METHODS

Three aliquots of chimpanzee plasma containing HCV and proven infectious HCV inoculum were dried and stored at room temperature, 1 aliquot for 16 hours, 1 for 4 days, and 1 for 7 days. A chimpanzee (CH247) was sequentially inoculated intravenously with each of these experimental inocula, beginning with the material stored for 7 days. Each inoculation was separated by at least 18 weeks of follow-up to monitor for infection. The concentration of HCV RNA was measured and quasi species were sequenced for each experimental inoculum and in serum samples from CH247.

RESULTS

Evidence of HCV infection developed in CH247 only after inoculation with the material stored for 16 hours. No infection occurred after inoculation with the material stored for 7 days or 4 days. Compared with the original infectious chimpanzee plasma, the concentration of HCV RNA was 1 log lower in all 3 experimental inocula. The same predominant sequences were found in similar proportions in the original chimpanzee plasma and in the experimental inocula, as well as in serum samples from CH247.

CONCLUSION

HCV in plasma can survive drying and environmental exposure to room temperature for at least 16 hours, which supports the results of recent epidemiologic investigations that implicated blood-contaminated inanimate surfaces, objects, and/or devices as reservoirs for patient-to-patient transmission of HCV. Healthcare professionals in all settings should review their aseptic techniques and infection control practices to ensure that they are being performed in a manner that prevents cross-contamination from such reservoirs.

Hepatitis C immune globulin (human) for the prevention of viral recurrence after liver transplantation

Immunoglobulin therapy has been used extensively in the treatment of infectious diseases. Hepatitis B immunoglobulin (HBIg) reduces the onset of infection in post-percutaneous exposure to Hepatitis B virus (HBV) and in infants of hepatitis B surface antigen (HBsAg)-positive mothers; it also significantly reduces the risk of recurrent HBV infection in liver transplant recipients, thus increasing the survival rate of this population. Prior to 1990, when plasma donors were not screened for the hepatitis C virus (HCV) antibody, the prevalence of HCV viremia after a liver transplant was found to be lower in those patients receiving HBIg containing anti-HCV antibodies. Phase I trials with chimpanzees demonstrated the ability of hepatitis C immune globulin (human) to decrease hepatic inflammation and to neutralize the HCV antibody, but this effect was not sustained over time. Phase I/II human studies have currently been unable to replicate the animal studies, but further trials are planned.

Clinical evaluation (Phase I) of a human monoclonal antibody against hepatitis C virus: safety and antiviral activity

BACKGROUND/AIMS

HCV-AB68, a human monoclonal antibody against the envelope protein of hepatitis C virus (HCV), neutralizes HCV in cell-culture and in the HCV-Trimera mouse model. A Phase 1 clinical trial was designed to test safety, tolerability, and antiviral activity of HCV-AB68 in patients with chronic HCV-infection.

METHODS/RESULTS

Single doses of HCV-AB68, 0.25-40 mg, administered to 15 patients were well tolerated with no moderate or serious adverse events (SAEs) reported. In six patients, HCV-RNA levels transiently decreased by 2- to 100-fold immediately following infusion and rebound to baseline in 24-48 h. Multiple doses of HCV-AB68, 10-120 mg, were administered to 25 patients. Doses were given weekly for 3 weeks, then 3x a week during the fourth week, after which patients were followed for 3 months. No drug-related SAEs were reported and no specific pattern of adverse events was evident. Eight out of 25 patients had at least a 1-log reduction and 17 had at least a 0.75-log reduction in HCV-RNA levels from baseline at one or more time points following HCV-AB68 infusion.

CONCLUSIONS

These data support the investigation of HCV-AB68 in the prevention of recurrent HCV-infection in patients who had received hepatic allografts for end-stage liver disease.

New therapies: oral inhibitors and immune modulators

Several new classes of antiviral drugs are undergoing development and should change the way that hepatitis C virus infection is treated in the future. It is likely that combinations of drugs that target different points in the viral replication and disease processes will prove most successful. It is hoped that such combinations will improve the efficacy, tolerability, and duration of antiviral treatment for this disease.

Hepatitis C virus entry: molecular biology and clinical implications

With an estimated 170 million infected individuals, hepatitis C virus (HCV) has a major impact on public health. A vaccine protecting against HCV infection is not available, and current antiviral therapies are characterized by limited efficacy, high costs, and substantial side effects. Binding of the virus to the cell surface followed by viral entry is the first step in a cascade of interactions between virus and the target cell that is required for the initiation of infection. Because this step represents a critical determinant of tissue tropism and pathogenesis, it is a major target for host cell responses such as antibody-mediated virus-neutralization-and a promising target for new antiviral therapy. The recent development of novel tissue culture model systems for the study of the first steps of HCV infection has allowed rapid progress in the understanding of the molecular mechanisms of HCV binding and entry. This review summarizes the impact of recently identified viral and host cell factors for HCV attachment and entry. Clinical implications of this important process for the pathogenesis of HCV infection and novel therapeutic interventions are discussed.

Monoclonal antibody HCV-AbXTL68 in patients undergoing liver transplantation for HCV: results of a phase 2 randomized study

A randomized, double-blind, dose-escalation study evaluated the safety and efficacy of hepatitis C virus (HCV)-Ab(XTL)68, a neutralizing, high-affinity, fully human, anti-E2 monoclonal antibody, in 24 HCV-positive patients undergoing liver transplantation. HCV-Ab(XTL)68 or placebo was administered at doses from 20-240 mg as 2-4 infusions during the first 24 hours after transplantation, followed by daily infusions for 6 days, weekly infusions for 3 weeks, and either 2 or 4 weekly infusions for 8 weeks. Serum concentrations of total anti-E2 obtained during daily infusions of 120-240 mg HCV-Ab(XTL)68 were 50-200 microg/mL above concentrations in the placebo group. Median serum concentration of HCV RNA dropped below baseline in all groups immediately after transplantation. On day 2, median change from baseline in HCV RNA was -1.8 and -2.4 log in the 120-mg and 240-mg groups, respectively, compared with -1.5 log with placebo. The difference was lost after day 7 when the dosing frequency was reduced. The coincidence of increases in anti-E2 with decreases in HCV RNA concentration indicate that the dose-related changes in HCV RNA concentration were a result of HCV-Ab(XTL)68 administration in the 120- and 240-mg groups. The overall incidence of nonfatal serious adverse events was higher with placebo (60%) vs. all active treatments combined (42%). In conclusion, HCV-Ab(XTL)68 may decrease serum concentrations of HCV RNA in patients after liver transplantation. Studies evaluating more frequent daily dosing at doses >120 mg are necessary to investigate sustained viral suppression in this population.

