Immune checkpoint inhibitors, including those targeting programmed cell death protein 1 (PD-1), are reshaping cancer therapeutic strategies. Evidence suggests, however, that tumor response and patient survival are determined by tumor programmed death ligand 1 (PD-L1) expression. We hypothesized that preconditioning of the tumor immune microenvironment using targeted, virus-mediated interferon (IFN) stimulation would up-regulate tumor PD-L1 protein expression and increase cytotoxic T cell infiltration, improving the efficacy of subsequent checkpoint blockade. Oncolytic viruses (OVs) represent a promising form of cancer immunotherapy. For brain tumors, almost all studies to date have used direct intralesional injection of OV, because of the largely untested belief that intravenous administration will not deliver virus to this site. We show, in a window-of-opportunity clinical study, that intravenous infusion of oncolytic human Orthoreovirus (referred to herein as reovirus) leads to infection of tumor cells subsequently resected as part of standard clinical care, both in high-grade glioma and in brain metastases, and increases cytotoxic T cell tumor infiltration relative to patients not treated with virus. We further show that reovirus up-regulates IFN-regulated gene expression, as well as the PD-1/PD-L1 axis in tumors, via an IFN-mediated mechanism. Finally, we show that addition of PD-1 blockade to reovirus enhances systemic therapy in a preclinical glioma model. These results support the development of combined systemic immunovirotherapy strategies for the treatment of both primary and secondary tumors in the brain.

免疫检查点抑制剂，包括针对程序性细胞死亡蛋白 1 (PD-1) 的抑制剂，正在重塑癌症治疗策略。然而，有证据表明，肿瘤反应和患者生存取决于肿瘤程序性死亡配体 1 (PD-L1) 的表达。我们假设，使用靶向病毒介导的干扰素 (IFN) 刺激预处理肿瘤免疫微环境将上调肿瘤 PD-L1 蛋白表达并增加细胞毒性 T 细胞浸润，从而提高后续检查点阻断的功效。溶瘤病毒（OV）代表了一种有前途的癌症免疫疗法。对于脑肿瘤，迄今为止几乎所有研究都使用直接病灶内注射 OV，因为人们普遍认为静脉注射不会将病毒输送到该部位，这一观点在很大程度上未经检验。我们在一项机会之窗临床研究中表明，静脉输注溶瘤人正呼肠孤病毒（本文称为呼肠孤病毒）会导致随后作为标准临床护理的一部分切除的肿瘤细胞的感染，无论是在高级神经胶质瘤还是在高级别胶质瘤中。与未接受病毒治疗的患者相比，脑转移增加了细胞毒性 T 细胞肿瘤浸润。我们进一步表明，呼肠孤病毒通过 IFN 介导的机制上调 IFN 调节的基因表达以及肿瘤中的 PD-1/PD-L1 轴。最后，我们证明在呼肠孤病毒中添加 PD-1 阻断剂可增强临床前神经胶质瘤模型的全身治疗。这些结果支持开发用于治疗脑部原发性和继发性肿瘤的联合全身免疫病毒治疗策略。