人胎盘间充质干细胞对T细胞应答负性调节机制及其防治GVHD作用研究

The major obstacle to allogeneic hematopoietic stem cell transplantation is the occurrence of acute graft-versus-host disease (GVHD) induced by activated T cells. So to induce T cell tolerance and to promote immune reconstitution are significance for haplotype successful transplantation. We have found that PD-L1 expressed by human placenta-derived mesenchymal stem cells (HPMSCs) played a key role in the immunosuppressive effects of HPMSCs on T cells. In this research we will focus on, in vivo and in vitro, whether PD-L1 expressed on HPMSCs will promote the suppression of HPMSCs on response of T cells, which from GVHD patients, through PD-1/PD-L1 signal pathway by changing the property of T cell TCRCDR3 and regulating the differentiation of regulatory T cells, et al. The signal regulatory mechanism of IFN-γ increasing the expression of PD-L1 on HPMSCs and promoting HPMSCs mediating inhibitory effects on T cells were explored in this study. Previously, we have found that PD-L1 could adjust the capacity of HPMSCs along SDF-1α/CXCR4 axial migration. Here, the possible mechanism of PD-L1 regulating the distribution of HPMSCs in the GVHD model mice will be investigated as well as the preventing effects of HPMSCs. All the results in this research will demonstrate the role, specially related to PD-1/PD-L1 signal pathway, of HPMSCs in controlling GVHD and reveal the molecular and cellular mechanism of HPMSCs mediating T cell suppression, which will enhance the process of HPMSCs in clinical application.

由T细胞活化增殖诱发的急性移植物抗宿主病（GVHD）是异基因造血干细胞移植成功的主要障碍。诱导T细胞耐受、加速免疫重建是解决单倍型移植成功的关键所在。项目拟在已发现人胎盘间充质干细胞（HPMSCs）通过其表达的PD-L1分子增强对T细胞抑制作用的基础上，通过体内外实验证明PD-L1在HPMSCs上表达可通过改变GVHD患者T细胞TCRCDR3特性、调节Treg分化等协同HPMSCs抑制T细胞应答。研究IFN-γ上调HPMSCs对PD-L1表达的信号调节机制及该机制正反馈调节HPMSCs对T细胞抑制作用机理。在已发现PD-L1可调节HPMSCs沿SDF-1α/CXCR4轴向迁移的基础上，研究PD-L1调节HPMSCs在GVHD模型体内的分布及其对GVHD防治效果的作用机制。实验结果将揭示HPMSCs对T细胞应答负性调节的细胞与分子机制，加速HPMSCs治疗GVHD的临床应用进程。

近年来对间充质干细胞（Mesenchymal stem cells, MSCs）负性调节T细胞功能的研究中发现，MSCs与T细胞上表达的膜分子参与了MSCs对T细胞的抑制作用，这为MSCs的临床应用提供了重要的理论基础。我们在已发现人胎盘间充质干细胞（human placenta derived mesenchymal stem cells, hPMSCs）表达负性调控分子PDL1的基础上，对PDL1和PDL2在hPMSCs上的表达特性及其信号调节机制，PDL1和PDL2在hPMSCs上表达对T细胞应答的负性调节机制及其对hPMSCs迁移、黏附等生物学行为的影响三方面做了进一步研究。发现hPMSCs除表达PDL1外，还高表达PDL2，且PDL2的表达水平高于PDL1；不同代的hPMSCs对PDL1和PDL2的表达有差异； PDL1和PDL2在hPMSCs上表达不仅参与了其对T 细胞活化增殖、周期及IL-17+T细胞亚群的调节作用，而且对hPMSCs的迁移黏附具有重要的调节作用。同时发现IFN-γ能够通过活化JAK-STAT通路上调hPMSCs对PDL1和PDL2的表达，进而增强hPMSCs对T细胞功能的负性调节作用。从一个全新视野探讨负性共刺激分子PDL1和PDL2对hPMSCs免疫调节特性的影响，为进一步研究hPMSCs对T细胞的免疫调节机制提供实验依据，推进hPMSCs在临床细胞治疗中的应用进程。