The regulatory T cells (Treg) used in this study will be produced from human umbilical cord blood. The umbilical cord blood will be freshly collected and immediately separated to buffy coat in a GMP laboratory, thus to be further sorted into Treg and other subsets. Then the Treg will be expanded ex-vivo for approximately 14 days until tested for its surface markers and suppressive ability. During the time of ex-vivo expansion, eligible autoimmune diabetes patients will be recruited and admitted to our hospital in order to go through required examinations. Once the Treg product has reached the safety and efficacy standards, the patient will receive the Treg product infusion under close surveillance of doctors and then go through regular follow-ups to investigate the safety and therapeutic effect of the Treg product on autoimmune diabetes patients.