Department of Immunology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
Front Immunol. 2022 Oct 5;13:996145. doi: 10.3389/fimmu.2022.996145. eCollection 2022.
The tumor microenvironment (TME) is a significant contributor to cancer progression containing complex connections between cellular and chemical components and provides a suitable substrate for tumor growth and development. Growing evidence shows targeting tumor cells while ignoring the surrounding TME is not effective enough to overcome the cancer disease. Fibroblasts are essential sentinels of the stroma that due to certain conditions in TME, such as oxidative stress and local hypoxia, become activated, and play the prominent role in the physical support of tumor cells and the enhancement of tumorigenesis. Activated fibroblasts in TME, defined as cancer-associated fibroblasts (CAFs), play a crucial role in regulating the biological behavior of tumors, such as tumor metastasis and drug resistance. CAFs are highly heterogeneous populations that have different origins and, in addition to their role in supporting stromal cells, have multiple immunosuppressive functions a membrane and secretory patterns. The secretion of different cytokines/chemokines, interactions that mediate the recruitment of regulatory immune cells and the reprogramming of an immunosuppressive function in immature myeloid cells are just a few examples of how CAFs contribute to the immune escape of tumors through various direct and indirect mechanisms on specific immune cell populations. Moreover, CAFs directly abolish the role of cytotoxic lymphocytes. The activation and overexpression of inhibitory immune checkpoints (iICPs) or their ligands in TME compartments are one of the main regulatory mechanisms that inactivate tumor-infiltrating lymphocytes in cancer lesions. CAFs are also essential players in the induction or expression of iICPs and the suppression of immune response in TME. Based on available studies, CAF subsets could modulate immune cell function in TME through iICPs in two ways; direct expression of iICPs by activated CAFs and indirect induction by production soluble and then upregulation of iICPs in TME. With a focus on CAFs' direct and indirect roles in the induction of iICPs in TME as well as their use in immunotherapy and diagnostics, we present the evolving understanding of the immunosuppressive mechanism of CAFs in TME in this review. Understanding the complete picture of CAFs will help develop new strategies to improve precision cancer therapy.
肿瘤微环境(TME)是癌症进展的重要贡献者,其中包含细胞和化学成分之间的复杂联系,并为肿瘤生长和发展提供了合适的基质。越来越多的证据表明,仅针对肿瘤细胞而忽略周围的 TME 不足以克服癌症疾病。成纤维细胞是基质的重要哨兵,由于 TME 中的某些条件,如氧化应激和局部缺氧,成纤维细胞被激活,并在肿瘤细胞的物理支持和肿瘤发生的增强中发挥突出作用。TME 中被定义为癌相关成纤维细胞(CAFs)的激活成纤维细胞在调节肿瘤的生物学行为方面发挥着关键作用,例如肿瘤转移和耐药性。CAFs 是高度异质的群体,具有不同的起源,除了它们在支持基质细胞方面的作用外,还具有多种免疫抑制功能,包括膜和分泌模式。不同细胞因子/趋化因子的分泌、调节免疫细胞募集的相互作用以及未成熟髓样细胞中免疫抑制功能的重编程,只是 CAFs 通过各种直接和间接机制对特定免疫细胞群体促进肿瘤免疫逃逸的几个例子。此外,CAFs 直接消除了细胞毒性淋巴细胞的作用。TME 隔室中抑制性免疫检查点(iICPs)或其配体的激活和过表达是使肿瘤浸润淋巴细胞失活的主要调节机制之一癌症病变中的淋巴细胞。CAFs 也是诱导或表达 iICPs 以及在 TME 中抑制免疫反应的重要参与者。基于现有研究,CAF 亚群可以通过 TME 中的 iICPs 以两种方式调节免疫细胞功能;激活的 CAFs 直接表达 iICPs 和通过产生可溶性因子间接诱导,然后上调 TME 中的 iICPs。本综述重点介绍了 CAFs 在 TME 中诱导 iICPs 的直接和间接作用及其在免疫治疗和诊断中的应用,以展示对 TME 中 CAFs 免疫抑制机制的不断发展的认识。了解 CAFs 的全貌将有助于开发新的策略来改善精准癌症治疗。