Mechanisms of transplant tolerance induction using costimulatory blockade.

The potential use of costimulation-blocking reagents to induce transplantation tolerance has recently created considerable excitement. Recent evidence has begun to delineate the mechanisms by which these powerful effects occur. It has become increasingly clear, firstly, that T cell costimulation is mediated by a delicate network of signaling pathways and, secondly, that interference with these systems can lead to numerous different tolerance mechanisms, including immune regulation, anergy and deletion.