Department of Dermatology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany.
German Cancer Consortium (DKTK), Partner Site Essen/Düsseldorf, Essen, Germany.
J Immunother Cancer. 2022 Jun;10(6). doi: 10.1136/jitc-2021-003863.
Immune-stimulatory agents, like agonists of the innate immune receptor RIG-I, are currently tested in clinical trials as an intratumoral treatment option for patients with unresectable melanoma, aiming to enhance anti-tumor T cell responses. Switching of melanoma toward a dedifferentiated cell state has recently been linked to T cell and therapy resistance. It remains to be determined whether RIG-I agonists affect melanoma differentiation, potentially leading to T cell resistance.
Patient metastases-derived melanoma cell lines were treated with the synthetic RIG-I agonist 3pRNA, and effects on tumor cell survival, phenotype and differentiation were determined. Transcriptomic data sets from cell lines and metastases were analyzed for associations between and melanoma differentiation markers and used to define signaling pathways involved in RIG-I-driven dedifferentiation. The impact of 3pRNA-induced melanoma dedifferentiation on CD8 T cell activation was studied in autologous tumor T cell models.
RIG-I activation by 3pRNA induced apoptosis in a subpopulation of melanoma cells, while the majority of tumor cells switched into a non-proliferative cell state. Those persisters displayed a dedifferentiated cell phenotype, marked by downregulation of the melanocytic lineage transcription factor MITF and its target genes, including melanoma differentiation antigens (MDA). Transition into the MITF/MDA cell state was JAK-dependent, with some cells acquiring nerve growth factor receptor expression. MITF/MDA persisters switched back to the proliferative differentiated cell state when RIG-I signaling declined. Consistent with our in vitro findings, an association between melanoma dedifferentiation and high levels was detected in transcriptomic data from patient metastases. Notably, despite their dedifferentiated cell phenotype, 3pRNA-induced MITF/MDA persisters were still efficiently targeted by autologous CD8 tumor-infiltrating T lymphocytes (TILs).
Our results demonstrate that RIG-I signaling in melanoma cells drives a transient phenotypic switch toward a non-proliferative dedifferentiated persister cell state. Despite their dedifferentiation, those persisters are highly immunogenic and sensitive toward autologous TILs, challenging the concept of melanoma dedifferentiation as a general indicator of T cell resistance. In sum, our findings support the application of RIG-I agonists as a therapeutic tool for the generation of long-term clinical benefit in non-resectable melanoma.
免疫刺激剂，如先天免疫受体 RIG-I 的激动剂，目前正在临床试验中作为不可切除黑色素瘤患者的一种肿瘤内治疗选择进行测试，旨在增强抗肿瘤 T 细胞反应。黑色素瘤向去分化细胞状态的转变最近与 T 细胞和治疗耐药性有关。目前尚不清楚 RIG-I 激动剂是否会影响黑色素瘤分化，从而导致 T 细胞耐药性。
用合成的 RIG-I 激动剂 3pRNA 处理患者转移灶来源的黑色素瘤细胞系，确定对肿瘤细胞存活、表型和分化的影响。分析细胞系和转移灶的转录组数据集，以确定与 RIG-I 驱动的去分化相关的信号通路。在自体肿瘤 T 细胞模型中研究 3pRNA 诱导的黑色素瘤去分化对 CD8 T 细胞激活的影响。
3pRNA 激活 RIG-I 可诱导部分黑色素瘤细胞凋亡，而大多数肿瘤细胞则转变为非增殖细胞状态。这些持久存在的细胞表现出去分化的细胞表型，特征是黑色素细胞系转录因子 MITF 及其靶基因下调，包括黑色素瘤分化抗原（MDA）。进入 MITF/MDA 细胞状态依赖于 JAK，部分细胞获得神经生长因子受体表达。当 RIG-I 信号下降时，MITF/MDA 持久存在的细胞会重新回到增殖分化的细胞状态。与我们的体外研究结果一致，在患者转移灶的转录组数据中检测到黑色素瘤去分化与高水平之间存在关联。值得注意的是，尽管它们表现出去分化的细胞表型，但 3pRNA 诱导的 MITF/MDA 持久存在的细胞仍能被自体 CD8 肿瘤浸润性 T 淋巴细胞（TIL）有效靶向。
我们的研究结果表明，RIG-I 信号在黑色素瘤细胞中驱动向非增殖性去分化持久存在的表型转换。尽管它们去分化了，但这些持久存在的细胞仍然高度免疫原性，对自体 TIL 敏感，这对黑色素瘤去分化作为 T 细胞耐药的一般指标的概念提出了挑战。总之，我们的研究结果支持 RIG-I 激动剂作为一种治疗工具的应用，以在不可切除的黑色素瘤中产生长期的临床获益。
