COMBINATION OF DECAY-ACCELERATING FACTOR EXPRESSION AND ALPHA-1,3-GALACTOSYLTRANSFERASE KNOCKOUT AFFORDS ADDED PROTECTION FROM HUMAN COMPLEMENT-MEDIATED INJURY

Background. Hyperacute rejection (HAR) currently prevents the use of p igs as organ donors for humans, It is now generally accepted that the key instigators of NAR are naturally occurring xenoantibodies against the terminal disaccharide galactose alpha 1,3-galactose (Gal), and the species incompatibility between human complement and porcine compleme nt regulatory molecules, Using two in vitro models and an ex vivo mous e heart perfusion model, are have shown previously that cells and tiss ues front Gal knockout (Gal KO) and transgenic mice expressing the hum an cell surface complement regulator decay-accelerating factor (DAF/CD 55) are partially, but not completely, protected fi om human complemen t-mediated injury. Methods. In the present study, Gal KO mice were cro ssed with DAF transgenic mice and bred to homozygosity (DAF/Gal KO). I solated splenocytes were incubated with human serum, and the protectiv e effect of DAF and Gal KO was assessed by measuring complement deposi tion and cell lysis. Hearts perfused ex vivo with human plasma were ex amined for human antibody and complement deposition, and assessed func tionally by measuring work performed by the heart. Results. Splenocyte s from DAF/Gal KO mice were found to be more resistant to complement-m ediated injury than cells from either DAF transgenic or Gal KO mice. I n addition, hearts from DAF/Gal KO mice, when perfused with human plas ma, displayed prolonged survival compared with hearts from Ga KO mice. This wa associated with a reduction in the extent of endothelial depo sition of IgG, IgM, and complement C3b. Conclusions. These findings de monstrate that expression of human DAF in association with elimination of the Gal epitope provides added protection from complement-mediated injury in these models of HAR.