Due to the strong correlation between a significant decrease in CD4 count and the frequency and magnitude of OIs such as Pneumocystis carinii pneumonia (PCP), Mycobacterium avium complex (MAC), and severe bacterial infections, CD4 count has become the major criterion for initiating antimicrobial prophylaxis for OIs. However, despite the benefits of these antimicrobial drugs, all are associated with adverse side effects, and patients with reconstituted immune systems following antiretroviral therapy may be receiving prophylaxis unnecessarily. Benefits to stopping prophylaxis include: (1) elimination of adverse effects from drugs; (2) reduction in drug costs; and (3) removal of selective pressure for the development of drug-resistant microbes. These benefits must be weighed against the disadvantages, however, such as more frequent determinations of CD4 counts to assure maintenance of immunocompetence, more frequent occurrence of serious OIs otherwise preventable with prophylaxis in patients lost to follow-up, and possible occurrence of atypical PCP because of prior exposure to anti-PCP drugs. [AS PER AMENDMENT 04/26/02: The extent of complete immune restitution has not yet been defined. An important corollary of an incomplete immune recovery is that vaccination schedules might need to be adjusted to obtain optimal responses in HIV-infected patients on highly active antiretroviral therapy (HAART). Therefore, a third dose of hepatitis A virus vaccine will be administered.]

After pre-entry and entry laboratory studies, patients are followed every 8 weeks until the last patient has completed 104 weeks of study observation. Hepatitis A vaccination is administered at entry and Week 24 to measure responses to neoantigen. [AS PER AMENDMENT 04/26/02: All patients (except those co-enrolled in P1024 on or after November 1, 2001) who have received 2 doses of hepatitis A virus vaccine during the study will be offered an opportunity to enroll in Step II of P1008. Patients in Step II receive a third dose of hepatitis A vaccination at Week 104 or later. Additional blood samples are taken 8 weeks later for antibody detection and peripheral blood mononuclear cell (PBMC) cryopreservation.] All serious bacterial infections that are Grade 3 or higher and OI events are recorded and compared to historical event rates. Virologic and immunologic marker studies are done in all patients and correlated with the risk of developing serious bacterial infections or OI events. Patients are considered to have reached an endpoint if they develop PCP, 2 serious bacterial infections, other Category C OI diagnoses, or CD4% less than 15% and re-initiation of PCP prophylaxis.