DNA vaccination with plasmids encoding the intracellular (HBcAg) or secreted (HBeAg) form of the core protein of hepatitis B virus primes T cell responses to two overlapping K-b- and K-d-restricted epitopes

Plasmid DNA encoding either the intracellular form HBcAg or the secreted form HBeAg of the core protein of hepatitis B virus (HBV) was injected into the muscle of H-2(b), H-2(d) or F-1(b x d) mice. Serum antibody responses and class I-restricted cytotoxic T lymphocyte (CTL) responses to HBcAg/ HBeAg were detected in all mice tested, Stable murine H-2(b) and H-2(d) transfectants that express either intracellular HBcAg or secreted HBeAg were constructed, With these cell lines we restimulated in vitro T cells primed in vivo and detected their specific cytolytic reactivity against naturally processed peptides. CD8(+) CTL responses elicited by DNA vaccination with plasmids encoding HBcAg or HBeAg were specific for the (previously described) K-b-binding HBcAg(93-100) peptide MGLKFRQL in H-2(b) mice or the (newly defined) K-d-binding HBcAg(87-95) peptide SYVNTNMGL in H-2(d) mice, The overlapping epitopes span residues 87-100 of HBcAg, and are present on HBcAg and HBeAg, CTL responses were equally well elicited in vivo by injecting HBcAg- or HBeAg-expressing plasmid DNA, and CTL efficiently recognize in vitro HBcAg- and HBeAg-expressing transfectants, DNA vaccination of F-1(b x d) mice with HBcAg- or HBeAg-expressing plasmid DNA primed CTL populations that recognized the K-b- or the K-d-restricted epitope. Both K-b- and K-d-binding peptides are thus generated from cytoplasmic/nuclear HBcAg and secreted HBeAg, These data make it unlikely that the appearance of HBeAg-negative variants during chronic HBV infection results from CTL-driven selection, DNA vaccination is an efficient technique to prime CTL responses against overlapping epitopes present on intracellular or secreted viral protein antigens.