Transplantation between monozygotic twins: how identical are they?

Advances in developmental biology have shown that monozygous twins may not be as phenotypically identical as once believed, and the mechanisms responsible for such differences are now becoming clearer. Whether such phenotypic differences are capable of triggering graft rejection of an organ transplanted between identical twins remains unknown but the risks seem low, and long-term transplant outcome is excellent. Available evidence to guide immunosuppressive therapy in this setting is limited but a prudent approach would include the use of steroids together with a calcineurin inhibitor after transplantation. However, once the inevitable inflammatory response associated with transplant surgery has resolved, cautious reduction and eventually withdrawal of immunosuppression should be possible.