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Gal-deficient porcine neonatal islets that express human CD55 and CD59 are protected from IBMIR in a baboon model

Wayne J. Hawthorne¹, Peta Phillips¹, Evelyn Salvaris², Joanne Hawkes¹, Helen Barlow², Penny Farrell³, Scott Heffernan³, Emanuel Favaloro¹, Simon C. Robson⁴, Andrew Lew⁵, Mark Nottle⁶, Anthony d’Apice², Peter Cowan², Philip J. O’Connell¹

¹Westmead Millennium Institute, University of Sydney, Westmead, Australia; ²St Vincent’s Hospital, Melbourne, Australia; ³Royal Prince Alfred Hospital, Sydney, Australia; ⁴Beth Israel Deaconess Medical Centre, Harvard Medical School, Boston, MA, United States; ⁵Walter and Eliza Hall Institute, Melbourne, Australia; ⁶University of Adelaide, Adelaide, Australia

Whilst genetic manipulation of galactose-α1,3-galactose (Gal) and/or transgenic expression of complement regulatory proteins have been shown to prolong the survival of vascularised xenografts, the effect of these on islet xenograft survival is unknown. The aim of this study was to determine the combined effect of removal of Gal and expression of human (h) CD55 and CD59 on neonatal islet cell cluster (NICC) xenograft survival. In this study, 1-5 day old wild type (WT) or GTKO/hCD55-hCD59 transgenic (GTKO-Tg) pigs were used as islet donors. Baboon recipients received an intraportal infusion of a mean of 10,000 IEQ/kg of either wild type (n=4) or GTKO-Tg (n=4) NICC. Graft function was evaluated in the immediate transplant period and at one month. Recipients of WT grafts received heparin and no immunosuppression and those with GTKO-Tg grafts received heparin, ATG induction and maintenance tacrolimus and mycophenolate mofetil. Within the first 12 hours after transplantation, WT NICC showed widespread thrombosis with substantial neutrophil and mononuclear cell infiltrate. There were decreases in systemic platelet counts and fibrinogen levels with an increase in D-dimer levels. In contrast, GTKO-Tg NICC exhibited no signs of early thrombosis nor mononuclear cell infitrate and systemic platelet counts, D-dimer and fibrinogen levels were essentially unchanged from baseline within the first 6 hours. However, D-dimer levels increased at 12 hours peaking at 72 hours, whilst platelet counts increased by day 7 and remained elevated until the conclusion of the experiment. Histological assessment of GTKO-Tg NICC grafts at one month revealed significant T and B cell infiltrates although insulin, glucagon and somatastatin positive clusters were still discernable. In conclusion, removal of Gal and expression of hCD55 and hCD59 in the setting of immune suppressive therapy prevented early destruction of NICC by IBMIR.