Mouse Myeloid panel on G-MDSCs from treated tumors

Immune checkpoint inhibition (ICI) has revolutionized treatment in cancers that are naturally immunogenic by enabling infiltration of T cells into the tumor microenvironment (TME) and promoting cytotoxic signaling pathways. Tumors possessing complex immunosuppressive TME’s such as breast and pancreatic cancers present unique therapeutic obstacles as response rates to ICI remain low. Such tumors often recruit myeloid-derived suppressor cells (MDSCs) whose functioning prohibits both T-cell activation and infiltration. We attempted to sensitize these tumors to ICI using epigenetic modulation to target MDSC trafficking and function to foster a less immunosuppressive TME. We showed that combining a histone deacetylase inhibitor, entinostat (ENT), with anti–PD-1, anti–CTLA-4, [A1] [A2] or both, significantly improved tumor-free survival in both the HER2/neu transgenic breast cancer and the Panc02 metastatic pancreatic cancer mouse models. Using flow cytometry, gene expression profiling, and ex vivo functional assays, we characterized populations of tumor-infiltrating lymphocytes (TILs) and MDSCs, as well as their functional capabilities. We showed that addition of ENT to checkpoint inhibition led to significantly decreased suppression by granulocytic-MDSCs in the TME of both tumor types. We also demonstrated an increase in activated granzyme-B–producing CD8+ T effector cells in mice treated with combination therapy. Gene expression profiling of both MDSCs and TILs identified significant changes in immune-related pathways. In summary, addition of ENT to ICI significantly altered infiltration and function of innate immune cells, allowing for a more robust adaptive immune response. These findings provide a rationale for combination therapy in patients with immune-resistant tumors, including breast and pancreatic cancers. To identify possible mechanisms for their impaired function, we utilized NanoString transcript profiling to evaluate broad changes in the transcriptome of isolated G-MDSCs induced by treatment.

免疫检查点阻断疗法（immune checkpoint inhibition, ICI）通过介导T细胞浸润肿瘤微环境（tumor microenvironment, TME）并激活细胞毒性信号通路，彻底革新了天然免疫原性癌症的治疗范式。而乳腺癌、胰腺癌等具有复杂免疫抑制性肿瘤微环境的肿瘤，其免疫检查点阻断疗法应答率仍然偏低，因此面临独特的治疗挑战。这类肿瘤通常会招募髓系来源抑制细胞（myeloid-derived suppressor cells, MDSCs），这类细胞的功能可同时抑制T细胞的活化与浸润。本研究尝试通过表观遗传调控靶向髓系来源抑制细胞的迁移与功能，以重塑免疫抑制性更低的肿瘤微环境，从而使这类肿瘤对免疫检查点阻断疗法增敏。本研究证实，将组蛋白去乙酰化酶抑制剂恩替诺特（entinostat, ENT）与抗PD-1、抗CTLA-4疗法单独或联合使用[A1][A2]，可显著提升HER2/neu转基因乳腺癌与Panc02转移性胰腺癌小鼠模型的无瘤生存率。本研究通过流式细胞术、基因表达谱分析与离体功能实验，对肿瘤浸润淋巴细胞（tumor-infiltrating lymphocytes, TILs）与髓系来源抑制细胞的群体特征及其功能活性进行了表征。研究发现，在免疫检查点阻断疗法基础上联用恩替诺特，可显著降低两种肿瘤模型肿瘤微环境中粒细胞性髓系来源抑制细胞的免疫抑制活性。同时，本研究还证实，联合治疗组小鼠体内活化的、分泌颗粒酶B的CD8+效应T细胞数量显著升高。对髓系来源抑制细胞与肿瘤浸润淋巴细胞的基因表达谱分析显示，免疫相关通路发生了显著改变。综上，在免疫检查点阻断疗法中加入恩替诺特，可显著改变先天免疫细胞的浸润状态与功能，从而促成更强烈的适应性免疫应答。上述研究结果为免疫抵抗性肿瘤（包括乳腺癌与胰腺癌）患者的联合治疗方案提供了理论依据。为明确髓系来源抑制细胞功能受损的潜在机制，本研究采用NanoString转录谱分析技术，对治疗诱导的分离粒细胞性髓系来源抑制细胞的转录组整体变化进行了评估。