The Importance of Tissue Factor Expression by Porcine NICC in Triggering IBMIR in the Xenograft Setting

Abstract

In islet transplantation, tissue factor (TF) has been reported to be involved in triggering the instant blood-mediated inflammatory reaction (IBMIR), which causes early massive loss of islets transplanted intraportally. TF is synthesized and secreted by several cell sources including islets and inflammatory cells such as neutrophils, monocytes, and platelets. In this study, we investigated whether xenografts-mediated IBMIR could be inhibited by selectively inhibiting TF production by islets using small interfering RNA (siRNA)-mediated TF gene knockdown. Porcine neonatal islet cell clusters (NICC) were transfected with siRNA specific for TF or a nonspecific siRNA. TF gene and protein expression were analyzed by real-time polymerase chain reaction and fluorescence-activated cell sorting, respectively. The effect of TF knockdown on IBMIR was evaluated using an in vitro tubing loop model of human blood-NICC interactions. TF siRNA transfection of NICC resulted in reduced TF gene and protein expression. TF siRNA transfected NICC showed a significant reduction in the formation of blood clots, platelet activation, thrombin generation, and complement activation after exposure to human ABO compatible blood in vitro. In addition, there was reduced neutrophil infiltration within blood clots containing TF siRNA transfected NICC. TF expression on porcine NICC is an important initiator of IBMIR in islet xenotransplantation. This study identifies porcine TF as a potential target for inhibiting this response.