Objectives Interleukin 21 (IL-21) and IL-12 have been known to be effective antitumor agents. In this study, we evaluated whether IL-21 in combination with IL-12 could enhance the cytotoxicity of peripheral blood mononuclear cells (PBMCs) in patients with cervical intraepithelial neoplasia III and cervical cancer.

Methods Peripheral blood mononuclear cells were isolated from peripheral blood of cervical intraepithelial neoplasia III patients (n = 17) and cervical cancer patients (n = 18). Peripheral blood mononuclear cells were cultured with IL-2 in low concentration as control group. Interleukin 2–stimulated PBMCs were cocultured with anti–human IL-21 neutralizing antibody, IL-21 alone, IL-12 alone, and IL-21 plus IL-12, respectively, as test groups. The cytotoxicity of PBMCs against SiHa tumor cells was examined by lactate dehydrogenase released assay. CD4⁺CD25⁺FOXP3⁺ T regulatory (Treg) cells and CD4⁺IL-17A⁺ T helper 17 (T_H17) cells were analyzed by flow cytometry. Proliferation and apoptosis were detected by CCK-8 (cell counting kit 8) assay and flow cytometry, respectively.

Results Compared with controls, IL-21 and IL-12 significantly elevated PBMC cytotoxicity against SiHa cells. Moreover, IL-21 plus IL-12 significantly elevated PBMC cytotoxicity in comparison to IL-21 alone and IL-12 alone. We also found that IL-21 plus IL-12 significantly decreased Treg and T_H17 cell proportion in comparison to controls. Notably, IL-21 plus IL-12 significantly decreased T_H17 cell proportion in comparison to IL-21 alone. Both IL-21 and IL-12 significantly decreased the apoptosis rate of PBMCs, whereas neither IL-21 nor IL-12 had significant effect on PBMC proliferation.

Conclusions The combination of IL-21 and IL-12 could efficiently stimulate PBMCs with cytotoxicity against SiHa cells, and the possible mechanisms may be due to down-regulated Treg and T_H17 cell differentiation.