Blocking Porcine Sialoadhesin Improves Extracorporeal Porcine Liver Xenoperfusion

Abstract

Background: Patients in fulminant hepatic failure (FHF) currently do not have a temporary means of support while awaiting liver transplantation. A potential therapeutic approach for patients in FHF is the use of extracorporeal perfusion with porcine livers as a form of “liver dialysis”. During a 72 hour extracorporeal perfusion of porcine livers with human blood, porcine Kupffer cells (KC) bind to and phagocytose human red blood cells (hRBC) causing the hematocrit to decrease to 2.5% of the original value. Our laboratory has identified sialoadhesin (Sn) on the surface of porcine KC as the lectin responsible for binding N-acetylneuraminic acid (Neu5Ac) on the surface of the hRBC. In order for extracorporeal porcine liver perfusion to be used as a therapy for patients in liver failure, all forms of anti-human rejection must be resolved. We evaluated whether targeting Sn prevents the recognition and subsequent destruction of hRBCs seen during extracorporeal porcine liver xenoperfusion. Methods:In vitro experiments were performed wherein cultured porcine macrophages (pMΦ) were pretreated with the anti-porcine Sn monoclonal antibody, 1F1. pMΦ were subsequently assayed for their ability to bind hRBC. Next, ex vivo experiments were performed wherein six wild type pig livers were perfused with isolated hRBCs for 72 hours. In one group, three livers were treated with 1F1. As a control group, three livers were treated with an antibody of the same isotype but with no known specificity for Sn. Results: We have shown that treatment of cultured pMΦ with 10ug/ml of 1F1 abolishes the ability of the pMΦ to bind hRBC (p < 0.001). Additionally, we have shown that the addition of 1F1 to an extracorporeal porcine liver xenoperfusion model significantly reduces the loss of hRBC over a 72 hour period (p < 0.01). Sustained liver function was demonstrated by continued bile production and other markers. Conclusions: This study suggests that the destruction of human erythrocytes in an extracorporeal porcine liver xenoperfusion model is, in part, mediated by Sn expressed on the surface of porcine KC. Furthermore, this data illustrates that the addition of anti-Sn antibody to the circulation of a pig-to-human xenoperfusion may inhibit the destruction of human erythrocytes by porcine KC. Future studies should be conducted utilizing livers derived from Sn deficient pigs.