Background:The ability of radiotherapy (RT) to drive anti-tumor immunity is limited by adaptive resistance. While RT induces inflammation and recruits activated tumor-infiltrating lymphocytes (TILs), including cytotoxic T lymphocytes (CTLs), the resulting radiation- and IFNγ-dependent PD-L1 expression restores an immunosuppressed tumor microenvironment. Unleashing an effective anti-tumor response may require the precise sequencing of RT and checkpoint blockade immunotherapy (CBI) to block PD-L1 signaling before it can mediate its suppressive effects.Methods:Flank tumors formed in BALB/c mice with syngeneic CT26 colon or 4T1 mammary carcinoma cells were treated with otherwise ineffective doses of ionizing radiation (10 Gy) followed by CBI (0.2 mg anti-PD-L1, i.v.) after 0, 1, 3, 5, or 7 days, comparing tumor response. Anti-PD-L1 delivery was measured by fluorescence, TILs by flow cytometry and immunofluorescence, PD-L1 expression by immunohistochemistry, and tumor size by calipers.Results:In both CT26 and 4T1 tumors, 10 Gy alone resulted in a transient growth delay associated with infiltrating CTLs peaking at 3 days and PD-L1 at 5 days. CTLs returned to baseline after 7 days, consistent with adaptive resistance. Anti-PD-L1 failed to potentiate radiation except when injected 5 days after 10 Gy, which prevented CTL depletion and led to tumor elimination. Potentially contributing to compound effects, anti-PD-L1 penetrated tumors and bound PD-L1 more efficiently after irradiation.Conclusions:Optimal timing to exploit radiation-induced permeability to enhance CBI delivery and interrupt adaptive resistance by blocking PD-L1 as it peaks may offer a general strategy to enhance external beam radiotherapy by protecting activated TILs and potentiating anti-tumor immune response.
背景：放射治疗（RT）激发抗肿瘤免疫的能力受到适应性抵抗的限制。虽然RT能诱导炎症并招募活化的肿瘤浸润淋巴细胞（TILs），包括细胞毒性T淋巴细胞（CTLs），但由此产生的辐射和IFNγ依赖性PD-L1表达会恢复免疫抑制的肿瘤微环境。要释放有效的抗肿瘤反应，可能需要精确安排RT和检查点阻断免疫疗法（CBI）的顺序，以便在PD-L1信号传导发挥抑制作用之前阻断它。 方法：在BALB/c小鼠侧腹形成的同源CT26结肠癌或4T1乳腺癌肿瘤中，使用原本无效剂量的电离辐射（10 Gy）进行治疗，随后在0、1、3、5或7天后给予CBI（0.2 mg抗PD-L1，静脉注射），比较肿瘤反应。通过荧光测量抗PD-L1的递送，通过流式细胞术和免疫荧光测量TILs，通过免疫组织化学测量PD-L1表达，通过卡尺测量肿瘤大小。 结果：在CT26和4T1肿瘤中，单独10 Gy的辐射导致短暂的生长延迟，与浸润的CTLs在3天达到峰值和PD-L1在5天达到峰值相关。CTLs在7天后恢复到基线水平，与适应性抵抗一致。抗PD-L1未能增强辐射效果，除非在10 Gy辐射后5天注射，这防止了CTL的耗竭并导致肿瘤消除。可能有助于复合效应的是，抗PD-L1在辐射后更有效地穿透肿瘤并与PD-L1结合。 结论：利用辐射诱导的通透性增强CBI递送，并在PD-L1达到峰值时阻断它以中断适应性抵抗的最佳时机，可能提供一种通用策略，通过保护活化的TILs和增强抗肿瘤免疫反应来增强外照射放疗。
Timing Anti-PD-L1 Checkpoint Blockade Immunotherapy to Enhance Tumor Irradiation
肿瘤(癌症)患者之家