Differential presentation of endogenous and exogenous hepatitis B surface antigens influences priming of CD8 + T cells in an epitope-specific manner

Little is known about whether presentation of endogenous and exogenous hepatitis B virus (HBV) surface antigens on APCs targeted by vaccination and/or virus-harboring hepatocytes influences de novo priming of CD8+ T cells. We showed that surface antigen-expressing transfectants exclusively display a Kb/S190 epitope, whereas cells pulsed with recombinant surface particles (rSPs) exclusively present a Kb/S208 epitope to CD8+ T cells. The differential presentation of these epitopes largely reflects the selective, but not exclusive, priming of Kb/S190- and Kb/S208-specific T cells in C57BL/6 mice by endogenous/DNA- or exogenous/protein-based vaccines, respectively. Silencing the Kb/S190 epitope (Kb/S190V194F) in antigen-expressing vectors rescued the presentation of the Kb/S208 epitope in stable transfectants and significantly enhanced priming of Kb/S208-specific T cells in C57BL/6 mice. A Kb/S190-mediated immunodominance operating in surface antigen-expressing cells, but not in rSP-pulsed cells, led to an efficient suppression in the presentation of the Kb/S208 epitope and a consequent decrease in the priming of Kb/S208-specific T cells. This Kb/S190-mediated immunodominance also operated in 1.4HBV-Smut transgenic (tg) hepatocytes selectively expressing endogenous surface antigens and allowed priming of Kb/S208- but not Kb/S190-specific T cells in 1.4HBV-Smut tg mice. However, IFN-γ+ Kb/S208-specific T cells could not inhibit HBV replication in the liver of 1.4HBV-Smut tg mice. These results have practical implications for the design of T-cell-stimulating therapeutic vaccines.