OBJECTIVETo construct a recombinant plasmid pIRES-GM-CSF-IL-21, and to investigate its antitumor effect on tumors in the mice.

METHODSFifty Bal b/c mice were included in this study. Cultured hepatoma H22 cells were inoculated in the left lobe of the liver to develop orthotopically transplanted liver tumor models. The mice with orthotopically transplanted liver tumor were randomly divided into 5 groups (n = 10): (1) Each mouse received injection of recombinant plasmid pIRES-GM-CSF-IL-21; (2) Received injection of plasmid pIRES-GM-CSF; (3) pIRES-IL-21; (4) Received injection of ampty plasmid pIRES (H22/neo group); (5) Received injection of PBS (H22 group) via the tail vein, respectively. Therefore, the anti-tumor effect was induced by both GM-CSF and IL-21, or by either of them alone. The serum levels of IFN-γ and IL-2 were detected by ELISA, and the cytotoxicity of spleen NK and CTL cells were tested by MTT colorimetry.

RESULTSComparing with the H22 and H22/Neo groups, the tumor weight in the mice of H22/GM-CSF group was (0.603 ± 0.223) g, H22/IL21-treated group (0.583 ± 0.290) g and H22/GM-CSF-IL21-treated group (0.303 ± 0.323) g, significantly lower than that in the H22 group [(1.591 ± 0.280) g] and H22/Neo group [(1.489 ± 0.155) g]. Among them the tumor growth was most significantly inhibited in the H22/GM-CSF-IL-21 group (0.303 ± 0.323) g, compared with that of H22 and H22/neo groups (P < 0.01). But there was no significant difference between the tumor weights of the H22/GM-CSF group and H22/IL-21 group, and between the tumor weights of the H22 and H22/Neo groups (P > 0.05). The levels of IFN-γ and IL-2 in peripheral blood of mouse models treated with H22/GM-CSF-IL-21 were significantly increased than that in the H22/GM-CSF group and H22/IL-21 group (all P < 0.01), but significantly decreased in the H22group and H22/Neo group (P < 0.01). The anti-tumor activity of splenic NK cells and CTLs in the H22/GM-CSF-IL21 group was significantly enhanced (P < 0.01), compared with the significantly decreased in the H22 and H22/Neo groups.

CONCLUSIONSOur results demonstrate apparent antitumor effect of the plasmid pIRES-GM-CSF-IL-21 on the orthotopically transplanted liver tumor in mice. The combination of both pIRES-GM-CSF and IL-21 is more effective than that of pIRES/IL21 or pIRES/GM-CSF treatment alone. In addition, the plasmid pIRES-GM-CSF-IL-21 can also promote the secretion of IFN-γ and IL-2 in vivo, and enhance the cytotoxic activity of splenic NK and CTLs against the transplanted liver tumor.