间充质干细胞（MSCs）是一群异质的祖细胞，具有多功能作用，包括组织再生、自我更新特性，并可分化为脂肪细胞、成骨细胞和软骨细胞等中胚叶系细胞。MSCs与肿瘤微环境（TME）接触并分化为肿瘤相关的MSC（TA-MSC）。肿瘤细胞释放化学趋化因子、细胞因子、生长因子等物质以吸引MSCs。TA-MSCs诱导上皮间质转化（EMT）程序，介导肿瘤生长进展、迁移和侵袭。MSCs在乳腺癌TME中在肿瘤进展、干细胞性、恶性以及治疗抵抗中的作用。MSCs的免疫调节作用通过细胞接触依赖机制和溶质物质介导。单核细胞/巨噬细胞、树突细胞、T细胞、B细胞和NK细胞均显示出MSCs的免疫调节能力。在由MSCs发起的复杂相互作用中，抗炎单核细胞/巨噬细胞和调节性T细胞（Tregs）发挥关键作用，揭示了它们的完全免疫调节潜力。MSCs分泌的细胞因子通常被认为是MSCs、单核细胞和Tregs之间的相互作用的原因。在这里，我们回顾了有关MSC介导的免疫调节的细胞和分子机制的现有知识，并着重关注MSCs在乳腺癌进展和其TME中的作用。 MSC缩写：间充质干细胞；TME：肿瘤微环境；TAMS：肿瘤相关巨噬细胞；ECM：细胞外基质；CAFs：癌相关成纤维细胞；CFUs：成纤维细胞集落形成单位；Tregs：调节性T细胞；Bregs：调节性B细胞；IFN-γ：干扰素γ；TNF-α：肿瘤坏死因子α；IL：白细胞介素；TGF-β：转化生长因子β；PGE2：前列腺素E2；CXCR：趋化因子受体；Blimp-1：B淋巴细胞诱导的分化蛋白-1；CCL：化学趋化因子结构域配体；EMT：上皮间质转化。

Mesenchymal stem cells (MSCs) are a heterogeneous group of progenitor cells that play a multifunctional role including tissue regeneration, self-renewal properties, and differentiate into cells of mesodermal lineage such as adipocytes, osteoblasts, and chondrocytes. MSCs come into contact with tumor microenvironment (TME) and differentiate into tumor-associated MSCs (TA-MSCs). Various substances such as chemokines, cytokines, growth factors, and others are released by tumor cells to recruit MSCs. TA-MSCs induced epithelial-mesenchymal transition (EMT) program which mediates tumor growth progression, migration, and invasion. Role of MSCs in the tumor progression, stemness, malignancy, and treatment resistance in the breast cancer TME. Immunomodulation by MSCs is mediated by a combination of cell contact-dependent mechanisms and soluble substances. Monocytes/macrophages, dendritic cells, T cells, B cells, and NK cells all show signs of MSCs' immunomodulatory capability. In a complicated interplay initiated by MSCs, anti-inflammatory monocytes/macrophages and regulatory T cells (Tregs) play a key role, as they unveil their full immunomodulatory potential. MSC- secreted cytokines are commonly blamed for the interaction between MSCs, monocytes, and Tregs. Here, we review the current knowledge of cellular and molecular mechanisms involved in MSC-mediated immunomodulation and focus on the role MSCs play in breast cancer progression and its TME.Abbreviation MSC: Mesenchymal Stem Cells; TME: Tumor Microenvironment; TAMS; Tumour-associated Macrophages; ECM: Extracellular matrix; CAFs: Cancer-associated Fibroblasts; CFUs: Colony-forming unit Fibroblasts; Tregs: T regulatory cells; Bregs; Regulatory B cells; IFN-γ: Interferon-gamma; TNF-α: Tumour Necrosis Factor-alpha; IL: Interleukin; TGF-β: transforming growth factorβ; PGE2: Prostaglandin E2; CXCR: Chemokine Receptor; Blimp-1; B lymphocyte-induced maturation protein-1; CCL: Chemokine motif ligand; EMT: Epithelial-mesenchymal transition.