The role of cytokines in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a frequent malignancy worldwide with a high rate of metastasis. The hepatitis B and C viruses are considered major etiological factors associated with the development of HCC, particularly as a result of their induction of chronic inflammation. There is increasing evidence that the inflammatory process is inherently associated with many different cancer types, including HCC. Specifically, this review aims to cover evidence for the potential roles of cytokines, an important component of the immune system, in promoting HCC carcinogenesis and progression. A global summary of cytokine levels, functions, polymorphisms, and therapies with regard to HCC is presented. In particular, the role of proinflammatory Th1 and anti-inflammatory Th2 cytokine imbalances in the microenvironment of HCC patients with metastasis and the possible clinical significance of these findings are addressed. Overall, multiple studies, spanning many decades, have begun to elucidate the important role of cytokines in HCC.

Future Therapies for Hepatitis C

Although pegylated interferon-α plus ribavirin has become the standard for treating chronic hepatitis C virus infection, a substantial number of patients do not tolerate therapy and require dose reduction or discontinuation, or do not respond to this combination therapy. Thus, new therapeutic options are needed. An increased knowledge of the hepatitis C virus and an understanding of its replication cycle, as well as advances in biotechnology, have stimulated the development of numerous new antiviral treatments for patients with hepatitis C virus infection. This review focuses on four classes of new agents: new interferons, ribavirin-like molecules, specific small-molecule hepatitis C virus inhibitors and new immune therapies, with particular emphasis on medications in the later stages of development.

Preclinical evaluation of two neutralizing human monoclonal antibodies against hepatitis C virus (HCV): a potential treatment to prevent HCV reinfection in liver transplant patients

Passive immunotherapy is potentially effective in preventing reinfection of liver grafts in hepatitis C virus (HCV)-associated liver transplant patients. A combination of monoclonal antibodies directed against different epitopes may be advantageous against a highly mutating virus such as HCV. Two human monoclonal antibodies (HumAbs) against the E2 envelope protein of HCV were developed and tested for the ability to neutralize the virus and prevent human liver infection. These antibodies, designated HCV-AB 68 and HCV-AB 65, recognize different conformational epitopes on E2. They were characterized in vitro biochemically and functionally. Both HumAbs are immunoglobulin G1 and have affinity constants to recombinant E2 constructs in the range of 10(-10) M. They are able to immunoprecipitate HCV particles from infected patients' sera from diverse genotypes and to stain HCV-infected human liver tissue. Both antibodies can fix complement and form immune complexes, but they do not activate complement-dependent or antibody-dependent cytotoxicity. Upon complement fixation, the monoclonal antibodies induce phagocytosis of the immune complexes by neutrophils, suggesting that the mechanism of viral clearance includes endocytosis. In vivo, in the HCV-Trimera model, both HumAbs were capable of inhibiting HCV infection of human liver fragments and of reducing the mean viral load in HCV-positive animals. The demonstrated neutralizing activities of HCV-AB 68 and HCV-AB 65 suggest that they have the potential to prevent reinfection in liver transplant patients and to serve as prophylactic treatment in postexposure events.

Novel approaches for therapy of chronic hepatitis C

Currently available anti-HCV therapy is effective in only half of the patients and limited by side effects that often necessitate discontinuation. Therefore, new treatment strategies are being developed including (i) the optimization of current regimens, (ii) the use of additional agents working via novel mechanisms, and (iii) anti-fibrotic strategies. Many new antiviral compounds are now being studied in preclinical and clinical trials. This review will focus on drugs that have already entered the stage of phase 2 or phase 3 studies.

Management of Recurrent Hepatitis C in Liver Transplant Recipients

Recurrent HCV infection is universal in liver transplant recipients who are viremic pretransplant. The rate of histologic disease progression after transplantation is more rapid, and the risk of cirrhosis by 5 to 10 years is about 30%. Several donor, recipient, and viral factors have been associated with worse post-transplant outcomes in recipients with recurrent hepatitis C. Whether or not HCV-infected recipients of live donor grafts have worse out-comes compared with deceased donor graft recipients is controversial. To maximize the long-term survival of recipients with HCV infection, eradication of infection is the ultimate goal. Treatment of recurrent HCV after liver transplantation can be undertaken at several different time points: (1) prophylactically, at the time of transplantation; (2) pre-emptively, in the early post-transplant period; and (3) after established recurrent histologic disease is present. Prophylactic therapy for HCV infection has no established role at present, but studies are ongoing. Preemptive therapy using IFN and RBV has resulted in variable SVR rates (9%-43%) and is generally poorly tolerated, especially if the patient has advanced liver disease pretransplantation. Treatment of established recurrent HCV disease with combination PEGIFN and RBV is associated with a SVR in about 30% to 35% of patients overall but is limited by high rates of dose reduction or drug discontinuation. In conclusion, successful HCV eradication in the post-transplant setting is difficult with current treatment options, but it is possible. Determination of the optimal doses of antiviral drugs in transplant patients and improvements in drug tolerability may be important first steps in achieving enhanced response rates. There is a need for new drugs in this population that have greater efficacy and a better safety profile.

Management of hepatitis C in liver transplant recipients

Recurrent hepatitis C virus (HCV) disease is the leading cause of graft loss in liver transplant recipients with pre-transplant HCV infection. While natural history is variable, median time to recurrent cirrhosis is less than a decade. Factors contributing to risk of recurrence and rate of fibrosis progression are only partially known. Older donor age, treatment of acute rejection, cytomegalovirus infection and high pre-transplant viral load are most consistently linked with worse outcomes. Whether these factors can be modified to positively impact on HCV disease progression is unknown. The main therapeutic approach for patients with recurrent HCV disease has been the treatment with interferon and ribavirin (RBV) once recurrent disease is documented or progressive. Efficacy is lower than in nontransplant patients and tolerability, especially of RBV, is a major limitation. Stable or improved fibrosis scores are seen in the majority of sustained responders. Optimal dose, duration and timing of treatment have not been determined. Alternative strategies under study include pre-transplant treatment of decompensated cirrhotics, preemptive antiviral therapy started within weeks of transplantation and prophylactic therapy using HCV antibodies. Ongoing studies may establish a future role for alternative treatment approaches. Additionally, limited overall efficacy of interferon-based therapy in the transplant setting highlights the urgent need for new drug therapies.

