Organ transplantation is regarded as the best therapy for end-stage organ failure. However, transplantation is not a naturally occuring phenomenon, and the immune system of transplanted individuals identifies transplanted tissue as foreign and potentially dangerous elements. A series of effector mechanisms are then deployed by the immune system to eliminate them. The transplanted organ is hence infiltrated by a myriad of immune cells, leading to an immune-mediated inflammatory process with consequent injury to the transplant, referred to as transplant rejection. Transplant rejection is the most powerful and diverse immune response known, therefore, therapeutic manipulation to allow the prolonged engraftment of transplant organs has been extremely challenging.