免疫检查点新分子PI3K相互作用蛋白1行肿瘤免疫治疗的机制和潜能探究

Searching for the new immune checkpoint and develop its inhibitor for the anticipation of better curative effect and lower side effect have become the focus of tumor immune therapy. The membrane protein PIK3IP1 is an inhibitor of P13K/AKT pathway and the related research focused on the tumor epithelium indicated that it’s an inhibitory protein. However, whether it also has effect on immune cells and tumor has not yet been identified. Our early research indicated that PIK3IP1 specifically expressed on immune cells like T cells. And the expression pattern can change with the different activation status in vivo and in vitro. PIK3IP1 can inhibit the proliferation and function of T cells in vivo. It also has blocking effect in vitro and promote the proliferation of T cells. PIK3IP1 knock-out mice show that the loss of the gene can induce innate immune response and inflammation, and the KO mice has more intense T cell reaction towards antigens. Meanwhile, PIK3IP1 can promote iTreg, and the changes in Treg and Th17 are related to the phenomenon described above. Based on the results we’ve achieved, we come up with the hypothesis that PIK3IP1 is a new immune checkpoint. It can inhibit the anti-tumor function of T cells and thus affect the growth of the tumors. This process is driven by the imbalance of Treg and Th17 cells. For the purpose of comprehensively evaluating the effect of PIK3IP1 on tumor antigen specific reaction and effect on tumor growth, we plan to use the anti-mouse monoclonal antibody of PIK3IP1 and the PIK3IP1 knock-out mice that we achieved earlier to build the tumor model based on melanoma and colorectal cancer, as well as the pre-cancerous lesion based on the tumorogenisis of oral mucosa induced by 4NQO. We also plan to identify the receptor or ligand that it interacts with, and further generate the PIK3IP1, Treg and Th17 cross knock-out mice in order to decide whether the phenomenon is related to the imbalance of Treg and Th17.This study is expected to provide a new target and idea in tumor immune therapy.

寻找更有效和低毒副作用的免疫检查点新分子成为肿瘤免疫治疗的焦点。膜蛋白PIK3IP1是PI3K/AKT通路抑制分子，已有研究显示其是肿瘤抑制蛋白，但免疫微环境中作用不明。本课题组前期研究显示PIK3IP1特异性表达于T细胞为主的免疫细胞，且随免疫激活改变；PIK3IP1可抑制T细胞增殖及效应功能；其基因缺失可自发炎症，KO鼠对新抗原有更强的T细胞反应，上述过程伴有Treg和Th17的比例变化。由此提出假说：PIK3IP1是新的免疫检查点分子，其可抑制T淋巴细胞抗肿瘤反应而影响肿瘤生长，这一过程可由Treg/Th17失衡介导。本研究拟利用前期获得的PIK3IP1单抗及敲除鼠，以黑色素瘤和结肠癌为肿瘤模型，以4NQO诱导口腔黏膜癌变为癌前模型，全面评估PIK3IP1对肿瘤抗原特异性反应和肿瘤生长的影响及治疗效能，及依赖Treg/Th17失衡发生的机制，研究有望为肿瘤免疫治疗提供新靶点。

免疫检查点治疗总体有效率低，寻找新的免疫检查点分子，以期获得更高的治疗有效性和更低的副作用已经成为肿瘤免疫治疗的焦点。. 本项目发现PI3K相互作用蛋白1 (Pik3ip1)主要高表达于T细胞，其在口腔鳞癌/肝癌患者T细胞的表达与T细胞增殖能力降低、功能受损相关。通过构建Pik3ip1基因敲除小鼠，并与OT-I小鼠杂交，发现Pik3ip1基因缺失促进肿瘤抗原特异性T细胞抗肿瘤免疫反应，抑制肿瘤生长。进一步通过过表达质粒构建、免疫共沉淀、激光共聚焦等揭示Pik3ip1通过胞外段寡聚以蛋白酶体的方式介导SLP76的降解从而抑制T细胞活化。Pik3ip1融合蛋白处理显著促进肿瘤生长，明显抑制T细胞活化及其效应因子的分泌。以上研究结果为肿瘤免疫治疗提供新的治疗靶点，相关结果已发表在Clinical Cancer Reseach，2019，JCR一区。. 同时，在4NQO诱导口腔黏膜上皮癌变模型中，我们发现PD-1阻断治疗可有效抑制口腔黏膜恶性转化，但部分小鼠对PD-1治疗出现耐药，进展为原位癌或浸润癌，进一步研究发现引流淋巴结中调节性T细胞（Treg）聚集和T细胞TIM-3表达上调可能介导了口腔癌PD-1治疗抵抗。该研究为打破免疫检查点治疗抵抗提供新的思路，相关结果已发表在Journal of Experimental and Clinical Cancer Research，2020，JCR一区。. 本项目揭示了新免疫检查点分子Pik3ip1抑制肿瘤抗原特异性T细胞抗肿瘤免疫反应的机制和口腔癌中经典免疫检查点分子PD-1治疗抵抗的可能机制，最终拟为打破免疫检查点治疗抵抗和提高肿瘤免疫治疗疗效提供新的思路和靶点。