A first indication that VDR agonists such as 1,25(OH)2D3 also induce a Treg phenotype in T cells from type 1 diabetes patients came from our data on CD134 (OX-40), a secondary co-stimulatory molecule that is constitutively expressed in naturally occurring CD4+ Tregs (nTregs) in mice and upregulated on the surface of human nTregs upon TCR cross-linking [29]. Here, CD4 is linked to type 1 diabetes mellitus.