靶向VprBP-Gstp1抑制T细胞衰老增强抗肿瘤免疫研究

T cells are the major players in anti-tumor immunity and cancer immunotherapy. However, T cells have to survive, thrive and win the war against tumor in the harsh microenvironment, where Treg cells and myeloid-derived suppressive cells (MDSCs) produce numerous reactive oxygen species (ROS), TGFβ and PD-L1 to inhibit T cell function. Among the inhibitory molecules, ROS not only negatively regulates T cell proliferation and function, but also contributes to T cell apoptosis and senescence. Although increased senescent T cells in cancer patients have been reported, the role of ROS induced senescent T cells in anti-tumor activity is largely unknown. We have shown VprBP, the cellular target of HIV-1 protein Vpr, is critical for T cell function. Recently, we found VprBP was down-regulated in aged senescent T cells and deletion of VprBP in young T cells lead to ROS induced senescence via down-regulation of glutathione-mediated detoxification enzyme Gstp1. We also found specifically increased senescent T cells in tumor microenvironment but not periphery lymphoid organs in B16 tumor model. Here we propose the central hypothesis that VprBP-Gstp1 plays an important role in preventing ROS induced T cell senescence in tumor microenvironment and targeting VprBP-Gstp1 could suppress T cell senescence and promote anti-tumor immunity.

作为抗肿瘤免疫和肿瘤免疫治疗中的关键细胞，T细胞发挥抗肿瘤功能首先要克服肿瘤微环境的免疫抑制作用。肿瘤微环境中的调节性T细胞、巨噬细胞和髓源抑制细胞能分泌大量的免疫抑制性分子例如活性氧、TGFβ和PD-L1等诱导T细胞衰老或者耗竭。其中活性氧不仅能抑制T细胞分裂和功能，还能诱导T细胞凋亡和衰老。人们普遍认为活性氧类能够诱导衰老，且在肺癌、头颈癌病人中也发现衰老的T细胞明显增加，但是诱导T细胞衰老的分子机理和T细胞衰老对抗肿瘤免疫的影响尚不清楚。我们发现HIV-1病毒的细胞宿主受体VprBP能够通过促进Gstp1的表达来抑制活性氧水平从而抑制T细胞衰老，而且小鼠黑色素瘤肿浸润T细胞的衰老显著增加。因此我们假设VprBP-Gstp1通路可能抑制肿瘤微环境中活性氧对肿瘤浸润T细胞衰老的作用，而靶向VprBP-Gstp1可以抑制活性氧造成的T细胞衰老从而增加T细胞的抗肿瘤免疫。

细胞衰老影响T细胞功能，导致机体抗肿瘤免疫反应受限。有报道指出，T细胞衰老会导致人体组织器官衰老，在肺癌和头颈癌患者中衰老T细胞明显增加。但T细胞衰老对抗肿瘤免疫的影响尚未见报道。我们的研究发现，年老小鼠T细胞较年轻小鼠T细胞衰老标志分子p16、KLRG1等表达显著上调；同样在肿瘤组织浸润的T细胞中也呈现明显的衰老表型；进一步研究发现VprBP在年老小鼠T细胞中表达下调，利用T细胞特异性VprBP基因敲除小鼠模型证实VprBP缺失会导致T细胞活性氧上调、衰老指标上调，表型与年老小鼠T细胞衰老表型相似，据此推测VprBP会调控T细胞衰老。通过IP-MS筛选得知VprBP能够结合并促进Gstp1表达，降低T细胞活性氧水平，高表达Gstp1能够促进T细胞增殖，抑制衰老。最后，利用CAR-T细胞治疗模型证实，Gstp1能够降低CAR-T细胞活性氧，促进增殖、抑制衰老、降低凋亡，增强CAR-T细胞体外杀伤肿瘤能力和细胞因子分泌能力，提高CAR-T细胞治疗小鼠肺癌移植瘤效果。因此，本研究证实VprBP能够通过Gstp1降低T细胞活性氧水平，抑制T细胞衰老，提高抗肿瘤免疫治疗效果，为基于T细胞的肿瘤免疫治疗提供理论基础。