Influence of polypeptide size and intracellular sorting on the induction of epitope-specific CTL responses by DNA vaccines in a mouse model.

We have analysed the influence of size, intracellular localisation, and sorting of various human immunodeficiency virus type 1 (HIV-1)-derived Gag and Env polypeptides containing well defined H2(d)-restricted cytotoxic T lymphocyte (CTL) epitopes on the induction of a humoral and cellular immune response after DNA vaccination. Thus, expression vectors were generated based on RNA- and codon-optimised genes encoding (i). budding competent full-length Gag, (ii). a myristylation defect mutant GagMyr(-), (iii). the isolated p24 capsid moiety of Gag as well as variants of these proteins, which were C-terminally fused HIV gp120-derived V3 epitope (R10I), respectively. These constructs were compared to different minitopes each encoding one of the H2(d)-restricted Gag epitopes A9I and E10F or the V3 epitope R10I that were directly linked to the C-terminus of an Ad2-E3 protein-derived ER signal peptide. Immunological evaluation of these constructs in BALB/c mice revealed that both, the budding competent as well as the intracellular Gag proteins were-irrespective of their molecular weights-equally efficient in the priming of Gag-specific humoral and cellular immune responses. In addition, the capacity of these constructs to stimulate Gag-specific humoral as well as H2-K(d) and H2-L(d) restricted cellular immune responses was not influenced by C-terminal fusion of the immunodominant H2-D(d) restricted V3 epitope. Chimeric GagV3 polyproteins encoding all three major CTL epitopes within a continuous polyprotein were more efficient to stimulate epitope-specific cellular immune responses than the selected minitopes. In addition, the minitopes failed to induce epitope-specific antibody responses. These results clearly show the advantages of complex polypeptides over minitopes regarding the induction of strong humoral and cellular immune responses.