One of the hallmarks of persistent hepatitis C is a characteristically weak HCV-specific T cell responses. Here, we asked whether the weakness of the HCV-specific cellular immune response could be due to poor priming of T cells. Specifically, we hypothesized that the noncytopathic nature of HCV results in absent or scarce virus-infected apoptotic cells as a source of exogenous antigen. To induce stronger T cell responses and to study the immunological implications of time-delayed dendritic cell apoptosis and antigen reprocessing in vivo, we created a novel system that allows replication of HCV sequences in antigen presenting cells as well as induction of apoptosis, transfer of cell associated antigens to secondary dendritic cells (crosspresentation) and subsequent priming of HCV-specific T cells (crosspriming). For this purpose, we generated a self-replicating cytopathic pestivirus RNA to enhance production and presentation of hepatitis C virus (HCV) antigens and to induce apoptosis in dendritic cell 24-48 hours after transfection. Replicon-transfected H-2b DCs were used to immunize HLA-A2 transgenic mice and induced protection upon challenge with a vaccinia virus expressing HCV antigens. Transfer of cellular material from vaccine DCs to endogenous antigen presenting cells, a phenomenon that underlies crosspriming, was visualized in lymph nodes and spleen and crossprimed CD8+ T cells were characterized. The findings are relevant for the rational design of vaccines that enhance T cell priming against noncytopathic pathogens like HCV.
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