[Acute hepatitis C in 2005]

There have been numerous new data in the field of acute hepatitis C in the past few years. The goal of this study was to gather recent results in the literature to determine the best current therapeutic strategy of acute hepatitis C. Epidemiology has made enormous progress with the disappearance of acute post transfusion hepatitis C. Infection by intravenous drug-addiction has became prevalent, and nosocomial and sexual modes of transmissions are now seen. At the same time, the average age of the infected patients has dropped by 13 years, and the proportion of acute forms with a spontaneously favourable outcome have increased compared to the period before 1995. Understanding of the predictive factors of cure have become important, particularly not to treat acute hepatitis C which will have a spontaneously favorable outcome. Waiting from 8 to 12 weeks after jaundice or symptomatic forms is recommended. The decision to treat must be made in the first 6 months, since the results are better compared to a late and longer treatment. Monotherapy by pegylated interferon for 6 months ensures more than 90% of sustained viral response. Shorter treatment is possible but high daily doses of interferon are necessary, reducing tolerance. Finally bi therapy with a interferon and ribavirin is not beneficial

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

A randomized, open-label study to evaluate the safety and pharmacokinetics of human hepatitis C immune globulin (Civacir) in liver transplant recipients

Chronic hepatitis C is the most common indication for liver transplantation, but viral recurrence is universal and progressive graft injury occurs in most recipients. Our aim was to assess the safety, pharmacokinetics (PK), and antiviral effects of high doses of a human hepatitis C antibody enriched immune globulin product (HCIG) in patients undergoing liver transplantation for chronic hepatitis C. This was a multicenter, randomized, open-label, controlled trial conducted at 4 transplant centers in the United States. A total of 18 patients with chronic hepatitis C, who underwent liver transplantation, were randomized to receive low-dose HCIG (75 mg/kg) or high-dose HCIG (200 mg/kg), or no treatment. A total of 17 infusions of HCIG were administered in each treated patient over 14 weeks using a time-dependent dosing strategy based on the PK of anti-hepatitis B immune globulin in liver transplant recipients. Hepatitis C virus levels, liver enzymes, and liver biopsies were obtained serially throughout the study period. PK profiles of HCV antibodies were determined on days 4, 10, and 98. HCIG infusions were safe and tolerated. The infusion rate could not be maximized because of symptoms for 18% to 30% of the doses. The half-life of HCIG was extremely short immediately after transplantation but was gradually prolonged. In the high-dose group, serum alanine aminotransferase (ALT) levels normalized in most subjects and no patient developed hepatic fibrosis. However, serum HCV RNA levels were not suppressed at either dose. In conclusion, HCIG, an anti-HCV enriched immune globulin product, appears to be safe in patients with chronic hepatitis C undergoing liver transplantation. Further studies are required to determine whether the drug has beneficial effects in this group of patients.

Treatment of recurrent hepatitis C after liver transplantation

Chronic hepatitis C virus (HCV) infection is the most common indication for liver transplantation in the United States and Europe, and more than 20,000 patients worldwide have undergone transplantation for complications of chronic hepatitis C. In North America, HCV accounts for 15% to 50% of the liver transplants performed in United States transplant programs. To maximize the long-term survival of liver transplant recipients who have HCV infection, eradication of infection is the ultimate goal. Pretransplant antiviral therapy with the goal of achieving viral eradication before transplantation is a consideration in some patients, especially those who have mildly decompensated liver disease. This article focuses on the management of liver transplant recipients who have HCV infection at the time of transplantation. Prophylactic and preemptive therapies, as well as treatment of established recurrent disease, are the strategies reviewed.

Human serum facilitates hepatitis C virus infection, and neutralizing responses inversely correlate with viral replication kinetics at the acute phase of hepatitis C virus infection

The factors leading to spontaneous clearance of hepatitis C virus (HCV) or to viral persistence are elusive. Understanding virus-host interactions that enable acute HCV clearance is key to the development of more effective therapeutic and prophylactic strategies. Here, using a sensitive neutralization assay based on infectious HCV pseudoparticles (HCVpp), we have studied the kinetics of humoral responses in a cohort of acute-phase patients infected during a single nosocomial outbreak in a hemodialysis center. The 17 patients were monitored for the spontaneous outcome of HCV infection for 6 months before a treatment decision was made. Blood samples were taken frequently (15 +/- 4 per patient). Phylogenetic analysis of the predominant virus(es) revealed infection by only one of two genotype 1b strains. While all patients seroconverted, their sera induced two opposing effects in HCVpp infection assays: inhibition and facilitation. Furthermore, the ability of sera to facilitate or inhibit infection correlated with the presence of either infecting HCV strain and divided the patients into two groups. In group 1, the progressive emergence of a relatively strong neutralizing response correlated with a fluctuating decrease in high initial viremia, leading to control of viral replication. Patients in group 2 failed to reduce viremia within the acute phase, and no neutralizing responses were detected despite seroconversion. Strikingly, sera of group 2, as well as naive sera, facilitated infection by HCVpp displaying HCV glycoproteins from different genotypes and strains, including those retrieved from patients. These results provide new insights into the mechanisms of viral persistence and immune control of viremia.

Cationic microparticles are a potent delivery system for a HCV DNA vaccine

We initially evaluated in mice the ability of naked DNA encoding intracellular forms of the E1E2 envelope proteins from HCV to induce antibody responses and compared the responses induced with the same plasmid adsorbed onto cationic poly (lactide co-glycolide) (PLG) microparticles. Although naked DNA was only able to induce detectable responses at the 100 microg dose level, making this approach impractical for evaluation in larger animals, PLG/DNA induced detectable responses at 10 microg. In addition, the PLG/DNA microparticles induced significantly enhanced responses to naked DNA when compared at the same dose level. Remarkably, PLG/DNA induced comparable responses to recombinant E1E2 protein adjuvanted with the emulsion MF59. Furthermore, PLG/DNA effectively primed for a booster response with protein immunization, while naked DNA did not. Therefore, PLG/DNA was selected for further evaluation in a non-human primate model. In a study in rhesus macaques, PLG/DNA induced seroconversion in 3/3 animals following three immunizations. Although the antibody responses appeared lower than those induced with recombinant protein adjuvanted with MF59, following a fourth dose, PLG/DNA and protein induced comparable responses. However, a single booster dose of recombinant protein administered to the animals previously immunized with PLG/DNA induced much higher responses. In addition, one of three animals immunized with PLG/DNA showed a cytotoxic T lymphocyte response in peripheral blood lymphocytes. In conclusion, cationic PLG microparticles with adsorbed HCV DNA generates potent immune responses.

