Department of Oncology, Nanfang Hospital, Southern Medical University, Guangzhou, 510515, Guangdong, P. R. China.
Department of Cardiology, Nanfang Hospital, Southern Medical University, Guangzhou, 510515, Guangdong, P. R. China.
Cancer Commun (Lond). 2023 May;43(5):562-581. doi: 10.1002/cac2.12420. Epub 2023 Apr 8.
Several clinical studies have uncovered a negative correlation between baseline tumor burden and the efficacy of immune checkpoint inhibitor (ICI) treatment. This study aimed to uncover the specific mechanisms underlying the difference in sensitivity to ICI treatment between tumors with high (HTB) and low (LTB) tumor burden.
For in vivo studies, several mouse models of subcutaneous tumors were established, and transcriptome sequencing, immunohistochemistry, and flow cytometry assays were used to detect the immune status in these subcutaneous tumors. For in vitro experiments, co-culture models, cytokine antibody arrays, western blotting, flow cytometry, and enzyme-linked immunosorbent assays were used to explore the underlying molecular mechanisms RESULTS: We found that MC38 or B16 subcutaneous tumors from the HTB group did not show any response to anti-programmed cell death protein-1 (PD-1) therapy. Through flow cytometry assays, we found that the infiltration with CD8 T cells was significantly decreased whereas M2-like macrophages were enriched in subcutaneous tumors of HTB groups compared with those of LTB group. These changes were not affected by the initial number of injected tumor cells or tumor age, nor could they be reversed by surgical tumor reduction. Intraperitoneal colony-stimulating factor 1 receptor (CSF-1R) inhibitor PLX3397 injection at different time points of tumor growth only had an effect when administered in the early tumor stage to maintain the "heat" of the tumor microenvironment during the process of tumor growth, thereby achieving a response to ICI treatment when the tumor grew to a large size. Mechanistically, we found that insulin-like growth factor binding protein 2 (IGFBP2) expression levels were significantly elevated in HTB tumor tissues. IGFBP2 promoted the programmed death-ligand 1 (PD-L1) expression in M2-like macrophages by activating signal transducer and activator of transcription 3 (STAT3), and PD-L1 M2-like macrophages exerted an immunosuppressive effect by inhibiting the proliferation and activation of CD8 T cells in a PD-L1-dependent fashion.
This study suggested that the low efficacy of ICI treatment in HTB tumors is mainly attributed to the intratumoral accumulation of PD-L1 M2-like macrophages via the IGFBP2-STAT3-PD-L1 signaling pathway and their substantial inhibitory effects on T cell proliferation and activation.
几项临床研究发现，基线肿瘤负担与免疫检查点抑制剂（ICI）治疗效果之间存在负相关。本研究旨在揭示高（HTB）和低（LTB）肿瘤负担肿瘤对 ICI 治疗敏感性差异的具体机制。
进行体内研究时，建立了几种皮下肿瘤的小鼠模型，并通过转录组测序、免疫组织化学和流式细胞术检测这些皮下肿瘤的免疫状态。进行体外实验时，采用共培养模型、细胞因子抗体阵列、Western blot、流式细胞术和酶联免疫吸附试验来探讨潜在的分子机制。
我们发现 MC38 或 B16 皮下肿瘤来自 HTB 组，对抗程序性细胞死亡蛋白-1（PD-1）治疗没有任何反应。通过流式细胞术检测，我们发现与 LTB 组相比，HTB 组的皮下肿瘤中 CD8 T 细胞浸润明显减少，而 M2 样巨噬细胞丰富。这些变化不受注射肿瘤细胞的初始数量或肿瘤年龄的影响，也不能通过手术切除肿瘤来逆转。在肿瘤生长的不同时间点给予腹腔内集落刺激因子 1 受体（CSF-1R）抑制剂 PLX3397 注射，仅在早期肿瘤阶段给药时有效，以维持肿瘤生长过程中肿瘤微环境的“热度”，从而在肿瘤生长到较大大小时对 ICI 治疗产生反应。从机制上讲，我们发现 HTB 肿瘤组织中胰岛素样生长因子结合蛋白 2（IGFBP2）的表达水平显著升高。IGFBP2 通过激活信号转导和转录激活因子 3（STAT3）促进 M2 样巨噬细胞中程序性死亡配体 1（PD-L1）的表达，PD-L1 M2 样巨噬细胞通过 PD-L1 依赖性方式抑制 CD8 T 细胞的增殖和激活发挥免疫抑制作用。
本研究表明，HTB 肿瘤中 ICI 治疗效果不佳主要归因于 IGFBP2-STAT3-PD-L1 信号通路导致肿瘤内 PD-L1 M2 样巨噬细胞的积累及其对 T 细胞增殖和激活的显著抑制作用。
