Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Ovarian Cancer Research Center, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
J Immunother Cancer. 2021 Feb;9(2). doi: 10.1136/jitc-2020-001636.
Tumor endothelial marker 1 (TEM1) is a protein expressed in the tumor-associated endothelium and/or stroma of various types of cancer. We previously demonstrated that immunization with a plasmid-DNA vaccine targeting TEM1 reduced tumor progression in three murine cancer models. Radiation therapy (RT) is an established cancer modality used in more than 50% of patients with solid tumors. RT can induce tumor-associated vasculature injury, triggering immunogenic cell death and inhibition of the irradiated tumor and distant non-irradiated tumor growth (abscopal effect). Combination treatment of RT with TEM1 immunotherapy may complement and augment established immune checkpoint blockade.
Mice bearing bilateral subcutaneous CT26 colorectal or TC1 lung tumors were treated with a novel heterologous TEM1-based vaccine, in combination with RT, and anti-programmed death-ligand 1 (PD-L1) antibody or combinations of these therapies, tumor growth of irradiated and abscopal tumors was subsequently assessed. Analysis of tumor blood perfusion was evaluated by CD31 staining and Doppler ultrasound imaging. Immunophenotyping of peripheral and tumor-infiltrating immune cells as well as functional analysis was analyzed by flow cytometry, ELISpot assay and adoptive cell transfer (ACT) experiments.
We demonstrate that addition of RT to heterologous TEM1 vaccination reduces progression of CT26 and TC1 irradiated and abscopal distant tumors as compared with either single treatment. Mechanistically, RT increased major histocompatibility complex class I molecule (MHCI) expression on endothelial cells and improved immune recognition of the endothelium by anti-TEM1 T cells with subsequent severe vascular damage as measured by reduced microvascular density and tumor blood perfusion. Heterologous TEM1 vaccine and RT combination therapy boosted tumor-associated antigen (TAA) cross-priming (ie, anti-gp70) and augmented programmed cell death protein 1 (PD-1)/PD-L1 signaling within CT26 tumor. Blocking the PD-1/PD-L1 axis in combination with dual therapy further increased the antitumor effect and gp70-specific immune responses. ACT experiments show that anti-gp70 T cells are required for the antitumor effects of the combination therapy.
Our findings describe novel cooperative mechanisms between heterologous TEM1 vaccination and RT, highlighting the pivotal role that TAA cross-priming plays for an effective antitumor strategy. Furthermore, we provide rationale for using heterologous TEM1 vaccination and RT as an add-on to immune checkpoint blockade as triple combination therapy into early-phase clinical trials.
肿瘤内皮标志物 1（TEM1）是一种在多种类型癌症的肿瘤相关内皮细胞和/或基质中表达的蛋白质。我们之前的研究表明，针对 TEM1 的质粒-DNA 疫苗免疫可降低三种小鼠癌症模型中的肿瘤进展。放射治疗（RT）是一种已确立的癌症治疗方法，超过 50%的实体瘤患者都接受这种治疗。RT 可诱导肿瘤相关血管损伤，引发免疫原性细胞死亡并抑制辐照肿瘤和远处未辐照肿瘤的生长（远隔效应）。RT 联合 TEM1 免疫疗法的联合治疗可能会补充和增强已建立的免疫检查点阻断。
在双侧皮下 CT26 结直肠或 TC1 肺癌肿瘤的小鼠中，用新型异源 TEM1 疫苗联合 RT 和抗程序性死亡配体 1（PD-L1）抗体或这些疗法的组合进行治疗，随后评估辐照和远隔肿瘤的肿瘤生长情况。通过 CD31 染色和多普勒超声成像评估肿瘤血液灌注的分析。通过流式细胞术、ELISpot 测定和过继细胞转移（ACT）实验分析外周和肿瘤浸润免疫细胞的免疫表型和功能分析。
我们证明，与单一治疗相比，将 RT 添加到异源 TEM1 疫苗接种中可降低 CT26 和 TC1 辐照和远隔远处肿瘤的进展。从机制上讲，RT 增加了内皮细胞上的主要组织相容性复合物 I 类分子（MHCI）表达，并改善了抗 TEM1 T 细胞对内皮的免疫识别，随后通过降低微血管密度和肿瘤血液灌注来测量严重的血管损伤。异源 TEM1 疫苗和 RT 联合治疗增强了肿瘤相关抗原（TAA）交叉呈递（即抗-gp70），并增强了 CT26 肿瘤中的程序性死亡蛋白 1（PD-1）/PD-L1 信号传导。阻断 PD-1/PD-L1 轴与双重治疗相结合进一步增加了抗肿瘤作用和 gp70 特异性免疫反应。ACT 实验表明，抗-gp70 T 细胞是联合治疗抗肿瘤作用所必需的。
我们的研究结果描述了异源 TEM1 疫苗接种和 RT 之间的新型合作机制，强调了 TAA 交叉呈递在有效抗肿瘤策略中的关键作用。此外，我们为将异源 TEM1 疫苗接种和 RT 作为免疫检查点阻断的附加物作为三重联合治疗纳入早期临床试验提供了依据。
