Antigens-specific antibody responses. Serum samples from mice vaccinated twice were harvested two weeks after the second immunization (The same mice as described in Figure 1). The titers of total IgG and three IgG subclasses (IgG1, IgG2a, IgG3) in each mouse serum were evaluated by standard ELISA assay (repeat once, 1:50 start dilution). The results are mean value (Log10 value) of each group of mice (n = 6) ± SD. Part A and Part B showed the total IgG and IgG subclasses responses to Gag, Env and Pol, respectively. pGag/ pEnv/ pPol: two immunizations, 50 μg pGag/ pEnv/ pPol and 50 μg empty vector each time; pGag + pTat/ pEnv + pTat/ pPol + pTat: two immunizations, 50 μg pGag/ pEnv/ pPol and 50 μg pTat each time.