程序性死亡-1(PD-1)抗体耐药是个涉及多基因多通路的复杂过程。文献报道骨髓来源抑制细胞（MDSCs）减少肿瘤微环境T淋巴细胞浸润是PD-1抗体无效的重要原因。课题组研究发现，在肠癌细胞中抑制环氧化酶-2(COX-2)通过前列素E2受体EP4介导减少MDSCs，MDSCs中肿瘤坏死相关凋亡诱导配体（TRAIL）显著上调，锁定TRAIL为COX-2调控MDSCs的关键基因。本项目拟通过对COX-2敲除或抑制确认COX-2对MDSCs的调控，检测肿瘤微环境T淋巴细胞变化；通过TRAIL中和抗体和RNA干扰，检测能否逆转COX-2抑制剂对MDSCs凋亡的影响；通过RNA干扰，探讨TRAIL表达是否通过EP4/蛋白激酶A（PKA）调控；通过小鼠肠癌模型实验确认联合治疗的效果；从而证明COX-2抑制剂通过EP4/PKA上调TRAIL增加MDSCs凋亡，增加T淋巴细胞浸润，增强PD-1抗体的疗效。

Resistant to Programmed Death-1(PD-1) blockade immunotherapy is a complex processes involving multiple genes and signaling pathways. Studies indicated that resistance to PD-1 blockade therapy can be explained by less infiltration of T lymphocytes in tumor micro environment and this may be mediated by Myeloid-Derived Suppressor Cells (MDSCs).We found that COX-2 inhibiting resulted in decreasing number of MDSCs, through prostaglandin E2 receptor-EP4. And the transcriptomics analysis of MDSCs after co-cultured with COX-2 knockout colorectal cancer cells, showed Tumor necrosis factor related apoptosis inducing ligand(TRAIL) was significantly upregulated in MDSCs, indicating TRAIL was the key target for modulating MDSCs. In the study, first step is to confirm COX-2 regulating MDSCs by COX-2 knockout or inhibition, detect the change of T lymphocytes in tumor microenvironment. TRAIL neutralized antibody or RNA interference is used to test whether MDSCs apoptosis causing by COX-2 knockout or inhibition could be reversed. With RNA interference, to verify TRAIL is regulated by EP4/PKA pathway. To investigate the efficacy of COX-2 inhibitor combined with PD-1 blockade in mice colon model. With these, it will be proved that COX-2 inhibitor inhibits COX-2 activity, leads to EP4 mediated TRAIL upregulation, results in increasing MDSCs apoptosis, which increases T lymphocytes in tumor microenvironment, thus enhance the efficacy of PD-1 blockade and provide preliminary data for future combination therapy.