HIV-1 specific cellular immunity plays an important role in controlling viral replication. In this first-in-human therapeutic vaccination study, a replication-defective HIV-1 vaccine (HIVAX) was tested in HIV-1 infected participants undergoing highly active antiretroviral therapy (HAART) to enhance anti-HIV immunity (Clinicaltrials.gov, identifier NCT01428596).,A010 was a randomized, placebo-controlled trial to evaluate the safety and the immunogenicity of a replication defective HIV-1 vaccine (HIVAX) given as a subcutaneous injection to HIV-1 infected participants who were receiving HAART with HIV-1 viral load <50 copies/ml and CD4 cell count >500 cells/mm(3). HIV-1 specific immune responses were monitored by INF- enzyme linked immunospot (Elispot) and intracellular cytokine staining (ICS) assay after vaccination. Following the randomized placebo-controlled vaccination phase, subjects who received HIVAX vaccine and who met eligibility underwent a 12-week analytical antiretroviral treatment interruption (ATI). Viral load was monitored throughout the study.,HIVAX was well tolerated in trial participants. Transient grade 1 to 2 (mild to moderate) injection site reactions occurred in 8 of 10 vaccinated participants. HIVAX was immunogenic in all vaccinated participants. The functionality of T cells was significantly enhanced after vaccination. Median viral load (3.45 log10 copies/ml, range of 96-12,830 copies/ml) at the end of the 12-week treatment interruption in HIVAX vaccinated group was significantly lower than the pre-treatment levels. Three vaccinated participants extended ATI for up to 2 years with stable CD4 cells and low viral loads.,HIVAX vaccine is generally safe, elicits strong anti-HIV-1 immune responses, and may play an important role in controlling viral load during treatment interruption in HIV-1 infected participants.