Soluble Factors Secreted from CD40 Ligand-Transfected Dendritic Cells Enhance TRAIL-Induced Apoptosis of Multiple Myeloma.

Dendritic cells (DCs) belong to a family of antigen presenting cells that play a crucial role in the regulation of cellular and humoral immune responses to bacteria, virus and cancer. Recent studies also revealed that IFN-stimulated monocyte-derived DCs expressed functional TNF-related apoptosis-inducing ligand (TRAIL), suggesting that DCs may become cytotoxic effector cells to tumors. In this study, we investigate whether gene transfer of CD40-ligand (CD40L), that is known to be a potent stimulator in DC maturation, could induce cytotoxic activity of DCs or modulate susceptibility to TRAIL that is expressed on cytotoxic T and NK cells. Human monocyte-derived DCs infected with adenovirus vector encoding human CD40L (CD40L-DC) were induced to express superior higher levels of T-cell costimulatory molecules, DC maturation markers, MHC molecules and the production of IL-12 than soluble CD40L or TNF-alpha treated DCs. In addition to the phenotypic alternation of CD40L-DC, we found that cultivation of multiple myeloma cells ARH-77 with CD40L-DC significantly inhibited the expression of phospho-AKT and induced apoptosis in vitro. However, we could not detect the expression of TRAIL and Fas-ligand on CD40L-DC by flow cytometry, suggesting that these molecules are not involved. To examine whether soluble factors produced by CD40L-DC contribute to tumor cell apotosis, we cultured myeloma cells MM1S or ARH-77 with CD40L-DC in transwell plates. We found that myeloma cells in transwell culture were not lysed for 48 hours, but the susceptibility of apoptosis by recombinant TRAIL protein could be increased. To investigate soluble factors that could affect TRAIL sensitivity of myeloma cells, we next tested the effect of neutralizing antibodies specific for CD40L and TRAIL or recombinant IFN-gamma that might modulate TRAIL sensitivity. However, antibodies and recombinant protein did not affect, indicating that these factors might be not involved. Our findings suggest that CD40L-transduced DCs have the ability of induction of TRAIL susceptibility of multiple myeloma cells mediated by soluble factors that are currently investigated.