A Randomized Phase I/II Pilot Study of Intermittent Withdrawal of Antiretroviral Therapy as an Immunization Strategy and Double-Blinded Immunization With ALVAC-HIV vCP1452 in Subjects With Persistent CD4+ Cell Counts Greater Than 400 Cells/mm3 and Plasma HIV-1 RNA Levels Less Than 50 Copies/ml

The best hope for long-term control of HIV infection in an individual likely rests with the resumption of effective HIV-specific immune responses. Intermittent antiretroviral therapy (ART) withdrawal, as an attempt to "immunize" the subject with his/her own active viral quasi-species population, represents an alternative approach to traditional immunization strategies. This study hopes to determine whether intermittent ART withdrawal serves to stimulate HIV-specific immune responses and control of viral replication. This approach will be compared with vaccination with ALVAC-HIV vCP1452. In addition, it is conceivable that intermittent ART withdrawal could boost and broaden the prime response to exogenous vaccine; that will also be studied.

Patients will continue receiving their potent ART (not provided by the study) and will be randomly assigned to one of four treatment strategies as follows:

Arm A: ALVAC placebo and potent ART for 92 weeks with a single 12- to 20-week therapy withdrawal period; Arm B: ALVAC placebo and potent ART for 84 weeks with a 4- to 6-week therapy withdrawal period, a 4-week therapy withdrawal period, and a 12- to 20-week therapy withdrawal period; Arm C: ALVAC vCP1452 vaccine and potent ART for 92 weeks with a single 12- to 20-week therapy withdrawal period; and Arm D: ALVAC vCP1452 vaccine and potent ART for 84 weeks with a 4- to 6-week therapy withdrawal period, a 4-week therapy withdrawal period, and a 12- to 20-week therapy withdrawal period.

Immunizations of placebo or vaccine wil be administered in 3 separate sets of 3 injections per set (9 total) and immunization schedules are the same for all patients, those undergoing intermittent therapy withdrawal (Arms B and D) and those who are not (Arms A and C).

This is a multiple-step study. Patients in Arms B and D will receive a 4-week period of potent ART therapy along with the first set of immunizations (Step 1) followed by therapy withdrawal for 4 to 6 weeks (Step 2). Alternating periods of therapy resumption (Step 3, consisting of 16 weeks on potent ART with the second set of vaccine administrations), a second therapy withdrawal (Step 4 for 4 weeks), and another therapy resumption (Step 5, consisting of 16 weeks on potent ART with the third set of vaccine administrations) will follow. Patients in Arms A and C will remain on Step 1 for the first 44 weeks on study.