PROCOAGULANT EFFECT OF THE OKT3 MONOCLONAL-ANTIBODY - INVOLVEMENT OF TUMOR-NECROSIS-FACTOR

We recently observed that the prophylactic administration of high doses of OKT3 monoclonal antibody (MoAb) in cadaveric renal transplantation favors the development of thromboses of the grafts' main vessels and of thrombotic microangiopathies. These clinical observations led us to perform sequential determinations of plasma levels of prothrombin fragment 1 and 2 (F 1 + 2) and fibrin degradation products (FDP) after the first injection of 5 or 10 mg OKT3 given as prophylaxis in kidney transplant recipients. The values observed have been compared with those of kidney transplant recipients not treated with OKT3. F 1 + 2 levels peaked four hours after the first injection of 5 mg OKT3 (mean +/- SEM: 4.82 +/- 0.73 vs. 1.75 +/- 0.37 nmol/liter in controls, P < 0.01), indicating activation of the common pathway of the coagulation cascade. FDP levels were already above baseline values at four hours and continued to increase until 24 hours (mean +/- SEM at 24 hr, 4729 +/- 879 vs. 1038 +/- 320 ng/ml in controls, P < 0.05), indicating a fibrinolytic process. The magnitude and the time course of the changes in F 1 + 2 and FDP plasma levels were similar whether the patients received 5 or 10 mg dose of OKT3. The levels of von Willebrand factor (VWF) antigen, a molecule released by activated or damaged endothelial cells, were also significantly increased after injection of OKT3 (mean +/- SEM at 24 hr, 3.67 +/- 0.18 vs. 2.17 +/- 0.11 U/ml in controls, P < 0.05). The procoagulant effects of OKT3 were further investigated in vitro on human umbilical vein endothelial cells (HUVEC). It was found that OKT3 induces peripheral blood mononuclear cells (PBMC) to release soluble mediators that trigger the generation of thrombin at the HUVEC surface by a tissue factor-dependent mechanism. The addition of chimeric anti-TNF-alpha MoAb to culture supernatants of OKT3-stimulated PBMC strongly inhibited the thrombin generation in this model. We conclude that OKT3 activates the coagulation cascade in vivo and that TNF-alpha is a mediator of the procoagulant effects of OKT3 at the endothelial cell level.