Abstract: Objective To assess the effect of tumor cell lysate (TCL) with low high-mobility group B1 (HMGB1) content for enhancing immune responses of dendritic cells (DCs) against lung cancer. Methods TCLs with low HMGB1 content (LH-TCL) and normal HMGB1 content (NH-TCL) were prepared using Lewis lung cancer (LLC) cells in which HMGB1 was inhibited with 30 nmol/L glycyrrhizic acid (GA) and using LLC cells without GA treatment, respectively. Cultured mouse DCs were exposed to different doses of NH-TCL and LH-TCL, using PBS as the control. Flow cytometry was used to detect the expressions of CD11b, CD11c and CD86 and apoptosis of the stimulated DCs, and IL-12 levels in the cell cultures were detected by ELISA. Mouse spleen cells were co-cultured with the stimulated DCs, and the activation of the spleen cells was assessed by detecting CD69 expression using flow cytometry; TNF-β production in the spleen cells was detected with ELISA. The spleen cells were then co-cultured with LLC cells at the effector: target ratios of 5:1, 10:1 and 20:1 to observe the tumor cell killing. In the animal experiment, C57/BL6 mouse models bearing subcutaneous LLC xenograft received multiple injections with the stimulated DCs, and the tumor growth was observed. Results The content of HMGB1 in the TCL prepared using GA-treated LLC cells was significantly reduced (P<0.01). Compared with NH-TCL, LH-TCL showed a stronger ability to reduce apoptosis (P<0.001) and promote activation and IL- 12 production in the DCs. Compared with those with NH-TCL stimulation, the DCs stimulated with LH-TCL more effectively induced activation of splenic lymphocytes and enhanced their anti- tumor immunity (P<0.05). In the cell co-cultures, the spleen lymphocytes activated by LH-TCL-stimulated DCs showed significantly enhanced LLC cell killing activity (P<0.01). In the tumor-bearing mice, injections of LH-TCL-stimulated DCs effectively activated host anti-tumor immunity and inhibited the growth of the tumor xenografts (P<0.05). Conclusion Stimulation of the DCs with LH-TCL enhances the anti-tumor immune activity of the DCs and improve the efficacy of DC-based immunotherapy for LLC in mice.

Key words: tumor cell lysates; mouse splenocytes; lung cancer cells; anti-tumor immunity; HMGB1