Tumor antigen-pulsed CD8α+ dendritic cells induce T cell-mediated graft-versus-tumor effect in vitro

The graft-versus-tumor (GVT) effect of T cells induced by tumor antigen-pulsed CD8 alpha(+) dendritic cells (DCs) in vitro was investigated in this study. Immature CD8 alpha(+) DCs were prepared from C57BL/6 (H-2(b)) bone marrow cells by using a cytokine cocktail. On the 3rd day of culture, CD8 alpha(+) DCs were pulsed by allogeneic (Balb/c, H-2(d)) EL9611 leukemia antigen, or RM-1 syngeneic prostate cancer antigen, with the concentration series of 0, 2.5, 5.0, 10.0, 20.0 mu g/mL, respectively, then antigen-loaded immature CD8 alpha(+) DCs were co-cultured with syngeneic T cells according to the DC/T ratio of 1:1, 2:1 and 4:1. T cell proliferation was measured by MTT assay. Cytokines including interferon gamma (IFN-gamma) and interleukin-10 (IL-10) in CD8 alpha(+) DCs and T co-culture supernatant were detected by using ELISA. Cytotoxic effect of antigen-specific T cells was tested by LDH release assay. Conventional mature DCs (mDCs) induced from C57BL/6 (H-2(b)) bone marrow cells by using granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) served as a control. The results showed that the proliferative activity of T cells stimulated by CD8 alpha(+) DCs loaded with allogeneic or syngeneic tumor antigen was augmented with the CD8 alpha(+) DC/T ratio increased (P < 0.05). When antigen concentration a parts per thousand currency sign 5 mu g/mL and CD8 alpha(+) DC/T ratio a parts per thousand currency sign 2:1, the ability of CD8 alpha(+) DCs to stimulate T cell proliferation was higher than mDC control in allogeneic tumor antigen-pulsed groups (P < 0.05), but not in syngeneic tumor antigen-pulsed groups (P > 0.05). The level of IFN-gamma and IL-10 in CD8 alpha(+) DCs and T cell co-culture supernatant were increased in both allogeneic and syngeneic antigen-pulsed groups (P < 0.05), and the cytokine level was higher in allogeneic antigen-pulsed groups than in syngeneic antigen groups when the CD8 alpha(+) DC/T was 1:1 or 2:1 (P < 0.05). There existed a negative correlation between the level of IL-10 and T cell proliferation. T cell cytotoxicity assay showed that when CD8 alpha(+) DCs were pulsed with allogeneic tumor antigen, the maximal T cell killing efficiency could reach (100 +/- 7.7)%, whereas syngeneic tumor antigen-pulsed group had only (65.0 +/- 3.4)%. It was concluded that syngeneic and allogeneic tumor antigen-pulsed immature CD8 alpha(+) DCs could stimulate T cells to exert the GVT effect in vitro, and the GVT effect was more obvious with allogeneic tumor antigen than with syngeneic tumor antigen. The optimal condition was low allogeneic tumor antigen pulsation (a parts per thousand currency sign 5 mu g/mL) and low CD8 alpha(+) DC/T ratio (1:1 and 2:1).