Tolerance of allografts achieved in mice via stable mixed hematopoietic chimerism relies
essentially on continuous elimination of developing alloreactive T cells in the thymus
(central deletion). Conversely, while only transient mixed chimerism is observed in
nonhuman primates and patients, it is sufficient to ensure tolerance of kidney allografts. In
this setting, it is likely that tolerance depends on peripheral regulatory mechanisms rather
than thymic deletion. This implies that, in primates, upsetting the balance between …