This invention also provides a method of generating antigen specific human suppressor CD8+CD28- T cells. This invention further provides a method of generating allopeptide antigen specific human suppressor CD8+CD28- T cells. Methods of tent for reduction of risk of rejection of allografts and xenografts and autoimmune diseases using the human suppressor CD8+CD28- T cells so produced are also provided, as are methods of preventing rejection and autoimmune diseases, and vaccines comprising the produced suppressor T cells. Methods of diagnosis to determine whether a level of immuno-suppressant therapy requires a reduction are provided.