Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, UK.
Department of Clinical Oncology, University of Hong Kong Faculty of Medicine, Hong Kong, Hong Kong.
J Immunother Cancer. 2024 Jul 25;12(7):e009443. doi: 10.1136/jitc-2024-009443.
Over the past decade, cancer immunotherapies have revolutionized the treatment of melanoma; however, responses vary across patient populations. Recently, baseline tumor size has been identified as an independent prognostic factor for overall survival in patients with melanoma receiving immune checkpoint inhibitors. MG1 is a novel oncolytic agent with broad tumor tropism that has recently entered early-phase clinical trials. The aim of this study was to characterize T-cell responses in human and mouse melanoma models following MG1 treatment and to establish if features of the tumor immune microenvironment (TIME) at two distinct tumor burdens would impact the efficacy of oncolytic virotherapy.
Human three-dimensional in vitro priming assays were performed to measure antitumor and antiviral T-cell responses following MG1 infection. T-cell receptor (TCR) sequencing, T2 killing assay, and peptide recall assays were used to assess the evolution of the TCR repertoire, and measure specific T-cell responses, respectively. In vivo, subcutaneous 4434 melanomas were characterized using RNA sequencing, immunohistochemistry, and flow cytometry. The effectiveness of intratumoral MG1 was assessed in advancing 4434 tumors and the generation of antitumor and antiviral T cells measured by splenocyte recall assays. Finally, combination MG1 and programmed cell death protein-1 antibody (αPD-1) therapy was investigated in advanced 4434 tumors.
MG1 effectively supported priming of functional cytotoxic T cells (CTLs) against tumor-associated antigens as well as virus-derived peptides, as assessed using peptide recall and T2 killing assays, respectively. TCR sequencing revealed that MG1-primed CTL comprised larger clusters of similar CDR3 amino acid sequences compared with controls. In vivo testing of MG1 demonstrated that MG1 monotherapy was highly effective at treating early disease, resulting in 90% cures; however, the efficacy of MG1 reduced as the disease burden (local tumor size) increased, and the addition of αPD-1 was required to overcome resistance in more advanced disease. Differential gene expression profiles revealed that increased tumor burden was associated with an immunologically colder TIME. Furthermore, analysis of TCR signaling in advancing tumors demonstrated a different dynamic of TCR engagement compared with smaller tumors, in particular a shift in antigen recognition by CD4+ cells, from conventional to regulatory subsets.
Addition of αPD-1 to MG1 is required to overcome viral therapy resistance in immunologically 'colder' more advanced melanoma, highlighting the importance of tumor burden to different types of immunotherapy.
在过去的十年中，癌症免疫疗法彻底改变了黑色素瘤的治疗方法；然而，不同患者群体的反应存在差异。最近，基线肿瘤大小已被确定为接受免疫检查点抑制剂治疗的黑色素瘤患者总生存期的独立预后因素。MG1 是一种新型溶瘤剂，具有广泛的肿瘤趋向性，最近已进入早期临床试验阶段。本研究的目的是描述 MG1 治疗后人类和小鼠黑色素瘤模型中的 T 细胞反应，并确定在两种不同肿瘤负荷下肿瘤免疫微环境（TIME）的特征是否会影响溶瘤病毒治疗的疗效。
进行了人体三维体外启动测定，以测量 MG1 感染后的抗肿瘤和抗病毒 T 细胞反应。使用 TCR 测序、T2 杀伤测定和肽召回测定分别评估 TCR 库的演变，并测量特定的 T 细胞反应。在体内，使用 RNA 测序、免疫组织化学和流式细胞术对皮下 4434 黑色素瘤进行了表征。通过脾细胞召回测定评估了肿瘤内 MG1 的有效性，并测量了抗肿瘤和抗病毒 T 细胞的产生。最后，研究了进展期 4434 肿瘤中 MG1 与程序性细胞死亡蛋白-1 抗体（αPD-1）联合治疗。
MG1 有效地支持了针对肿瘤相关抗原和病毒衍生肽的功能性细胞毒性 T 细胞（CTL）的启动，这分别通过肽召回和 T2 杀伤测定进行了评估。TCR 测序显示，与对照组相比，MG1 启动的 CTL 包含更大的相似 CDR3 氨基酸序列簇。体内测试表明，MG1 单药治疗对早期疾病非常有效，治愈率达 90%；然而，随着疾病负担（局部肿瘤大小）的增加，MG1 的疗效降低，需要添加αPD-1 才能克服更晚期疾病的耐药性。差异基因表达谱显示，肿瘤负担增加与免疫更冷的 TIME 相关。此外，在进展中的肿瘤中分析 TCR 信号表明，与较小的肿瘤相比，TCR 结合具有不同的动态，特别是 CD4+细胞的抗原识别从常规向调节亚群的转变。
MG1 联合αPD-1 是克服免疫“更冷”的更晚期黑色素瘤中病毒治疗耐药性所必需的，这凸显了肿瘤负担对不同类型免疫疗法的重要性。
