IL-21诱导M2型肿瘤相关巨噬细胞向M1型分化的分子机制

Macrophage plays various important roles in tumor occurrence, development and metastasis. It is often referred to as classical (M1, proinflammatory and antitumor macrophage) and alternative (M2, protumoral and immunosuppressive macrophage) activation. In malignant tumors, tumor-infiltrating macrophage (TAM, tumor-associated macrophage) resemble alternatively activated macrophages (M2-type), that promote tumor growth, angiogenesis and metastasis and suppress antitumor immunity. At present, the regulatory mechanisms of macrophage polarization to M1 and M2 phenotypes are still not clear. The systemic study on the molecular mechanism of macrophage differentiation in tumor microenvironment in vivo is lack. In our previous study, we found that intratumoral injection of IL-21 skewed TAM polarization away from the M2-like phenotype to M1-like phenotype, which dramatically improve the therapeutic effects of anti-Her2/neu antibody. Based on this in vivo model of TAM polarization induced by intratumoral injection of IL-21, this project is designed to detect the gene expression difference between the M1- and M2-like types of TAMs, identify the key molecules regulating macrophage differentiation, and study the molecular mechanisms for these candidate molecules to regulate macrophage differentiation in cell and animal model level. The purpose of this study is to identify the key target regulating differentiation of macrophages in tumor microenvironment, leading to the establishment of new strategies for cancer therapy.

巨噬细胞在肿瘤发生、发展和转移中发挥多种重要生物学作用。巨噬细胞分为经典活化（M1，促炎和抗肿瘤）型和替代活化（M2，抑制免疫和促肿瘤生长）型。进展中的肿瘤，浸润的巨噬细胞（TAM）表现为M2型，具有促肿瘤生长、血管生成、转移和抑制免疫的活性。目前关于巨噬细胞向M1/M2分化的分子调控机制还不清楚，对肿瘤微环境中TAM分化的分子机制更缺乏系统性研究。我们课题组前期研究发现，瘤内注射IL-21能够将促肿瘤生长的M2型TAM转化为抗肿瘤的M1型,显著提高抗Her2/neu抗体的肿瘤治疗效果。本项目在此IL-21体内诱导TAM分化模型的基础上，运用Microarray技术，分析比较M1/M2型肿瘤巨噬细胞的基因表达差异，筛选和鉴定调控M1/M2型巨噬细胞分化的关键分子，并从细胞和动物模型水平上研究其调控巨噬细胞分化的分子机制，从而找到调控肿瘤浸润巨噬细胞极性分化的关键靶点，建立肿瘤治疗新策略。

巨噬细胞在肿瘤发生、发展、转移、以及抵抗治疗化疗中均发挥重要作用，是肿瘤治疗研究的重要靶点。目前以肿瘤相关巨噬细胞（TAM）为靶点的治疗策略主要有：删除巨噬细胞、阻止巨噬细胞向肿瘤浸润、抑制TAM的功能等。我们前期研究发现肿瘤内注射IL-21，能将促肿瘤生长的M2型巨噬细胞转变成抗肿瘤的M1型巨噬细胞，提高抗Her2抗体的肿瘤治疗效果。本项目证明了肿瘤浸润巨噬细胞（TAM）表达IL-21R；IL-21可以直接作用于巨噬细胞并改变其极性；IL-21对TAM的极化作用不依赖于T细胞或NK细胞。为了有效地将IL-21靶向Her2/neu阳性肿瘤，我们通过构建抗Her2/neu抗体与IL-21融合蛋白，将免疫抑制的M2型TAM极化为刺激免疫的M1型，显著增强抗Her2/neu抗体治疗诱发的抗肿瘤免疫反应，提高治疗效果。该部分结果已发表（J Immunol，2015)，将为靶向TAM的肿瘤免疫治疗提供新的思路。此外，我们在IL-21诱导TAM分化过程中，检测了调控单核巨噬细胞分化的重要转录因子的表达水平，同时分析了其蛋白修饰水平对单核细胞分化的调控作用。研究发现SUMO化修饰对单核细胞分化具有重要调控作用，SUMO化水平升高显著抑制单核细胞源树突状细胞的成熟和抗原递呈功能。同时还发现调控单核细胞分化的一个关键转录因子存在较高水平的SUMO化水平，并通过突变鉴定到该转录因子的一个SUMO化位点。这些发现为日后的研究提供了重要线索和理论依据，开辟了新的重要方向。