骨肉瘤细胞来源外泌体诱导CCL22分泌招募gMDSC塑造肺转移前龛的作用及机制研究

肺转移前龛（pre-metastatic niche）是肿瘤肺转移形成的关键影响因素。前期发现骨肉瘤肺转移前龛中富集粒细胞型髓源性抑制细胞（gMDSC），靶向清除gMDSC可抑制肺转移；深入研究发现骨肉瘤外泌体介导CCL22分泌间接招募gMDSC浸润。由此我们推测“骨肉瘤细胞来源外泌体作用于肺间质细胞，诱导其分泌CCL22，通过CCL22-CCR4招募gMDSC形成肺转移前龛，协助肿瘤肺转移”。本项目将在转基因小鼠、不同骨肉瘤细胞移植瘤模型中，明确骨肉瘤细胞、肺间质细胞及gMDSC之间沟通互作机制；通过单细胞RNA-seq，分析肺转移前龛中gMDSC异质性，揭示其内在亚群分型标记；进一步建立由同位素标记FATP2抗体特异性靶向标记gMDSC，通过SPECT检测骨肉瘤肺转移前龛的方法。本项目成功开展将建立骨肉瘤肺转移前龛gMDSC亚型分布图谱，并为靶向gMDSC早期可视化及治疗肺转移提供依据

Pre-metastatic niche is a key influencing factor in the formation of tumor lung metastasis. We found that granulocytic myeloid-derived suppressor cells (gMDSCs) were profoundly increased in the lung pre-metastatic niche of osteosarcoma. Depleting of gMDSCs using anti-ly6g antibody significantly inhibited lung metastasis. Further study indicated that osteosarcoma cells derived exosomes facilitate the formation of pre-metastatic niche in the lung. Moreover, primary osteosarcoma cells induced CCL22 secretion in the pre-metastatic lung, which could recruit gMDSC infiltration. Hence, we put forward the hypothesis that osteosarcoma cell-derived exosomes act on pulmonary stromal cells, recruiting gMDSCs through CCL22-CCR4 chemokine-chemokine receptor network. This project will identify the interaction mechanism among osteosarcoma cells, pulmonary stromal cells and gMDSCs in transgenic mice and various murine osteosarcoma models. Single-cell RNA-seq will be adopted to reveals the heterogeneity of gMDSCs and specific markers for subgroup typing. Furthermore it will be promising to assess the feasibility of SPECT imaging with 99mTc-FATP2 antibody, a published gMDSCs specific marker, to detect gMDSCs and identify the progression of disease. The successful implementation of this project will establish the distribution map of gMDSCs subtypes in the pre-metastatic niche of osteosarcoma, and illustrate the feasibility of visualizing the pre-metastatic niche using FATP2-antibody based SPECT imaging.