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

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，因其与结直肠癌及相应的远处转移的相关性而受到越来越多的关注。研究发现了核梭菌影响肿瘤微环境的几种机制。有趣的是，据报道，核梭菌可以保护肿瘤细胞免受免疫细胞的杀伤。从机制上讲，NK细胞和T细胞表达的抑制受体TIGIT参与抑制抗肿瘤免疫。最近，核仁梭菌也被发现特异性结合CEACAM1，这是一种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与CEACAM1的相互作用抑制了结直肠癌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细菌参与CEACAM1对肿瘤微环境中肿瘤细胞杀伤的影响。在第一部分中，将产生缺乏结合CEACAM1的核梭菌突变体，并确认最近鉴定的三聚体自转运体粘连素是CEACAM1的梭菌配体。在第二部分中，我们将首先测试从人类结直肠癌标本中分离的具核梭菌临床菌株与CEACAM1的结合是否保守。此外，我们还将研究核梭菌与CEACAM1结合对肿瘤浸润淋巴细胞抗肿瘤免疫的影响。最后，利用表达人CEACAM1的转基因小鼠，评估核梭菌与CEACAM1结合对体内肿瘤生长的影响。综上所述，本项目将破译F. nucleatum - ceacam1相互作用对肿瘤微环境中抗肿瘤免疫的影响。我们的长期目标是将这些发现转化为新的靶向治疗，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.