Characterization of host-range and cell entry properties of the major genotypes and subtypes of hepatitis C virus

Because of the lack of a robust cell culture system, relatively little is known about the molecular details of the cell entry mechanism for hepatitis C virus (HCV). Recently, we described infectious HCV pseudo-particles (HCVpp) that were generated by incorporating unmodified HCV E1E2 glycoproteins into the membrane of retroviral core particles. These initial studies, performed with E1E2 glycoproteins of genotype 1, noted that HCVpp closely mimic the cell entry and neutralization properties of parental HCV. Because sequence variations in E1 and E2 may account for differences in tropism, replication properties, neutralization, and response to treatment in patients infected with different genotypes, we investigated the functional properties of HCV envelope glycoproteins from different genotypes/subtypes. Our studies indicate that hepatocytes were preferential targets of infection in vitro, although HCV replication in extrahepatic sites has been reported in vivo. Receptor competition assays using antibodies against the CD81 ectodomain as well as ectopic expression of CD81 in CD81-deficient HepG2 cells indicated that CD81 is used by all the different genotypes/subtypes analyzed to enter the cells. However, by silencing RNA (siRNA) interference assays, our results show that the level of Scavenger Receptor Class-B Type-I (SR-BI) needed for efficient infection varies between genotypes and subtypes. Finally, sera from chronic HCV carriers were found to exhibit broadly reactive activities that inhibited HCVpp cell entry, but failed to neutralize all the different genotypes. In conclusion, we characterize common steps in the cell entry pathways of the major HCV genotypes that should provide clues for the development of cell entry inhibitors and vaccines.

Inhibition of hepatitis C virus nonstructural protein, helicase activity, and viral replication by a recombinant human antibody clone

Hepatitis C virus (HCV) nonstructural protein 3 (NS3), with its protease, helicase, and NTPase enzymatic activities, plays a crucial role in viral replication, and therefore represents an ideal target for the development of anti-viral agents. We have developed a recombinant human antibody (Fab) that reacts with the helicase domain of HCV NS3. The affinity-purified Fab antibody completely inhibited the helicase activity of HCV NS3 at equimolar concentration. To evaluate the effect of the Fab on HCV replication, the clone encoding the Fab gene was put into an expression vector, which converts Fab into a complete IgG1 antibody. Using a DNA-based transfection model, we demonstrated that intracellular expression of this antibody resulted in significant reduction of HCV-negative strand RNA synthesis. Intracellular expression of this antibody into either a stable cell line replicating subgenomic RNA, or a transient full-length HCV replication model, reduced both HCV RNA and viral protein expression. These results support the use of recombinant antibody fragments to inhibit NS3 enzyme as a novel, feasible, and effective approach for inhibiting HCV replication.

A critical role for the chimpanzee model in the study of hepatitis C

Chimpanzees remain the only recognized animal model for the study of hepatitis C virus (HCV). Studies performed in chimpanzees played a critical role in the discovery of HCV and are continuing to play an essential role in defining the natural history of this important human pathogen. In the absence of a reproducible cell culture system, the infectivity titer of HCV challenge pools can be determined only in chimpanzees. Recent studies in chimpanzees have provided new insight into the nature of host immune responses-particularly the intrahepatic responses-following primary and secondary experimental HCV infections. The immunogenicity and efficacy of vaccine candidates against HCV can be tested only in chimpanzees. Finally, it would not have been possible to demonstrate the infectivity of infectious clones of HCV without chimpanzees. Chimpanzees became infected when RNA transcripts from molecular clones were inoculated directly into the liver. The infection generated by such transfection did not differ significantly from that observed in animals infected intravenously with wild-type HCV. The RNA inoculated into chimpanzees originated from a single sequence, and the animals therefore had a monoclonal HCV infection. Monoclonal infection simplifies studies of HCV, because virus interaction with the host is not confounded by the quasispecies invariably present in a natural infection. It furthermore permits true homologous challenge in studies of protective immunity and in testing the efficacy of vaccine candidates. Finally, this in vivo transfection system has made it possible to test for the first time the importance of genetic elements for HCV infectivity.

Neutralizing antibodies to hepatitis C virus (HCV) in immune globulins derived from anti-HCV-positive plasma

The role of humoral immunity in hepatitis C virus (HCV) infections is uncertain. Nevertheless, there is increasing evidence for neutralizing antibodies to HCV in the serum or plasma of chronically infected individuals. Immune globulins prepared by ethanol fractionation of plasma had long been considered safe until a commercial immune globulin product, Gammagard, prepared from plasma from which units containing anti-HCV had been excluded, transmitted HCV to recipients. Studies suggested that the exclusion might have removed neutralizing antibodies from the plasma and hence compromised the safety of the resulting immune globulins. In the present study, by using chimpanzees and a recently validated in vitro system based on neutralization of infectious HCV pseudoparticles, we found broadly reactive neutralizing and protective antibodies in experimental immune globulin preparations made from anti-HCV-positive donations. Neutralizing antibodies were also found in Gammagard lots made from unscreened plasma that did not transmit hepatitis C but not in Gammagard lots, which were prepared from anti-HCV-screened plasma, that did transmit hepatitis C. The results provide an explanation for the mechanism by which the safety of this product was compromised. Immune globulins made from anti-HCV-positive plasma and containing broadly reactive neutralizing antibodies may provide a method of preventing HCV infection.

Prophylactic and preemptive therapies for hepatitis C virus-infected patients undergoing liver transplantation

1. Preclinical data from chimpanzees and studies in hepatitis B virus/hepatitis C virus (HCV) coinfected transplant recipients suggest prophylactic HCV antibody therapy may have a role in the prevention of HCV recurrence. 2. There are insufficient data available to evaluate the efficacy of this therapeutic approach. A small study found no benefit. Other ongoing studies using alternative antibody preparations and more intensive dosing schedules are underway. 3. Preemptive antiviral therapy, started within the first 4 weeks posttransplantation and prior to the onset of clinical signs and symptoms, is effective in some patients (5-33%) and is not associated with an increased risk of acute rejection. Tolerability of antiviral agents in the early posttransplantation period may be a factor limiting treatment efficacy. 4. It is unclear whether the preemptive antiviral treatment is superior to delaying treatment until recurrent disease is present and controlled trials addressing this issue are needed.

