Schlussbericht zum DZIF-Vorhaben: TI 07.002 - MD/PhD programme Till Bunse

Abstract

A prominent feature of chronic HBV infection – in contrast to other chronic virus infection - is that HBV-specific T cells are scarce. This could have different reasons: either HBV-specific T cells do not expand or they simply undergo apoptosis. This may be due to antigen recognition in the wrong context, unbalanced co-stimulation/co-inhibition or – as we propose here - due to a lack of essential metabolites. The liver is an essential metabolic and detoxifying organ. Thus, the metabolic micromilieu is adapted to tolerate antigens derived from the gastrointestinal tract preventing immunes responses that could harm healthy liver tissue. While being beneficial for the organism overall, this may prevent effective antiviral immune responses. Viruses, like the hepatitis B virus (HBV), profit from this situation and persist in the liver environment. We investigated the impact of nutrient deprivation caused by infection with HBV on the adaptive immune response and in particular on T cell functionality. As liver samples from patients with chronic hepatitis B showed changes in the composition of amino acids associated with reduced T cell activation, we will determined amino acid compositions and abundance in HBV-infected hepatocytes and liver of chronically HBV infected mice and humans. We studied HBV-specific T cell responses, and cultured T cells grafted with HBV-specific T-cell receptors on HBV infected cells to study their cytotoxicity dependent on HBV antigen expression levels. We vaccinate mice infected with an AAV transferring replication competent HBV genomes (AAV-HBV) in conditions expressing different levels of antigens for different durations. In the vaccinated mice, metabolomic analysis of liver were successfully performed, HBV-specific T cell responses were determined, and HBV-specific T cells from the liver was analysed on a single cell level. The complex omix data sets are currently under evaluation. We already observed reduced cytotoxic efficacy of HBV-specific T cells when Arginin was absent in the incubation medium as evidenced by reduced release of cytokines, particularly interferon-gamma and granzyme B.