Creation of superagonist epitope sequences in the hepatitis B envelope protein using mutagenesis and DNA vaccination

DNA vaccination is a simple and efficient method for the induction of cytotoxic T lymphocytes (CTLs). In the present study, we have examined the effect of the mutations of each of the 12 amino acids of the HBsAg Ld-restricted CTL epitope on the ability of the modified proteins to induce CTLs after DNA-based immunization. Replacement of glutamine or serine by alanine codons in the whole envelope gene created a protein that induced higher CTL activity against cells bearing the wildtype peptide-MHC complex than against the wildtype sequence itself. These results represent the first example of immunogenic mutant sequences (superagonists) that induce higher CTL activity against the wildtype CTL epitope than does the wildtype protein. Because the entire mutant protein is being expressed from the modified plasmid, any of the various steps in epitope processing could be affected by the mutations and lead to increased class I immunogenicity of the peptide sequence.