Allo-HSCT后MSC对胸腺的保护和修复作用及机理研究

The thymus is the primary lymphoid organ, crucial for T lymphocytes reconstitution following allo-HSCT. In the recipients of allo-HSCT, the toxicity of conditioning regimen and GVHD damage the thymic microenvironment, which result in the production of autoreactive T-cells and the reduction of nTregs. These autoreactive T cells and decreasing nTregs induce or aggravate the development of a/cGVHD. MSCs as the important component of stromal cells, have the potential to differentiate to TEC or secrete soluble factors which play a pivotal role in the generation of thymocyte and promoting the proliferation of TEC. Our previous studies found that MSCs could ameliorate GVHD by modulating thymic function and peripheral immune. But the mechanisms are still unclear. Based on the roles of MSCs in thymic microenvironment and our previous study, we proposed the hypothesis that MSCs could preserve and restore injured thymus after HSCT by modulating GVHD, secreting soluble factors and differentiating to TEC. To address this hypothesis, in this study we administrated in vitro experiments, the clinically relevant experimental allo-HSCT model and allo-HSCT recipients to investigate the influence and mechanisms of MSCs to thymic structure and regeneration, the level of soluble factors in thymic microenvironment and thymic function before and after aGVHD. These studies will reveal the mechanisms of MSCs preserving and restoring injured thymus after allo-HSCT, and supply theoretical basis for MSCs in preventing and treating GVHD.

胸腺是allo-HSCT后T细胞重建的中枢场所。预处理和GVHD损伤胸腺微环境可导致自身反应性T细胞产生和天然Treg生成减少，进而诱导或加重a/cGVHD的发生发展。MSC作为胸腺微环境中基质细胞重要成分，可向TEC分化或分泌可溶性因子等参与T细胞发育和促进TEC增殖。我们前期研究发现：MSC除通过影响外周免疫调控GVHD外，还可通过影响胸腺发挥调节GVHD作用，但具体机理不清楚。本研究基于MSC在胸腺微环境中作用和我们前期研究结果提出：MSC可通过抗GVHD、旁分泌可溶性因子和直接向TEC分化等作用保护和修复HSCT后胸腺损伤的假说。为验证此假说，在体外、动物模型和GVHD病人中研究：MSC在aGVHD发生前后对胸腺组织结构与再生、胸腺微环境中可溶性因子、胸腺功能等影响及机理，揭示allo-HSCT后MSC对胸腺的保护和修复作用及机理，为临床MSC防治GVHD提供理论依据。

胸腺是allo-HSCT后T细胞重建的中枢场所。预处理和GVHD损伤胸腺微环境可导致TEC凋亡和胸腺功能丧失。allo-HSCT受体胸腺功能不足会导致自体反应性T细胞持续产生和天然Treg生成减少，进而诱导或加重a/cGVHD的发生发展。MSC作为胸腺微环境中基质细胞重要成分，可向TEC分化或分泌可溶性因子等参与T细胞发育和促进TEC增殖。我们前期研究发现：MSC除通过影响外周免疫调控GVHD外，还可通过影响胸腺发挥调节GVHD作用，但具体机理不清楚。本研究通过在体外、GVHD动物模型和GVHD病人中研究发现：⑴aGVHD可导致胸腺损伤，且后续cGVHD严重程度与胸腺损伤程度有关；⑵MSC预防性输注可减少aGVHD的发生，MSC治疗性输注可显著改善aGVHD小鼠的症状并延长小鼠的生存时间；⑶MSC可通过细胞与细胞直接接触及分泌细胞因子的间接作用减少TEC凋亡、促进TEC增殖和成熟，尤其是MSC提高mTEC中Aire+细胞比例。同时MSC还促进抑炎性因子释放、减少促炎性因子释放，改善胸腺内环境；⑷MSC促进CD4+CD8+T, CD4+CD8-T, CD4-CD8+T, Treg胸腺细胞的生成；⑸CCL25-CCR9轴在引导MSC归巢至胸腺中起着重要作用，CCR9阳性MSC可能是重塑胸腺的主要效应细胞。此研究证明了MSC可通过CCL25-CCR9轴归巢至GVHD受体受损的胸腺，并通过改善TEC提高阴性选择、平衡T细胞亚群，改善GVHD结局，揭示allo-HSCT后MSC对胸腺的保护和修复作用及机理，为临床MSC防治GVHD提供理论依据。既往关于MSC防治GVHD的机制研究主要聚焦在MSC抑制外周免疫细胞的增殖和功能上，尚不清楚MSC对胸腺等中枢免疫器官的作用。