Enhancement of primary and secondary cellular immune responses against human immunodeficiency virus type 1 Gag by using DNA expression vectors that target Gag antigen to the secretory pathway

In this study, we have investigated the influence of antigen targeting afte r DNA vaccination upon the induction of cellular immune responses against h uman immunodeficiency virus type 1 (HIV-1) Gag. In addition to the standard version of HIV-1 Gag, we constructed Gag expression vectors that encode a secreted (Sc-Gag) and a cytoplasmic (Cy-Gag) Gag molecule. Although all thr ee HIV-1 Gag expression vectors induced detectable humoral and cellular imm une responses, after intramuscular injection the DNA vector encoding the Sc -Gag generated the highest primary cytotoxic T-lymphocyte (CTL) and T-helpe r responses. Mice immunized with one of the HIV-1 Gag DNA vectors (but not with the control vector pcDNA3.1) developed a protective immune response ag ainst infection with recombinant vaccinia virus expressing HIV-1 Gag, and t his response persisted for 125 days. The magnitude of the protection correl ated with the levels of Gag-specific ex vivo CTL activity and the number of CD8(+) T cells producing gamma interferon. The DNA vector encoding the Sc- Gag induced higher levels of protection and greater secondary CTL responses than did the DNA vector encoding Cy-Gag.