IMMUNOLOGY Achieving immune tolerance to transplanted tissues remains a major hurdle in organ transplantation. Increasingly, it is becoming clear that protocols aimed at improving graft-specific tolerance will need to consider regulatory T cells, because these lymphocytes are known to be important in suppressing immune responses. Graca et al. have explored the mechanism behind a form of profound acquired tolerance, induced in rodents through administration of therapeutic nondepleting antibodies directed at T lymphocytes. Recipient mice that underwent this treatment accepted foreign skin grafts from donor mice. In their current work, the retransplantation (from the recipients) of the tolerated grafts onto third-party mice was sufficient to induce tolerance in those mice to subsequent grafts that otherwise would have been rejected. Regulatory T cells that had infiltrated the grafted tissue (after the initial transplant) were responsible for the transfer of tolerance, because depleting the T cells from the skin graft after transplanting it a second time resulted in rejection. These results are supportive of a functional role for suppressive regulatory T cells within transplanted tissue. — SJS J. Exp. Med. 195 , 1641 (2002).