Enhancement of the fibrinolytic activity of sheep endothelial cells by retroviral vector-mediated gene transfer

In an attempt to enhance the fibrinolytic activity of endothelial cells (EC), a retroviral vector containing the human tissue-type plasminogen activator (t-PA) cDNA was constructed. Sheep EC were stably transduced with the vector, resulting in a 30-fold increase in t-PA activity over that detected in EC transduced with a control vector. Southern and Northern analyses confirmed the presence of both the vector sequence and the appropriate mRNA transcripts. Secretion of high levels of recombinant human t-PA continued in vitro for the duration of the experiments, up to 11 weeks after transduction, although the rate of t-PA secretion decreased in some of the EC lines. Zymographic analysis of conditioned medium from t-PA-transduced EC showed the presence of two new molecular species with plasminogen activator activity that could be specifically immunoprecipitated with a monoclonal antihuman t-PA antibody. The relative molecular masses of these species (60 to 80 and 110 Kd) suggest that they represent recombinant human t-PA both free and bound to sheep plasminogen activator inhibitor 1 (PAI-1). Consistent with this interpretation, the 110-Kd species could be specifically immunoprecipitated with antiserum to PAI-1. These studies demonstrate that retroviral vector-mediated gene transfer may be used to increase total EC fibrinolytic activity.