The Effect Of Cancer-associated Fibroblasts Subgroups Leading To Poor ICB Response And Its Possible Regulatory Mechanism In Gastric Cancer

Background:Gastric cancer(GC)is the third leading cause of cancer deaths worldwide.Immune checkpoint blockade(ICB)has shed light on cancer treatment in a variety of solid tumors,but the benefit of anti-PD1 monotherapy provides less than 20%survival benefits for advanced GC patients.The tumor microenvironment(TME)is considered one of the important reasons for ICB resistance.Cancer-associated fibroblasts(CAFs)are the most abundant population in the TME,and play a key role in tumorigenesis,metastasis,cancer stem cell renewal,chemoresistance,and immune escape.CAFs have been proven to be highly heterogeneous,and have been reported to be associated with ICB resistance,but the mechanism has not been fully reported.Methods:Our previous single-cell RNA-seq of GC revealed that POSTN+FAP+extracellular matrix CAFs(eCAFs)communicated with macrophages.We first used immunofluorescence staining to identify the existence of eCAFs in tissue samples of GC patients.The correlation between eCAFs and ICB response was evaluated in TCGA-STAD and real-world GC patients.Then we performed immune infiltration analysis and correlation analysis to understand the relationship between eCAFs and macrophage chemotaxis.Subsequently,we extracted human gastric cancer cell lines exosomes and constructed eCAFs in vitro.Overexpression and knockdown of POSTN-CAFs were carried out to explore the effect of POSTN expression level on the chemotaxis of macrophages in vitro and in vivo.The underlying mechanisms were investigated using qRT-PCR,Western blotting,lentiviral transduction,IHC,IF,and chemotaxis assays.All statistical analyses were carried out by R software(v.4.0.2).Results:We first confirmed first confirmed the existence of POSTN+FAP+eCAF subpopulations in tumour tissues of GC patients.We retrospectively analysed that the abundance of eCAFs was negatively correlated with the ORR of anti-PD1 in TCGA-STAD and real-world GC patients.Then we found that MSCs could uptake gastric tumor cells exosomes and differentiate into CAFs with high expression of POSTN and FAP.Overexpression of POSTN in CAFs strengthened macrophage chemotaxis,while CAFs with POSTN interference showed the opposite result in vitro and in vivo.Consistently,the cell density of POSTN+CAFs was positively correlated with CD 163+macrophages in the tumour tissues of GC patients.The results showed that POSTN secreted by CAFs enhanced macrophage chemotaxis by activating the Akt signalling pathway in macrophages in vitro and vivo.In addition,we found that POSTN+FAP+eCAFs might exist in multiple solid tumours and are relevant for ICB resistance.Conclusion:eCAFs promoted macrophage chemotaxis via the secretion of POSTN.High expression of POSTN likely predicts poor response to ICB in GC and multiple solid tumours.POSTN downregulation may be considered a candidate therapeutic target to improve ICB efficacy.