The synergistic anti-tumor effect of radiofrequency and cytokine-induced killer cells in mice

Abstract

Objective This study aimed to evaluate the anti-tumor immunity of the combination treatment with radiofrequency ablation (RFA) and cytokine-induced killer cells (CIK). Methods Mice were inoculated with B16 melonoma or CT26 colon cancer cell line on bilateral flanks, and randomly divided into four groups in which RFA for tumor right flank, CIK cell infusion, RFA plus CIK and no intervention was administrated, respectively. The growth curve of the left tumor and survival curve of mice were recorded. The amount and subset of the lymphocytes infiltrating into the tumor on the left flank were analyzed by flow cytometry in B16 tumor-bearing mice. In addition, the number and phenotype of adoptive CIK migrating into the tumor were tested. Results A short-lived inhibition of tumor growth was observed in mice treated with RFA or CIK alone. Combination treatment with RFA and CIK significantly inhibited the growth of tumors on contralateral flank. The median survival of mice treated with RFA and CIK was (42.0±3.3) d, which was significant longer than that in untreated mice (20.5±2.2) d, RFA alone (26.0±2.2) d, CIK alone (31.5±2.2) d (P<0.01). The number of immune cells, including CD8+ , CD4+ T, natural killer (NK: CD3-NK1.1+ ) and NKT (CD3+ NK1.1+ ), infiltrating into the contralateral tumor, was respectively (2.41±1.03)×106 cell/g tumor, (4.52±1.63)×106 cell/g tumor, (1.62±0.31)×106 cell/g tumor, (0.42±0.08)×106 cell/g tumor, significantly increased in mice treated with RFA plus CIK, as comparing to mice treated with RFA and CIK alone. An elevated CD8+ /regulatory T cells [Treg: CD4+ forkhead box P3 (Foxp3)+ ] ratio (3.85±0.63)and decreased accumulation of myeloid-derived suppressor cells (MDSC), which the frequency in tumor was (8.92±3.05)%, were observed in RFA plus CIK group. Compared to mice treated with surgery plus CIK, the number of adoptive CIK cells migrating into the contralateral tumor was increased in mice treated with RFA plus CIK. In addition, the expressions of Ki-67, inducible costimulator (ICOS) and Granzyme B on adoptive CIK cells were upregulated in RFA plus CIK-treated mice, the frequency was respectively (79.12±1.51)%, (56.13±2.12)%, (63.51±1.82)%. Conclusion RFA promoted adoptive CIK cells migrating into a distant tumor and enhanced the proliferation and activity of intratumoral CIK cells. Combination treatment with RFA and CIK induced a boosted immune response in tumor microenvironment out of ablation zone and resulted in a synergistic anti-tumor effect. Key words: Radiofrequency ablation; Cytokine-induced killer cells; Colon cancer; Melanoma; Anti-tumor immunity