Abstract： Objective To study the combined effect of interleukin-21 gene transfer and ionizing radiation on the growth of cervical carcinoma HeLa cells.Methods Previously constructed Ad-IL-21 gene was amplified by infecting 293A cells and the titer was measured by TCID50 method. HeLa cells were transfected with Ad-1L-21 and then irradiated with 6 Gy 137Cs γ-rays.The cells were divided into 5 groups,including blank control,Ad-LaeZ group,Ad-IL-21 group,radiation group and Ad-IL-21 combined with radiation group (combination group).The cell growth,cell cycle,apoptosis,and the expressions of IL-21 gene and protein in HeLa cells were detected.Results Ad-IL-21 was successfully amplified and the titer of Ad-11.-21 was 9 × 1010 pfu/ml.Compared with Ad-IL-21 group and radiation group,the cell growth of combination group was significantly inhibited at 96 h after transfection ( F =85.26,72.98,P ＜ 0.05 ).The cells in combination group were arrested in G1 phase and decreased at S phase( F =36.69,34.83,P ＜ 0.05),while the cellular apoptosis increased markedly ( F =28.23,25.57,P ＜ O.05 ). The gene expression of 1L-21 in the combination group was 1.54- and 2.43-fold of Ad-IL-21 group and blank control group,respectively (F=22.31,36.65, P ＜ 0.05 ), while the protein expression of IL-21 in the combination group was 1.62-fold and 2.31-fold of Ad-IL-21 group and blank control group,respectively ( F =27.36,35.86,P ＜ 0.05 ).Conclusions Ad-IL-21 gene transfection combined with radiation has synergic effect on the inhibition of cervical carcinoma cell growth.