<p>CT26 cells stably expressing GM-CSF (A) or IL-18 (B) were stained with mouse anti-HA antibody, followed by FITC-conjugated goat anti-mouse IgG for 30 min. Mock-transduced CT26 cells were used as a negative control (black). (C) CT26/GM-CSF/IL-18 was doubly stained by anti-GM-CSF and anti-IL-18 primary antibodies, followed by FITC and PE-conjugated secondary antibodies (Experimental details were described in Materials and Methods). The left panel is negative control, in which CT26/GM-CSF/IL-18 was stained by secondary antibody alone. The right panel is the result of double staining, in which CT26/GM-CSF/IL-18 cells was stained with first and secondary antibodies. Fluorescence intensity of membrane-bound cytokines was analyzed by flow cytometry. (D) Mock-transduced CT26, CT26/GM-CSF, CT26/IL-18, and CT26/GM-CSF/IL-18 cells were seeded into 12-well plates at the density of 5×10<sup>4</sup> cells per well. The number of viable cells of was counted with the hemocytometer every twenty-four hours. Independent experiments were repeated three times.</p
