S100A8诱导PD-L1表达参与肿瘤免疫逃逸的机制

肿瘤检查点抑制剂(anti-PD-1、PD-L1、CTLA4等)成为肿瘤治疗的新希望，寻找能预测其疗效的标志物，及其作用的分子机制成为当务之急。调控PD-L1表达的机制包括细胞外的因素，如炎症因子；和细胞内源性因素，如遗传变异和表观遗传变异。我们前期发现炎症介质钙卫蛋白S100A8、A9在小鼠溃疡性结肠炎-癌变转化全过程中持续高表达，招募巨噬细胞，促进结肠癌细胞增殖和侵袭转移。自制的anti-S100A9的中和抗体能有效治疗该小鼠疾病模型。我们新近发现，S100A8、A9蛋白能够显著升高巨噬细胞的PD-L1表达水平，抑制T细胞增殖与功能，促进肿瘤的免疫逃逸。本项目中，我们将全面分析S100A8诱导巨噬细胞表达PD-L1，及其促进肿瘤免疫逃逸的机制，并利用临床标本和PDX模型探讨它作为预测标志物和治疗靶点的可能性。

Cancer immunotherapy has become highly successful against an array of distinct hematological.and solid metastatic malignancies. Immune checkpoint inhibitors (ICIs) targeting the PD-1, PD-L1, and CTLA-4 induce sustained clinical responses in a sizable minority of cancer patients. To identify proper biomarkers that correlate with response to ICIs therapy, and the underlying mechanisms of the therapy has becoming an urgent task. .PD-L1 and PD-L2 engage PD-1 on T cells and induce PD-1 signaling, which then causes multiple effects in T cells including exhaustion, alterations in glycolytic and mitochondrial metabolism, and reduced cell cycle activity. Tumor cells (or macrophages, dendritic cells) expressing PD-L1 on their surface use the PD-1 pathway to evade an effective antitumor immune response. The regulation factors of PD-L1 expression has been under intensive investigation, which includes extrinsic factors such as inflammatory cytokines, and intrinsic factors, such as genetic mutation of oncogene (e.g. c-Myc, K-RAS, JAK, etc) and epigenetic mechanisms. .We previously dynamically and globally dissect the alteration of key pathways and molecules in the development from colitis to colorectal cancer in the AOM-DSS murine model. Evidence from our gene expression profiling reveals that pro-inflammatory cytokines S100A8/A9 were strikingly upregulated throughout the entire process of AOM-DSS induced inflammation-cancer link. .We reported that S100A8 was induced by inflammation and then promoted colorectal tumorigenesis downstream by activating Id3. S100A8 and S100A9 acted as chemoattractant proteins by recruiting macrophages, promoting the proliferation and invasion of colon cancer cell, as well as spurring the cycle that culminates in the acceleration of cancer metastasis in a nude mouse model. S100A8 regulated colon cancer cell cycle and proliferation by inducing Id3 expression while inhibiting p21. .Administration of a neutralizing anti-S100a9 antibody significantly ameliorated AOM-DSS -induced colitis-related carcinogenesis. Gene expression profiling showed that key pathways known to be involved in colitis-related carcinogenesis process, such as Wnt signaling pathway, PI3K–Akt signaling pathway, cytokine–cytokine receptor interaction, and ECM–receptor interaction pathway, were suppressed after treatment with anti-S100a9 antibody in the AOM-DSS mouse model. .We recently discovered that S100A8 and S100A9 proteins can promote the expression of PD-L1 of murine macrophage cells. The underlying mechanism is related to TLR4-NF-kB pathway, as well as other possibilities. The upregulation of PD-L1 in macrophages can inhibit T cell proliferation, CD8+T cell killing function and inhibit T cell IL4, IL17a, IFN-g secretion. Treatment cells with anti-PD-L1 neutralizing antibody to block PD1-PD-L1 pathways can reverse the inhibition of T cell functions. We also found that S100A8 treated macrophages promoted tumor immune evasion in vivo. .Based on these findings, we suggest a hypothesis in this proposal that the inflammatory mediator S100A8 is an important extrinsic inducer of PD-L1 for macrophages. S100A8 could be a useful biomarker for predicting the outcome of anti-PD-L1 therapy in clinic. Targeting of S100A8 will be a promising strategy to assist immune checkpoint inhibitors. .In this study, we will dissect the molecular mechanisms underlying how S100A8 regulating PD-L1 expression in macrophages. By inducing PD-L1, how S100A8 inhibits anti-tumor responses initiated by macrophages (as antigen-present cells) and T cells (as effect cells) both in vitro and in vivo. We will promote our study in clinic specimens to evaluate the utility for S100A8 levels as biomarker for predicting the outcome of anti-PD-L1 therapy in cancer patients. PDX (Patient-derived xenograft) model will be employed to assess whether targeting S100A8 is helpful for immune checkpoint blockade.