Class I MHC-restricted CTLs are an important component of the host immune response against viral infections, and CTL effectors can often be isolated from infected individuals. However, the mechanism responsible for the induction of CTLs is incompletely understood because, in part, of the difficulty in generating such cells in vitro from naive precursors. In the present study we have used human peripheral blood dendritic cells (DCs), devoid of CD4+ T cells, to sensitize naive CD8+ T cells to exogenous Ags, resulting in the generation of Ag specific CTL effectors. With this system, Ag-specific CTL lines were generated to a complex glycoprotein, keyhole limpet hemocyanin, and to multiple small (9-15 amino acids) synthetic peptides derived from conserved regions of the HIV-1 gag and envelope proteins. The HIV-1-specific CTLs demonstrated potent HLA class I restricted killing of both Ag pulsed and virally infected target cells. In contrast to Ag-pulsed DCs, Ag-pulsed monocytes failed to sensitize CTL precursors although they could be used as feeders for purposes of CTL expansion and as target cells in cytolytic assays. With the use of the system described herein, a detailed analysis of the primary human T cell response to foreign Ags is now feasible, and CTL of desired specificity can be generated for potential clinical use in adoptive immunotherapy protocols.