VACCINE: Development and evaluation of vectored vaccines for HCV using an enhanced gene expression technology in a novel rodent hepacivirus model

Hepatitis C virus (HCV) is a major pathogen worldwide, causing progressive and often severe liver disease in the estimated 160 million people infected with the virus. In the UK, a substantial proportion of the estimated 350,000 individuals chronically infected with HCV will eventually develop cirrhosis and liver cancer (hepatocellular carcinoma; HCC) if left untreated. While there is treatment available, conventional therapies based on interferon are effective in only a proportion of those treated while more recently developed antiviral therapy that directly targets the virus is expensive and its use will remain cost-limited for many years. Importantly, such treatments will not stem the spread of HCV and the large numbers of new infections recorded every year; even those who have been effectively treated remain prone to re-infection. HCV also poses a much greater medical problem worldwide where access to treatment will remain limited in much the same as HIV therapy. HCV-related deaths worldwide exceed 350,000 per year, of the same order to those attributed to AIDS, TB and malaria.

Large scale immunisation with a safe and effective HCV vaccine would induce life-long immunity to HCV and prevent further spread of the virus to those currently at risk for infection. Secondly, the therapeutic use of a vaccine in which immunisation would control and clear infection in those already infected with HCV would prevent and in many cases reverse development of liver disease complications, such as cirrhosis and HCC associated with long term chronic infection. The development of such vaccines would therefore have profound effects on global health.

The development of HCV vaccine has been hampered by a lack of animal models with which to test different type of vaccine. It has also proven exceptionally difficult to develop vaccines that induce long-lived protective immunity - even clearance of natural infections does not protect from subsequent re-infection, quite unlike the situation of poliovirus, measles and hepatitis A virus (as examples) for which effective vaccines have been developed.

We believe the solution to the problems is to generate novel vaccines in which viral proteins, such as those from HCV, are inserted into another virus, cytomegalovirus (CMV) or adenovirus (AdV). A feature of CMV infections is that although harmless, infection leads invariably to persistent infections. Infections with CMV containing inserted HCV genes, once established, would therefore continuously immunise the body against HCV, much more so than infection with HCV itself. The most compelling evidence for the effectiveness of this method of immunisation arises from HIV vaccine research, where CMV vectors were effective at preventing infection of macaques with SIV, a monkey version of HIV. Furthermore, the CMV/SIV vaccine was able to clear infection from macaques already infected with SIV. A human version of this CMV vaccine, containing HIV genes, is currently entering human clinical trial. AdV-vectored vaccines for HCV have proven efficacy in animal models and are currently in human phase I/II clinical trial.

The other development that will enable us to develop an effective HCV vaccine is the very recent discovery of a virus called rodent hepacivirus (RHV), closely related to HCV, that infects rats and causes the same pattern of liver disease and frequency of persistence as HCV in humans. In our planned project, we will develop CMV and AdV vectors containing genes from RHV to directly evaluate whether this approach can generate protective immunity and can clear RHV infection in rats that are chronically infected with the virus. Based on previous experience with CMV/SIV vaccine candidates in macaques, we believe this strategy will also prove effective for HCV and if confirmed, could translate through very rapidly into human clinical trials.

This project comprises the construction of a new type of vaccine vectored by cytomegalovirus (CMV) for immunisation against a rodent homologue of hepatitis C virus and its evaluation in a rodent / virus model along with an adenovirus (AdV) construct of previously demonstrated efficacy in animal models. Rodent hepacivirus (RHV) recapitulates in rats the liver-specific pathology, immune response and persistence observed in HCV infections in humans. Vectored constructs will be engineered to express transgenes of RHV and evaluated for efficacy as both a protective and therapeutic vaccine in a small animal model.

The infectivity and immune responses to CMV and AdV-vectors in rats will be evaluated. Levels of RHV antigen expression will be determined and the effectiveness of a novel strategy to enhance gene expression through compositional alterations in transgene sequences investigated. We previously showed that frequencies of CpG and UpA dinucleotides in RNA viruses limit virus replication and gene expression; CMV and AdV both show evidence for similar host-imposed restrictions on expression that can be circumvented using synthetic transgenes with minimised CpG/UpA frequencies. The strength, breadth and durability of T cell responses to RHV and titres of neutralising antibodies in rats infected with vectors expressing compositionally altered constructs will be determined.

In the 2nd phase of the project, CMV and AdV constructs will be evaluated for efficacy as a prophylactic vaccine in rat challenge experiments. As a therapeutic vaccine, RHV clearance will be monitored in RHV persistently infected rates post immunisation. Demonstration of efficacy of vaccines in this rodent model and determination of immune correlates of protection would translate directly into the future development and clinical trials of human vaccines for HCV.

Enhancing the quality of life, health and wellbeing. The clinical and humanitarian impact of the successful development of an effective prophylactic and therapeutic vaccine for HCV is almost immeasurable. It is currently estimated that over 160 million people are chronic carriers of the virus, with 350,000 representing a likely conservative estimates of the number of deaths arising from infection complications annually. Although interferon and more recently targeted antiviral therapy is increasingly successful in treating HCV, only large scale prophylactic immunisation can significantly reduce the spread and incidence of new HCV infections worldwide. An effective therapeutic vaccine may not only clear infection in chronic carriers of HCV, but also confer life-long immunity to re-infection.

The proposed work is based around a consortium of scientists with a combination of expertise in virology, immunology and vaccination models that will contribute significantly to achieving the ultimate aim of an effective HCV vaccine. It exploits new vectors for generating powerful and prolonged immune responses to viral antigens, novel means to enhance expression of immunogens and finally a new in vivo small animal model of HCV infection that recapitulates aspects of its pathogenesis, host response and persistence. This is crucial in devising effective strategies for vaccination and identifying immune correlates of protection that will directly translate into human vaccine development.

Economic impacts. The ground work in animal models will not create an immediate clinical impact on HCV-infected individuals in the UK or worldwide, but its successful development in a small animal model will accelerate its further development through human clinical trials and licensing. Its ultimate clinical impact is therefore substantial. In the UK alone, it may significantly reduce the need for costly treatment with directly acting antivirals (DAAs), both by clearing existing infections and conferring protection from re-infection on the one hand, and by targeted prophylactic immunisation of those at risk for HCV infection on the other. Both interventions will significantly reduce the incidence of new infections.

Economic prosperity and industry. By any financial metric, an effective HCV vaccine would contribute significantly to economic prosperity, enhance UK competitiveness in the vaccine field and confer major benefits to UK-based vaccine manufacturers such as GSK. Our work will also increase innovative research capacity within a number of academic organisations that seek to develop new vaccines for other infectious diseases.

Technological advances. Society will also benefit through technological advances made within the strategic aims of the projects. CMV and adenovirus vector platforms are highly flexible and can be developed for other infectious disease for which existing vaccine approaches are ineffective or cost-limited. Modulating gene expression through compositional modification of transgenes is an approach that may be more broadly exploited in other vaccine vectors and in the wider biotechnology field.

A realistic time scales for benefits to be achieved is 6 years for evaluation of the CMV- and AdV-vectored strategies for immunisation, the translation of knowledge in the design of HCV vaccine constructs for use in humans and the necessary clinical trial to demonstrate its efficacy as a therapeutic and prophylactic vaccine.