Managing occupational risks for hepatitis C transmission in the health care setting

Hepatitis C virus (HCV) infection is a significant contemporary health problem in the United States and elsewhere. Because it is primarily transmitted via blood, hepatitis C infection presents risks for both nosocomial transmission to patients and occupational spread to health care workers. Recent insights into the pathogenesis, immunopathogenesis, natural history, and treatment of infection caused by this unique flavivirus provide a rationale for the use of new strategies for managing occupational hepatitis C infections when they occur. This article reviews this developing information. Recently published data demonstrate success rates in the treatment of "acute hepatitis C syndrome" that approach 100\%, and although these studies are not directly applicable to all occupational infections, they may provide important clues to optimal management strategies. In addition, the article delineates approaches to the prevention of occupational exposures and also addresses the difficult issue of managing HCV-infected health care providers. The article summarizes currently available data about the nosocomial epidemiology of HCV infection and the magnitude of risk and discusses several alternatives for managing exposure and infection. No evidence supports the use of immediate postexposure prophylaxis with immunoglobulin, immunomodulators, or antiviral agents. Based on the very limited data available, the watchful waiting and preemptive therapy strategies described in detail in this article represent reasonable interim approaches to the complex problem of managing occupational HCV infections, at least until more definitive data are obtained.

Prevention of Viral Hepatitis

Despite the availability of vaccines against hepatitis A and B, acute viral hepatitis due to these agents continues to be among the most commonly reported notifiable infectious diseases in the United States. Currently available hepatitis A and B vaccines are highly immunogenic and well tolerated, but vaccine coverage needs to be expanded. Use of the hepatitis A vaccine in children age 2 years and older should be more widespread than is currently the case. Hepatitis A vaccine has been shown to be cost effective when given to children in regions with high attack rates and to patients with chronic hepatitis C. Routine newborn immunization against hepatitis B has been a successful approach to disease control and is among the most cost-effective interventions. Use of the hepatitis B vaccine for all sexually active individuals with more than one sex partner should be recommended for this sexually transmitted disease. The availability of a combined hepatitis A and B vaccine should facilitate vaccine coverage in those individuals at risk for both infections. For those hepatitis infections for which no vaccine is currently available, namely hepatitis C, D, and E, reducing exposure risk by modifying lifestyle behaviors is the only control measure available. Early education and counseling about high-risk behaviors for the acquisition of blood-borne hepatitis viruses needs to be expanded to young children and adolescents. The eventual eradication of hepatitis virus infections through universal immunization is plausible for those agents for whom human beings are the only host and effective vaccines have been developed. If hepatitis E is shown to be a zoonosis with an extensive reservoir in pigs, eradication of this agent may be very difficult.

Treatment of recurrent hepatitis C

1. Treatment of established recurrent hepatitis C with interferon-alpha monotherapy does not achieve sustained virologic response (SVR). 2. Treatment of established recurrent hepatitis C with combination interferon plus ribavirin achieves SVR rates of 17% to 27%, but dropout rates approach 30%. 3. Pretransplant prophylaxis against recurrent hepatitis C with combination interferon plus ribavirin is poorly tolerated in patients with decompensated hepatitis C cirrhosis. 4. Posttransplant prophylaxis with combination interferon plus ribavirin prevents both recurrent viremia and hepatitis in 15% to 20% of patients, but dropout rates approach 50%. 5. Hepatitis C virus genotype is the best predictor of response to antiviral prophylaxis and treatment of recurrent hepatitis C. 6. Interferon-alpha therapy is not associated with an increased risk of allograft rejection in liver transplant recipients. 7. Ribavirin therapy is associated with increased hemolysis in liver transplant recipients. 8. Preliminary data suggest pegylated interferon monotherapy will have similar efficacy but better tolerability than combination interferon plus ribavirin. 9. In a recent study, posttransplant immunoprophylaxis with polyclonal hepatitis C immunoglobulin had no effect on recurrent viremia or hepatitis.

Previously infected and recovered chimpanzees exhibit rapid responses that control hepatitis C virus replication upon rechallenge

Responses in three chimpanzees were compared following challenge with a clonal hepatitis C virus (HCV) contained in plasma from an animal that had received infectious RNA transcripts. Two of the chimpanzees (Ch1552 and ChX0186) had recovered from a previous infection with HCV, while the third (Ch1605) was a naïve animal. All animals were challenged by reverse titration with decreasing dilutions of plasma and became serum RNA positive following challenge. Ch1605 displayed a typical disease profile for a chimpanzee. We observed increasing levels of serum RNA from week 1 postinoculation (p.i.), reaching a peak of 10(6) copies/ml at week 9 p.i., and alanine aminotransferase (ALT) elevations and seroconversion to HCV antibodies at week 10 p.i. In contrast, both Ch1552 and ChX0186 exhibited much shorter periods of viremia (4 weeks), low serum RNA levels (peak, 10(3) copies/ml), and minimal ALT elevations. A comparison of intrahepatic cytokine levels in Ch1552 and Ch1605 showed greater and earlier gamma interferon (IFN-gamma) and tumor necrosis factor alpha responses in the previously infected animal, responses that were 30-fold greater than baseline responses at week 4 p.i. for IFN-gamma in Ch1552 compared to 12-fold in Ch1605 at week 10 p.i. These data indicate (i) that clonal HCV generated from an infectious RNA transcript will lead to a typical HCV infection in naïve chimpanzees, (ii) that there are memory immune responses in recovered chimpanzees that control HCV infection upon rechallenge, and (iii) that these responses seem to be T-cell mediated, as none of the animals had detectable antibody against the HCV envelope glycoproteins. These observations have encouraging implications for the development of a vaccine for HCV.

