311.6: Extended survival of 9- and 10-gene-edited pig heart xenografts with ischemia minimization and CD154 costimulation blockade-based immunosuppression

Background: Xenotransplantation has made significant advances recently using pigs genetically engineered to remove carbohydrate antigens, alone or with addition of various human complement, coagulation, and anti-inflammatory ‘transgenes’. Here we evaluated results associated with 3-, 9-, or 10-GE pig hearts treated using an established costimulation-based immunosuppressive regimen and a cold-perfused storage technique designed to minimize graft ischemia, as used for the recent clinical heart xenograft case. Methods: Eight baboons received heterotopic abdominal heart transplants from GE pigs using Steen’s cold-perfusion ischemia minimization. Three reference hearts were from 3-GE pigs (GalKO.β4GalNT2KO.CD55) [NSRRC, Columbia, MO]. Three pigs were 9-GE (GalKO.β4GalNT2KO. GHRKO. CD46. CD55.TBM.EPCR.CD47.HO-1) and 2 were 10G (9-GE+CMAHKO) [Revivicor, Blacksburg, VA]. Induction with ATG (5mg/kg on d-3 and -1) and aCD20 (20mg/kg on d-1, d0) was followed by aCD154 [Tonix Pharmaceuticals, Chatham, NJ] or primatized hu5c8 [NHPRRC, Boston, MA]; 20mg/kg/wk x6 mo, then 10 mg/kg/wk), MMF (40mg/kg/d), and tapered corticosteroid. Periop aIL6R Ab and C1 esterase inhibitor were given. IV heparin was given for the first 8-10 days. Results: Two of the 3-GE grafts functioned well initially but failed within 5 days, with graft necrosis and rupture associated with complement deposition, intravascular thrombi, and myocardial infarction, while the third failed intraoperatively with refractory ventricular fibrillation. One 9-GE graft was lost intraoperatively due to a technical issue. One 9-GE heart in a baboon with a strongly positive preop crossmatch failed with antibody mediated rejection at d13. One 10-GE heart failed at d113 with combined cellular and antibody mediated rejection. One 10-GE and 1 9-GE heart have preserved graft function, normal myocardium on protocol biopsies, and slowly progressive graft hypertrophy after 210 and 350 days, respectively (both ongoing). Transient intraventricular clot in some 9- and 10-GE grafts peri-transplant resolved with heparin; no treatment-related complications were seen. Conclusion: Relative to reference genetics without thrombo-regulatory and anti-inflammatory gene expression, 9- or 10-GE pig hearts exhibit promising performance in the context of a clinically applicable regimen including ischemia minimization and aCD154-base IS, justifying further evaluation in an orthotopic model. We acknowledge Revivicor and the National Swine Resource and Research Center for providing swine for research purposes. We acknowledge Tonix Pharmaceuticals for providing their pharmaceutical drugs for research purposes.