CXCR2+MDSCs亚群在PD1/PDL1阻断治疗乳腺癌无效或抵抗中的作用和机制研究

The efficacy of PD1/PDL1 blockage in advanced tumor therapy has been significantly increased both in pre- and clinical trials by its specific regulative function on tumor microenvironment. However, the positive response ratio is approximately 20%, this means that there are nearly 80% patients who is non-response or resistant to PD1/PDL1 blocking treatment. Therefore, it is very important to identify the mechanisms of non-response or resistance, to find the key factors that control the positive response to anti-PD1/PDL1 for predicting therapeutic outcome, and to identify targets for combination therapy with PD1/PDL1 blockage. Our previous studies demonstrated that CXCR2+MDSCs could expand and recruit in spleen, blood, lymph node and tumor tissues, and promoted tumor cells epithelial mesenchymal transition (EMT), increased the immunosuppressive molecular such as PD1, PDL1, TIM3, LAG3, and LITAG expression in T cells and induced T cells exhaustion, resulting in inhibiting anti-tumor immune response and promoting tumor progression. Furthermore, in PD1/PDL1 blockage experiments, compared with positive response groups, there are more CXCR2+MDSCs and less CD4+T and CD8+T cells in system and local tumor microenvironment in non-response or resistant groups in breast cancer and ovarian cancer mice models. This project based on these studies and will further address the function of CXCR2+MDSCs in PD1/PDL1 blockade treatment, find the key factor(s) to control the positive response, whether combination with anti-PD1/PDL1 and key factor(s) inhibitor can prolong survival of tumor-bearing mice, inhibit or even regress tumor growth. These finding can offer value clues for application of PD1/PDL1 blockade in breast cancer, specifically in triple-negative breast cancer therapy, further provide orientation to make strategy for combination treatment.

PD1/PDL1阻断治疗因其独特的肿瘤微环境免疫调控功能在多种肿瘤临床试验中疗效显著，但应答率仅20%左右，即近80%的患者无应答，因此阐明决定其应答的机制和关键因素对于治疗效果的预判和联合治疗靶标的选择至关重要。我们前期研究发现在乳腺癌进展中CXCR2+MDSCs亚群在免疫系统和肿瘤局部显著扩增，促进肿瘤EMT转变，诱导CTL耗竭，加速肿瘤进展和转移；且在PD1/PDL1阻断治疗无效荷瘤小鼠中发现大量该亚群募集，上述结果提示该亚群与PD1/PDL1阻断治疗无效相关。本课题旨在此基础上，采用高通量筛选、活体成像、多光谱分析等平台，阐明该亚群在PD1/PDL1阻断治疗中的作用；明确该亚群是否可以作为PD1/PDL1治疗策略选择或疗效预判的靶标；联合阻断该亚群与PD1/PDL1能否显著延长生存期，以期为PD1/PDL1阻断在乳腺癌尤其三阴性乳腺癌的治疗提供参考，也为联合治疗靶标的选择提供方向。

PD1/PDL1阻断治疗因其独特的肿瘤微环境免疫调控功能在多种肿瘤临床试验中疗效显著，但应答率仅20%左右，即近80%的患者无应答，因此阐明决定其应答的机制和关键因素对于治疗效果的预判和联合治疗靶标的选择至关重要。本课题采用高通量筛选、活体成像及多光谱分析等平台，探讨了该亚群在PD1/PDL1阻断治疗中的作用；研究了该亚群作为PD1/PDL1治疗策略靶标的可能性；初步揭示了导致PD1/PDL1的阻断治疗无效或抵抗的机制。结果显示，PD1/PDL1抗体阻断治疗无效或抵抗的荷瘤小鼠中免疫抑制性细胞亚群CXCR2+MDSC亚群的数量和占比显著增加，且与其他抗肿瘤免疫细胞CD4+和CD8+ 细胞的数量和比例呈负相关；单细胞测序发现促进乳腺癌淋巴结转移的CXCR2+MDSC细胞可以细分为5个亚群，其中Ly6G+MDSC亚群呈优势扩增或募集，且该亚群优势表达炎症相关因子基因。分选原位肿瘤和淋巴结转移瘤转录组测序结果显示转移瘤中Npg，Hba-a1, S100a9, Ifitm6, ifitm, Fos等基因表达显著上调；CXCR2抑制剂联合PD1/PDL1中和性抗体阻断治疗能够抑制乳腺癌进展，显著提升荷瘤小鼠生存率。上述结果说明Ly6G+CXCR2+MDSC亚群在PD1/PDL1抗体阻断治疗无效或抵抗中扮演重要角色，CXCR2抑制剂能够敏感（逆转）PD1/PDL1抗体治疗抵抗。此外，乳腺癌肿瘤组织中CXCR2的表达与PDL1呈显著正相关，而PDL1的表达与乳腺癌患者肿瘤组织内浸润的免疫细胞亚群包括CD4+ T，CD8+ T细胞，中性粒细胞和DC的浸润呈显著正相关，提示CXCR2或PDL1的表达可能不影响免疫细胞的瘤内募集，但CXCR2+MDSC细胞亚群营造的肿瘤局部微环境通过诱导慢性炎症，从而导致抗肿瘤适应性免疫应答无法启动或激活进而导致即使阻断PD1/PDL1信号亦无法恢复T细胞的抗瘤效应。因此，靶向Ly6G+CXCR2+MDSC亚群可能为乳腺癌患者的治疗提供新的解决方案。

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