Objective To investigate the effect of epithelial-mesenchymal transition (EMT) on biological activity of natural killer (NK) cells in esophageal squamous cell carcinoma (ESCC). Methods Western blot selected EMT EC9706 and non EMT KYSE150 from six esophageal cancer cell lines. NK cells were collected from 10 cases of healthy volunteers. According to different co-culture conditions, the medium was divided into 1640 normal medium stimulus-NK group (NC group), EC9706 cell supernatant stimulus-NK group (EC9706 group) and KYSE150 cell supernatant stimulus-NK group (KYSE150 group). The expression of NK cells surface/intracellular molecules was detected by flow cytometry after co-culture of NK cells with different conditioned medium for 72 h. 10 ng/mL transforming growth factor-β （TGF-β） treated KYSE150 cell line for 7 d to induce EMT. KYSE150 EMT and KYSE150 supernatant were collected and co-cultured with NK cells, respectively. 72 h later, flow cytometry was used to detect the expression of surface/intracellular molecules of NK cells, degranulation ability of CD107a, killing effect of target cell K562, proliferation and apoptosis of NK cells. Results Two EMT-treated and four non-EMT-treated esophageal squamous cell carcinoma lines were selected from the six strains, and one EC9706 and one KYSE150 respectively were selected for subsequent experiments. The purity of NK cells was more than 90% and T CM(155mm]cells P P P P
