Genetic modification of source pigs for xenograft organs (heart, kidney, liver, lung) provide the only viable near-term solution to the critical world-wide shortage of donor organs for human clinical transplantation. Functional inactivation of the pig alpha 1,3 gal gene (GTKO pigs), in combination with transgenic expression of a human complement inhibitor gene (hCD46) addresses both hyperacute gal-mediated antibody rejection, as well as, inhibition of non-gal antibody responses and complement pathway associated responses in vivo in pig-to-non-human primate (NHP) transplant studies. Further genetic modification of the source pigs has the potential to address both safety and efficacy issues, since by building immunosuppressant gene expression into the donor organ, one can modulate cell mediated rejection with reduced drug levels of exogenous agents, and by further adding human anti-thrombotic genes and anti-inflammatory genes, one can inhibit both humoral and cell-mediated rejection, as well as inflammatory responses and thrombosis , thus abrogating both early and chronic immune-mediated destruction, as well as acute vascular rejection of organ xenografts. The goal of this transgenic pig core is to produce genetically modified pigs as source animals, specifically for replacement organ procurement to meet the needs for in vitro, ex vivo, and in vivo studies (described in Projects 1-2) aimed at improving xeno-organ survival towards providing a human-compatible tissues, in sufficient scale, to overcome the deficiencies in donor organ availability for human patients. Pigs have been produced which express a dominant negative mutant of pig SLA class II genes (CIITA DN) resulting in functional suppression of T cell mediated activation. CIITA-transgenic pigs will be crossed onto the GTKO/hCD46 genetic background for use in NHP studies. Further, pigs with transgenic expression and function of the anti-thrombotic/anti-inflammatory genes, human thrombomodulin (hTM) and human endothelial cell protein C receptor (EPCR) will be combined with the GTKO/CD46/CIITA background in order to address AVR and thrombotic microangiopathy. Bioactivity of these therapeutic transgenes has been confirmed, and such pigs will be replicated by the pig core to meet the goals outlined in Projects 1-2.
Transgenic pigs provide an unlimited and renewable resource aimed at overcoming the critical shortage donor organs for human clinical transplantation. Genetic modification of the source pigs has relevance not only in scale, but also safety and efficacy, since by removing specific pig genes, and adding human genes, one can not only prevent rejection, and reduce levels of immunosuppression, but also inhibit thrombosis and inflammation thus addressing current barriers to successful pig to human organ transplantation.
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