Live and killed rhabdovirus-based vectors as potential hepatitis C vaccines

A highly attenuated, recombinant rabies virus (RV) vaccine strain-based vector was utilized as a new immunization strategy to induce humoral and cellular responses against hepatitis C (HCV) glycoprotein E2. We showed previously that RV-based vectors are able to induce strong immune responses against human immunodeficiency virus type I (HIV-1) antigens. Here we constructed and characterized three replication-competent RV-based vectors expressing either both HCV envelope proteins E1 and E2 or a modified version of E2 which lacks 85 amino acids of its carboxy terminus and contains the human CD4 transmembrane domain and the CD4 or RV glycoprotein cytoplasmic domain. All three constructs stably expressed the respective protein(s) as indicated by Western blotting and immunostaining. Moreover, surface expression of HCV E2 resulted in efficient incorporation of the HCV envelope protein regardless of the presence of the RV G cytoplasmic domain, which was described previously as a requirement for incorporation of foreign glycoproteins into RV particles. Killed and purified RV virions containing HCV E2 were highly immunogenic in mice and also proved useful as a diagnostic tool, as indicated by a specific reaction with sera from HCV-infected patients. In addition, RV vaccine vehicles were able to induce cellular responses against HCV E2. These results further suggest that recombinant RVs are potentially useful vaccine vectors against important human viral diseases.

Experimental and emerging therapies for chronic hepatitis C virus infection

Hepatitis C virus infection is prevalent throughout the world and is associated with substantial morbidity, mortality and health economic burden. No effective preventative measure, including vaccination, is currently available. Incremental and substantial progress in the rate of viral eradication using interferon-based therapies has been made over the past decade. The most recent advance has been related to the development of a pegylated form of IFN-alpha by two independent pharmaceutical companies. Pegylation of IFN-alpha appears to prolong its half-life, allowing for less frequent dosing. Reports have suggested that pegylated interferons are also associated with better efficacy for viral eradication in patients with hepatitis C virus. Slower progress also has been made in developing non-interferon-based therapeutic agents against hepatitis C virus, including protease inhibitors, helicase inhibitors, ribozymes, antisense therapies, cytokine-based therapies and T-cell-based therapeutic vaccines.

The chimpanzee model of hepatitis C virus infections

The chimpanzee (Pan troglodytes) is the only experimental animal susceptible to infection with hepatitis C virus (HCV). The chimpanzee model of HCV infection was instrumental in the initial studies on non-A, non-B hepatitis, including observations on the clinical course of infection, determination of the physical properties of the virus, and eventual cloning of the HCV nucleic acid. This review focuses on more recent aspects of the use of the chimpanzee in HCV research. The chimpanzee model has been critical for the analysis of early events in HCV infection because it represents a population for which samples are available from the time of exposure and all exposed animals are examined. For this reason, the chimpanzee represents a truly nonselected population. In contrast, human cohorts are often selected for disease status or antibody reactivity and typically include individuals that have been infected for decades. The chimpanzee model is essential to an improved understanding of the factors involved in viral clearance, analysis of the immune response to infection, and the development of vaccines. The development of infectious cDNA clones of HCV was dependent on the use of chimpanzees, and they will continue to be needed in the use of reverse genetics to evaluate critical sequences for viral replication. In addition, chimpanzees have been used in conjunction with DNA microarray technology to probe the entire spectrum of changes in liver gene expression during the course of HCV infection. The chimpanzee will continue to provide a critical aspect to the understanding of HCV disease and the development of therapeutic modalities.

Current and future therapies of hepatitis C

With recent advances in the treatment of chronic hepatitis C, patients with elevated aminotransferase levels, detectable HCV RNA in the serum, and chronic inflammation are candidates for therapy. The best initial therapy is interferon plus ribavirin, achieving a sustained response rate in 40% of patients. The duration of therapy should be based on HCV genotype (48 weeks for genotype 1; 24 weeks for other genotypes). Serum HCV RNA should be measured at week 24 to assess response and guide further therapy in patients with genotype 1 infection. Patients unsuitable for combination therapy can be treated with interferon monotherapy. Side effects, dose modification and discontinuation are generally more frequent with interferon plus ribavirin, but can be managed with close follow-up and careful monitoring. With rapid developments in treatment, new therapies will require careful prospective evaluation according to HCV genotype and viral-load characteristics. Recommendations for therapy will probably change every few years, and novel approaches may provide effective therapy for most patients with hepatitis C.

Recombinant human monoclonal antibodies against different conformational epitopes of the E2 envelope glycoprotein of hepatitis C virus that inhibit its interaction with CD81

The antibody response to the envelope proteins of hepatitis C virus (HCV) may play an important role in controlling the infection. To allow molecular analyses of protective antibodies, we isolated human monoclonal antibodies to the E2 envelope glycoprotein of HCV from a combinatorial Fab library established from bone marrow of a chronically HCV-infected patient. Anti-E2 reactive clones were selected using recombinant E2 protein. The bone marrow donor carried HCV genotype 2b, and E2 used for selection was of genotype 1a. The antibody clones were expressed as Fab fragments in E. coli, and as Fab fragments and IgG1 in CHO cells. Seven different antibody clones were characterized, and shown to have high affinity for E2, genotype 1a. Three clones also had high affinity for E2 of genotype 1b. They all bind to conformation-dependent epitopes. Five clones compete for the same or overlapping binding sites, while two bind to one or two other epitopes of E2. Four clones corresponding to the different epitopes were tested as purified IgG1 for blocking the CD81-E2 interaction in vitro; all four were positive at 0.3-0.5 microg/ml. Thus, the present results suggest the existence of at least two conserved epitopes in E2 that mediate inhibition of the E2-CD81 interaction, of which one appeared immunodominant in this donor.

