Introduction: It has recently been reported that Flt3L-induced bone marrow-derived Dendritic Cells (FLDCs) induce donor-specific tolerance and prolong the acceptance of donor skin grafts. In the present study, we examined whether this attractive regimen is applicable to the pancreatic islet transplantation. Methods: BALB/c male mice were used as donors. C57BL/6J male mice were used as recipients. Recipients were divided as follows: with FLDCs (FLDCs group) and without FLDCs (control group). In the FLDCs group, bone marrow cells were harvested, then cultured with 100 ng/mL Flt3L. At day 8, loosely adherent cells were harvested and used as immature FLDCs. FLDCs were injected into a recipient's tail vein twice. To block the costimulatory signals through CD28/B7 and CD40/CD40L, hCTLA4-Ig and anti-CD40L monoclonal antibody (mAb) was injected intraperitoneally three times after FLDCs infusion. Natural killer (NK) depletion was carried out by injecting mouse anti-NK1.1 mAb (PK136) twice before FLDCs were transferred. The exactly same amount of each mAb was administered to the recipients in the control group. Streptozotocin (170 mg/kg) was injected intravenously through a tail vein 3 days before FLDCs infusion. On day 8 after FLDCs infusion, islets were isolated by collagenase digestion. Sufficient amount (1,400 IEQs) or marginal amount (600 IEQs) of the islet grafts were transplanted under the subcapsular space of the left kidney. The blood glucose levels of all transplanted mice were measured twice a week, and the curative rate was evaluated by the blood glucose level at 28 days after islet transplantation. In order to assess whether the infusion of FLDCs could induce donor-specific tolerance, the mixed-lymphocyte reaction (MLR) assays were performed during 14 to 28 days after islet transplantation. In the MLR assay, C3H male mice were used as a third party. Results: The characterization of FLDCs by FACS analysis was as follows; CD11c+B220-: 35.78%±1.29, CD11c+B220+: 38.75%±1.73. In the MLR assay, the stimulation index of the recipient lymphocytes against BALB/c strain was significantly lower in the FLDCs group compared with that of the control group (1,400 IEQs: 1.72±0.10 vs. 2.72±0.19 p=0.0001 (n=23), 600 IEQs: 2.05±0.31 vs. 2.52±0.27 p=0.264 (n=16)). Of particular note, this tendency was more pronounced in the normoglycemic mice (1.52±0.12 vs. 2.79±0.19 p=0.0004 (n=19)). Nevertheless, the curative rate of the transplanted mice was considerably lower in the FLDCs group compared with that of the control group irrespective of the amount of transplanted islet grafts (1,400 IEQs: 25% vs. 50% p=0.26 (n=24), 600 IEQs: 12.5% vs. 62.5% p=0.05 (n=16)). Conclusion: These data show that Flt3L-induced dendritic cells were effectively able to suppress donor-specific immune reaction especially when normoglycemia had been achieved, but not enough to prolong the graft survival in pancreatic islet transplantation.