A surface-bound form of human C1 esterase inhibitor improves xenograft rejection

The purpose of the present study was to investigate the effect of the C1 esterase inhibitor (C1-INH) molecule against human complement attack on a swine endothelial cell (SEC) membrane. Human C1-INH functions as an inhibitor for complement reaction in the first step of the classical pathway in the fluid phase.

A surface-bound form of human C1-INH (C1-INH-PI) consisting of a full-length coding sequence of C1-INH and a glycosylphosphatidylinositol (GPI) anchor of the decay-accelerating factor (CD55) was constructed, and stable Chinese hamster ovarian tumor (CHO) cell lines and SEC lines expressing C1-INH-PI were then prepared by transfection of the constructed cDNA. The basic function of the transfected molecules on the xenosurface was investigated using CHO transfectants for the sake of convenience. The efficacy of C1-INH-mediated protection of SEC from human complement was then assessed as an in vitro hyperacute rejection model of a swine-to-human discordant xenograft.

Flowcytometric profiles of the stable CHO and SEC transfectants with C1-INH-PI showed a medium level of expression of these molecules. The C1-INH levels were significantly reduced as a result of phosphatidylinositol-specific phospholipase C (PI-PLC) treatment, suggesting that the molecules were present as the PI-anchor form. Approximately 51.3 x 10(4) and 13.3 x 10(4) molecules of C1-INH-PI blocked human complement-mediated cell lysis by approximately 75% on the CHO cell and by 60-65% on the SEC cell, respectively. In addition, the complement-inhibiting activity of human C1-INH molecules is not homologously restricted.

The results suggest that the surface-bound form of C1-INH represents a good candidate as a safeguard against hyperacute rejection of xenografts.