Thrombocytes in Cancer Immunity

 描述(申请人提供)：血小板或血小板主要起止血作用。它们越来越多地通过转化生长因子β、血管内皮生长因子、基质金属蛋白酶-2、三磷酸腺苷等介质参与肿瘤的进展和转移。此外，血小板可以通过GPIB、P-选择素和TREM-I配体激活中性粒细胞，从而调节先天免疫和炎症。它们还被证明通过CD40L-CD40途径激活树突状细胞(DC)，并通过将细菌抗原运送到DC促进抗原交叉递送。然而，令人惊讶的是，尽管在许多大型临床研究中，抗血小板药物似乎有效地防止了癌症的进展，但在该领域中，血小板在抗肿瘤免疫中的作用几乎没有受到关注，而且仍然不明确。特别是，癌症相关性血小板增多症与不良的临床结果相关，但其潜在机制尚不清楚。一个特定而重要的问题与血小板通过激活的血小板分泌体(SAP)中的大量分子在塑造癌症相关免疫中的作用有关。我们的初步研究表明，SAP通过一种稳定的、可分离的可溶性因子抑制CD4和CD8T细胞的激活和效应功能。此外，利用我们独特的由于失去gp96(血小板GPIb-IX-V复合体的必备伴侣)而导致的血小板减少的小鼠模型，我们发现血小板显著促进甲基胆蒽(MCA)诱导的纤维肉瘤。在血小板减少的环境中，肿瘤的发展与循环中髓系来源的抑制细胞(MDSCs)的减少、更丰富的肿瘤浸润性CD8T细胞以及T细胞效应器功能的增强显著相关。最后，采用过继T细胞转移策略，我们发现血小板减少通过体内CD8T细胞促进抗黑色素瘤免疫，这与MDSCs的减少相关。我们的研究使我们假设，血小板通过促进MDSCs和抑制T细胞的激活和功能，在癌症免疫监测中发挥负性和免疫调节作用。这一新的假设将通过四个具体目标来解决。目的1通过回答在PF4-gp96 KO小鼠中MCA诱导的纤维肉瘤的减少是否是由于增强的获得性免疫来确定血小板是否参与了癌症免疫监测。我们还将确定，血小板缺陷是否会增强针对多种肿瘤系统的肿瘤特异性免疫启动。目的2将使用我们有希望的生化策略来确定血小板分泌组钝化CD4和CD8T细胞激活的分子机制。目的3将在肿瘤特异性CD8 T细胞过继治疗肿瘤的背景下揭示血小板-MDSC相互作用的机制。我们的最终目标将使我们能够优化针对血小板的策略，以加强黑色素瘤的免疫治疗。总而言之，我们的研究将揭示基于免疫的潜在机制，即血小板促进癌症，并将巩固免疫治疗和抗血小板药物相结合作为抗癌新策略的想法。

 DESCRIPTION (provided by applicant): Thrombocytes or platelets function primarily in hemostasis. Increasingly, they have been implicated in cancer progression and metastasis via TGFβ, VEGF, MMP-2, ATP and other mediators. Moreover, platelets can regulate innate immunity and inflammation by activating neutrophils via GPIb, p-selectin and TREM-I ligand. They have also been shown to activate dendritic cells (DCs) via a CD40L-CD40 pathway, and promote antigen cross-presentation through shuttling bacterial antigens to DCs. Surprisingly, however, the roles of platelets in anti-tumor immunity have received little attention in the field and are still undefined, despite anti-platelet agents appearing to be effective in preventing cancer progression in a number of large clinical studies. In particular, cancer-associated thrombocytosis correlates with the poor clinical outcome, but the underlying mechanism is unclear. A specific and important question is related to the role of platelets in shaping cancer-associated immunity via a multitude of molecules in the secretome of activated platelets (SAP). Our preliminary studies have demonstrated that SAP suppresses activation and effector function of both CD4 and CD8 T cells by a soluble factor that is stable and fractionable. Moreover, using our unique mouse model of thrombocytopenia due to the loss of gp96, an obligatory chaperone for the platelet GPIb-IX-V complex, we show that platelets significantly promote methylcholanthrene (MCA)-induced fibrosarcoma. Tumor development in the thrombocytopenic environment correlated significantly with the reduction of circulating myeloid-derived suppressor cells (MDSCs), more abundant tumor-infiltrating CD8 T cells, and increased T cell effector function. Finally, using an adoptive T cell transfer strategy, we found that thrombocytopenia promoted anti-melanoma immunity by CD8 T cells in vivo that correlated with the reduction of MDSCs. Our studies led us to hypothesize that platelets play negative and immunoregulatory roles in cancer immunosurveillance via promoting MDSCs and suppressing T cell activation and functionality. This novel hypothesis will be addressed by the four specific aims. Aim 1 will determine if platelets participate in cancer immune surveillance by answering if reduction of MCA-induced fibrosarcoma in PF4-gp96 KO mice is due to enhanced adaptive immunity. We will also determine if platelet defect enhances priming of tumor-specific immunity against multiple tumor systems. Aim 2 will use our promising biochemical strategy to define the molecular mechanism by which the platelet secretome blunts CD4 and CD8 T cell activation. Aim 3 will uncover the mechanism of platelet-MDSC cross-talk in the context of adoptive therapy of tumors with tumor-specific CD8 T cells. Our final aim will allow us to optimize a platelet- targeted strategy to enhance immunotherapy of melanoma. Collectively, our study will uncover underlying immune-based mechanisms by which thrombocytes promote cancer and it will solidify the idea of a combination of immunotherapy and anti-platelet agents as a novel and effective strategy against cancer.