A, BALB/c mice (n=3) were primed with 100μg of HIV-1 Gag DNA vaccine with or without the agonistic anti-4-1BB Ab at week 0 and boosted with MVA-Gag at week 12. Sera were collected at 1 week after the boost and total Gag-specific IgG was determined by ELISA. B, Mice (n=10) were primed with plasmid DNA (20μg) at week 0 and boosted with MVA-Gag at week 4. Gag-specific IgG was determined by ELISA at one week following the boost. C, Mice (n=10) were primed and boosted with plasmid DNA (20μg) at week 0 and at week 4 respectively. Total Gag-specific IgG was evaluated at two weeks after the DNA boost. Sera from unimmunized naïve mice were used as negative control. The bars represent mean ± SEM of Gag-specific IgG titer in serum. *, p= 0.05. NA, Not available.