Protection against hyperacute xenograft rejection of transgenic rat heartsexpressing human decay accelerating factor (DAF) transplanted into primates

Background: Production of transgenic pigs for multiple transgenes is part o f a potential strategy to prevent immunological events involved in xenograf t rejection. Use of a genetically engineerable rodent as a donor in primate s could allow testing in vivo of the effects of different transgenes on con troling xenograft rejection. As a first step in the development of a donor containing multiple transgenes, transgenic rats for human decay-acceleratin g factor (DAP) were used as heart donors to test their resistence against c omplement (C)-mediated rejection by non-human primates. Materials and Methods: Transgenic rats were generated by using a construct containing the human DAF cDNA under the transcriptional control of the endo thelial cell (EC)-specific human ICAM-2 promoter. DAF expression was evalua ted by immunohistology and by FAGS analysis of purified ECs. Resistance of transgenic hearts against C-mediated damage was evaluated by ex vivo perfus ion with human serum and by transplantation into cynomolgus monkeys. Results: Immunohistological analysis of DAF expression in several organs fr om two transgenic lines showed uniform expression on the endothelium of all blood vessels. ECs purified from transgenic hearts showed 50% DAF expressi on compared to human ECs and >70% reduction of C-dependent cell lysis compa red to control rat ECs. Hemizygous transgenic hearts perfused with human se rum showed normal function for >60 min vs. 11.2 +/- 1.7 min in controls. He mi- or homozygous transgenic hearts transplanted into cynomolgus monkeys sh owed longer survival (15.2 +/- 7 min and >4.5 hr, respectively) than contro ls (5.5 +/- 1.4 min). In contrast to hyperacutely rejected control hearts, rejected homozygous DAF hearts showed signs of acute vascular rejection (AV R) characterized by edema, hemorrhage, and an intense PMN infiltration. Conclusions: We demonstrate that endothelial-specific DAF expression increa sed heart transplant survival in a rat-to-primate model of xenotransplantat ion. This will aid in the analysis of AVR and of new genes that may inhibit this form of rejection, thus helping to define strategies for the producti on of transgenic pigs.