Combined treatment with regulatory T cells and vascularized bone marrow transplantation creates mixed chimerism and induces donor-specific tolerance to vascularized composite allografts without cytoreductive conditioning.

We demonstrate herein that combination treatment with regulatory T cells (Tregs) and vascularized bone marrow transplantation (VBMT) can achieve stable mixed chimerism and long-term transplantation tolerance to vascularized composite allografts (VCA) without requiring cytoreductive recipient conditioning in rats. An appreciable number of Tregs of recipient origin was shown at the interface between recipient and transplanted VCA tissues, implicating a significant role for Tregs in protecting VCA from rejection. This cytoreduction-free protocol using co-treatment with Tregs and VBMT warrants further investigation toward potential clinical application for VCA transplantation.