Combined Islet and Hematopoietic Stem Cell Allotransplantation: A Clinical Pilot Trial to Induce Chimerism and Graft Tolerance

To prevent graft rejection and avoid immunosuppression‐related side‐effects, we attempted to induce recipient chimerism and graft tolerance in islet transplantation by donor CD34+hematopoietic stem cell (HSC) infusion. Six patients with brittle type 1 Diabetes Mellitus received a single‐donor allogeneic islet transplant (8611 ± 2113 IEQ/kg) followed by high doses of donor HSC (4.3 ± 1.9 × 106 HSC/kg), at days 5 and 11 posttransplant, without ablative conditioning. An ‘Edmonton‐like’ immunosuppression was administered, with a single dose of anti‐TNFα antibody (Infliximab) added to induction. Immunosuppression was weaned per protocol starting 12 months posttransplant. After transplantation, glucose control significantly improved, with 3 recipients achieving insulin‐independence for a short time (24 ± 23 days). No severe hypoglycemia or protocol‐related adverse events occurred. Graft function was maximal at 3 months then declined. Two recipients rejected within 6 months due to low immunosuppressive trough levels, whereas 4 completed 1‐year follow‐up with functioning grafts. Graft failure occurred within 4 months from weaning (478 ± 25 days posttransplant). Peripheral chimerism, as donor leukocytes, was maximal at 1‐month (5.92 ± 0.48%), highly reduced at 1‐year (0.20 ± 0.08%), and was undetectable at graft failure. CD25+T‐lymphocytes significantly decreased at 3 months, but partially recovered thereafter. Combined islet and HSC allotransplantation using an ‘Edmonton‐like’ immunosuppression, without ablative conditioning, did not lead to stable chimerism and graft tolerance. This study attempted to induce stable chimerism and graft tolerance in patient with type 1 diabetes receiving combined islet and hematopoietic stem cells transplant, under an ‘Edmonton‐like’ immunosuppression, without ablative conditioning, with weaning starting 12 months post‐transplant. Chimerism declined over time and was undetectable at 1 year, while islet graft failure occurred within 4 months from weaning.