Potent Anti-Hepatitis C (HCV) T Cell Immune Responses Induced in Mice Vaccinated with DNA-launched RNA Replicons and MVA-HCV.

Hepatitis C is a liver disease caused by the Hepatitis C virus (HCV) affecting 71 million people worldwide with no licensed vaccines that prevent infection. Here, we have generated four novel alphavirus-based DNA-launched self-amplifying RNA replicon (DREP) vaccines expressing either structural Core-E1-E2 or nonstructural p7-NS2-NS3 HCV proteins of genotype 1a placed under the control of an alphavirus promoter, with or without an alphaviral translational enhancer (grouped as DREP-HCV and DREP-e-HCV, respectively). DREP vectors are known to induce cross-priming and further stimulation of immune responses through apoptosis, and here we demonstrate that they efficiently trigger apoptosis-related proteins in transfected cells. Mice immunized with the DREP vaccines as a prime followed by a heterologous boost with a recombinant modified vaccinia virus Ankara (MVA) vector expressing the nearly full-length genome of HCV (MVA-HCV), induced potent and long-lasting HCV-specific CD4+ and CD8+ T cell immune responses that were significantly stronger compared to a homologous MVA-HCV prime/boost immunization, being the DREP-e-HCV/MVA-HCV combination the most immunogenic regimen. HCV-specific CD4+ and CD8+ T cell responses were highly polyfunctional, of effector memory phenotype and mainly directed against E1-E2 and NS2-NS3, respectively. Additionally, DREP/MVA-HCV immunization regimens induced higher antibody levels against HCV E2 protein than homologous MVA-HCV immunization. Collectively, these results provided an immunization protocol against HCV inducing high levels of HCV-specific T cell responses, as well as humoral responses. These findings reinforce the combined use of DREP-based vectors and MVA-HCV as promising prophylactic and therapeutic vaccines against HCV. IMPORTANCE HCV represents a global health problem as more than 71 million people are chronically infected worldwide. Direct-acting antiviral agents can cure HCV infection in most patients, but due to their high cost and the emergence of resistant mutants they do not represent a feasible and affordable strategy to eradicate the virus. Therefore, a vaccine is an urgent goal that requires efforts in understanding the correlates of protection for HCV clearance. Here, we describe for the first time the generation of novel vaccines against HCV based on alphavirus DNA replicons expressing HCV antigens. We demonstrate that potent T cell immune responses, as well as humoral immune responses against HCV can be achieved in mice by using a combined heterologous prime/boost immunization protocol consisting in the administration of alphavirus replicon DNA vectors as a prime followed by a boost with a recombinant modified vaccinia virus Ankara vector expressing HCV antigens.