Core C Summary Shortage of available allogeneic donor organs represents the greatest unmet medical need in the field of transplantation today. The survival of pig-to-primate organ transplants has improved markedly over the past three decades but unfortunately remains insufficient for clinical application. Further progress in this field will likely depend upon genetic modifications of porcine source animals both to overcome molecular incompatibilities with primate recipients and to allow the induction of immunological tolerance. The objectives of this proposal are to produce such pigs and to identify additional genetic modifications that will help attain the goal of clinically relevant xenograft survival. Advanced genetic engineering techniques, including site-specific recombinase-driven gene additions and edits using the precision CRISPR-Cas9 system, will be used to specifically modify our inbred swine with modifications addressing incompatibilities in hematopoietic cytokines (tolerance through hematopoietic chimerism), to eliminate epitopes recognized by pre-existing antibodies common to human and baboon recipients (B4galNT2-dependent) and to direct human CD47 to kidney cells in which it may play an important protective role (podocytes). Genetically modified pigs incorporating the new modifications will be tested in Projects 1 and 2 for efficacy in promoting organ survival and mixed chimerism for tolerance induction in primate and humanized mouse models.