Ccr2缺失的T细胞在肿瘤发展和抗PD-1治疗中的作用及机制研究

After the mature T cells migrate from the thymus, they enter the peripheral lymphatic circulation to participate in various immune responses in the body. Tumor microenvironment is the main site of interaction between tumor cells and host immune cells. Many cells, including T cells, can secrete chemokines in tumor microenvironment. Different groups of immune cells are recruited into the tumor microenvironment through the interaction between chemokines and chemokine receptors, thus altering the tumor microenvironment and the immune response of the tumor, thus having a distinct impact on the tumor development and the outcome of treatment. Although anti-PD-1 monoclonal antibodies and other immunotherapy drugs have been approved and put into clinical practice, but clinical results show that only a few cancer patients really benefit from the treatment of anti-PD-1 monoclonal antibodies and other immuno-checkpoint inhibitors, which suggests that the mechanism of immuno-checkpoint inhibitors needs further study..We found that in the spleen of Ccr2-deficient mice had a large number of activated T cells, and the expression of PD-1 on the surface of T cells increased. Although the expression level of PD-1 on T cells increased, Ccr2-deficient mice showed stronger anti-tumor ability. Based on results, we speculate that Ccr2 deficiency affects central immune tolerance of T cells, resulting in increased expression of activated T cells and PD-1 molecules in spleen. However, the mechanism of Ccr2 affecting the expression of PD-1 on T cell surface and the effect of Ccr2 deletion on anti-PD-1 immune therapy remain to be studied. In this study, we investigate the effect of Ccr2 deletion on the expression of PD-1 and the mechanism of anti-PD-1 immune therapy.

在胸腺发育成熟的T细胞从胸腺迁出之后参与机体内的各类免疫应答。肿瘤微环境中的T细胞不仅影响肿瘤发生和发展，还对肿瘤免疫治疗产生很大的影响。虽然抗PD-1单抗等多种免疫治疗药物陆续被批准并投入到临床当中，但是临床结果显示目前仅仅一部分的肿瘤患者真正从中受益，这提示免疫检查点抑制剂的作用机制还需要深入的研究。.我们发现Ccr2缺失小鼠的脾脏有大量的活化表型的T细胞，而且T细胞表面PD-1分子表达水平升高。虽然T细胞表面PD-1分子表达水平升高，但是Ccr2缺失小鼠抗肿瘤能力更强。根据我们的实验结果，我们推测Ccr2缺失影响T细胞中枢免疫耐受造成脾脏中的活化T细胞增多和PD-1分子表达水平升高。但是Ccr2影响T细胞表面PD-1分子表达机制以及Ccr2缺失对抗PD-1免疫治疗产生的影响尚待研究。因此本研究中我们探讨Ccr2缺失对PD-1表达水平及抗PD-1免疫治疗的影响及机制。

肿瘤微环境中的T 细胞不仅影响肿瘤的发生和发展，还对肿瘤免疫治疗产生很大的影响。尽管抗PD-1等免疫治疗药物陆续被批准并投入到临床当中，但是临床结果显示目前仅仅一部分的肿瘤患者真正冲中收益。这提示抗PD-1免疫治疗机制尚需进一步研究。我们在研究中发现了CCR2 缺失的小鼠外周淋巴器官中有大量的活化表型的T细胞。进一步研究显示CCR2 的缺失影响了T细胞表面PD-1分子的表达水平。我们在后续的实验中进一步发现，CCR2 的缺失也影响了抗PD-1免疫治疗的效果并阐明了其部分机制。我们的结果显示，CCR2 缺失小鼠的脾脏中出现了更多的活化表型T细胞，而且CCR2 缺失后CD4 和CD8 T细胞表面PD-1分子表达水平分别为39% 和5.7%， 这一比例远高于WT 小鼠17% 和2.5% 左右的水平。荷瘤小鼠的结果提示，CCR2 KO 小鼠体内肿瘤生长速度明显高于WT 小鼠。后续抗PD-1免疫治疗实验也提示，CCR2 缺失后抗PD-1免疫治疗效果也远低于WT 小鼠。我们的实验结果显示，这种差异可能来自CCR2 影响了T细胞表面PD-1分子的表达水平。此外，我们也用体内和体外实验证明了CCR2的缺失也影响了T细胞的细胞因子分泌功能。我们进一步探索了CCR2 影响T 细胞表面PD-1分子表达水平的机制。探索结果显示CCR2 缺失小鼠T细胞PD-1分子表达水平只是在外周淋巴器官中高于WT小鼠，新近迁出以及胸腺内正在发育的T细胞中并无相同趋势。这提示CCR2 可能是影响了T细胞在胸腺内阴性选择过程，从而导致未经充分阴选的细胞迁出至外周淋巴器官并导致过度活化。.我们的研究结果显示，CCR2缺失会抑制T细胞的功能并降低抗PD-1免疫治疗的疗效；CCR2可能通过影响T细胞在胸腺内阴性选择过程，从而影响T细胞表面PD-1分子的表达水平。我们的结果提示T细胞表面CCR2 分子的表达水平也许可以用来预测抗PD-1免疫治疗的疗效。