Investigating and Manipulating Immune Responses to Hepatotropic Pathogens Using Synthetic DNA

Hepatotropic pathogens, such as Hepatitis B virus (HBV), Hepatitis C virus (HCV) and malaria Plasmodium often escape cellular immune clearance, resulting in chronic infections. With billions at the risk of infection, the need for an immune therapy that will incite protective immune responses against these pathogens is more important now than ever. To develop effective therapies against these pathogens, it is important to understand the mechanisms by which liver-primed CD8 T cells become defective. In this report, I directly compared liver-primed CD8 T cells to secondary lymphoid tissue-primed CD8 T cells for differentiation, function, and memory programming in a highly controlled fashion. We used hydrodynamic tail vain injection of synthetic plasmids to establish liver-specific antigen expression in the P14 transgenic mouse model, and studied the priming of CD8 T cells. Intrahepatically activated CD8 T cells exhibited unique expansion, memory differentiation, polyfunctionality and cytotoxicity compared to T cells primed in the periphery. The difference in their expansion resulted in lower memory CTL frequency, which led to reduced protection against lethal viral challenge. These results demonstrated that defective liver priming of naïve CD8 T cells contributes to the lower frequency of antigen-specific CTLs observed during liver infection in HBV and HCV patients, which helps these pathogens to escape immune clearance. The results from the study provide evidence that, the eradication of HBV and HCV infected hepatocytes will require both the induction of a strong antigen-specific immune response and the subsequent deployment of that response towards the liver. We therefore assessed the ability of a synthetic DNA vaccine encoding a recombinant plasmid of the HBcAg and HBsAg to drive immunity in the liver. Intramuscular vaccination accompanied by electroporation induced both strong antigen-specific T cell and high titer antibody responses systematically and in the liver. Furthermore, immunized mice showed strong cytotoxic responses that eliminate adoptively transferred HBV-coated target cells in the spleen and liver. These data provide important insight into the generation of peripheral immune responses that are recruited to the liver; an approach that could be beneficial in the search for vaccines or immune-therapies for liver disease