PO.TB10.17 · 肿瘤生物学
唾液酸-Siglec轴在胰腺癌免疫逃逸中的作用
Role of sialic acid-siglec axis in pancreatic cancer immune evasion
作者与单位 Authors & Affiliations
摘要 Abstract
中文摘要
胰腺导管腺癌（PDAC）是一种侵袭性恶性肿瘤。导致PDAC高致死率的一个关键因素是免疫逃逸。肿瘤细胞通过激活包括巨噬细胞在内的免疫细胞上的免疫检查点蛋白来抑制抗肿瘤免疫。Siglec受体是巨噬细胞上主要的检查点分子之一。Siglec的配体是唾液酸。为通过Siglec实现免疫抑制，PDAC细胞通过上调ST6GAL1等唾液酸转移酶的表达来增加其表面唾液酸化水平。ST6GAL1在N-聚糖上添加alpha2,6连接的唾液酸。在PDAC细胞中，alpha2,6唾液酸化和ST6GAL1表达均显著升高。我们此前的研究揭示了ST6GAL1具有强大的肿瘤自主功能。我们最新的未发表结果提示，ST6GAL1的促瘤效应亦由其为巨噬细胞Siglec创造唾液酸聚糖配体的作用所驱动。极化为免疫抑制性M2表型的巨噬细胞是PDAC进展的关键促成因素。我们研究的目标是确定巨噬细胞Siglec是否为阻止M2极化、从而恢复抗肿瘤免疫并阻止PDAC进展的有前景的治疗靶点。我们在基因工程小鼠PDAC模型中研究了巨噬细胞极化，模型采用胰腺特异性敲入致癌性K-ras（KC小鼠）或K-ras联合ST6GAL1敲入（KSC小鼠）。单细胞RNA测序、流式细胞术和免疫组织化学显示，KSC小鼠胰腺中M2巨噬细胞数量较KC小鼠增多。与过表达ST6GAL1的PDAC细胞共培养的巨噬细胞显示M2标志物表达增加。但加入Siglec阻断抗体可逆转ST6GAL1介导的M2极化，表明ST6GAL介导的巨噬细胞M2极化是通过Siglec信号传导实现的。此外，我们测定了巨噬细胞的吞噬能力，这是巨噬细胞抗肿瘤行为的公认功能读数。免疫荧光显微镜和流式细胞术显示，巨噬细胞的吞噬能力被过表达ST6GAL1的PDAC细胞抑制，但通过Siglec阻断抗体得以恢复。总体而言，我们的数据表明PDAC细胞上的alpha2,6唾液酸与巨噬细胞上的Siglec结合，诱导巨噬细胞极化为免疫抑制性M2表型。综上，这些结果揭示了针对具有高ST6GAL1水平的PDAC患者，将Siglec作为一种有前景的免疫检查点治疗靶点的潜在机制。传统的基于T细胞的检查点治疗在PDAC中疗效有限。靶向Siglec检查点为增强巨噬细胞（PDAC肿瘤微环境中主要的免疫细胞类型）的抗肿瘤活性提供了机会。
查看英文原文 English abstract
Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy. A key factor contributing to the lethality of PDAC is immune evasion. Tumor cells suppress anti-tumor immunity by activating immune checkpoint proteins on immune cells including macrophages. Siglec receptors are one of the main checkpoint molecules on macrophages. The ligand for Siglecs is sialic acid. To effectuate immune suppression via Siglecs, PDAC cells increase their surface sialylation by upregulating the expression of sialyltransferases such as ST6GAL1. ST6GAL1 adds an alpha2,6-linked sialic acid to N-glycans. Both alpha2,6 sialylation and ST6GAL1 expression are markedly increased in PDAC cells. Our prior studies revealed potent tumor-autonomous functions for ST6GAL1. Our new unpublished results suggest that the tumorigenic effects of ST6GAL1 are also driven by its role in creating sialoglycan ligands for macrophage Siglecs. Macrophages that are polarized to an immunosuppressive M2 phenotype are key contributors to PDAC progression. The goal of our study is to determine whether macrophage Siglecs are promising therapeutic targets for preventing M2 polarization, thus restoring anti-tumor immunity and preventing PDAC progression. We investigated macrophage polarization in our genetically engineered mouse models of PDAC, utilizing either pancreas-specific knock-in of oncogenic K-ras (KC mouse) or K-ras in combination with ST6GAL1 knock-in (KSC mouse). Single-cell RNA sequencing, flow cytometry, and immunohistochemistry showed an increased number of M2 macrophages in KSC vs. KC pancreata. Macrophages co-cultured with ST6GAL1-overexpressed PDAC cells showed increased expression of M2 markers. But adding Siglec-blocking antibodies reversed the ST6GAL1-mediated M2 polarization, indicating that the ST6GAL-mediated M2 polarization of macrophages is mediated through Siglec signaling. Additionally, we determined the phagocytotic capacity of macrophages, which is an established functional readout for anti-tumor behavior of macrophages. Immunofluorescence microscopy and flow cytometry showed that the phagocytotic capability of macrophages was suppressed by ST6GAL1-overexpressed PDAC cells but recovered by Siglec blocking antibody. Overall, our data demonstrate that alpha2,6 sialic acids on PDAC cells engage with Siglecs on macrophages to induce polarization of macrophages into an immunosuppressive M2 phenotype. Collectively, these results reveal a potential mechanism for targeting Siglecs as a promising immune checkpoint therapy for PDAC patients with high levels of ST6GAL1. Traditional T cell-based checkpoint therapies have limited effectiveness in PDAC. Targeting Siglec checkpoints presents an opportunity to enhance the anti-tumor activity of macrophages, the primary immune cell type within the PDAC tumor microenvironment.
利益披露 Disclosure
B. Haldar, None..
K. Hardiman, None..
S. Bellis, None.