The Mechanism Of GC-MSCs Promote Gastric Cancer Cells Immune Escape Through Regulating PD-1/PD-L1 Pathway

Objective: First,we want to explore the influence of gastric cancer tissues-derived mesenchymal stem cell-like cells(GC-MSCs)to induce the expression of surface molecule programmed death 1(PD-1)and programmed death-ligand 1(PD-L1)on gastric cancer cells in tumor microenvironment.Next,we will study the mechanism of the regulation by GC-MSCs to PD-L1 expression.The last,we get ready ro reveal the important role of GC-MSCs in immune escape and to provide the experimental basis to clarify the GC-MSCs immune regulation mechanism.Methods: The expression of PD-1 and PD-L1 in gastric cancer tissues and its corresponding para-carcinoma tissues were detected by immunohistochemistry and Western blot.The expression of PD-1 and PD-L1 in gastric cancer cell lines were tested by Flow cytometry and verified by Western blot.The supernatant of GC-MSCs and BM-MSCs were collected to be used to treat SGC-7901 and MGC-803 cells for24 h,then,Flow cytometry was utilized to exam the expression of PD-L1 on gastric cancer cells treated with the supernatant and immunofluorescence was used to confirm.Killing effect of activated peripheral blood mononuclear cell(PBMC)to gastric cancer cells stimulated by supernatant of mesenchymal stem cells(MSCs)was detected through LDH method.In order to explore the mechanism of PD-L1 regulation by GC-MSCs to cancer cells,c-Myc inhibitor JQ1 was used to treat SGC-7901 and MGC-803 cells for 24 h,subsequently,PD-L1 expression were examed by Western blot.Apoptosis of tumor cells treated by 1?M/m L JQ1 detected by Flow cytometry,simultaneously,part of treated tumor cells co-cultured with activated PBMC at the ratio of 1:10 for 48 h,crystal violet staining was utilized to observe the survival tumor cells after being killed by PBMC.Results: Not only in gastric cancer tissues but also in corresponding para-carcinoma tissues,PD-1 and PD-L1 both have expressed,particularly,PD-1 and PD-L1 expression in tumor tissues is markedly higher than that in tissue adjacent to carcinoma.Different expression level of PD-1 and PD-L1 are in gastric cancer cell lines,among SGC-7901,MGC-803,HGC-27,BGC-823 and AGS cells,SGC-7901 cells are with higher PD-L1,PD-1 expression and MGC-803 cells are with lower expression.GC-MSCs can up-regulate the expression of PD-L1 on gastric caner cells at the same time,gastric cancer cells treated by supernatant of GC-MSCs are easier to escape lymphocyte killing,however,above mentioned functions of BC-MSCs are indistinctive.Our preliminary mechanism study suggested that GC-MSCs induce PD-L1 expression of gastric cancer cells through c-Myc,and JQ1,the inhibitor of c-Myc,was utilized to treat gastric cancer cells,consequently,with the decreased expression of c-Myc,PD-L1 also have been inhibited.Accordingly,tumor immune escape derived by GC-MSCs has been repressed with c-Myc inhibition.Conclusions: GC-MSCs up-regulated PD-L1 expression through c-Myc and induced the immune escape of gastric cancer cells.The difference of cytokines between GCMSC-CM and BMMSC-CM may be the key factor in PD-L1 regulation of gastric cancer cells by GC-MSCs,which will be a promising target of immune therapy for anti-PD-1 and anti-PD-L1 in gastric cancer.