Down-regulation of Treg by interference of enhances the killing effect of CIK on leukemia cell HL-60

OBJECTIVE: Cytokine-induced killer cells (CIK) is a type of immune cell with antitumor activity induced by a variety of cytokines. Regulatory T cells (Treg) is a T cell subgroup featured as immunosuppressive function. Existing CIK cultivation system may inevitably induce Treg. Forkhead box protein 3 (Foxp3) is an essential transcription factor for Treg function. This study aimed to investigate the effects of CIK on the leukemia cell HL-60. MATERIALS AND METHODS: This work silenced Foxp3 expression on the basis of CIK induction, aiming to investigate its killing effect on HL-60 cells. Peripheral blood mononuclear cells were separated and differentiated to CIK in vitro. CD3(+)CD56(+) and CD4(+)CD25(+)Foxp3(+) Treg cells were detected by flow cytometry. CIK cells were co-cultured with HL-60 cells under the effector-target ratio at 20:1, 10:1, and 5:1, respectively. The killing activity of CIK on HL-60 cells was determined by CCK-8 assay. RESULTS: The ratio of CD3(+), CD3(+)CD8(+), and CD3(+)CD56(+) cells gradually increased during CIK induction. Foxp3 interference significantly reduced Treg cell ratio on the 7th day (p < 0.05). Treg cell ratio was significantly lower in Foxp3 interference group at 1.62% +/- 0.07% compared with control (p < 0.05). The killing activity of CIK on HL-60 cells enhanced following the increase of effector-target ratio. Interference of Foxp3 significantly elevated the killing activity of CIK on HL-60 cells with effector-target ratio dependence (p < 0.05). CIK can effectively suppress HL-60 cell growth. Treg significantly inhibited the anti-tumor effect of CIK. CONCLUSIONS: Interference of Foxp3 expression significantly declined Treg level and attenuated its suppression impact on CIK, thus enhancing the killing effect of CIK on HL-60 cells.