Background: Millions of people each year sustain injuries, have tumors surgically removed, or are born with defects that require complex reconstructive surgeries to repair. In the case of hand, forearm, or arm amputation, prostheses only provide less than optimal motor function and no sensory feedback. However, hand and arm transplantation is a means to restore the appearance, anatomy, and function of a native hand. Although over 70 hand transplants have been performed to date and good functional results have been achieved, widespread clinical use has been limited due to adverse effects of life-long and high-dose immunosuppression needed to prevent graft rejection. Risks include infection, cancer, and metabolic problems, all of which can greatly affect recipients' quality of life, make the procedure riskier, and jeopardize the potential benefits of hand transplantation.