Analysis of the interaction of Fusobacterium nucleatum and CEACAM1 and its impact on antitumor immunity

具核梭杆菌是一种革兰氏阴性厌氧菌，主要存在于口腔中。近年来，由于其与结直肠癌及其相应的远处转移的相关性而受到越来越多的关注。发现了F.核质影响肿瘤微环境。有趣的是，F。据报道，nucleatum保护肿瘤细胞免受免疫细胞杀伤。机制上，观察到NK和T细胞表达的抑制性受体TIGIT的接合抑制抗肿瘤免疫。最近，F。还发现具核质特异性结合CEACAM1，CEACAM1是由上皮细胞和免疫细胞表达的抑制性跨膜蛋白。我们的中心假设是，F。nucleatum和CEACAM1抑制结直肠癌的肿瘤微环境中免疫细胞介导的肿瘤细胞杀伤。因此，本研究项目的目的是阐明CEACAM1的细菌接合对肿瘤微环境中肿瘤细胞杀伤的影响。在第一部分中，F.将产生缺乏结合CEACAM1的具核突变体，并且最近鉴定的三聚体自身转运蛋白粘附素将被证实为CEACAM1的梭菌配体。在第二部分中，将首先测试与CEACAM1的结合在F.从人结肠直肠癌标本中分离的核仁。此外，F.将研究结合CEACAM1的nucleatum对肿瘤浸润淋巴细胞的抗肿瘤免疫的影响。最后，使用表达人CEACAM1的转基因小鼠，研究F.总之，本项目将阐明F. nucleatum与CEACAM1结合对肿瘤生长的影响。在肿瘤微环境中，细胞核质-CEACAM1-相互作用对抗肿瘤免疫的影响。我们的长期目标是将这些发现转化为新的靶向疗法，以激活抗肿瘤免疫。

Fusobacterium nucleatum is a gram-negative anaerobic bacterium primarily found in the oral cavity. In recent years, it has gained increasing attention for its association with colorectal carcinoma and corresponding distant metastases. Several mechanisms were discovered by which F. nucleatum impacts the tumor microenvironment. Intriguingly, F. nucleatum was reported to protect tumor cells from immune cell killing. Mechanistically, engagement of the inhibitory receptor TIGIT expressed by NK and T cells was observed to inhibit antitumor immunity. Very recently, F. nucleatum was also found to specifically bind to CEACAM1, an inhibitory transmembrane protein expressed by epithelial and immune cells. Our central hypothesis is, that the interaction between F. nucleatum and CEACAM1 inhibits immune cell-mediated killing of tumor cells in the tumor microenvironment of colorectal cancer. Thus, the aim of this research project is to elucidate the effect of bacterial engagement of CEACAM1 on tumor cell killing in the tumor microenvironment. In the first part, F. nucleatum mutants deficient in binding CEACAM1 will be generated and the recently identified trimeric autotransporter adhesin will be confirmed as the fusobacterial ligand for CEACAM1. In the second part, it will first be tested whether binding to CEACAM1 is conserved among clinical strains of F. nucleatum isolated from human colorectal carcinoma specimens. In addition, the effect of F. nucleatum binding to CEACAM1 on antitumor immunity by tumor infiltrating lymphocytes will be investigated. Finally, using transgenic mice expressing human CEACAM1, the impact of F. nucleatum binding to CEACAM1 on tumor growth in vivo will be assessed.In summary, this project will decipher the influence of the F. nucleatum – CEACAM1-interaction on antitumor immunity in the tumor microenvironment. Our long-term aim is to translate these findings into new targeted therapies to activate antitumor immunity.