Melanoma Patients with Low Frequency of CTL Precursors -specific CTLs from Peripheral Blood Lymphocytes

l'i plidi presentation by autologous dendritic cells (DCs) is a new to»!to activate tumor antigen-specific T cells in melanoma patients. However, it is not known whether autologous DCs, differentiated by two of the most efficient protocols (from CD34* progenitors or from monocytes), are equally effective as professional antigen-presenting cells (APCs) when the patients have a low frequency of peptide-specific precursors. To this end, a limiting dilution assay was applied to evaluate the frequency of antigenspecific CTL precursors (CTLpst in peripheral blood of HLA-A*020I + melanoma patients. Then, from two melanoma patients showing low frequency of CTLps to melanoma antigen-A/melanoma antigen recogni/ed by T cell (Melan-A/Mart-l),7_,5 peptide. autologous DCs were differentiated from granulocyte colony-stimulating factor-mobilized CI)34+ progenitors or from monocytes. CD34*and monocyte-derived DCs were characterized by a similar proportion of CDIa+ cells expressing HI.A class II antigens and CD54, CD80, and CD86 molecules. Both types of DC presented Melan-A/Mart-l27_,5 and tyrosinase,69_,77 peptides to melanoma-specific CTL clones and were equally effective as peptidepulsed APCs in the activation of influenza A niatrix51(_fi<1-specificCTLs from high-frequency precursors ( 1294/10'' and 1789/10'' lymphocytes in the two patients). However, efficient activation of Melan-A/Mart-127_,5specific CTLs from low-frequency precursors (158/I06 and 77/106 lym phocytes) of the two patients was markedly dependent on the use of peptide-loaded CD34+-derived DCs. These results suggest that CD34+and monocyte-derived DCs are not functionally equivalent APCs for the activation of low-frequency peptide-specific CTLps.