But previous attempts to transplant unaltered pig tissue into humans have failed,due to immune rejection of the tissue. 但是，由于种间组织免疫系统的相互排异反应，从前那些用未经改良的猪器官做的移植试验都失败了。
The concept of local immunity also suggests that the immunologic apparatus of the lung is available as a target system. 局部免疫的概念还表明，肺的免疫结构是一种靶系统。
