title: Robust tolerance to fully allogeneic islet transplants achieved by chimerism with minimal conditioning.
abstract: 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.
authors.affiliation: Surgical Medical Research Institute, Department of Surgery, University of Alberta, Canada.
authors.forename: Bin
authors.initials: B
authors.lastname: Luo
authors.forename: Sulaiman A
authors.initials: SA
authors.lastname: Nanji
authors.forename: Colleen D
authors.initials: CD
authors.lastname: Schur
authors.forename: Rena L
authors.initials: RL
authors.lastname: Pawlick
authors.forename: Colin C
authors.initials: CC
authors.lastname: Anderson
authors.forename: A M James
authors.initials: AM
authors.lastname: Shapiro
mesh_terms: 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
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; D007166:Immunosuppressive Agents; D023201:CD40 Ligand; D003520:Cyclophosphamide; D002066:Busulfan; D020123:Sirolimus