Molecular biological modification of the target organ

临床器官移植的最终目的是建立受体的免疫耐受。理想情况下，这不是通过干扰受体的免疫防御机制，而是通过改变供体移植物的免疫原性来实现的，从而使受体的免疫抑制风险最小化。这一概念是目前研究的基础，移植物是受者免疫攻击的靶器官。从分子生物学的角度来看，移植器官的这种细胞毒性是细胞凋亡的结果。我们推测，细胞凋亡的预防可以通过使用基因操作调节凋亡相关分子来实现。我们使用肝细胞和内皮细胞作为靶细胞。我们已经发现，他克莫司，常用的免疫抑制剂，是能够减少Fas抗原表达的肝细胞。已知内皮细胞是缺血再灌注损伤和免疫细胞毒性的主要靶点。这种类型的细胞毒性也被认为是细胞凋亡的结果。我们能将人铜、锌超氧化物歧化酶（Cu，Zn-SOD）导入内皮细胞。这些细胞变得对自由基具有抗性，自由基是与移植物保存损伤相关的细胞毒性的主要形式。同时，我们发现细胞内钙离子浓度的增加与内皮细胞凋亡有关，这表明钙离子阻断是防止细胞凋亡的有效手段，因此，我们认为，对凋亡相关分子的生物学操作可以防止器官移植中的细胞毒性，最终可能建立免疫耐受。

The ultimate goal of the clinical organ transplantation is to establish an immunological tolerance of the recipient. Ideally, this is to be achieved not by interfering the recipient's immunological defense mechanism but by altering the immunogeneicity of the donor graft, thus minimizing the risk of immunosuppression of the recipient. This concept is the basis of the present research.The graft is a target organ which is succumbed to immunological attack by the recipient. From the aspect of molecular biology, this type of cytotoxicity of the graft organ results from apoptosis of the cell. We hypothesize that prevention of apoptosis can be achieved by modulating the apoptosis-associated molecules with the use of genetic manipulation. We used hepatocytes and endothelial cells as the target cells. We have found that tacrolimus, commonly used immunoxsuppressant, is capable of reducing Fas antigen expression of the hepatocytes. The endothelial cells are known to be the prime target of both ischemia reperfusion injury and immunological cytotoxicity. This type of cytotoxicity is also noted to be as a result of apoptosis. We were able to transfect human copper, zinc-super oxide dismutase (Cu, Zn-SOD) into the endothelial cells. These cells became resistant to the free radical which is the principal form of cytotoxicity associated with preservation injury of the graft. Simultaneously, we found that cytosolic calcium is increased in association with endothelial cell apoptosis which suggests calcium blocking as a useful means for prevention of apoptosis.We, therefore, believe that biological manipulation of the apoptosis-associated molecules can prevent cytotoxicity in organ transplantation which may ultimately establish immunological tolerance.