MRC Centre for Reproductive Health, Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, UK.
Cancer Research UK Beatson Institute, Glasgow, UK.
J Immunother Cancer. 2021 Jan;9(1). doi: 10.1136/jitc-2020-001740.
Metastatic breast cancer is a leading cause of cancer-related death in women worldwide. Infusion of natural killer (NK) cells is an emerging immunotherapy for such malignant tumors, although elimination of the immunosuppressive tumor environment is required to improve its efficacy. The effects of this "metastatic" tumor environment on NK cells, however, remain largely unknown. Previous studies, including our own, have demonstrated that metastasis-associated macrophages (MAMs) are one of the most abundant immune cell types in the metastatic tumor niche in mouse models of metastatic breast cancer. We thus investigated the effects of MAMs on antitumor functions of NK cells in the metastatic tumor microenvironment.
MAMs were isolated from the tumor-bearing lung of C57BL/6 mice intravenously injected with E0771-LG mouse mammary tumor cells. The effects of MAMs on NK cell cytotoxicity towards E0771-LG cells were evaluated by real-time fluorescence microscopy. The effects of MAM depletion on NK cell activation, maturation, and accumulation in the metastatic lung were evaluated by flow cytometry (CD69, CD11b, CD27) and hybridization () using colony-stimulating factor 1 (CSF-1) receptor conditional knockout (-cKO) mice. Finally, metastatic tumor loads in the chest region of mice were determined by bioluminescence imaging in order to evaluate the effect of MAM depletion on therapeutic efficacy of endogenous and adoptively transferred NK cells in suppressing metastatic tumor growth.
MAMs isolated from the metastatic lung suppressed NK cell-induced tumor cell apoptosis via membrane-bound transforming growth factor β (TGF-β) dependent mechanisms. In the tumor-challenged mice, depletion of MAMs increased the percentage of activated (CD69) and mature (CD11bCD27) NK cells and the number of NK cells as well as NK cell-mediated tumor rejection in the metastatic site. Moreover, MAM depletion or TGF-β receptor antagonist treatment significantly enhanced the therapeutic efficacy of NK cell infusion in suppressing early metastatic tumor outgrowth.
This study demonstrates that MAMs are a main negative regulator of NK cell function within the metastatic tumor niche, and MAM targeting is an attractive strategy to improve NK cell-based immunotherapy for metastatic breast cancer.
转移性乳腺癌是全球女性癌症相关死亡的主要原因。自然杀伤 (NK) 细胞输注是治疗此类恶性肿瘤的一种新兴免疫疗法，但需要消除免疫抑制性肿瘤微环境才能提高其疗效。然而，这种“转移性”肿瘤微环境对 NK 细胞的影响在很大程度上仍不清楚。之前的研究，包括我们自己的研究，已经表明转移相关巨噬细胞 (MAMs) 是转移性乳腺癌小鼠模型中转移性肿瘤灶中最丰富的免疫细胞类型之一。因此，我们研究了 MAMs 对转移性肿瘤微环境中 NK 细胞抗肿瘤功能的影响。
从经静脉注射 E0771-LG 小鼠乳腺肿瘤细胞的 C57BL/6 小鼠的肿瘤肺部分离 MAMs。通过实时荧光显微镜评估 MAMs 对 NK 细胞对 E0771-LG 细胞的细胞毒性的影响。通过流式细胞术 (CD69、CD11b、CD27) 和集落刺激因子 1 (CSF-1) 受体条件敲除 (-cKO) 小鼠杂交 () 评估 MAM 耗竭对 NK 细胞在转移性肺部的激活、成熟和积累的影响。最后，通过生物发光成像确定小鼠胸部转移性肿瘤负荷，以评估 MAM 耗竭对抑制转移性肿瘤生长的内源性和过继转移 NK 细胞治疗效果的影响。
从转移性肺部分离的 MAMs 通过膜结合转化生长因子β (TGF-β) 依赖性机制抑制 NK 细胞诱导的肿瘤细胞凋亡。在肿瘤挑战的小鼠中，MAMs 的耗竭增加了激活的 (CD69) 和成熟的 (CD11bCD27) NK 细胞的百分比，以及 NK 细胞的数量以及 NK 细胞介导的转移性部位肿瘤排斥反应。此外，MAM 耗竭或 TGF-β 受体拮抗剂治疗显著增强了 NK 细胞输注抑制早期转移性肿瘤生长的治疗效果。
这项研究表明，MAMs 是转移性肿瘤微环境中 NK 细胞功能的主要负调控因子，靶向 MAMs 是提高 NK 细胞为基础的免疫疗法治疗转移性乳腺癌的一种有吸引力的策略。
