Cytokine production by HIV-1-specific CTL clones stimulated with HIV-1-infected CD4+ T cells prepulsed with epitope peptide. CD4+ T cells were infected with NL-432 or NL-M20A. On day 9 postinfection, NL-432- or NL-M20A-infected CD4+ T cells prepulsed with or without peptide were mixed with HIV-1-specific CTL clone SF2-33-135 (effector/stimulator ratio of 1:5) and then incubated for 6 h. Intracellular staining of IFN-γ, TNF-α, or MIP-1β was performed, and cytokine-positive cells were analyzed by flow cytometry. The percentage of p24 Ag-positive cells in CD4+ T cells infected with NL-432 or NL-M20A was 41.2 and 38.5%, respectively.