Regulatory cells and cell signatures in clinical transplantation tolerance

Experimental models of transplantation provide strong support for the role of regulatory cells in tolerance. However, limited studies of humans who display sustained tolerance following transplantation have not definitively demonstrated a role for regulatory cells in this process. Rather than excluding or minimizing the contribution of regulatory cells to the development of transplantation tolerance, we suggest the possibility that multiple lineages of cells exert regulatory effects that contribute to the development of tolerance, that these regulatory effects are not constant but vary over time, and that the role of regulatory cells varies based on the organ transplanted. More detailed studies will be necessary to elucidate the role of regulatory cells in clinical transplantation and tolerance.