Recent advances in our understanding of immunological tolerance and the processes that lead to its breakdown have helped to illuminate the etiology of many of the autoimmune diseases that affect up to 1 in 20 members of the population. The prospect of reestablishing a state of self-tolerance in the face of progressive autoimmunity is no longer the distant possibility it once seemed: various strategies have proven successful in animal models of disease, raising hopes for their eventual application in the clinic. Furthermore, the demonstration that tolerance may be extended from self to foreign tissues offers tangible alternatives for the treatment of transplant rejection, which may one day avoid the need for immunosuppression with its attendant risks and long-term side effects. Such an exciting transition phase in the field of immunological tolerance
requires rigorous analysis to gauge the effectiveness of novel approaches to its induction.