In human immune systems generated from bone marrow CD34+ cells of type I diabetic (T1D) donors, we have demonstrated a defect in Treg differentiation of an islet autoreactive TCR (R. Madley and M. Sykes, unpublished data), suggesting that durable mixed chimerism may have the potential to reverse autoimmunity by a similar dominant Treg-mediated mechanism in human T1D patients. This evidence concerns the gene CD34 and type 1 diabetes mellitus.