受者“Unlicensed”Ly49+NK细胞亚群在特异性调节异基因移植排斥反应中的作用及机制

Conflicting results have been reported regarding the effects of donor (or recipient) natural killer (NK) cell allo-reactivity resulting from recipients (or allograft) lacking MHC class I (ligand mismatch) for NK cell inhibitory receptors, on the clinical outcomes of allogeneic hematopoietic stem cell transplantation (AHSCT). Based on the inhibitory receptors of NK cells recognizing self MHC-I molecules or not, NK cells can be divided into two sub-populations: "licensed" or "unlicensed" NK cell subsets. We have previously reported that recipient "licensed" Ly49+ NK cell subsets are responsible for allo-rejection in murine transplantation models (Blood. 2012,119:1590-8). Recently, we found the differential effects of recipient "licensed" and "unlicensed" Ly49+ NK cell subsets on engraftment of allograft. The current project intends to determine the role and immune mechanism of recipient "unlicensed" Ly49+ NK cell subsets for specific regulation in allograft rejection. .Using a fully MHC-mismatched murine AHSCT model, C57BL/6 (H2b) used as donors and B10.D2 (H2d) used as recipients, the effects of recipient "unlicensed" Ly49+ ligand-matched NK cell subsets (expressing Ly49C/I which binds to donor H2b) allografts on recipient NK cell allo-reactivity will be investigated by examining allogeneic donor engraftment, as well graft-versus-host disease (GVHD)/graft-versus-tumor (GVT) effect. Our hypothesis is that allo-rejection could be down-regulated, after recognition of donor MHC class I by inhibitory receptors of recipient derived "unlicensed" Ly49+ NK cell subsets. The data obtained from this aim may have significant implications in the exploitation of NK cells post-AHSCT. This represents a novel means of using recipient NK cell subsets to facilitate allogeneic donor engraftment and balance GVHD and GVT effects.

NK细胞抑制性受体与配体（MHC-I类分子）不合在异基因造血干细胞移植中的作用备受瞩目，但目前临床研究结论并不一致，甚至相反。NK细胞，依据其抑制性受体是否识别自身MHC-I类分子，可分为"Licensed"和"Unlicensed"两个亚群。利用小鼠MHC不合异基因造血干细胞移植模型，申请人曾证明受者"Licensed"Ly49+NK细胞是参与异基因移植排斥反应的主要效应细胞；最近我们发现，受者"Unlicensed"Ly49+NK细胞有促进异基因移植物植入的作用。本课题拟继续探讨受者"Unlicensed"Ly49+NK细胞在异基因移植排斥反应中的作用及机制，研究受者"Unlicensed"Ly49+NK细胞抑制性受体与"非己"移植物配体相合或错配对异基因移植物植入、GVHD/GVT的不同影响，从免疫反应机制上阐明受者NK细胞抑制性受体与配体的最佳收益组合，为优化移植方案提供新思路。

自然杀伤（natural killer，NK）细胞表达的抑制性受体是调节其免疫杀伤活性的关键分子。依据其抑制性受体是否识别自身MHC-I类分子，分为“Licensed”和“Unlicensed”两个亚群。我们利用小鼠MHC不合异基因骨髓移植模型，研究受者“Unlicensed”Ly49+NK细胞在异基因移植排斥反应中的作用及机制。研究证明，与受者“Licensed”Ly49+NK 细胞作用相反，受者“Unlicensed”Ly49+NK 细胞亚群不仅不排斥，反而促进了异基因供者移植物的早期植入；其机制是通过受者“Unlicensed”NK 细胞与异基因移植物配体（MHC-I 分子）识别后释放GM-CSF。随后，我们研究了受者“Unlicensed”Ly49+NK 细胞抑制性受体与“非己”移植物配体相合对异基因T淋巴细胞植入/移植物抗宿主病（GVHD）的影响。为排除受者T细胞介导异基因移植排斥反应的影响，有关急性/慢性GVHD的研究选择了独特的小鼠异基因移植模型。我们发现，在相关的小鼠急性/慢性GVHD模型中，当抑制性受体与异基因靶细胞MHC-I 分子相合的受者“Unlicensed”Ly49+NK 细胞被体内清除后，供者T细胞植入减少，减轻了受者急性/慢性GVHD；因此证明，受者“Unlicensed”Ly49+NK 细胞具有促进异基因T细胞植入/加重GVHD的作用。我们还发现，体内清除受者“Licensed”或“Unlicensed” NK细胞亚群后，对异基因T细胞诱导的小鼠狼疮样慢性GVHD发病有显著影响，而对降植烷诱导的狼疮样小鼠发病无影响，以上结果提示受者“Unlicensed”NK 细胞在狼疮样慢性GVHD发病中的作用与其特异性调节异基因移植排斥反应相关联。NK 细胞 Licensing 学术观点的最初提出是基于 NK 细胞自身免疫耐受机制的研究，本课题则从 NK 细胞亚群异体移植免疫耐受的角度对 NK 细胞 Licensing 学术观点进行了修正与完善，证明异基因供者移植物表达的 MHC-I 类分子能否被受者“Unlicensed”Ly49+NK 细胞抑制性受体所识别，是影响受者“Unlicensed”Ly49+NK 细胞活性的重要因素。本课题通过阐明受者 NK 细胞抑制性受体与配体的最佳收益组合，将为优化异基因骨髓移植方案提供新思路。