乳腺癌是女性最常见恶性肿瘤，转移是其致死主因，有研究提示转移发生与转移前免疫微环境形成密切相关，还报告中性粒细胞在其中具有重要作用，但因中性粒细胞异质性导致其机制存在争议。我们动物研究首次发现乳腺癌肺转移前免疫微环境形成的起始时间节点早于文献报道，与一群新型衰老中性粒细胞亚群（aging neutrophil，Naging）密切相关，还发现Naging能促进肺转移。为此，我们利用动物肺转移模型，拟通过流式细胞分选、高通量转录组测序、活细胞体内示踪等技术，系统性探索Naging在乳腺癌肺转移前免疫微环境形成初始的作用及关键机制；明确Naging生物学特性及其诱导机制；评价靶向干预Naging及其关键诱导因子对阻断乳腺癌肺转移的应用价值。由此提出“衰老诱导因子-新型Naging-转移前免疫微环境”促进乳腺癌肺转移的假说。项目完成将丰富转移前免疫微环境相关理论，为防治肿瘤转移提供新思路和新靶点。

Breast cancer is the most common malignant tumor in women and tumor metastasis is the main cause of death. It has been reported that metastasis is closely linked to the formation of pre-metastastic immune niche. Immune cells are one of the major constitutes in the lung to affect metastasis formation, in which neutrophils play an significant role. Owning to neutrophils heterogeneity, numerous research results were inconsistent. In general, the specific mechanism of neutrophils in pre-metastastic immune niche formation need to be further clarified. Our previous animal studies found an accurate time point of breast cancer lung pre-metastastic immune niche, which was earlier than current literature. In addition, a novel group of aging neutrophils (Naging), which was firstly found in tumor, that promoting lung metastasis of breast cancer. Therefore, we set up lung metastatic MMTV-PyMT mammary tumour mouse model and cell lines induced mouse model to carry out a series of studies about pre-metastastic immune niche. The technology platforms comprise flow cytometry sorting, high-throughput transcriptome sequencing, multifactorial screening and living cell tracking in vivo etc. In these way we aim to elaborate the biological characteristics of Naging and its induction mechanism in vivo and in vitro; More crucially, we will uncover the underlying mechanism of Naging in breast cancer lung pre-metastastic immune niche formation; In addition we will evaluate its potential value by targeting Naging and tumor secretory aged inducing factor. Based on these findings, we put forward a scientific hypothesis "Aged inducing factor- A Novel Naging cell- pre-metastastic immune niche" that promotes lung metastasis in breast cancer. These studies will elucidate the roles and mechanisms of novel aging neutrophils subsets in lung metastasis of breast cancer. Furthermore, the subject study will enrich the theoretical knowledge about pre-metastastic immune niche and may help identify novel targets for effective prevention and immunotherapy for human breast cancer metastasis.