Dominant transplantation tolerance. Opinion.

Long-term allograft survival in the absence of continuous immunosuppression can be induced following a short treatment of nondepleting antibodies, such as those that target CD4 or CD154 (CD40 ligand). It is now established that this may involve dominant tolerance mechanisms that are maintained by CD4+ regulatory T cells present within the lymphoid tissue and the tolerated graft. The phenotype of these cells, their relationship to CD4+CD25+ T cells, and the mechanism of action are still controversial.