Antibodies to human adhesion molecules and von Willebrand factor: In vitrocross-species reactivity in the xenotransplantation setting

Endothelial cell activation is thought to play an important role in xenogra ft rejection through cell retraction and expression of pro-coagulant and pr o-inflammatory factors. Identification of antibodies recognizing porcine en dothelial molecules would be useful to study and manipulate the inflammator y response to a xenograft. The aim of this study was to investigate the cro ss-reactivity of antibodies directed against human adhesion molecules and v on Willebrand factor (vWF). Binding of monoclonal antibodies (mAbs) directe d against human CD31, CD44, CD49, CD54, CD62E, CD102, and CD106 was evaluat ed on resting and activated endothelial cells from human and pig by flow cy tometry. Among 30 antibodies tested, 4 were shown to react with pig cells. Two of them, directed against human CD62E (E-selectin) and rabbit CD106 (VC AM-1) reacted strongly with activated and/or resting pig cells, whereas two others, directed to human CD31 (PECAM) and CD44 (H-CAM), bound weakly to p ig cells. In addition, we analyzed the cross-reactivity of five polyclonal or monoclonal antibodies to human or pig vWF with human, baboon, rhesus, pi g, and rat vWF. Binding of antibodies was tested by ELISA by using platelet lysates as source of VWF from the different species. Four anti-human or po rcine VWF antibodies exhibited a broad reactivity with vWF from all species , whereas one anti-human vWF antibody was specific for primate vWF. In this study, we identified a small number of cross-reacting antibodies that may prove useful to study in vitro and in vivo xenogeneic responses. However, t he weak antibody cross-reactivity observed with most porcine molecules poin ts our the necessity of producing species-specific antibodies to study the immune response to xenografts or for use as specific immunosuppressive ther apeutic reagents.