No role of alpha-Gal in human monocyte-endothelial cell interactions in vitro

Dual islet transplantation modeling of the instant blood-mediated inflammatory reaction

Islet xenotransplantation is a potential treatment for diabetes without the limitations of tissue availability. Although successful experimentally, early islet loss remains substantial and attributed to an instant blood-mediated inflammatory reaction (IBMIR). This syndrome of islet destruction has been incompletely defined and characterization in pig-to-primate models has been hampered by logistical and statistical limitations of large animal studies. To further investigate IBMIR, we developed a novel in vivo dual islet transplant model to precisely characterize IBMIR as proof-of-concept that this model can serve to properly control experiments comparing modified xenoislet preparations. WT and α1,3-galactosyltransferase knockout (GTKO) neonatal porcine islets were studied in nonimmunosuppressed rhesus macaques. Inert polyethylene microspheres served as a control for the effects of portal embolization. Digital analysis of immunohistochemistry targeting IBMIR mediators was performed at 1 and 24 h after intraportal islet infusion. Early findings observed in transplanted islets include complement and antibody deposition, and infiltration by neutrophils, macrophages and platelets. Insulin, complement, antibody, neutrophils, macrophages and platelets were similar between GTKO and WT islets, with increasing macrophage infiltration at 24 h in both phenotypes. This model provides an objective and internally controlled study of distinct islet preparations and documents the temporal histology of IBMIR.

Downregulation of tissue factor (TF) by RNA interference induces apoptosis and impairs cell survival of primary endothelium and tumor cells

Tissue factor (TF) has been implicated in the thrombotic complications seen during vascular rejection of allografts and may contribute to intimal hyperplasia in chronic allograft vasculopathy. Downregulation of endothelial TF expression post-transplantation could therefore be of therapeutic value. Lentivirus-mediated RNA interference was used in primary endothelial cells (EC) to investigate its effects on TF protein expression and functional activity. Lentivirus-mediated expression of a TF-specific short-interfering (si) RNA with green fluorescent protein as a reporter gene (siRNATF-GFP) resulted in a 42 +/- 3.9% reduction in EC surface-expressed TF as compared with cells expressing a scrambled siRNATF sequence (P = 0.025). The TF content in EC lysates was reduced from 6.85 +/- 1.99 ng to 3.05 +/- 0.82 ng (P = 0.006). Factor X (FX) activation was not impaired on the apical EC surface. The subendothelial matrix of ECs with low TF expression showed significantly reduced TF activity compared with non-transduced cells or with cells harboring the empty vector. ECs expressing siRNATF-GFP exhibited reduced reporter gene (GFP) expression and cell density and an altered morphology. Transfection of control cells with high (J82 cells) or low (MiaPaCa-2 cells) TF expression with siRNATF oligonucleotides caused apoptosis of the J82 but not of the MiaPaCa-2 cells. Thus, lentivirus-mediated RNA interference reduces the TF expression of activated ECs but does not affect FX activation by TF/FVIIa expressed on the apical surface. The downregulation has nevertheless substantial negative effects on the viability of ECs and TF-expressing control cells. These findings imply that certain levels of TF are required for the maintained viability and growth of endothelium and TF-expressing tumor cells.