荷瘤状态下促瘤中性粒细胞对NK细胞抗肿瘤功能的抑制作用及其机制

A weaker antitumor capability of NK cells was found in many types of human cancers and murine models, and the mechanisms were not completely elucidated. In our recent studies, we found that the function of polymorphonuclear leukocytes (PMNs or neutrophils) was converted from tumor-suppressing to tumor-promoting in tumor-bearing status, and these PMNs could weaken the antitumor capability of NK cells. Meanwhile, we also found that the tumor-promoting PMNs can be reversed to tumor-suppressing cells, and normal NK cells are required for better antitumor efficacy based on the PMNs function reversion, so the weaker antitumor capability of NK cells might be the bottleneck of synergistic antitumor function of PMNs and NK cells. In this project, we will investigate the material basis (including the expression of NK activating/inhibitory receptors, cytotoxicity molecular; the capability of chemotaxis and activation; the maturation status) of decreased antitumor capability of NK cells. Meanwhile, the molecular mechanisms of how PMNs inhibit NK cells will be also investigated. In additional, we will further investigate the effect of NK activating factor IL-2, IL-18, IL-15 and anti-CD40 antibody on the recovery of NK cells function. Our study is expected to clarify the material basis and mechanism of NK cells dysfunction mediated by tumor-promoting PMNs. The results may not only be important for the theory of immunoregulation, but also lead to a new strategy of tumor therapy by recovering the antitumor function of neutrophils and NK cells together in presence of tumor.

肿瘤中自然杀伤细胞（NK）的抗肿瘤功能减弱，其机制未完全阐明。我们研究发现：荷瘤状态下，中性粒细胞（PMN）的功能转变为促肿瘤生长，促瘤生长的PMN又可导致NK的抗肿瘤功能下降，提示促瘤PMN对NK功能的抑制是NK功能异常的机制之一。同时观察到：促瘤PMN可逆转为抑瘤细胞，且需要在正常NK的协同下才可发挥较强的抗肿瘤功能，而NK功能异常将是PMN与NK协同抗肿瘤功能的瓶颈。本项目将探索PMN介导的NK功能异常的物质基础（NK激活/抑制性受体、细胞毒性分子，趋化、激活能力，成熟状态等的改变），研究PMN削弱NK功能的分子机制及作用形式，并研究NK激活剂IL-2、IL-18、IL-15及CD40抗体等对异常功能NK细胞功能恢复的作用。本项目有望阐明PMN介导的NK功能异常的机制，具有重要的理论价值，可为建立荷瘤状态下以逆转PMN功能为基础、联合恢复NK功能的肿瘤免疫治疗提供思路和依据。

荷瘤状态下，全身免疫状态的改变导致中性粒细胞获得促瘤功能，进而导致NK细胞的抗肿瘤功能受到抑制。诱导性的中性粒细胞功能异常能调节NK细胞的抗肿瘤功能，但是“叛变”的中性粒细胞调节NK细胞抗肿瘤功能的详细机制并不清楚。本研究报道，荷瘤状态的中性粒细胞可以损伤NK细胞的抗肿瘤功能、浸润能力。CCR1的表达下调是NK细胞浸润能力下降的原因。中性粒细胞可以降低NK细胞激活性受体NKG2D与NKp46d的反应性。体内诱导性表达的PD-L1（中性粒细胞表达）、PD-1（NK细胞表达）及PD-L1/PD-1信号轴是抑制NK细胞抗肿瘤免疫的主要原因。全身G-CSF浓度上升促进中性粒细胞表达PD-L1，并且G-CSF通过G-CSFR/JAK2-STAT3通路促进PD-L1的表达。肿瘤来源的IL-18增强PD-1的表达，使用IL-18BP阻断IL-18或采用siRNA敲低IL-18的表达可阻断IL-18诱导的PD-1上调。中性粒细胞—NK细胞作用表现依赖于细胞—细胞接触，将二者共培养与非直接接触系统的时候，中性粒细胞对NK细胞功能的抑制作用消失。本研究强调了PD-L1/PD-1信号通路在中性粒细胞抑制NK细胞功能中的重要作用。产G-CSF与IL-18可能通过激活免疫抑制信号或削弱NK细胞的抗肿瘤功能介导进而导致患者的预后更差。靶向G-CSF与IL-18可能成为在肿瘤中和治疗中进一步清除残存肿瘤细胞的可能途径。