The timing of mesenchymal stromal cell (MSC) infusion has an effect on their immunomodulatory and inflammatory properties, say researchers. Casiraghi and colleagues demonstrated, using a sensitized mouse model of kidney transplantation, that infusion of syngeneic MSCs before transplantation resulted in the expansion of donor-specific T-regulatory cells into lymphoid organs, prolonged allograft survival and promoted the development of tolerance. By contrast, post-transplantation infusion of MSCs led to premature graft dysfunction.