Vaccination of chimpanzees with plasmid DNA encoding the hepatitis C virus (HCV) envelope E2 protein modified the infection after challenge with homologous monoclonal HCV

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. Development of vaccines to prevent HCV infection, or at least prevent progression to chronicity, is a major goal. In mice and rhesus macaques, a DNA vaccine encoding cell-surface HCV-envelope 2 (E2) glycoprotein stimulated stronger immune responses than a vaccine encoding intracellular E2. Therefore, we used DNA encoding surface-expressed E2 to immunize chimpanzees 2768 and 3001. Chimpanzee 3001 developed anti-E2 after the second immunization and antibodies to hypervariable region 1 (HVR1) after the third immunization. Although chimpanzee 2768 had only low levels of anti-E2 after the third immunization, an anamnestic response occurred after HCV challenge. CTL responses to E2 were not detected before challenge, but a strong response was detected after HCV challenge in chimpanzee 2768. An E2-specific CD4+ response was detected in chimpanzee 2768 before challenge and in both chimpanzees postchallenge. Three weeks after the last immunization, animals were challenged with 100 50% chimpanzee-infectious doses (CID(50)) of homologous monoclonal HCV. As a control, a naive chimpanzee was inoculated with 3 CID(50) of the challenge virus. The vaccine did not generate sterilizing immunity because both vaccinated chimpanzees were infected. However, both vaccinated chimpanzees resolved the infection early whereas the control animal became chronically infected. Compared with the control animal, hepatitis appeared earlier in the course of the infection in both vaccinated chimpanzees. Therefore, DNA vaccine encoding cell surface-expressed E2 did not elicit sterilizing immunity in chimpanzees against challenge with a monoclonal homologous virus, but did appear to modify the infection and might have prevented progression to chronicity.

Risk and management of blood-borne infections in health care workers

Exposure to blood-borne pathogens poses a serious risk to health care workers (HCWs). We review the risk and management of human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) infections in HCWs and also discuss current methods for preventing exposures and recommendations for postexposure prophylaxis. In the health care setting, blood-borne pathogen transmission occurs predominantly by percutaneous or mucosal exposure of workers to the blood or body fluids of infected patients. Prospective studies of HCWs have estimated that the average risk for HIV transmission after a percutaneous exposure is approximately 0.3%, the risk of HBV transmission is 6 to 30%, and the risk of HCV transmission is approximately 1.8%. To minimize the risk of blood-borne pathogen transmission from HCWs to patients, all HCWs should adhere to standard precautions, including the appropriate use of hand washing, protective barriers, and care in the use and disposal of needles and other sharp instruments. Employers should have in place a system that includes written protocols for prompt reporting, evaluation, counseling, treatment, and follow-up of occupational exposures that may place a worker at risk of blood-borne pathogen infection. A sustained commitment to the occupational health of all HCWs will ensure maximum protection for HCWs and patients and the availability of optimal medical care for all who need it.

Antibodies for the prevention and treatment of viral diseases

This paper reviews current use and evolving role of polyclonal and monoclonal antibody products for the prevention and treatment of viral diseases. Antibodies continue to be indicated for prophylaxis either prior to an anticipated exposure especially in situations of travel, or more commonly following an exposure. The predominant indication for use of antibody products is to prevent infection. With the availability of vaccines for the prevention of chickenpox, hepatitis A, hepatitis B, measles, rabies and smallpox, the role of passive immunization is reserved for susceptible individuals and those at high risk for complications of infection. Risks of transmission of infections associated with use of human plasma-derived products have been reduced by improvements in donor screening and virus removal and inactivation procedures. An additional safety concern has been addressed by the removal of thimerosal as a preservative. Within the last 5 years, two antibodies have been licensed for a viral indication, RespiGam and Synagis both for prevention of respiratory syncytial virus infection. RespiGam is a human plasma derived antibody and Synagis is a humanized monoclonal antibody, the first such antibody to be licensed for an infectious disease indication. CytoGam for prevention of cytomegalovirus infection in kidney transplant patients has recently been granted an expanded indication to include use in lung, liver, pancreas and heart transplant patients. As the use of therapeutics becomes more sophisticated, researchers may find better ways of using antibody products.

Risk and management of blood-borne infections in health care workers

Exposure to blood-borne pathogens poses a serious risk to health care workers (HCWs). We review the risk and management of human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) infections in HCWs and also discuss current methods for preventing exposures and recommendations for postexposure prophylaxis. In the health care setting, blood-borne pathogen transmission occurs predominantly by percutaneous or mucosal exposure of workers to the blood or body fluids of infected patients. Prospective studies of HCWs have estimated that the average risk for HIV transmission after a percutaneous exposure is approximately 0.3%, the risk of HBV transmission is 6 to 30%, and the risk of HCV transmission is approximately 1.8%. To minimize the risk of blood-borne pathogen transmission from HCWs to patients, all HCWs should adhere to standard precautions, including the appropriate use of hand washing, protective barriers, and care in the use and disposal of needles and other sharp instruments. Employers should have in place a system that includes written protocols for prompt reporting, evaluation, counseling, treatment, and follow-up of occupational exposures that may place a worker at risk of blood-borne pathogen infection. A sustained commitment to the occupational health of all HCWs will ensure maximum protection for HCWs and patients and the availability of optimal medical care for all who need it.

Recurrent hepatitis C after liver transplantation: clinical and therapeutical issues

Hepatitis C virus (HCV) reinfection after liver transplantation is almost constant, assessed by the persistence of HCV RNA in 90% of cases. Acute hepatitis appeared in 75% of patients at a median of 4 months' post-transplantation. The 5-year actuarial rate of acute and chronic hepatitis on the graft is 75% and 60%, respectively. The rate of HCV cirrhosis on the graft is variable from 8 to 25% at 5 years. After transplantation, HCV viraemia is dramatically increased and correlates with the occurrence of acute hepatitis on the graft. Intrahepatic levels of HCV are high at the time of acute hepatitis, and decrease with constitution of chronic graft hepatitis lesions, implying an immunological response to the viral infection. A relationship between genotype 1b and the prevalence of HCV hepatitis on the graft has been suggested in European but not American series. The influence of the age of the recipient, quasispecies, viral compartmentalization, immunosuppressive treatment, and of HLA matching is being evaluated. The 5-year patient survival is around 65-80%. However, the occurrence of cirrhosis with a risk of graft failure may decrease the 10 and 15-year patient survival. Attempts to give prophylactic post-transplant antiviral treatment are under evaluation. Antiviral treatment of post-transplant graft lesions with combination therapy interferon-ribavirin gave promising results but indications and duration of treatment should be evaluated. In conclusion, HCV reinfection is frequent, but medium-term survival is good. However, the long-term graft and patient survival remains unknown, and efficient prevention and treatment of HCV graft is mandatory.

Current Views on Hepatitis C Virus Infection

Hepatitis C virus infection affects more than 4 million people in the United States and is a leading cause of liver failure necessitating transplantation. Effective combination therapies are now available for subgroups of patients at risk for progression to cirrhosis. The benefits of therapy in immunosuppressed hosts, such as HIV-infected patients and liver transplant recipients, are less well established.

