The efficacy of chemotherapy is limited by intratumoral senescent cells that persist through the upregulation of PD-L2

Anti-cancer therapies often result in a subset of surviving cancer cells that undergo therapy induced senescence (TIS). Senescent cancer cells strongly modify the intratumoral microenvironment favoring immunosuppression and, thereby, tumor growth. An emerging strategy to optimise current therapies is to combine them with treatments that eliminate senescent cells. To this end, we undertook an unbiased proteomics approach to identify surface markers contributing to senescent cells immune evasion. Through this approach, we discovered that the immune checkpoint inhibitor PD-L2, but not PD-L1, is upregulated across multiple senescent human and murine cells. Importantly, blockade of PD-L2 strongly synergises with genotoxic chemotherapy, causing remission of solid tumors in mice. We show that PD-L2 inhibition prevents the persistence of chemotherapy-induced senescent cells, which exert cell-extrinsic immunomodulatory actions. In particular, upon chemotherapy, tumors deficient in PD-L2 fail to produce cytokines of the CXCL family, do not recruit myeloid-derived suppressor cells (MDSCs) and are eliminated in a CD8 T cell-dependent manner. We conclude that blockade of PD-L2 improves chemotherapy efficacy by reducing the intratumoral burden of senescent cells and their associated recruitment of immunosuppressive cells. These findings provide a novel strategy to exploit vulnerabilities arising in tumor cells as a result of therapy-induced damage and cellular senescence Overall design: Panc02 murine pancreatic adenocarcinoma cells, WT or PD-L2-KO, were treated (n = 4) with doxorubicin to induce senescence, and gene expressión was analyzed by RNAseq.

抗癌治疗往往会导致部分存活癌细胞发生治疗诱导性衰老（therapy-induced senescence, TIS）。衰老癌细胞可显著重塑肿瘤微环境，促进免疫抑制，进而推动肿瘤生长。当前优化现有治疗方案的新兴策略之一，是将常规疗法与清除衰老细胞的干预手段相结合。为此，我们采用无偏倚蛋白质组学方法，旨在鉴定参与衰老细胞免疫逃逸的表面标志物。借此我们发现，免疫检查点分子PD-L2（而非PD-L1）在多种衰老的人类及小鼠细胞中均会上调表达。值得注意的是，阻断PD-L2可与基因毒性化疗产生强效协同作用，使小鼠体内的实体瘤实现完全缓解。我们证实，PD-L2抑制可阻止化疗诱导的衰老细胞持续存活，这类细胞可发挥细胞外的免疫调节功能。具体而言，接受化疗后，PD-L2缺陷的肿瘤无法产生CXCL家族细胞因子，也不能招募髓系来源抑制细胞（myeloid-derived suppressor cells, MDSCs），并会以CD8 T细胞依赖性方式被机体清除。我们得出结论：阻断PD-L2可通过降低肿瘤内衰老细胞的负荷及其介导的免疫抑制细胞招募，提升化疗疗效。上述研究发现为靶向利用治疗诱导损伤及细胞衰老所引发的肿瘤细胞脆弱性提供了全新策略。整体实验设计：将野生型或PD-L2基因敲除（PD-L2-KO）的Panc02小鼠胰腺腺癌细胞用阿霉素处理（生物学重复n=4）以诱导细胞衰老，并通过RNAseq分析基因表达。