The successful conversion of Tregs from naive CD4+ T cells in vitro and in vivo by TGF-β has not only proven that foxp3 can be induced from naive CD4+ T cells; it has also opened up a way to induce antigen-specific Tregs for potential immunotherapy for autoimmune diseases, allergy/asthma, and transplantation. Here, CD4 is linked to autoimmune disease.