PD-1抑制剂联合放疗加重肺损伤的机制及干预靶点研究

Immunotherapy (anti-PD-1/PD-L1) has become a crucial modality for non-small-cell lung cancer treatment. Radiation therapy (RT) remains one of the most effective strategies for lung cancer treatment. Anti–PD-1 treatment and RT synergistically promote antitumor effect and show promise in combined therapy. However, both anti-PD-1 and RT may cause immune-related lung injury, and the toxicity may be overlapped, even be enhanced. In our previous study, we revealed that compared with wildtype (WT) mice, PD-1 gene knockout mice (PD-1-/-) developed an enhanced lung injury and increased death after lung-targeting irradiation (LIR); anti-PD-1 enhanced lung injury was positively correlated with the production of TGF-β1 by macrophages; blocking TGF-β1 significantly alleviated the anti-PD-1 enhanced lung injury. Current research and our previous works indicated that anti-PD-1 may indirectly recruit and activate the macrophages via CD8+ T cells, and directly bind to and activate the PD-1+ alveolar macrophages, subsequently inducing increased secretion of TGF-β1. In the further study, we will complete the preliminary studies and determine the exact molecular mechanism of anti-PD-1 related lung injury through using the macrophage-specific Tgfb1 knockout mice, adoptive cell transfer of PD-1- T cell and macrophages. Furthermore, the distinct role of PD-1+ and PD-1- alveolar macrophages will be investigated. The study will provide a potential preventative and therapeutic avenue for the immune-related lung injury, and the further strategy to enhance the anti-tumor effect of combined therapy.

以PD-1抑制剂（anti-PD-1）为代表的免疫治疗与放射治疗是肺癌治疗的重要手段，两者联合具有更好的临床疗效，但都会诱发免疫性肺损伤，且存在毒性重叠及放大效应。我们前期工作发现：anti-PD-1加重小鼠放射性肺损伤；相较于野生型小鼠，PD-1敲除小鼠接受肺部靶向放疗后肺损伤更重，死亡增加；anti-PD-1加重肺损伤与巨噬细胞活化分泌TGF-β1密切相关，阻断TGF-β1后肺损伤减轻。结合文献推测anti-PD-1通过CD8+T细胞，间接促进巨噬细胞的募集及活化；anti-PD-1也可直接结合表达PD-1的肺泡巨噬细胞，促进其分泌TGF-β1。我们将通过巨噬细胞特异敲除TGF-β1小鼠、PD-1敲除的巨噬细胞及T细胞过继实验等揭示anti-PD-1加重肺损伤的机制，以及表达PD-1的肺泡巨噬细胞所特有的功能特征。有望为免疫性肺损伤的防治及提高联合治疗的疗效提供新的思路。

免疫治疗和放射治疗是肺癌治疗的重要手段，PACIFIC研究开启了放免的联合治疗时代。联合治疗在提升了临床疗效的同时也引发了对肺损伤的关注，但肺损伤的相关机制尚不明确。我们的研究发现PD-1抑制剂联合肺部放疗加重了小鼠肺损伤；进一步使用基因鼠进行验证发现：相较于野生型小鼠，PD-1敲除的基因鼠接受肺部放疗后肺损伤明显加重。PD-1抑制剂通过促进CD8+T细胞和巨噬细胞在受照射肺部浸润及促纤维化因子TGF-β1的分泌导致小鼠肺纤维化；阻断CD8+T细胞、巨噬细胞及细胞因子TGF-β1后，小鼠肺部淋巴细胞浸润减轻，死亡率减少。流式分析进一步明确PD-1抑制剂促进巨噬细胞分泌TGF-β1是加重肺炎的关键环节。PD-1抑制剂一方面通过激活CD8+T细胞，间接促进巨噬细胞的募集及活化，分泌TGF-β1；另一方面PD-1抑制剂直接结合PD-1+的巨噬细胞，促进其活化，分泌TGF-β1。本课题创新性的发现了PD-1抑制剂联合放疗加重肺损伤的机制，为放免联合治疗导致的肺炎提供了具有治疗前景的干预靶点，对于进一步提高免疫放疗的疗效具有积极的临床指导意义。