Introduction: One of the major advances in xenotransplantation is the ability to modify donor pig genetics. Using rapidly evolving techniques of pig cloning and gene editing, we are now able to produce pigs with multiple genetic modifications.. The ideal genetic construct is still to be determined but the results of sequential iterations is encouraging.

Methods: In a heterotopic model specific pathogen free baboons were utilized as recipients due to low levels of non Gal antibody. Starting with alpha 1-3 galactoside transferase knockout (GTKO) as a base, seven different groups of pigs were donors with transgenic expression of one to five human genes. These genes included CD46, hDAF, CD39, EPCR, TBM, A20, CD47 and TFPI.. The genetic modifications were designed to avoid complement and coagulation pathway incompatibilities as well as to help modulate the B and T cell response. All groups received our standard immunosuppression that targets inhibition of complement, elimination of B and T cells, and costimulation blockade.

Results: The graft survival with different donor genetic modifications was as follows: GTKO. hCD46 (236 days), GTKO.hDAF (7 days), GTKO.hCD46 (without B cell elimination) (8 days), GTKO.hCD39 (47 days), GTKO.hDAF.hEPCR (47 days), GTKO.hCD46.hTBM (945 days), GTKO.hCD46.hTBM.hCD39.hEPCR.hDAF (>143 days) and GTKO.hCD46.hEPCR.hDAF.hTFPI.hCD47(>68). The last two groups are still ongoing. In the last three groups co stimulation blocking antibody was also changed from anti CD154 antibody to anti CD40 antibody to avoid consumptive coagulopathy.

Conclusion. We have demonstrated significant progress in graft survival by replacing incompatible pig genes with human genes which aided in avoiding several complications like thrombotic microangiopathy, consumptive coagulopathy and also ameliorated the cellular inflammatory process. Further genetic modifications are in progress to produce donor organs with the ideal genetic makeup to facilitate clinical cardiac xenotransplantation.

CITATION INFORMATION: Horvath K, Singh A, Chan J, Thomas M, Lewis B, Ayares D, Corcoran P, Mohiuddin M. The Impact of Sequential Gene Modifications on Cardiac Xenograft Survival. Am J Transplant. 2016;16 (suppl 3).

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