Prospects for a hepatitis C virus vaccine

Construction of the Vero cell culture system that can produce infectious HCV particles

The hepatitis C virus is a major cause of chronic liver disease worldwide. Lack of culture system supporting virus production has been one of the major impediments in HCV research and vaccine development. Here, we use a HCV (1b) full-length cDNA clone that replicates and produces integrated and infectious virus particles in cultured Vero cells. Evidence shows that the replication of virus particles is robust, producing over 10(8) copies of positive RNA per milliliter of the culture cells within 48 h. Sucrose density gradient centrifugation of the cell lysate reveals that the HCV virions have a density of about 1.17 g/ml and a spherical morphology with an average diameter of about 55 nm. Secreted virus is infectious for Huh7 cells and can be neutralized by CD81- and E2-specific antibodies. This system establishes a powerful framework for studying the virus life cycle and developing vaccine research.

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.

Biotechnology and vaccines: application of functional genomics to Neisseria meningitidis and other bacterial pathogens

Since its introduction, vaccinology has been very effective in preventing infectious diseases. However, in several cases, the conventional approach to identify protective antigens, based on biochemical, immunological and microbiological methods, has failed to deliver successful vaccine candidates against major bacterial pathogens. The recent development of powerful biotechnological tools applied to genome-based approaches has revolutionized vaccine development, biological research and clinical diagnostics. The availability of a genome provides an inclusive virtual catalogue of all the potential antigens from which it is possible to select the molecules that are likely to be more effective. Here, we describe the use of "reverse vaccinology", which has been successful in the identification of potential vaccines candidates against Neisseria meningitidis serogroup B and review the use of functional genomics approaches as DNA microarrays, proteomics and comparative genome analysis for the identification of virulence factors and novel vaccine candidates. In addition, we describe the potential of these powerful technologies in understanding the pathogenesis of various bacteria.

Molecular therapies for viral hepatitis

Current treatment modalities available for hepatitis B virus (HBV) or hepatitis C virus (HCV) infections are not efficient. The enormous disease burden caused by these two infections makes the development of novel therapies critical. For HCV, the development of an effective vaccine is urgent in view of the escalating number of infected individuals. Molecular therapies for HBV and HCV infection can be directed at reducing viral load by interfering with the life cycle of the viruses or at generating immune response against viral epitopes. The antiviral approaches consist of the delivery or expression of antisense RNAs, ribozymes or dominant negative proteins. Viral biology can be interrupted by attacking various potential targets within the two viruses. DNA-based vaccination strategies are being explored for both prevention and treatment of these diseases. Both non-viral and recombinant viral vectors are being developed for safe, effective and long-term gene transfer to the liver. Although no "ideal" vector is available at this time, the ingenuity of numerous investigators is leading to the improvement of the vector systems, promising successful application of gene therapy to the prevention and treatment of viral hepatitis in the foreseeable future.

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.

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.