OBJECTIVE: We investigated how melanoma cells and membrane-bound granulocyte/macrophage colony stimulating factor (mbGM-CSF) melanoma cell lines affect the differentiation of dendritic cells (DC) from CD14+ monocytes.
METHOD OF STUDY: The malignant melanoma cell lines (Conley and Jorp) and mbGM-CSF-positive cell lines (Conley B-F8 and Jorp C-E6) were cultured and cell-free supernatants were collected from each cell line cultures to assess the GM-CSF level. Adherent monocytes were cocultured for 6–7 days with irradiated mbGM-CSF and wild type melanoma cells (50 Gy) at each 1 : 1 and 0.1 : 1 ratio in six-well culture plates in ex vivo culture medium containing interleukin (IL)-4. Immunophenotyping was performed by triple color immunofluorescence staining with flow cytometry analysis.
RESULTS: GM-CSF was detected at low levels in the culture supernatants of Conley B-F8 (0.48 ng/106 cells/24 hr), whereas there was no detectable GM-CSF in that of Conley melanoma cell line. Monocytes cultured with GM-CSF/IL-4 generated the expression of high levels of HLA DR, CD1a and CD86, while the expression of CD14 and CD83 were in low amounts. However, the addition of GM-CSF to these cultures resulted in an increased expression of these markers and decreased that of CD14. Monocytes cocultured with Jorp C-E6 illustrated similar expression pattern of CD1a, HLA DR and CD14 in the presence or absence of GM-CSF as Conley B-F8 melanoma cell line. Monocytes cocultured with Conley B-F8 melanoma cells at 1 : 1 and 0.1 : 1 ratio showed no significant difference in expression of CD1a, CD14 and CD83 between the two ratios.
CONCLUSION: Our results illustrate the feasibility to generate monocyte-derived DC from coculture with melanoma tumor cells in the presence of GM-CSF and IL-4. However, mbGM-CSF tumor cells did not significantly enhance the DC differentiation through juxtacrine stimulation unless soluble GM-CSF was added in the culture media.