CHARACTERIZATION OF PIGS TRANSGENIC FOR HUMAN DECAY-ACCELERATING FACTOR

Background. To prevent the central role played by complement activatio n in the hyperacute rejection of pig organs transplanted into primates , pigs transgenic for human decay accelerating factor (HDAF) have rece ntly been produced. The data presented here extend previous immunohist ochemical findings by documenting the immunological characterization a nd the levels of expression of HDAF in these transgenic pigs. Methods. Animals from 30 independently derived lines were included in this stu dy. HDAF expression was characterized by immunoprecipitation and epito pe mapping. Quantitative analysis was performed by radiometric assays followed by Scatchard analysis and by double-determinant radioimmunoas say. Deposition of iC3b on porcine aortic endothelial cells was determ ined by radioimmunoassay. DNA slot-blot analysis and densitometric sca nning were used to evaluate HDAF transgene copy number. Results. The i ntegrity of HDAF expressed by these transgenic pigs could be demonstra ted, HDAF was present in 72% of the organs analyzed, although consider able variation in expression occurred, both between animals and within the same pig. High levels of HDAF on porcine aortic endothelial cells resulted in iC3b deposition at levels as low as that detected on huma n endothelial cells. Twenty-six organs expressed levels of HDAF greate r than those observed in the equivalent human tissue. HDAF expression did not correlate with the number of copies of the transgene incorpora ted into the porcine genome. Conclusions. Transgenic pigs, which expre ss levels of functional HDAF even greater than those observed in human s, have successfully been produced. Pigs transgenic for human compleme nt inhibiting molecules could represent a source of organs for future clinical xenotransplantation.