The ability to genetically engineer and breed animals has stimulated recent excitement about xenotransplantation. This excitement stems in part from the idea that if genetic engineering might be used to optimally modify the source of a transplant to make it compatible with the recipient, then the need for immunosuppression might be decreased or eliminated. This has been achieved only in part.
Transgenic techniques have been used to express human genes for complement regulatory proteins and carbohydrate-modifying enzymes in lines of pigs. For example, the human decay-accelerating factor and CD59 genes, which inhibit complement reactions, have been introduced into lines of pigs in an effort to prevent complement-mediated tissue injury. These efforts have prevented the severest form of complement-mediated rejection, hyperacute rejection.1-7-1 Genes that would modify synthesis of Gala1-3Gal, such as H transferase, have also been expressed, but expression of that sugar has not been fully eradicated by this approach.
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