We examined the relationship between the profile of HIV-specific T helper (Th) cell responses, cytotoxic T lymphocyte (CTL) activity, HIV viral load, and CD4 + T cell counts during longitudinal studies in children with perinatal HIV infection. Patients with AIDS demonstrated undetectable or low levels of HIV-specific Th and CTL activities, and exhibited almost exclusively Th0 type of responses with low IFN-+ and IL-4 production. The levels of IL-2 expression in the envelope (env) peptide-stimulated peripheral blood mononuclear cells were increased in children with a slowly progressive disease, concomitant with higher numbers of CD45RO + memory T cells and increased proportions of Th1 clones. In these patients, high levels of env peptide-specific IL-2 expression correlated with increases in HIV-specific CTL responses, whereas a delay in the generation of HIV-specific CTL activity was associated with lower IL-2 production and elevated Th2 responses. Patients with slow disease progression produced higher levels of g -chemokines than those detected in children with AIDS. These results suggest that an impaired development of HIV-specific cellular responses and inhibition of T cell differentiation during infancy are associated with fast disease progression. They also point to a protective role of noncytotoxic antiviral activity that might complement HIV-specific CTL responses in children with a slowly progressive disease.