A Phase II Double-Blind, Randomized, Placebo-Controlled Study to Evaluate the Antiretroviral Effect of Immunization With the MRK Ad5 HIV-1 Gag Vaccine in HIV-1 Infected Individuals Who Interrupt Antiretroviral Therapy

Antiretroviral therapy (ART) has a significant impact on HIV disease; however, HIV cannot be cured with current drug regimens. While the majority of patients initially benefit from ART, drug regimens subsequently fail for many patients due to drug resistance, poor adherence, or toxicity. If given while HIV replication is kept in check by ART, an HIV vaccine may be able to generate an effective long-term immune response capable of controlling the virus, even if ART is discontinued.

The MRK Ad5 HIV-1 gag vaccine uses a replication-defective adenovirus vector and has been found safe in clinical trials of both HIV infected and HIV uninfected adults. This study will evaluate the ability of immunization with the MRK Ad5 HIV-1 gag vaccine to control HIV replication in individuals undergoing treatment interruption. The study will enroll individuals whose HIV replication has been successfully suppressed with ART for at least 2 years.

Participants in this study will be randomly assigned to receive either vaccine or placebo. Both vaccine and placebo will be injected into the upper arm muscle. Participants will take their antiretroviral medications during the first 3 months of the study. Injections will be given on Day 1, Week 4, and Week 26. A study nurse will call participants 1 or 2 days after each injection and participants will be asked to fill out a card with any reactions they have to the injections. About 3 months after the third injection, participants will stop taking their antiretroviral medications for 4 months. Participants will have study visits every 2 to 3 weeks while off medication. After 4 months, participants will have the option of restarting antiretroviral medications or continuing without medication. Participants will then have study visits every 2 months for 8 months. Study visits will include physical exams and blood collection.

All participants will continue to see their primary care provider for HIV treatment and will be restarted on antiretroviral medications if clinically indicated. Participants or their primary care provider will be contacted by phone for updates every 6 months for an additional 3.5 years.