A role for regulatory T cells in acceptance of ESC-derived tissues transplanted across an major histocompatibility complex barrier.

We have previously reported that ESC-derived tissues are subject to some level of immune privilege, which might facilitate induction of immune tolerance. Herein, we further demonstrate that fully allogeneic ESC-derived tissues are accepted with a regimen of coreceptor blockade even in recipients known to be relatively resistant to such a tolerizing protocol. Moreover, ESC-derived tissues could be spontaneously accepted across a class I major histocompatibility complex disparity. We further show that CD4(+)FoxP3(+) regulatory T cells (Treg) appear to be essential for this natural "privileged" state as their ablation with an anti-CD25 mAb results in rejection of ESC-derived tissue. This same treatment exposes activation of macrophages and effector CD8(+) T cells, suggesting that these cells are subject to regulatory T cell control. Thus, spontaneous acceptance of ESC-derived tissues mimics the acquired immune privilege induced by coreceptor blockade and is determined by Treg-mediated suppression.