The mouse chorionic gonadotropin β-subunit-like (muCGβ1) molecule produced by tumor cells elicits the switch of T-cell immunity response from T_H2 to T_H1 in mice immunized with DNA vaccine based on rhesus monkey homologous CGβ (rmCGβ)

Background. CGβ is expressed not only in placenta, but also in a wide range of tumors. To study DNA vaccine based on xenogeneic CGβ for cancer immuno-therapy, we investigated whether rhesus monkey CGβ (rmCGβ) DNA vaccine could induce protective T-cell responses and humoral responses in mouse. Methods. We constructed a plasmid containing the rmCGβ coding sequence. Two cloned syngeneic SP2/0 myeloma cell lines that stably express muCGβ1 (SP2/0-muCGβ1) and HN (SP2/0-HN) protein were established. Inoculation of these cell lines was made into mice that had been immunized with DNA vaccine. Specific IgG and IgG type were measured by ELISA and the cytokine expression was detected with RT-PCR. To measure the lymphocyte metabolic activity, the MTS assay was used. Results. After injection of SP2/0-muCGβ into mice that had been immunized with DNA vaccine, a significant increase in the IgG2a specific to the antigen (p < 0.05) and a decrease in the specific IgG1 (p < 0.05) were measured. The expression of T_H1 but not T_H2 cytokines, including IFN-γ and IL-2, were detected in the splenocytes. However, injection of tumor cells expressing irrelevant or mock molecules into immunized mice could not induce these changes. The survival rate of vaccine-immunized mice injected with SP2/0-muCGβ1 was as high as 58.3% after 55 days. Conclusions. The rmCGβ DNA vaccine has proved to be a potential strategy for protection against tumors with homologous molecules. The muCGβ1 produced by tumors is able to elicit an immunity switch from T_H2 to T_H1 in vaccinated mice.