Effect of EPCR and HLA-E expression by pig lung on coagulation and NK-cell related processes in a xenogenic lung-human blood perfusion model
Xenotransplantation, using pig organs, is a promising solution to the shortage of human donor organs. However, this approach is limited by hyperacute rejection initiated by the binding of natural antibodies to terminal galactosyl residues (Gal) and other surface proteins on pig cells, which trigger complement and coagulation activation. To bypass this, pigs have been genetically modified to lack galactosyltransferase, the key enzyme for Gal expression (GalKO) and to express human complement regulatory proteins, such as membrane co-factor protein (CD46). These genetic modifications significantly increased xenograft survival, by preventing most of antibody-complement-mediated rejection.
However, even GalTKO.hCD46 xenografts, particularly lungs, still get injured, demonstrating that other mechanisms must be involved. Recent work performed with transgenic pig organs points to dysregulated coagulation and inflammation caused by adhesion of platelets and white blood cell populations, including natural killer (NK) cells. During recent evaluation of pigs expressing various human transgenes, expression of human endothelial protein C receptor (EPCR) appeared to significantly improve lung outcome. However, the mechanisms of action remain unclear. Another recent genetic modification includes expression of a human histocompatibility antigen type E (HLA-E) by pig cells, which is designed to block human NK cell activation.
Our study will focus on the effects of EPCR and HLA-E expression by pig lung in a xenogenic lung-human blood perfusion model, by measuring changes in platelet/coagulation pathway activation, NK cell adhesion, and effects on inflammation. In particular, we will extend preliminary observations that pig cells migrate out from the organ and circulate in the human blood perfusate.