title: Rabbit antithymocyte globulin induction and sirolimus monotherapy supports prolonged islet allograft function in a nonhuman primate islet transplantation model.
abstract: BACKGROUND
  We reported that rabbit anti-thymocyte globulin (RATG) induction followed by maintenance immunosuppression with sirolimus supports human kidney allograft survival and asked if this combination would promote islet allograft survival in our primate model.
  
  
  METHODS
  Using intra-arterial streptozotocin infusion, we rendered four cynomolgus primates diabetic with undetectable C-peptide levels. Animals were maintained on insulin therapy for at least 1 month, and then islets from mixed lymphocyte reaction mismatched primates were infused into the portal vein. Immediately before the islet allotransplant and for 6 additional days, primates were infused with RATG (20 mg/kg) and given a sirolimus dose to achieve a 24-hr trough level of 8 to 14 ng/mL.
  
  
  RESULTS
  The regimen resulted in profound peripheral and lymph node lymphocyte depletion for up to 1 month. Repopulation was gradual thereafter. One primate remained insulin-independent for 169 days and rejected after a sirolimus-dose reduction. Two primates died on day 23 while insulin independent because of wound dehiscence, and a third died on day 30 with high sirolimus levels. Liver sections revealed well-vascularized islets with no signs of inflammation.
  
  
  CONCLUSIONS
  Using a nonhuman primate islet transplant model, RATG plus sirolimus supports islet survival as long as proper sirolimus levels are maintained, but the therapy is limited by sirolimus toxicity. Our findings suggest that RATG is not toxic for islets and thus may be considered in future clinical trails while recognizing that sirolimus monotherapy, with its difficult-to-achieve therapeutic dosing, may not be sufficient to maintain long-term islet allograft function in an autoimmune environment.
authors.affiliation: NIDDK Transplantation and Autoimmunity Branch, National Institute Health, Bethesda, MD 20892, USA. BoazH@Intra.niddk.nih.gov.
authors.forename: Boaz
authors.initials: B
authors.lastname: Hirshberg
authors.forename: Edwin H
authors.initials: EH
authors.lastname: Preston
authors.forename: He
authors.initials: H
authors.lastname: Xu
authors.forename: Michel G
authors.initials: MG
authors.lastname: Tal
authors.forename: Ziv
authors.initials: Z
authors.lastname: Neeman
authors.forename: David
authors.initials: D
authors.lastname: Bunnell
authors.forename: Scott
authors.initials: S
authors.lastname: Soleimanpour
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Hale
authors.forename: Allan D
authors.initials: AD
authors.lastname: Kirk
authors.forename: David M
authors.initials: DM
authors.lastname: Harlan
mesh_terms: D000818:Animals; D000961:Antilymphocyte Serum / Q000627:therapeutic use*; D006085:Graft Survival / Q000502:physiology*; D007150:Immunohistochemistry; D007166:Immunosuppressive Agents / Q000627:therapeutic use*; D007328:Insulin / Q000032:analysis; D007515:Islets of Langerhans / Q000166:cytology; D016381:Islets of Langerhans Transplantation / Q000276:immunology* / Q000502:physiology; D018655:Lymphocyte Count; D008252:Macaca fascicularis; D023421:Models, Animal; D011817:Rabbits; D020123:Sirolimus / Q000627:therapeutic use*; D013997:Time Factors; D014184:Transplantation, Homologous
chemical_list: D000961:Antilymphocyte Serum; D007166:Immunosuppressive Agents; D007328:Insulin; D020123:Sirolimus