ENHANCEMENT OF THE FUNCTIONAL REPERTOIRE OF THE RAT PARIETAL PERITONEAL MESOTHELIUM IN-VIVO - DIRECTED EXPRESSION OF THE ANTICOAGULANT AND ANTIINFLAMMATORY MOLECULE THROMBOMODULIN

We have used our previously described ex vivo mesothelial cell (MC)-me diated gene therapy strategy (Gene Ther, 2:393-401, 1995) to modify th e functional properties of the rat parietal peritoneal mesothelium in vivo by expression of a membrane-bound recombinant protein on the MC s urface. Rat primary MCs were stably transfected (using strontium phosp hate DNA coprecipitation) with a plasmid containing the gene for rat t hrombomodulin (TM), a transmembrane glycoprotein that functions as an essential cofactor for the physiological activation of the anticoagula nt protein C by the enzyme thrombin, As demonstrated by immunohistoche mistry and by direct equilibrium binding with radiolabelled thrombin, genetically modified MCs expressed high levels of TM antigen on their surface in vitro. As judged by a thrombin-dependent protein C activati on assay, such MC membrane-bound TM was biologically active. Once rese eded on the denuded parietal peritoneal surface of syngeneic recipient s, these TM-transfected MCs continued to express TM antigen in vivo fo r at least 90 days. Moreover, the recombinant TM expressed on the reco nstituted parietal mesothelium retained its ability to activate protei n C in a thrombin-dependent manner. Our data indicate that MC-mediated expression of TM can be used to augment the anticoagulant properties of the parietal peritoneal surface. In general, our results suggest th at ex vivo MC-mediated gene therapy can be used to deliver other thera peutic transmembrane proteins to the MC surface to enhance the functio nal repertoire of the parietal mesothelium in vivo.