INFβ/ISG15/B7H4对结直肠癌微环境中CTL细胞的调控及其作用机制

Cellular immunosuppression of the cytotoxic lymphocytes in the microenvironment is one of the important conditioned states for the survival and progression of cancer. Our previous studies have shown that high expression of ISG15 in the colorectal cancer (CRC) tissues is associated with poor prognosis and liver metastasis of patients with CRC. CRC cells highly expressed ISG15 and B7H4 after exogenous IFNβ stimulation. When murine colonic cells were stimulated with IFNβ and transplanted into mice, the mice died in a short time, and a low level of CTLs infiltrated into the grafted tumors, CTLs showed a decreased capability of cancer cell-killing as well. These data suggested that CRC cells might take advantages of IFNβ in the microenvironment, and up-express ISG15 and B7H4, thereby inhibit the lethal effect of CTLs in the tumor microenvironment. This study demonstrates IFNβ/ISG15/B7H4 modulates cytotoxic lymphocytes in colorectal cancer microenvironment and CTLs immunosuppressive effects in the microenvironment. Finally, the findings should be verified in the human CRC tissues and the CTLs in the peripheral blood of CRC patients. This study is aimed to demonstrate a novel mechanics of colorectal cancer and microenvironment through the signal pathway of IFNβ/ISG15/B7H4 in provoking cellular immunosuppression and strengthen cancer progression. The mechanistic findings may give rise to provide potential molecules for cancer immunotherapy.

肿瘤微环境中细胞毒性T细胞（CTLs）功能的抑制是肿瘤发生与进展的重要原因。我们前期研究发现：结直肠癌组织高表达ISG15与患者不良预后和肝转移有关；IFNβ刺激的结直肠癌细胞同时高表达ISG15和B7H4；将鼠源性结肠癌细胞株用IFNβ刺激后植入小鼠，小鼠生存期缩短及肿瘤组织内CTLs浸润减少，CTLs杀伤癌细胞的能力降低。这些结果提示，结直肠癌细胞利用微环境中IFNβ增强ISG15、B7H4的表达，进而抑制肿瘤微环境中CTLs的杀伤效应。本项目将展现INFβ/ISG15/B7H4信号途径的调控作用及对肿瘤微环境浸润CTLs的抑制效应，并在人类结直肠癌组织标本和结直肠癌患者外周血CTLs中进行验证。项目研究旨在阐明结直肠癌及其微环境通过IFNβ/ISG15 /B7H4信号通路的调控，抑制CTLs功能，促进肿瘤进展的新理念，为肿瘤免疫治疗提供潜在的靶向分子。

本研究前期发现与结直肠癌CRC转移相关的重要分子：干扰素刺激基因15（ISG15），ISG15的高表达与CRC的临床进展和不良预后密切相关，并且外源性干扰素β（IFNβ）能够刺激CRC细胞高表达ISG15，同时伴有细胞免疫抑制分子B7H4的高表达。本研究阐述肿瘤微环境中IFNβ诱导CRC细胞高表达ISG15和B7H4的分子机制，并验证高表达B7H4的细胞免疫抑制状态。研究发现IFNβ能够有效刺激CRC细胞高表达ISG15，且具有时间与剂量依赖性。高表达ISG15的CRC组织，与患者不良预后有关。ISG15高表达时，伴有免疫抑制相关分子B7H4的表达，并且能够抑制树突状细胞的抗原递呈。CT16.WT细胞移植于Balb/c小鼠，模拟肿瘤-微环境状态，IFNβ刺激后的癌细胞，小鼠生存能力下降，癌细胞高表达ISG15、B7H4，癌细胞内浸润CD8+淋巴细胞显著减少。临床组织标本检测，B7H4表达增高、CD8+浸润细胞减少，均与CRC患者不良预后有关。ISG15、B7H4、CD8共标记示ISG15high/B7H4high/CD8low的患者群，预后最差，提示CRC细胞通过适应微环境中IFNβ的刺激，通过高表达ISG15、B7H4，抑制微环境中CD8+淋巴细胞的浸润，促进肿瘤的进展。研究项目初步提示了肿瘤细胞与微环境的相互适应性，肿瘤细胞利用微环境因素，通过作用于微环境中的免疫细胞，抑制免疫杀伤功能，而导致肿瘤进展。通过这一机制，抑制IFNβ的分泌、靶向作用于ISG15、B7H4，可能有助于治疗结直肠癌，并且能够显著降低治疗过程中产生的毒副作用。利用微环境、影响肿瘤微环境，抑制环境中的免疫功能，可能是肿瘤进展的主要原因。