基于自发性肺癌模型的T细胞耗竭机制研究

T cell exhaustion occurs when antigen-specific T cells experience continuous antigen stimulation during chronic infection or cancer, which results in dysfunction of killing tumor cells. The response rates of checkpoint inhibitors targeting PD1, PDL1 or CTLA4 of exhausted tumor-infiltrating T cells were not uniform upon patients, suggesting a deeper understanding was required for the mechanisms of T cell exhaustion. The LCMV chronic infection model was often used for studying T cell exhaustion, while it has a great limitation of simulating human cancers due to the antigen difference. Besides, it's also difficult to trace certain T cells at different time points in clinical tumor samples. Here, we will perform single-cell RNA sequencing to dissect tumor-infiltrating T cell populations in a spontaneous lung cancer model with EGFR mutation, and to identify cell subgroups with distinct exhaustion degree. By tracing the TCR pools and transcriptome changes, we aim to identify key genes of T cell exhaustion in human cancers, and to provide novel targets for immunotherapies.

抗原特异的T细胞在慢性感染或癌症等抗原的持续刺激下会出现T细胞耗竭现象，从而失去杀伤肿瘤细胞的能力。目前已有PD1、PDL1、CTLA4等蛋白抑制剂靶向肿瘤浸润的耗竭T细胞，然而其疗效并不均一，暗示我们需要更加深入地理解肿瘤浸润T细胞的耗竭机制。小鼠LCMV病毒慢性感染模型常被用于研究T细胞耗竭，但该模型抗原单一，模拟癌症发生的程度十分有限；而临床样本由于采样的特殊性，无法连续追踪同一个体的T细胞。本研究创新性地选取带有表皮生长因子受体（epidermal growth factor receptor, EGFR）突变的小鼠自发性肺癌模型来模拟癌症的发展，在不同时间点对肿瘤浸润T细胞类群进行单细胞测序分析，从而鉴定处于不同耗竭状态的细胞类群以及其表达谱特征。通过追踪不同时间点T细胞类群的TCR以及T细胞表达谱变化，找到调控肿瘤浸润T细胞耗竭过程的关键基因，为免疫治疗提供新的潜在靶点。

T细胞耗竭被认为在癌症中普遍存在，其原因为具有杀伤肿瘤功能的T细胞在长时间接受肿瘤微环境中抗原的刺激后出现失能状态。目前多种癌症免疫治疗方法均致力于阻止或逆转毒性T细胞耗竭，然而疗效在不同癌种及不同病人中并不均一，暗示了未被发现的T细胞耗竭相关基因的存在。本研究主要利用单细胞测序技术在自发的小鼠肺癌模型中探索潜在的与T细胞耗竭相关的新基因和新机制，并利用E.G7淋巴瘤模型来验证潜在基因的生物学功能，发现特异性敲除CXCR6或ZBTB38基因均会使该组小鼠的肿瘤生长速度相比于对照组加快，暗示了CXCR6和ZBTB38基因均可能参与了肿瘤微环境中T细胞的杀伤/耗竭过程。在进一步的实验中发现，敲除ZBTB38基因会导致肿瘤浸润TNFα+的CD8+ T细胞群的比例下降，暗示了ZBTB38可能是通过TNFα通路发挥功能。因此，本研究将为癌症的免疫治疗提供新思路和新靶点。