Abstract: Objective The Objective of this study was to identify the feasibility of adoptive reinfusion in NK cells to treat colorectal cancer and to explore new therapeutic strategies by detecting the killing efficiency of NK cells and PD-1 monoclonal antibody(mAb)+ NK cells in five kinds of colorectal cancer cell lines. Methods NK cells were cultured by inducing peripheral blood mononuclear cells in vitro,and a CCK-8 assay was used to detect NK cells and PD-1 mAb + NK cells to kill the efficiency of five colorectal cancer LOVO,Caco-2,HT-29,HT-115 and HRT-18 cell lines,the ratio of effect-to-target,and compare the killing effects of the two effector groups on colorectal cancer cells through statistics. Results The killing efficiencies of NK cells against the five target cells were significantly different(P＜0.01).The killing efficiencies of NK cells against the same target cells were significantly different at different effect target ratios(P＜0.05).The killing efficiencies of PD-1 mAb combined with NK cells on Caco-2(effect-target-ratio 2∶1),HT-29(effect-target-ratio 5∶1 and 10∶1)and HT-115(effect-target-ratio 0.1∶1 and 0.5∶1)cells were significantly different from those of NK cells alone(P＜0.05),and there was no significant difference among other groups(P＞0.05). Conclusion When using NK cells adoptive transfusion to treat colorectal cancer,controlling the effect-target ratio at 2:1 may be a safe and effective ratio;Killing efficiency of NK cells on colorectal cancer has nothing to do with its degree of differentiation;PD-1 mAb can be combined with adoptive reinfusion of NK cells in the treatment of colorectal cancer and has certain therapeutic significance.

Key words: NK cells, PD-1 mAb, Colorectal cancer, Effect-target ratio, Combination therapy