局部肿瘤低分割放疗后MDSC的动态变化及其趋化与激活机制研究

Hypofractionated radiotherapy is a common method for local radiotherapy of malignant tumors, which can promote the transformation of “cold tumors” into “hot tumors” and thus promote anti-tumor immunity. However, studies have found that hypofractionated radiotherapy can also generate immunosuppression microenvironment and promote treatment resistance and tumor metastasis. Our and other studies have confirmed that hypofractionated radiotherapy can induce myeloid derived suppressor cells (MDSCs) to accumulate in the tumor and led to immunosuppression. Specific molecular mechanisms need to be further elucidated. To study the dynamic changes of MDSCs in tumors and in vivo caused by hypofractionated radiotherapy, especially to elucidate the mechanism of MDSCs chemotaxis and activation, which is extremely important for clinicians to select the optimal timing and method for inhibiting MDSC, and to optimize the combination therapy strategy in clinical practice. We previously demonstrated that MDSCs in the early stage of radiotherapy were aggregated in tumor and subpopulation changed, accompanied by high expression of chemokine receptors CXCR2, CXCR4, and PD-L1. In this study, we will further study the dynamic changes and subgroup functions of MDSC on the basis of the previous findings to elucidate the molecular mechanisms of MDSCs chemotaxis and activation in tumor, and to verify the inhibition effect on MDSC, caused by differential inhibition of CXCR2, CXCR4, etc., and on intratumor accumulation and killing activity of cytotoxic immune cells, such as CART and OVA-CTL on this basis, to optimized the combination therapy strategy. The implementation of this project will provide an important foundation for further understanding of radiotherapy-induced MDSC chemotaxis and activation as well as specific intervention of MDSC to improve the therapeutic efficacy of malignant tumors.

低分割放疗是恶性肿瘤局部放疗的常用方式，可促进“冷肿瘤”转变成“热肿瘤”进而增强抗肿瘤免疫。但低分割放疗还可产生抑制性免疫微环境，促进治疗抵抗和肿瘤转移。我们前期结果和其他研究都证实低分割放疗可以诱导MDSC在瘤内聚集并产生免疫抑制，具体分子机制亟待深入阐明。研究MDSC在肿瘤局部和系统的动态变化，特别是阐明其向瘤内趋化及激活的机制，对选择靶向MDSC最佳时机和方法，及进一步联合治疗极为重要。我们前期证实MDSC放疗早期即在瘤内聚集和发生亚群变化，并伴有CXCR2、CXCR4以及PD-L1高表达。本项目将在前期基础上进一步研究MDSC的动态改变和亚群功能，阐明其向瘤内趋化激活的分子机制，验证CXCR2、CXCR4等不同抑制对MDSC抑制作用和对CAR-T、CTL联合治疗在瘤内聚集及杀伤活性的影响。项目实施将为深入了解放疗诱导MDSC趋化与激活，靶向干预MDSC提高免疫治疗疗效提供重要基础。

低分割放疗是恶性肿瘤局部放疗的常用方式，可促进“冷肿瘤”转变成“热肿瘤”进而增强抗肿瘤免疫。但低分割放疗还可产生抑制性免疫微环境，促进治疗抵抗和肿瘤转移。我们前期研究证实低分割放疗可以诱导T细胞及免疫抑制细胞MDSC在瘤内聚集，并高表达免疫抑制分子PD-L1。本项目首先增加不同肿瘤模型验证低分割放疗对于肿瘤局部及全身免疫细胞的动态影响。结果表明低分割放疗可调动外周血中T细胞及MDSC向瘤内聚集。按照研究计划，进一步阐明MDSC向瘤内趋化及激活的机制。我们发现低分割放疗可以通过趋化因子及其受体募集外周血MDSC瘤内浸润，并在瘤内激活。进一步，通过测序和细胞因子芯片技术分析发现，放疗后骨髓、脾脏及肿瘤中MDSCs 上趋化因子受体CCR2 和CXCR2 基因表达上调，外周血和肿瘤中对应的趋化因子CCL2、CXCL1、CXCL2 和CXCL5 升高，因此我们推测放疗主要通过趋化因子-趋化因子受体途径募集MDSC 进入肿瘤，特别是CXCR2 和CCR2 轴。为了验证上述推测，我们使用CXCR2 拮抗剂和敲除CCR2，发现二者均可显著抑制瘤内及血液中MDSC 的聚集。CXCR2 拮抗剂还可增加T 细胞浸润，优化抗肿瘤免疫力。因此，我们利用上述放疗后MDSC 向肿瘤浸润的趋化信号与时机，使用CXCR2 拮抗剂抑制了放疗诱导的瘤内MDSC的聚集，联合EpCAM-CAR T 细胞治疗，在患有乳腺癌的小鼠中观察到了显著的抗肿瘤作用，为CAR-T 治疗实体瘤提供优化的治疗策略。. 此外，在此项目支持下，我们拓展延伸相关研究内容。我们发现不同分割方式（5Gy ×5，8Gy×3，单次5Gy，单次10Gy）放疗后，均可在放疗结束后早期诱导瘤内MDSC的聚集。并且放疗也可诱导T细胞向瘤内浸润。本研究为免疫疗法联合放射疗法的合理设计提供了理论依据。. 在本项目支持下共发表 SCI 论文 4 篇，目前正在撰写论文1篇，培养博士研究生4名，硕士研究生3名。