Robust tolerance to fully allogeneic islet transplants achieved by chimerism with minimal conditioning.
BACKGROUND
Whether mixed chimeras induced by nonmyeloablative conditioning are tolerant to challenge with donor allogeneic islet grafts is unknown. Here we investigate whether our nonmyeloablative, costimulation blockade-free and sirolimus (SRL)-based protocol could facilitate mixed chimerism via bone marrow transplantation (BMT) and induce islet allograft tolerance.


METHODS
After low dose (1-3 Gy) total body irradiation (TBI, day -1), with or without prior lymphocyte depletion, C57BL/6 mice were transfused with 40 x 10(6) BALB/c bone marrow cells (day 0) and received SRL (3 mg/kg/day) for 4 weeks. Chimerism was monitored by flow cytometry and the recipients were rendered diabetic chemically and challenged with donor islets.


RESULTS
Mixed chimerism was achieved in mice treated with TBI 3 Gy/SRL but it declined over time in 60% (9/15) of them. Long-term stable chimerism was established in 100% of recipients over 50 weeks with either antilymphocyte serum (ALS, 9/9), anti-CD4 (4/4), or anti-CD4 plus anti-CD8 (5/5) prior to BMT. TBI conditioning could be reduced to 1 Gy, with 90% (9/10) maintaining chimerism in the long-term. When TBI was substituted with cyclophosphamide (CTX) or busulfan (BUS), all mice remained chimeric in the long-term. The chimeras showed no proliferative response to donor antigen and accepted both first and second donor-specific islet grafts indefinitely while rejecting third-party grafts.


CONCLUSIONS
This data provides the first evidence that stable fully allogeneic chimeras induced with BMT after nonmyeloablative conditioning with SRL and lymphocyte-depleting antibodies exhibit robust donor-specific tolerance to islet grafts.
Luo
Bin
B
Surgical Medical Research Institute, Department of Surgery, University of Alberta, Canada.
Nanji
Sulaiman A
SA
Schur
Colleen D
CD
Pawlick
Rena L
RL
Anderson
Colin C
CC
Shapiro
A M James
AM
D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D016026:Bone Marrow Transplantation / Q000379:methods; D002066:Busulfan / Q000494:pharmacology; D015704:CD4 Antigens / Q000096:biosynthesis; D023201:CD40 Ligand / Q000737:chemistry; D016827:CD8 Antigens / Q000096:biosynthesis; D003520:Cyclophosphamide / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental; D005434:Flow Cytometry; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007515:Islets of Langerhans / Q000166:cytology*; D007959:Lymphocyte Culture Test, Mixed; D008212:Lymphocyte Depletion; D008214:Lymphocytes / Q000166:cytology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D010641:Phenotype; D020123:Sirolimus / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology; D013997:Time Factors; D018183:Transplantation Chimera / Q000276:immunology*; D019172:Transplantation Conditioning / Q000379:methods*; D023001:Transplantation Tolerance; D014184:Transplantation, Homologous / Q000379:methods*; D016896:Treatment Outcome
D015704:CD4 Antigens; D016827:CD8 Antigens; D007166:Immunosuppressive Agents; D023201:CD40 Ligand; D003520:Cyclophosphamide; D002066:Busulfan; D020123:Sirolimus