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.

After 44 to 46 weeks on study, patients in all arms will have therapy withdrawn for 12 to 20 weeks (Step 6). Following completion of Step 6, patients whose viral load are below 10,000 copies/ml will be encouraged to remain off potent ART (Step 7) until completion of the study, as long as CD4 T-cell levels remain 50 percent or more of their baseline levels. Participants who successfully complete Step 7 will be invited to enter Step 9, a 48-week optional protocol extension. Otherwise, patients will restart their potent ART regimens (Step 8) and receive virologic and CD4 T-cell monitoring until completion of the study.

All patients will be monitored at regular clinic visits. Viral load and CD4 T-cell counts will be measured at each visit. Patients in all arms may participate in substudy A5101s (Male Genital Secretions) or substudy A5137s (Female Genital Secretions), and patients in Arms B and D may participate in substudy A5111s (Latent Infected T-Cell Clearance).