650. Development of Combination Therapy of Bifidobacterium-Based Oral Vaccine Displaying HCV-NS3 with Interferon-α

INTRODUCTION: Hepatitis C virus (HCV) is a major cause of chronic liver diseases, such as liver cirrhosis and hepatocellular carcinoma. The efficacy of the standard-of-care including interferon-α and ribavirin for chronic HCV infection is limited, especially in HCV genotype 1, the most prevalent genotype in Japan. It is considered that chronic HCV infection correlates strongly with failure of host immune response against HCV. Although HCV specific immune responses play an especially significant role in clearing virus, no effective vaccine against HCV was approved at present. We had successfully developed a recombinant Bifidobacterium based novel oral vaccine against HCV infection, displaying a HCV-nonstructural protein 3 (NS3) fusion peptide on the bacterial cell surface. We had found that this oral vaccine could induce HCV-NS3 specific CTL in mice. Then, in this study, to determine the therapeutic efficacy of this oral vaccine, the functional HCV specific cellular immune response was investigated by using HCV-NS3/4A antigen expressing tumor mouse model. Furthermore, to enhance the therapeutic efficacy, we combined interferon-α therapy with this oral vaccine in the mouse model. EXPERIMENTAL SUMMARY: Bifidobacterium longum (B. longum 2165) expressing NS3 fusion peptide derived HCV-genotype 1b was prepared and then heat inactivated for 5 min at 65 ° C for oral vaccination. For the tumor challenge, C57BL/6N mice were subcutaneously injected EL-4 lymphoma cells stably expressing HCV-NS3/4A, and then orally administered 2.4×108 CFU of inactivated B. longum 2165, active B. longum 2165, active B. longum transfected control vector (B. longum 2012), or PBS every other day for 4 weeks. In addition, for the combination therapy with interferon-α, inactivated B. longum 2165 and PBS groups were combined with 20,000 units of interferon-α subcutaneous injection every 4 days during vaccination. In the results, B. longum 2165 with interferon-α combination therapy significantly delayed tumor growth compared with the other treatments. For in vitro cytotoxicity assay, splenocytes were collected from immunized mice and restimulated with EL4-NS3/4A and IL-2. In the B. longum 2165 with interferon-α treated group, the cytotoxicity of splenocytes against EL4-NS3/4A was significantly higher than that of the other groups. CONCLUSION: This study demonstrated multiple oral vaccinations of B. longum 2165 could induce functional NS3 specific cellular immune responses in mice. Moreover, interferon-α combination therapy with the vaccine could strongly enhance the therapeutic efficacy of this vaccine. These findings support the feasibility of this therapeutic oral vaccine as additional agent of interferon based standard therapy against chronic HCV infection.