Intrastructural help for HIV Env. A) Mice were immunized with Ad-Sgp and boosted with SIV VLPs containing HIV Env 6 and 9 weeks later. Mean and SEM of Env-specific IgG1 and IgG2a antibody levels 2 weeks after the last VLP immunization from 6 animals per group are given. B-D) Mice were immunized with an HIV GagPol expression plasmid (Hgp) or empty pcDNA as control by intramuscular DNA electroporation. Gag specific CD4+ T-cell responses were analyzed 14 days after priming by intracellular cytokine staining of in vitro restimulated splenocytes. Shown are the percentages of cytokine producing cells among the total CD4+ T-cell population (B). HIV gp120 specific antibody levels of the subtypes IgG1 (C) and IgG2a (D) in the sera of immunized mice were determined by ELISA four weeks after DNA prime (day 28), one and two weeks after the first (day 42 and 49) and one week after the second VLP boost (day 64). Columns represent the mean values with SEM of 5–6 animals. *P < 0.05, **P < 0.005, Mann Whitney U test.