In vivo studies showed that dendritic cell (DC) dysfunction occurred in tumor microenvironment. As tumors were composed of many kinds of cells,the direct effects of tumor cells on immature DCs (imDCs) are needed for further studies in vitro. In the present study,bone marrow-derived imDCs were incubated with lymphoma,hepatoma and menaloma cells in vitro and surface molecules in imDCs were determined by flow cytometry. Then,imDCs incubated with tumor cells or control imDCs were further pulsed with tumor lysates and then incubated with splenocytes to perform mixed lymphocyte reaction. The DC-dependent tumor antigen-specific T cell proliferation,and IL-12 secretion were determined by flow cytometry,and enzyme-linked immunosorbent assay respectively. Finally,the DC-dependent tumor-associated antigen-specific CTL was determined by enzyme-linked immunospot assay. The results showed that tumor cell-DC incubation down-regulated the surface molecules in imDCs,such as CD80,CD54,CD11b,CD11a and MHC class Ⅱ molecules. The abilities of DC-dependent antigen-specific T cell proliferation and IL-12 secretion were also decreased by tumor cell incubation in vitro. Most importantly,the ability for antigenic-specific CTL priming of DCs was also decreased by incubation with tumor cells. In the present in vitro study demonstrated that the defective abilities of DCs induced by tumor cell co-incubation and the co-incubation system might be useful for future study of tumor-immune cells direct interaction and for drug screen of immune-modulation. In vivo studies showed that dendritic cell (DC) dysfunction occurred in tumor microenvironment. As the tumors were composed of many kinds of cells, the direct effects of tumor cells on immature DCs (imDCs) were needed for further studies in vitro. , bone marrow-derived imDCs were incubated with lymphoma, hepatoma and menaloma cells in vitro and surface molecules in imDCs were determined by flow cytometry. Then, imDCs incubated with tumor cells or control imDCs were further pulsed with tumor lysates and then incubated with splenocytes to perform mixed lymphocyte reaction. The DC-dependent tumor antigen-specific T cell proliferation, and IL-12 secretion were determined by flow cytometry, and enzyme-linked immunosorbent assay respectively. determined by enzyme-linked immunospot assay. The results showed that tumor cell-DC incubation down-regulated the surface molecules in imDCs, such as CD80, CD54, CD11b, CD11a and MH The classifications of DC-dependent antigen-specific T cell proliferation and IL-12 secretion were also decreased by tumor cell incubation in vitro. Most importantly, the ability for antigenic-specific CTL priming of DCs was also decreased by incubation In the present in vitro study demonstrated that the defective abilities of DCs induced by tumor cell co-incubation and the co-incubation system might be useful for future study of tumor-immune cells direct interaction and for drug screen of immune- modulation.