Background. The licensing of Zostavax has demonstrated that therapeutic vaccination can help control chronic viral infection. Unfortunately, HIV therapeutic vaccine trials have shown only marginal efficacy.Methods. Seventeen HIV-infected individuals with viral loads <50 copies/ml and CD4 T cell counts >350 cells/µl were randomized to the vaccine or placebo arm. Vaccine recipients received three intramuscular injections of HIV DNA (4&emsp14;mg) coding for clade B Gag, Pol, Nef, and clade A, B, C Env, followed by a replication-deficient Ad5 boost (1010 PFU) encoding all DNA vaccine antigens, except Nef. Humoral, total T cell and CD8 cytotoxic T lymphocyte (CTL) responses were studied pre- and post-vaccination. Single copy viral loads and latently infected CD4 T cell frequencies were determined. VRC 101 is a double-blind trial registered with ClinicalTrials.gov (NCT00270465).Results. Vaccination was safe and well tolerated. Significantly stronger HIV-specific T cell responses against Gag, Pol, and Env, with increased polyfunctionality and a broadened epitope-specific CTL repertoire, were observed post-vaccination. No changes in single copy viral load or the frequency of latent infection were observed.Conclusions. Vaccination of individuals with existing HIV-specific immunity improved the magnitude, breadth and polyfunctionality of HIV-specific memory T cell responses, but did not impact markers of viral control.