**9. Induction of tolerance**

Transplant tolerance is defined as a state of donor-specific unresponsiveness without a need for ongoing pharmacologic immunosuppression. Safe, reliable strategies for the induction of full tolerance have not yet been developed[28]. However, during the study of achieving immune tolerance, methods to induce states of "partial tolerance" have been discovered; in these cases, lower-than-conventional amounts of ongoing pharmacologic immunosuppression are required to prevent rejection. Nonetheless, immune tolerance remains the holy grail of transplantation immunology and clinical transplantation[29].
