Molecular remodelling of human CD46 for xenotransplantation: designing a potent complement regulator without measles virus receptor activity

Abstract

SUMMARYIn pig-to-human discordant xenotransplantation, human complement (C) is a major barrier to long survival of xenografts. The current idea on how to cope with this barrier is that human complement regulatory proteins are forcibly expressed on xenografts to serve as safeguards against host C-induced hyperacute rejection of xenografts. Co-expression of decay-accelerating factor (DAF) (CD55) and membrane cofactor protein (MCP) (CD46) would be the ®rst choice for this trial, because most of the human cells are protected from C-mediated damage by two different modes with these two kinds of Cregulators. Many problems have arisen, however, for MCP expression on grafts. (i) MCP acts as a measles virus receptor, which may function to render donor pigs measles virus (MV) sensitive. (ii) MCP signals immune suppression which causes devastation of the recipient's immune responses. (iii) MCP exerts relatively low self-protective activity against C compared with other cofactors; development of more ef®cient forms is desirable. (iv) Grafts with a high expression level of MCP are dif®cult to produce. In this study, we made a number of cDNA constructs of MCP, expressed them on swine endothelial cell lines, and tested cell-protective potency and MV susceptibility. The short consensus repeat 1 (SCR1)-deleted MCP with glycosyl phosphatidylinositol (GPI)-anchored form (D1MCP-PI) of MCP was found to be most suitable for the purpose of overcoming these problems. However, it was also found that MV induces two modes of cytopathic effect (CPE) on swine endothelial cells, either MCPdependent or -independent. Here, we discuss these two points which will be raised through study of MCP-transgenic animals.

Complement Component 3 Negatively Regulates Antibody Response by Modulation of Red Blood Cell Antigen

“…While injection of RBCs from other species, such as sheep RBCs, results in a robust immune response and has been used for many years to study host immunity ( 100 – 104 ), sheep and other foreign RBCs are rapidly cleared ( 29 ), which can result in an artificial acceleration of an immune response that can compromise direct comparison of host regulation of complement outcomes during Ab development. Furthermore, interspecies complement regulators are often less effective at regulating complement ( 105 , 106 ), likewise reducing the ability to directly examine the outcome of complement regulation in an otherwise syngeneic system. Chemical attachment of antigen to the cell surface damages RBCs ( 107 , 108 ), and also results in rapid clearance and the production of an inflammatory response that prevents isolation of a single antigenic determinant on an otherwise normal cell as a distinct variable when seeking to determine the outcome of target antigen exposure on self.…”

Production and characterization of a pig line transgenic for human membrane cofactor protein

“…Begum et al. proposed to eliminate the possible incidence of human MCP mediated measles virus infection by remodeling MCP [23].…”

“…However, Schneider-Schaulies et al reported that MCP expression in porcine PBLs does not alter their susceptibility to measles virus [22]. Begum et al proposed to eliminate the possible incidence of human MCP mediated measles virus infection by remodeling MCP [23].…”

Complement regulation in the GalT KO era

“…The delta-SCR1 forms of MCP might then represent a practical form for clinical xenotransplantation. This is because, delta-SCR1 of MCP is capable of regulating complement in almost the same manner as the wild form and becomes free from the measles virus [61]. However, SCR1 of MCP may have some relationship to C4 cleavage [62].…”