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

Background. The purpose of the present study was to investigate the effect of the C1 esterase inhibitor (C1-INH) molecule against human complement att ack on a swine endothelial cell (SEC) membrane. Human C1-INH functions as a n inhibitor for complement reaction in the first step of the classical path way in the fluid phase. Methods. A surface-bound form of human C1-INH (CI-INR PI) consisting of a f ull-length coding sequence of CI-INH and a glycosylphosphatidylinositol (GP I) anchor of the dec:ly-accelerating factor (CD55) was constructed, and sta ble Chinese hamster ovarian tumor (CHO) cell lines Emd SEC lines expressing C1-INR-PI were then prepared by transfection of the constructed cDNA. The basic function of the transfected molecules on the xenosurface was investig ated using CHO transfectants for the sake of convenience, The efficacy of C 1-INH-mediated protection of SEC from human complement was then assessed as an in vitro hyperacute rejection model of a swine-to-human discordant xeno graft, Results. Flowcytometric profiles of the stable CHO and SEC transfectants wi th 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 1 0(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, respectiv ely. In addition, the complement-inhibiting activity of human C1-INH molecu les is not homologously restricted. Conclusions. The results suggest that the surface-bound form of C1-INH repr esents a good candidate as a safeguard against hyperacute rejection of xeno grafts.