Phases of apoptosis of melanoma cells, but not of normal melanocytes, differently affect maturation of myeloid dendritic cells

In this study, we investigated whether maturation of monocyte-derived myelo id dendritic cells (DCs) is differentially affected by the uptake of dying human melanoma cells in distinct phases of apoptosis. Maturation of monocyt e-derived DCs, as documented by phenotype analysis and T-cell immunostimula tory activity, was inhibited by phagocytosis of dying melanoma cells contai ning a large fraction of cells in early apoptosis (Annexin-V+ and propidium iodide(-)) but promoted by the same tumors when in late apoptosis/secondar y necrosis (Annexin-V+ and propidium iodide(+)) or when dying by primary ne crosis. These opposite effects on DC maturation were observed after the upt ake of early or late apoptotic cells from most vertical growth phase primar y tumors and all metastases but not after the uptake of dying cells from a radial growth phase primary tumor or normal adult melanocytes. Inhibition o f DC maturation by early apoptotic melanoma cells correlated with expressio n of interleukin-10 in neoplastic cells and was prevented by preincubating the tumor cells with a neutralizing antibody to interleukin-10 before tumor uptake by DCs. Cross-presentation of the melanoma-associated antigen gp100 (209-217) to peptide-specific CTLs by HLA-A*0201(+) DCs was achieved 48-72 h after phagocytosis of HLA-A*0201(-) melanoma cells in apoptosis, or prima ry necrosis, but only when tumor necrosis factor-alpha was added to DCs 4 I t after the initiation of tumor phagocytosis. These results suggest that ph ases of apoptosis and neoplastic transformation affect maturation of myeloi d DCs that take up dying cells of the melanocyte lineage. However, neoplast ic cells in late apoptosis, or even in primary necrosis, induce only a part ial DC differentiation not sufficient to achieve cross-presentation of tumo r antigens to CTLs unless further DC maturation is promoted by additional s ignals. These results suggest a novel mechanism of tumor escape that may pr event the development of antitumor immunity through the maturation block in duced in DCs by neoplastic cells in the early phase of apoptosis.