Expression and functional analysis of glycosyl-phosphatidyl inositol-linked CD46 in transgenic mice

Background. Complement activation plays a pivotal role in hyperacute xenogr aft rejection. In humans, activation of complement is regulated by a number of cell surface regulatory proteins. Membrane cofactor protein (CD46) is o ne such regulator that protects cells by acting as a cofactor for the facto r I-mediated cleavage of C3b and C4b. Transgenic animals expressing human C D46 may provide organs that are resistant to complement attack. However, at tempts to generate mice expressing human CD46 using cDNA-based constructs h ave been largely unsuccessful. Methods. Transgenic mice expressing a glycosyl-phosphatidyl inositol (GPI)- linked form of CD46 were generated by microinjection of a hybrid CD46/CD55 cDNA under the control of the human intercellular adhesion molecule-2 promo ter. Expression of CD46-GPI on the vascular endothelium was determined by i mmunohistochemistry. The ability of CD46-GPI to protect mouse tissues from human complement attack was determined using an ex vivo isolated perfused h eart model. Results. Three founder animals expressing CD46-GPI were identified. Histolo gical analysis showed strong and uniform expression of CD46-GPI on the vasc ular endothelium of all organs examined. Ex vivo perfusion of transgenic mo use hearts with human plasma showed a reduction in C3c deposition and a sli ghtly prolonged function compared with controls. Conclusions. High-level expression of CD46-GPI was achieved in transgenic m ice by using a modified cDNA-based construct. The CD46-GPI was functional, providing some protection from complement-mediated damage in the ex vivo mo del, and may be useful in xenotransplantation if expressed in combination w ith CD55 and CD59.