Enhanced Priming of Multispecific, Murine CD8+ T Cell Responses by DNA Vaccines Expressing Stress Protein-Binding Polytope Peptides

A polytope DNA vaccine (pCI/pt10) was used that encodes within a 106-residue sequence 10-well characterized epitopes binding MHC class I molecules encoded by the K, D, or L locus (of H-2 d , H-2 b , and H-2 k haplotype mice). The pCI/pt10 DNA vaccine efficiently primed all four K b /D b -restricted CD8 + T cell responses in H-2 b mice, but was deficient in stimulating most CD8 + T cell responses in H-2 d mice. Comparing CD8 + T cell responses elicited with the pCI/pt10 DNA vaccine in L d+ BALB/c and L d− BALB/c dm2 (dm2) mice revealed that L d -restricted CD8 + T cell responses down-regulated copriming of CD8 + T cell responses to other epitopes regardless of their restriction or epitope specificity. Although the pt10 vaccine could thus efficiently co prime multispecific CD8 + T cell responses, this priming was impaired by copriming L d -restricted CD8 + T cell responses. When the pt10 sequence was fused to a 77-residue DnaJ-homologous, heat shock protein 73-binding domain (to generate a 183-residue cT 77 -pt10 fusion protein), expression and immunogenicity (for CD8 + T cells) of the chimeric Ag were greatly enhanced. Furthermore, priming of multispecific CD8 + T cell responses was readily elicited even under conditions in which the suppressive, L d -dependent immunodominance operated. The expression of polytope vaccines as chimeric peptides that endogenously capture stress proteins during in situ production thus facilitates copriming of CD8 + T cell populations with a diverse repertoire.