Autologous dendritic cells derived from CD34+ progenitors and from monocytes are not functionally equivalent antigen-presenting cells in the induction of Melan-A/Mart-127-35-specific CTLs from peripheral blood lymphocytes of melanoma patients with low frequency of CTL precursors

Peptide presentation by autologous dendritic cells (DCs) is a new tool 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 antigen-specific CTL precursors (CTLps) in peripheral blood of HLA-A*0201⁺ melanoma patients. Then, from two melanoma patients showing low frequency of CTLps to melanoma antigen-A/melanoma antigen recognized by T cell (Melan-A/Mart-1)_27-35 peptide, autologous DCs were differentiated from granulocyte colony- stimulating factor-mobilized CD34⁺ progenitors or from monocytes. CD34⁺- and monocyte-derived DCs were characterized by a similar proportion of CD1a⁺ cells expressing HLA class II antigens and CD54, CD80, and CD86 molecules. Both types of DC presented Melan-A/Mart-1_27-35 and tyrosinase_{369- 377} peptides to melanoma-specific CTL clones and were equally effective as peptide-pulsed APCs in the activation of influenza A matrix_58-66- specific CTLs from high-frequency precursors (1294/10⁶ and 1789/10⁶ lymphocytes in the two patients). However, efficient activation of Melan- A/Mart-1_27-35-specific CTLs from low-frequency precursors (158/10⁶ and 77/10⁶ lymphocytes) 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.