低分割放疗对肿瘤免疫微环境的影响及免疫调节作用研究

Hypofration radiotherapy has been used wildly in clinic, and its clnical effects have been demonstrated by several researches. It was revealed that hypofraction radiotherapy involved in the host's immune modulation, and could impact the host's immune response by changing the micro environment.But whether hypofration can inhibit or promote antitumor immunity was controversy.More and more basic research revealed that high dose radiation in single fration could mediate antitumor immunity. High dose radiation in single fration was often used in basic research, but multiple-fraction radition was more popular in clinic use. Multiple-fraction radiation may cause dynamic changes to tumor microenvironment because lymphocytes are sensitive to radiation. Our pilot studies which delivered hypofration radiotherapy to high potential metastases model of breast cancer 4T1 in mice demonstrated that the level of MDSC increased in early phase of radiotherapy,and then lymphocytes increased obviously and the antibody emerged in late phase of the radiotherapy. And this revealed preliminary that hypofraction radiotherapy could induce the antitumor immunity. In this study, we will observe the dynamic change of the key immunal molecular regulating factors, and the dynamic change of composition and activity of the immune cells in tumors, by the use of tumor model in mice on the basis of our pilot study. And we will also explor the effects of the specific antitumor immunity which is impacted by the change of the molecular. The execution of this study is helpful to provide basic research data for improving the treatment effects through immune intervention in the adjuvant therapy combinated with hypofraction radiotherapy.

低分割放疗在临床上应用广泛并显示出临床获益。研究表明，低分割放疗参与机体免疫调节，通过改变免疫微环境影响机体免疫应答，但究竟是抑制肿瘤免疫还是促进肿瘤免疫，目前尚有争议，越来越多的基础研究的证据支持单次高剂量放疗介导抗肿瘤免疫。但基础研究中，多采用高剂量的单次照射，而临床中常采用高剂量多次放疗，由于淋巴细胞对放疗敏感，多次放疗可能导致肿瘤微环境动态变化。本项目前期在小鼠高转移潜能的4T1乳腺癌模型采用低分割多次放疗，结果发现放疗早期瘤内MDSC增加，治疗后期大量淋巴细胞增加，并观察到抗体产生，初步证实可能诱导了抗肿瘤免疫。在本项目中，我们将在前期工作基础上，拟在小鼠肿瘤模型中，动态观察肿瘤细胞关键免疫调节分子的动态变化，瘤内免疫细胞的成分和活性的动态变化，并探讨这些分子变化对诱导特异的抗肿瘤免疫的影响。本项目的实施有望为临床低分割放疗的免疫干预提升治疗疗效提供研究基础。

随着放疗技术的发展，低分割放疗在包括乳腺癌、直肠癌、肺癌等多种肿瘤中应用并显示出更好的临床优势。大剂量放疗究竟是抑制肿瘤免疫还是促进肿瘤免疫目前仍有争议。在不同肿瘤模型中、不同放疗模式下，放疗对肿瘤免疫的作用不同。我们在直肠癌和乳腺癌模型中，分别采用了大剂量单次照射和低分割多次放疗，结果表明在4T1乳腺癌模型中，在12Gy*4次的放疗模式下，放疗前后肿瘤中T淋巴细胞、MDSC、DC和巨噬细胞的数量有增高趋势，但无有统计学意义的差别，12Gy*1次的放疗在乳腺癌模型中使MDSC向M2型极化，抑制抗肿瘤免疫而促进肿瘤的生长。12Gy*1次的放疗在CT26结直肠癌模型中观察到与乳腺癌模型中相同的现象，而5Gy*5次的低分割放疗在CT26结直肠癌模型中促进了肿瘤微环境中的CD8+T、CD4+T细胞的浸润，对肿瘤微环境中的DC细胞、MDSC细胞的变化影响不大，促进了MICA、PD-L1的产生，抑制了p-STAT3 705、Gal-1、p-STAT1 的产生，显示了放疗对抗肿瘤免疫的促进作用。结论：在低分割放疗中，同时存在免疫抑制因素和调节免疫的积极因素，并随着放疗方式和放疗进程发生变化，最终的免疫应答取决于积极因素和抑制因素的强弱。低分割放疗对免疫的抑制或促进作用可能存在剂量和时间依赖性。