Karamitopoulou Eva, Andreou Andreas, Wenning Anna Silvia, Gloor Beat, Perren Aurel
Institute of Pathology, University of Bern, Switzerland.
Department of Visceral Surgery, Insel University Hospital, University of Bern, Switzerland.
Eur J Cancer. 2022 Jul;169:64-73. doi: 10.1016/j.ejca.2022.03.033. Epub 2022 May 2.
Tumor mutational burden (TMB: somatic mutations per megabase, mut/Mb) predicts the efficacy of immunotherapy. Here, we link TMB levels with the activation of immune pathways and intratumoral immune responses in pancreatic adenocarcinoma (PDAC) to explore immunoarchitectural patterns associated with high TMB.
We assessed TMB in 161 resected, microsatellite stable (MSS) PDACs, including 41 long-term survivors (LTS). Five microsatellite instable (MSI-high) cases were also assessed. Cases were classified into TMB-high (≥10 mut/Mb), TMB-intermediate (>5 < 10 mut/Mb), and TMB-low (≤5 mut/Mb) categories. Tumors additionally underwent mRNA in situ hybridization for immune pathway genes and were immunoprofiled by multiplex immunofluorescence followed by automated image analysis.
We detected 12 TMB-high, 28 TMB-intermediate, and 121 TMB-low cases. TMB-high tumors comprised ten LTSs (10/41; 24%) and two conventional PDACs (2/120; 1.7%). They exhibited the highest T cell density with significantly increased CD3CD4T helper and CD208dendritic cell (DC) counts, compared to all other cases. CD3CD8cytotoxic T cells were significantly closer to tumor cells and T helper cells closer to DCs in TMB-high PDACs. Immune pathways involved in T cell activation, immune cell adhesion/migration, antigen presentation, and cytokine signaling were upregulated in most TMB-high and many TMB-intermediate tumors. ARID1A and ERBB4 alterations were more frequent in TMB-high PDACs. All MSI-high PDACs were TMB-high.
TMB-high cases frequently belong to specific PDAC subsets with prolonged survival such as LTSs and MSI-high PDACs. They display strong anti-tumor immune responses fueled by a T helper cell/DC-mediated priming of the cytotoxic T cells. Moreover, they frequently harbor further actionable alterations.
肿瘤突变负荷（TMB：每兆碱基的体细胞突变数，突变/Mb）可预测免疫治疗的疗效。在此，我们将TMB水平与胰腺腺癌（PDAC）中免疫途径的激活及肿瘤内免疫反应相联系，以探索与高TMB相关的免疫结构模式。
我们评估了161例接受手术切除、微卫星稳定（MSS）的PDAC患者的TMB，其中包括41例长期存活者（LTS）。还评估了5例微卫星不稳定（MSI高）病例。病例被分为高TMB（≥10突变/Mb）、中TMB（>5<10突变/Mb）和低TMB（≤5突变/Mb）类别。肿瘤还进行了免疫途径基因的mRNA原位杂交，并通过多重免疫荧光进行免疫分析，随后进行自动图像分析。
我们检测到12例高TMB、28例中TMB和121例低TMB病例。高TMB肿瘤包括10例LTS（10/41；24%）和2例传统PDAC（2/120；1.7%）。与所有其他病例相比，它们表现出最高的T细胞密度，CD3CD4辅助性T细胞和CD208树突状细胞（DC）计数显著增加。在高TMB的PDAC中，CD3CD8细胞毒性T细胞与肿瘤细胞的距离显著更近，辅助性T细胞与DC的距离更近。在大多数高TMB和许多中TMB肿瘤中，参与T细胞激活、免疫细胞黏附/迁移、抗原呈递和细胞因子信号传导的免疫途径上调。在高TMB的PDAC中，ARID1A和ERBB4改变更常见。所有MSI高的PDAC均为高TMB。
高TMB病例通常属于特定的PDAC亚组，如LTS和MSI高的PDAC，其生存期延长。它们表现出由辅助性T细胞/DC介导的细胞毒性T细胞启动所驱动的强烈抗肿瘤免疫反应。此外，它们经常存在其他可采取行动的改变。
