The role of HIV-specific cytotoxic T-lymphocytes (CTL) in controlling viremia and protecting against disease progression following vertical infection may be dependent upon CTL functional responses as well as on the timing of detection, magnitude, and breadth of the responses. Novel and sensitive assay systems (MHC-peptide tetramers, ELISPOT assays, intracellular cytokine assays) have enhanced the detection and characterization of virus-specific CTL responses in the peripheral blood. This study will use these novel methods to examine the timing of detection, magnitude, specificity, and in vitro functional properties of HIV-specific CTL in infants; to evaluate the effects of potent combination antiretroviral therapy on HIV-specific CTL in infants; and to evaluate the immunogenicity of recombinant pox-based vaccines in HIV infected infants with prolonged viral suppression following early potent combination antiretroviral therapy.