Various kinds of immunotoxin have been prepared with genetic engineering method.The most succcessful one among them is interleukin-2(IL-2) immunotoxin,which consists of IL-2 protein fused with pseudomonas exotoxin or diphtheria exotoxin. The IL-2 moiety in this type of immunotoxin acts as a targeting ingredient,so that to kill the target cells positive for IL-2 receptors. The IL-2 immunotoxin is being applied to treat transplantation rejections,autoimmune diseases and T cell lymphomas , etc. So far,a promising therapeutic efficiency has been achieved during the Ⅰ/Ⅱ phase clinical trials.