The molecular biology of hepatitis C virus. Genotypes and quasispecies

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. HCV is a positive-strand genotype RNA virus with extensive genetic heterogeneity; HCV isolates define 6 major genotypes, and HCV circulates within an infected individual as a number of closely related but distinct species, termed a quasispecies. This article reviews characteristic aspects of HCV molecular biology and their implications for treatment and vaccine development.

Recurrence of hepatitis C virus after loss of virus-specific CD4(+) T-cell response in acute hepatitis C

BACKGROUND & AIMS

The prospective comparison of patients with acute hepatitis C virus (HCV) who spontaneously clear the virus with those who cannot achieve viral elimination and progress to chronic hepatitis offers the unique opportunity to analyze natural mechanisms of viral elimination.

METHODS

We studied the HCV-specific CD4(+) T-cell response in 38 patients with acute HCV and correlated the clinical course with the antiviral immune response. The individual HCV-specific T-cell response was assessed in a proliferation assay ((3)H-thymidine uptake) and an enzyme-linked immunospot assay.

RESULTS

Patients were classified according to their clinical course and pattern of CD4(+) T-cell responses in 3 categories: first, patients mounting a strong and sustained antiviral CD4(+)/Th1(+) T-cell response who cleared the virus (HCV RNA-negative; n = 20); second, patients who were unable to mount an HCV-specific CD4(+) T-cell response and developed chronic disease (n = 12); and third, patients who initially displayed a strong CD4(+) T-cell response and eliminated the virus (HCV PCR-negative) but subsequently lost this specific T-cell response (n = 6). The loss of the HCV-specific CD4(+) T-cell response was promptly followed by HCV recurrence.

CONCLUSIONS

The results indicate that a virus-specific CD4(+)/Th1(+) T-cell response that eliminates the virus during the acute phase of disease has to be maintained permanently to achieve long-term control of the virus. The induction and/or maintenance of virus-specific CD4(+) T cells could represent a promising therapeutic approach in HCV infection.

Hepatitis viruses and the safety of blood donations

Since the beginning of blood transfusions concomitant transmission of viral hepatitis has been a frequent and serious side-effect. A first measure to reduce the frequency of transmission was the screening of blood donors for elevated levels of liver enzymes in the blood, which was introduced in Germany in the 1960s, but not in most other countries. After the discovery of hepatitis B virus (HBV), donors in all countries have been screened since the 1970s for its surface antigen (HBsAg). When it was realized that there was at least one other type of virus that was even more frequently transmitted, screening for liver enzymes and HBV antibodies (anti-HBc) was introduced as a surrogate marker in most, but not all, countries in the 1980s. Furthermore, donors at risk for parenterally transmitted viruses were excluded. The discovery of the hepatitis C virus (HCV) genome and the development of sensitive anti-HCV assays has meant that reliable detection of persistently infected HCV carriers has been possible since 1991. Recently infected donors, however, are infectious for several weeks or months before anti-HCV is detectable. Therefore, starting in April 1999 all donations in Germany have to be tested, by nucleic acid amplification tests, for the presence of HCV RNA, although preliminary experience shows that such recent HCV infections are very rare. Newly detected viruses, named GBV-C or HGV and TTV, have been detected in patients with non-A-E post-transfusion hepatitis, but their association with the disease seems to be coincidental. These viruses cause persistent viraemia and are quite prevalent world-wide, but do not cause any known disease. At present, transfusion-transmitted hepatitis has been virtually eliminated, and any improvement in safety will be very small and will require huge costs.

Viral safety of blood derivatives by immune neutralization

Despite careful donor selection and virus inactivation procedures, transmission of viruses by transfusion of blood and blood derivatives is still a threat. Outbreaks of hepatitis A among hemophiliacs having received highly purified, immune globulin depleted coagulation factor concentrates, put the importance of immune neutralization of viruses in blood derivatives in focus. Neutralizing antibodies may block several steps in the virus infection of a cell, from binding of virus to the cellular receptor to the uncoating of virus after uptake in the cell. The efficacy of antibody neutralizing activity depends on the availability and stability of the neutralizing epitopes. Hepatitis A and B viruses are very efficiently neutralized by antibodies and immune escape mutants rarely emerge. Anti-parvovirus B19 antibodies do not fully inactivate the virus, at least in low concentrations, but may prevent development of disease. The neutralizing epitopes on hepatitis C virus and human immunodeficiency virus are located on hypervariable regions of virus membrane proteins. The effects of neutralizing antibodies are thus marginal as immune escape mutants emerge at a relatively high frequency for both viruses. The neutralizing activity of anti-cytomegalovirus antibodies is also questionable as persons may become reinfected with cytomegolvirus despite high levels of antibodies. Plasma and plasma derivatives produced from large donor pools have the potential of being very efficient transmitters of viruses. Neutralizing antibodies are Nature's own, and very important barriers against the spread of many known and unknown viruses contaminating the plasma pools.

High titers of antibodies inhibiting the binding of envelope to human cells correlate with natural resolution of chronic hepatitis C

Most cases of hepatitis C virus (HCV) infection result in chronic disease; however, a very small fraction of patients naturally clear the virus and resolve chronic hepatitis. In an attempt to correlate immune response with chronic disease resolution, we compared the antibody response in patients with different outcomes of the infection. Antibody responses to HCV structural proteins were assessed in 34 patients originally diagnosed with acute hepatitis. Five cases resolved acute infection, 22 developed chronic hepatitis, and 7 naturally resolved chronic hepatitis C. To estimate HCV neutralizing antibodies we used the neutralization of binding (NOB) assay, which evaluates inhibition of the envelope-2 protein binding to human cells. Enzyme-linked immunosorbent assay was used for the quantitative assessment of serum antibodies. The presence of HCV RNA was ascertained by reverse transcription-polymerase chain reaction. In 6 of 7 patients naturally recovered from chronic hepatitis C, the emergence and the persistence (for more than 3 months) of high serum titers (>1/600) of NOB antibodies coincided with virus clearance and clinical resolution of hepatitis. NOB antibody activity was observed in only 2 of 5 patients recovered from acute hepatitis C. Chronic patients who did not show any resolution during the course of the study developed low or no NOB antibodies. Because of the correlation between prolonged high NOB titers and natural resolution of chronic hepatitis C, vaccination or passive immunization aimed at high titers of NOB antibodies may be valuable new therapeutic approaches for chronic hepatitis C.