阻断程序性死亡 (PD)-1 或其配体 (PD-L1) 的抗体彻底改变了癌症治疗，但许多患者并未获得持久的益处。 PD-(L)1 难治性患者需要刺激抗肿瘤免疫的新疗法。干扰素基因刺激物 (STING) 蛋白是一种细胞质 DNA 的先天传感器，是一个有前景的靶标，目前有多种激动剂正在开发中。然而，最近大多数临床试验的缓解率较低，且缓解机制仍不清楚。我们报告了一名抗 PD-L1 难治性默克尔细胞多瘤病毒 (MCPyV) 阳性、转移性默克尔细胞癌 (MCC) 患者的详细生物标志物分析，该患者接受瘤内 (IT) STING 激动剂 (ADU-S100) 加静脉注射治疗抗 PD-1 抗体（spartalizumab），并经历了持久的客观反应，注射和非注射病变均得到消退。我们通过单细胞 RNA 测序分析了患者治疗前和治疗后的肿瘤和外周血样本，30-参数流式细胞术、T 细胞受体测序和多重免疫组织化学。我们使用负载 MCPyV 肽的人类白细胞抗原 (HLA)-I 四聚体分析了癌症特异性 CD8 T 细胞。我们还分析了另外 88 个 MCC 肿瘤标本和 MCC 细胞系的肿瘤微环境 (TME) 中的 STING 表达和信号传导。我们在基线时在患者肿瘤中观察到高水平的 MCPyV 特异性 T 细胞（T 细胞的 12%）。这些癌症特异性 CD8 T 细胞表现出衰竭特征，包括高 TOX 和低 TCF1 蛋白。使用 STING 激动剂加抗 PD-1 治疗后，IT CD8 T 细胞扩增了三倍。我们还观察到 MCC TME 中抗原呈递可能改善的证据（HLA-I 阳性癌细胞增加四倍以上）。在我们患者肿瘤内的任何癌细胞或其他 88 个 MCC 肿瘤中均未检测到 STING 表达，但在所有 89 个 MCC 肿瘤内的免疫和基质细胞中观察到高 STING 表达。我们的结果表明，STING 激动剂可能能够间接在MCC 通过 TME 中的免疫细胞和基质细胞发出信号，可能不一定需要癌细胞中表达 STING。这种方法对于 TME 中已经被炎症细胞浸润但通过 HLA-I 下调逃避免疫检测的肿瘤可能特别有效。© 作者（或其雇主）2024。CC 允许重复使用BY-NC。禁止商业再利用。请参阅权利和权限。英国医学杂志出版。

Antibodies blocking programmed death (PD)-1 or its ligand (PD-L1) have revolutionized cancer care, but many patients do not experience durable benefits. Novel treatments to stimulate antitumor immunity are needed in the PD-(L)1 refractory setting. The stimulator of interferon genes (STING) protein, an innate sensor of cytoplasmic DNA, is a promising target with several agonists in development. However, response rates in most recent clinical trials have been low and mechanisms of response remain unclear. We report detailed biomarker analyses in a patient with anti-PD-L1 refractory, Merkel cell polyomavirus (MCPyV)-positive, metastatic Merkel cell carcinoma (MCC) who was treated with an intratumoral (IT) STING agonist (ADU-S100) plus intravenous anti-PD-1 antibody (spartalizumab) and experienced a durable objective response with regression of both injected and non-injected lesions.We analyzed pretreatment and post-treatment tumor and peripheral blood samples from our patient with single-cell RNA sequencing, 30-parameter flow cytometry, T cell receptor sequencing, and multiplexed immunohistochemistry. We analyzed cancer-specific CD8 T cells using human leukocyte antigen (HLA)-I tetramers loaded with MCPyV peptides. We also analyzed STING expression and signaling in the tumor microenvironment (TME) of 88 additional MCC tumor specimens and in MCC cell lines.We observed high levels of MCPyV-specific T cells (12% of T cells) in our patient's tumor at baseline. These cancer-specific CD8 T cells exhibited characteristics of exhaustion including high TOX and low TCF1 proteins. Following treatment with STING-agonist plus anti-PD-1, IT CD8 T cells expanded threefold. We also observed evidence of likely improved antigen presentation in the MCC TME (greater than fourfold increase of HLA-I-positive cancer cells). STING expression was not detected in any cancer cells within our patient's tumor or in 88 other MCC tumors, however high STING expression was observed in immune and stromal cells within all 89 MCC tumors.Our results suggest that STING agonists may be able to work indirectly in MCC via signaling through immune and stromal cells in the TME, and may not necessarily need STING expression in the cancer cells. This approach may be particularly effective in tumors that are already infiltrated by inflammatory cells in the TME but are evading immune detection via HLA-I downregulation.© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.