The Immune Microenvironment, Genome–Wide Copy Number Aberrations and Survival in Mesothelioma

IntroductionResults of recent clinical studies of immune checkpoint inhibitors in malignant pleural mesothelioma (MPM) have dampened initial enthusiasm. However, the immune environment and targets of these treatments such as program cell death protein 1 (PD-1) and its ligand PD-L1 have not been well characterised in MPM. Using a large cohort of patients, we investigated PD-L1 expression, immune infiltrates and genome-wide copy number status and correlated them to clinicopathological features.Patients and methodsTissue microarrays were constructed and stained with PD-L1(clone E1L3N, CST), CD4, CD8 and FOXP3 antibodies. PD-L1 positivity was defined as ≥5% membranous staining regardless of intensity and PD-L1+hi as ≥50%. Genomic DNA from a representative subset of 113 patients was used for genome-wide copy number analysis. The percent genome alteration (PGA) was computed as a proxy for genomic instability, and statistical analyses were used to relate copy number aberrations (CNA) to other variables.ResultsAmongst 329 patients evaluated, PD-L1+ was detected in 130/311 (41.7%), but PD-L1+hi was only seen in 30/311 (9.6%). PD-L1+ correlated with non–epithelioid histology and increased infiltration with CD4+, CD8+ and FOXP3+ lymphocytes. PD-L1+hi expression correlated with worse prognosis (HR = 2.37; 95%CI= 1.57-3.56; P < 0.001) on univariate analysis, but not in multivariate analysis. Higher PGA was associated with epithelioid histology and poorer survival (HR = 1.59; 95%CI= 1.01-2.5; P = 0.04), but not PD-L1 expression.ConclusionPD-L1 expression was associated with non-epithelioid MPM, poor clinical outcome and increased immunological infiltrates. Increased genomic instability did not correlate with PD-L1 expression, but was associated with poorer survival.EGA study EGAS00001002323

引言
近期针对恶性胸膜间皮瘤（malignant pleural mesothelioma, MPM）开展的免疫检查点抑制剂临床研究结果，削弱了学界最初的研究热情。然而，此类治疗的免疫微环境与靶点，如程序性细胞死亡蛋白1（program cell death protein 1, PD-1）及其配体PD-L1，在MPM中尚未得到充分表征。本研究依托大型患者队列，对PD-L1表达、免疫浸润情况及全基因组拷贝数状态进行了检测，并将其与临床病理特征进行关联分析。

患者与方法
构建组织微阵列，采用PD-L1（克隆号E1L3N，CST）、CD4、CD8及FOXP3抗体进行免疫组化染色。PD-L1阳性定义为膜染色阳性比例≥5%（不考虑染色强度），PD-L1高表达（PD-L1+hi）定义为膜染色阳性比例≥50%。选取113例患者的代表性样本提取基因组DNA，开展全基因组拷贝数分析。以基因组改变比例（percent genome alteration, PGA）作为基因组不稳定性的替代指标，并通过统计学分析将拷贝数变异（copy number aberrations, CNA）与其他变量进行关联。

结果
纳入评估的329例患者中，130/311例（41.7%）检测到PD-L1阳性，仅30/311例（9.6%）呈现PD-L1高表达。PD-L1阳性与非上皮样组织学类型、CD4+、CD8+及FOXP3+淋巴细胞浸润增加呈正相关。单因素分析显示，PD-L1高表达与不良预后相关（风险比（hazard ratio, HR）=2.37；95%置信区间（confidence interval, CI）=1.57~3.56；P<0.001），但该关联在多因素分析中无统计学意义。较高的PGA与上皮样组织学类型及不良生存结局相关（HR=1.59；95%CI=1.01~2.5；P=0.04），但与PD-L1表达无关联。

结论
PD-L1表达与非上皮样MPM、不良临床结局及免疫浸润增加相关。基因组不稳定性升高与PD-L1表达无关联，但与不良生存结局相关。
欧洲基因组表型档案（European Genome-phenome Archive, EGA）研究EGAS00001002323