An accelerated vaccine schedule with a poly-antigenic hepatitis C virus MVA-based candidate vaccine induces potent, long lasting and in vivo cross-reactive T cell responses

Abstract

We designed and evaluated in HLA-class I transgenic mouse models a hepatitis C virus (HCV) T cell-based MVA vectored vaccine expressing three viral antigens known to be targets of potent CD8+- and CD4+-mediated responses. An accelerated (3 week-based) vaccination induced specific CD8+ T cells harboring two effector functions (cytolytic activity – both in vitro and in vivo- and production of IFNγ) as well as specific CD4+ T cells recognizing all three vaccine antigens. Responses were long lasting (6 months), boostable by a fourth MVA vaccination and in vivo cross-reactive as demonstrated in a surrogate Listeria-based challenge assay. This candidate vaccine has now moved into clinical trials.

Introduction

Approximately 3% of the world's population is infected with hepatitis C virus (HCV) [1] and about 80% of infected people develop a chronic infection leading to liver failure in 4% cases [2]. Standard treatment combining interferon α (IFNα) and ribavirine is effective in about half of the treated patients, however associated with significant toxicity and cost, and remains counter-indicated in a non-neglectable number of cases [3]. Novel therapies are in development, mainly targeting the viral protease or polymerase [4]. However, preliminary clinical data indicate that these new antivirals display low efficiency when used as stand-alone therapy, and it is becoming clear that the HCV therapeutic field is moving towards a complex association of multiple, costly drugs. The need for alternative therapeutic strategies, relying on complementary mechanisms than those currently exploited by antiviral molecules candidate, is well recognized.

Studies in humans and chimpanzees have indicated that failure to generate broad and long-lasting HCV-specific CD4+ and CD8+ T lymphocyte mediated immune responses during the acute phase of infection correlates with development of chronicity [5]. Conversely, patients displaying a functional and maintained Th1 CD4+ T lymphocyte-mediated response, associated with the mounting of matured and multifunctional effector CD8+ T lymphocytes, exert a more efficient control of viremia and are prone to evolve towards recovery [6], [7], [8], [9], [10], [11]. Multiple studies have established that non-structural antigens, and in particular NS3, are the preferential targets of responses associated with natural or therapeutic viral clearance [12], [13], [14]. In contrast, although the field is moving quickly due to novel assays recently developed, the contribution of anti-HCV antibodies in infection outcome remains controversial as these antibodies are typically present in face of ongoing chronicity [15], [16], [17].

Over the last 10 years, a wide variety of HCV vaccine efforts have been pursued. Various formulations, ranging from classical adjuvanted-recombinant proteins to dendritic cell-based vaccines, have been tested in mice, macaques and for a few, in chimpanzees [18]. It is striking to observe that only a few vector-based vaccines have been evaluated so far such as recombinant DNA [19], [20], recombinant bacteria [21] or adenoviruses [22], [23]. Most surprisingly, one of the safest known vaccine vector used to-date in the clinic, namely the modified non-replicative vaccinia virus Ankara strain (MVA), has seldom been evaluated towards the development of HCV vaccines. This highly attenuated strain of vaccinia virus that has been used in the campaign for eradication of smallpox has demonstrated a safety profile in more than 100,000 people [24], [25]. In the case of HCV, only two pre-clinical studies based on MVA vaccines have so far been reported: one describing MVA candidates expressing HCV envelop glycoproteins E1 and E2, either as wild-type or membrane-targeted immunogens [26], the other reporting on a vaccine combining two MVA expressing the three structural proteins (core, E1 and E2) as well as the non-structural protein 3 [20]. However, encouraging results with MVA-based vaccines have been observed for example, in the field of HIV or malaria vaccine development, where numerous studies involve MVA vaccine candidates either used alone or in prime-boost combinations [27], [28], [29]. These studies have run from evaluations performed in HLA-A2 transgenic murin models to small non-human primates and to clinical trials [30], [31]. Another poxvirus that has been tested in the HCV vaccine field is a HCV recombinant canarypox virus reported to induce potent T cell immune responses although this candidate has been only tested in a DNA prime-canarypox virus boost regimen [32]. The superior safety profile of MVA combined with its powerful immunogenic potential; argue unambiguously in favour of developing a potent HCV MVA-based vaccine, both for prophylactic and therapeutic application.

With the aim to develop a safe, poly-antigenic, T cell-based HCV vaccine, we have engineered and preclinically evaluated a recombinant MVA vaccine candidate encoding for HCV non-structural (NS) proteins NS3, NS4 and NS5B. We report here that an accelerated schedule of vaccination using this vaccine is able to induce CD4+ and CD8+ T lymphocyte-mediated responses targeted at all three vaccine immunogens and recognizing class I T cell epitopes recognized during the natural infection. Potent and specific CD8+ T cell-mediated responses are long lasting (detectable up to 6 months) and can be efficiently recalled when boosted at a later time with the original MVA NS34–NS5B. Using a challenge model based on HCV recombinant Listeria monocytogenes that can infect liver, we show that the accelerated schedule of vaccination with the MVA NS34–NS5B results in in vivo cross-reactive responses.