Background. The allogeneic islets transplantation is an ideal therapeutic strategy for patients with diabetes mellitus. However, it has been difficult to induce immunological tolerance against islets grafts. TheCD4+CD25+ regulatory T-cells (Treg) play a role in suppressing T-cell activation. Thus, we evaluated whether Treg can regulate donor-specific T-cell tolerance that received allogeneic islets into the hepatic parenchyma (ITxHP) along with Treg. Methods. C3H/He mice were used as donors and streptozotocin-induced diabetic BALB/c mice were recipients. The protocol included three groups : Group A recipients received only 300 IE islets Group B was given 300 IE islets and whole splenocytes Group C was given 300 IE islets and Treg purified from peripheral lymph nodes. Results. For all mice in Groups A and B, the fasting blood sugar exceeded 250mg/dl and graft rejection was observed. GVHD was observed earlier in Group B than in Group A. In contrast graft survival exceeded 30 days for two mice in Group C (50%, mean POD 28.5±24.0, Plt0.05). Mixed lymphocyte reaction showed that T-cells from tolerant mice had very weak responses against spleen cells from C3H mice. Conclusions. The simultaneous ITxHP with CD4+CD25+ T-cells administration prolonged islet graft survivals and induced donor-specific hyporesposiveness
