Regulation of melanoma epitope-specific cytolytic T lymphocyte response by immature and activated dendritic cells, in vitro.

Dendritic cell (DC)-based immunization in cancer has proven to be a promising approach. However, just as DCs are crucial accessory cells in generating immune responses, they also seem to participate in tolerance induction, especially against peripheral "self" antigens. The bulk of the evidence that DCs present peripheral self antigens to induce tolerance has, however, come mostly from studies in transgenic animal models. A tolerogenic function of DCs for peripheral self antigens in a human model has not been critically examined. In this study using the Melan-A/MART-1(27-35) peptide as a model for self but melanoma-associated antigen-against which human hosts often harbor CD8(+) CTL precursors with high frequencies-we confirm that although immature dendritic cells (iDCs) are inefficient antigen presenting cells (APCs), fully activated DCs efficiently activate melanoma epitope-specific CD8(+) CTL precursors, in vitro. We, however, show that in a direct epitope presentation schema, iDCs neither delete nor anergize epitope-specific CD8(+) T cells in primary or secondary stimulation. Interestingly, iDCs and activated DCs can delete a large fraction of the epitope-specific CTLs on tertiary stimulation. The deletion is induced in an epitope-specific manner and through apoptosis. These observations, therefore, have implications on the DC-based cancer vaccine designs and are relevant in the inquiry into the role of DCs on tolerance induction.