COMPLETE INHIBITION OF ENDOTOXIN-INDUCED COAGULATION ACTIVATION IN CHIMPANZEES WITH A MONOCLONAL FAB FRAGMENT AGAINST FACTOR VII VIIA/

Gram-negative sepsis is oftentimes complicated by activation of coagul ation with disseminated intravascular coagulation and microthrombosis. This may contribute to the associated morbidity, multiple organ failu re and death. Recent studies have established that the tissue factor-d ependent pathway of blood coagulation has a significant participatory role in the initial endotoxin-induced activation of coagulation. Tissu e factor (TF), expressed on the surface of activated monocytes and end othelial cells forms cell surface complexes with free circulating fact ors VII and VIIa. The latter complex proteolytically activates factors X and IX. Recent in vivo experiments have shown that a rapidly neutra lizing TF monoclonal antibody prevents and arrests the endotoxin-induc ed activation of coagulation and similar studies have shown to reduce mortality in baboons. In this study we describe the preparation of a f actor VII/VIIa neutralizing monoclonal Fab fragment and characterize i ts effect on in vivo activation of coagulation during experimental end otoxemia in chimpanzees. Four chimpanzees received a bolus intravenous injection of 4 ng/kg endotoxin in combination with Fab fragments of a factor VII/VIIa neutralizing murine monoclonal antibody (12D10) at a dose of either 50 mu g/kg (n = 2) or 100 mu g/kg (n = 2). Four control animals received a bolus injection of endotoxin alone. Administration of the 12D10 Fab fragments, immediately preceding the endotoxin bolus injection, effectively blocked the endotoxin-induced activation of co agulation. Plasma levels of products of in vivo activation, namely F12, TAT complexes and FpA remained at baseline values. The administrati on of 12D10 resulted in a rapid decline in factor VII/VIIa antigen lev els which remained below 5 ng/ml for 180-240 min, followed by a rapid return to baseline levels. Endotoxin administration resulted in activa tion of the fibrinolytic fibrinolytic system as reflected by a rapid i ncrease in plasma plasmin-alpha(2)-antiplasmin complexes. Administrati on of 12D10 was without effect on the endotoxin-induced fibrinolytic a ctivation. In conclusion, this study confirmed the importance of the T F:VII complex in the initial, endotoxin-induced activation of coagulat ion which was completely blocked by neutralizing all free and tissue f actor-complexed factor VII/VIIa by a specific monoclonal Fab fragment. Activation of fibrinolysis was not influenced. Therefore, neutralizat ion of factor VII/VIIa might be a promising therapeutic option in prev enting endotoxin-induced microthrombosis during Gram-negative sepsis.