Search

The hepatitis C virus (HCV) nonstructural (NS) 5A protein has been shown to promote viral persistence by interfering with both innate and adaptive immunity. At the same time, the HCV NS5A protein has been suggested as a target for antiviral therapy. In this study, we performed a detailed characterization of HCV NS5A immunogenicity in wild-type (wt) and immune tolerant HCV NS5A-transgenic (Tg) C57BL/6J mice. We evaluated how efficiently HCV NS5A-based genetic vaccines could activate strong T cell responses. Truncated and full-length wt and synthetic codon-optimized NS5A genotype 1b genes were cloned into eukaryotic expression plasmids, and the immunogenicity was determined after i.m. immunization in combination with in vivo electroporation. The NS5A-based genetic vaccines primed high Ab levels, with IgG titers of >104 postimmunization. With respect to CD8+ T cell responses, the coNS5A gene primed more potent IFN-γ–producing and lytic cytotoxic T cells in wt mice compared with NS5A-Tg mice. In addition, high frequencies of NS5A-specific CD8+ T cells were found in wt mice after a single immunization. To test the functionality of the CTL responses, the ability to inhibit growth of NS5A-expressing tumor cells in vivo was analyzed after immunization. A single dose of coNS5A primed tumor-inhibiting responses in both wt and NS5A-Tg mice. Finally, immunization with the coNS5A gene primed polyfunctional NS5A-specific CD8+ T cell responses. Thus, the coNS5A gene is a promising therapeutic vaccine candidate for chronic HCV infections.

The hepatitis C virus (HCV)-specific T cell response in patients with chronic HCV is dysfunctional. In this study, we aimed at restoring immunological function through therapeutic vaccination in a transgenic mouse model with impaired HCV-specific T cell responses due to a persistent presence of hepatic HCV nonstructural (NS)3/4A Ags. The HCV-specific T cells have an actively maintained dysfunction reflected in reduced frequency, impaired cytokine production, and impaired effector function in vivo, which can be partially restored by blocking regulatory T cells or programmed cell death ligand 1. We hypothesized that the impairment could be corrected by including sequences that created a normal priming environment by recruiting “healthy” heterologous T cells and by activating innate signaling. Endogenously expressed hepatitis B core Ag (HBcAg) can recruit heterologous T cells and activate TLR (TLR7) signaling. Hence, by combining HCV NS3/4A with different forms of HBcAg we found that heterologous sequences somewhat improved activation and expansion of NS3/4A-specific T cells in a wild-type host. Importantly, the signals provided by HBcAg effectively restored the activation of HCV-specific T cells in a tolerant NS3/4A-transgenic mouse model. The adjuvant effect could also be transferred to the priming of dysfunctional HLA-A2–restricted NS3-specific T cells in vivo. Thus, recruiting healthy heterologous T cells to the site of priming may also help restore HCV-specific responses present in a chronically infected host.