Remodeling Chondroitin-6-sulfate-mediated Immune Exclusion Enhances Anti-PD-1 Response In Microsatellite-stable Colorectal Cancer

BackgroundImmune checkpoint inhibitors represented by anti-PD/1/PD-L1 have changed the pattern of tumor treatment.Immunotherapy has become the standard treatment for patients with microsatellite instability-high colorectal cancer.However,compared with 5?15%of microsatellite instability-high patients,immunotherapy for microsatellite-stable(MSS)colorectal cancer patients,which accounts for nearly 90%,is barely effective.The reasons for the poor response to immunotherapy of MSS colorectal cancer include:low tumor mutation burden,insufficient tumor neoantigens,low tumor infiltrating lymphocytes,and increased infiltration of immunosuppressive cells(such as tumor-associated macrophages).In response to the above mechanisms,a number of studies have tried to prevent immune evasion using drugs including the bispecific antibody that increases antigen presentation,the MEK inhibitor that regulates the MAPK pathway,regorafenib that improves the tumor microenvironment,and adenosine receptor inhibitors that regulate metabolism.Immunometabolism is an emerging field that investigates the interaction between the immune system and metabolic processes.Nutrient substrates competition or metabolic products accumulation regulate the infiltration and activity of immune cells.In-depth exploration of the interaction of immune metabolism may provide new ideas for solving the dilemma of MSS colorectal cancer immunotherapy.Methods and ResultsWe performed unsupervised clustering based on comprehensive metabolic pathway in the TCGA MSS colorectal cancer cohort,and identified 3 types of significantly different metabolic subtypes.Among them,patients with stroma metabolism subtypes have the worst prognosis.Stroma metabolism subtype had high level of M2 macrophages,stroma remodeling,angiogenesis and TGF-? signaling,which are immune exclusion phenotype markers.Therefore,we extend it to the stroma metabolism-immune exclusion phenotype.Transcriptome association analysis showed that chondroitin sulfate metabolism is a key immune evasion factor for stroma metabolism.We enrolled a cohort(n=96)of tissue specimens from MSS colorectal cancer primary tumors in three clinical centers and performed digital pathological analysis of metabolites and immune cells.Results indicated that chondroitin-6-sulfate of stromal cells in the invasive margin correlates with M2 macrophages accumulation and CD8+T cell immune exclusion phenotype.Further through 2D/3D co-culture models,immunofluorescence and flow cytometry,we found that the chondroitin-6-sulfate metabolites were derived from cancer-associated fibroblasts and could synergistically activate JAK/STAT3 and Hedgehog pathways to induce M2 polarization of macrophages.Finally,in vivo models confirmed that targeting chondroitin-6-sulfate can significantly enhance the efficacy of anti-PD-1 monoclonal antibody in MSS colorectal cancer;the combination of chemotherapy or regorafenib can achieve better therapeutic effects and become potential combination therapy strategy.ConclusionThis study found that the chondroitin-6-sulfate metabolite is a key factor in the immune evasion of MSS colorectal cancer.Specifically,chondroitin-6-sulfate metabolites were derived from cancer-associated fibroblasts and could synergistically activate JAK/STAT3 and Hedgehog pathways to induce M2 polarization of macrophages.The combined strategy of targeting chondroitin-6-sulfate and anti-PD-1 antibody enhances the immunotherapy efficacy of MSS colorectal cancer.