LONGITUDINAL ANALYSIS OF THE EXPRESSION OF HUMAN DECAY-ACCELERATING FACTOR (HDAF) ON LYMPHOCYTES, IN THE PLASMA, AND IN THE SKIN BIOPSIES OF TRANSGENIC PIGS

Pigs transgenic for the regulators of human complement activation, suc h as decay accelerating factor (DAF), membrane cofactor protein (MCP), and CD59, have recently been produced as a means to overcome the orga n shortage for clinical transplantation. Histological investigations i n DAF transgenic pigs have demonstrated that large amounts of the tran sgenic protein are expressed on the endothelium of the organs, where h yperacute rejection is known to initiate. Several papers have recently appeared in the literature that show considerable variability in the expression of a transgene over the lifespan of a transgenic animal. In order to evaluate the consistency in the expression of the transgene in our human DAF (HDAF) transgenic pigs, we have analyzed 22 newborn t ransgenic pigs and 5 control littermates (group A) over a 6-month peri od and 11 long-term surviving transgenic animals (group B). In all the animals from group A, HDAF expression was investigated on peripheral blood mononuclear cells (PBMC) and in the plasma as a free circulating molecule at weekly intervals in the first month of life and monthly t hereafter. In the same animals, HDAF expression was also analyzed on e ndothelial cells using sequential ear biopsies. Moreover, HDAF express ion was evaluated on the endothelial cells of our longest surviving tr ansgenic animals (group B) and compared with that observed in the biop sy taken at birth. Over the observation period, considerable variabili ty was found in the blood of most animals from group A, both in the pe rcentage of cells expressing the transgene and the mean number of HDAF molecules per cell. In the same animals, free circulating HDAF levels were shown to be very high at birth, progressively declining to a nad ir reached between the second and the fifth week of life. No statistic ally significant correlation could be found between these three hemato logical parameters. Over the duration of the study, consistent express ion of HDAF in the tissues was, however, found at the different time p oints in all the newborn animals from group A. Moreover, very high lev els of HDAF, at least comparable to those observed at birth, were stil l detected in the skin biopsies of all the animals from group B after more than 18 months of life (mean: 25.18 +/- 3.46; range: 21-31 months ). Thus, our data show that over an observation period of up to 6 mont hs, there is consistency in the expression of HDAF on the endothelium of serially collected skin biopsies from HDAF transgenic pigs and that levels of HDAF similar to those observed at birth are expressed by th ese transgenic animals after more than 2 years of life. Hematological parameters such as expression of HDAF on PBMC or measurements of free circulating HDAF in the plasma do not seem to correlate with the expre ssion of HDAF on the endothelial cells.