Abstract: This study aims at constructing three-plasmid system of the lentiviral vector carrying the programmed death ligant 1（PD-L1）gene and investigating the expression of PD-L1 in human breast carcinoma cell MDA-MB-231. A pMAGic 7.1 recombinant lentiviral expression vector,plasmid △8.91 and pVSVG were co-transfected into 293T cells for packaging virus,using polyethylenimine（PEI）as transfected solution. The lentiviral products were added to infect and extract stably-expressed MDA-MB-231 cells,and finally the PD-L1 expression of mRNA and protein levels were detected. The results showed as followings：（1）The PD-L1 expression in MDA-Mb-231 was the highest,compared with other two breast cancer cells. （2）At 48 h after co-transfecting three plasmids,the fluorescence intensity reached over 90%. Moreover,the fluorescence intensity reached almost 20% at 48 h after using virus infecting MDA-MB-231 cells. （3）There were low PD-L1 expressions of mRNA and protein levels in the stably-expressed MDA-MB-231 cell lines,and the pMAGic-sh1 had the best effect on it among the three plasmids. （4）After adding viruses,the cell proliferation declined in interfering groups,and the cell proliferation rate in the pMAGic-sh1 interfering groups was 64.77% at 7 days of adding virus compared with the negative group. （5）Mixed lymphatic experiments showed that the tumor inhibition rate of sh-1 group was 35.8%,which was 3.06 times of that in normal group,and the T lymphocyte proliferation rate significantly enhanced. In conclusion,the three-plasmid system of lentiviral vector containing PD-L1 gene using PEI reagent is successfully established. The study demonstrates that the PD-L1 expression of mRNA and protein is lower through the virus infecting system,and interfering groups have lower cell proliferation rate and they enhance the T lymphocyte proliferation rates and its ability to kill tumor cells.

Key words: breast cancer, programmed death factor ligant 1 gene, lentiviral vector, PEI, co-transfected