Tumor-infiltrating dendritic cells (DCs) that are blocked in an immature stage of differentiation and are tolerogenic also stimulate the differentiation of Tregs. Although p Tregs seem to compose a significant portion of the Tregs in the periphery [7] ,not much is known about the signals essential for the generation of these cells and there are no reliable markers that permit discrimination between the t Treg and p Treg populations. Recently , a few studies suggested that Helios, a member of the Ikaros transcription family seems to be expressed on thymic naïve Tregs but not on in vivo or in vitro induced Tregs [8],however, later publications could not confirm this