Oral Combination Vaccine, Comprising Bifidobacterium Displaying Hepatitis C Virus Nonstructural Protein 3 and Interferon-α, Induces Strong Cellular Immunity Specific to Nonstructural Protein 3 in Mice.

We previously generated an oral hepatitis C virus (HCV) vaccine using Bifidobacterium displaying the HCV nonstructural protein 3 (NS3) polypeptide. NS3-specific cellular immunity is important for viral clearance and recovery from HCV infection. In this study, we enhanced the cellular immune responses induced by our oral HCV vaccine, Bifidobacterium longum 2165 (B. longum 2165), by combining interferon-α (IFN-α) as an adjuvant with the vaccine in a mouse experimental model. IFN-α is a widely used cytokine meeting the standard of care (SOC) for HCV infection and plays various immunoregulatory roles. We treated C57BL/6N mice with B. longum 2165 every other day and/or IFN-α twice a week for a month and then analyzed the immune responses using spleen cells. We determined the induction of NS3-specific cellular immunity by cytokine quantification, intracellular cytokine staining, and a cytotoxic T lymphocyte (CTL) assay targeting EL4 tumor cells expressing NS3/4A protein (EL4-NS3/4A). We also treated mice bearing EL4-NS3/4A tumor with the combination therapy in vivo. The results confirmed that the combination therapy of B. longum 2165 and IFN-α induced significantly higher IFN-γ secretion, higher population of CD4+ T and CD8+ T cells secreting IFN-γ, and higher CTL activity against EL4-NS3/4A cells compared with the control groups of phosphate-buffered saline, B. longum 2165 alone, and IFN-α alone (p < 0.05). We also confirmed that the combination therapy strongly enhanced tumor growth inhibitory effects in vivo with no serious adverse effects (p < 0.05). These results suggest that the combination of B. longum 2165 and IFN-α could induce a strong cellular immunity specific to NS3 protein as a combination therapy augmenting the current SOC immunotherapy against chronic HCV infection.