Efficacy and safety of ABI793, a novel human antihuman CD154 monoclonal antibody, in cynomolgus monkey renal allotransplantation

Background. Anti-CD154 monoclonal antibodies (mAbs) cause long-term graft survival in preclinical allotransplantation experiments. This is the first report on the efficacy and safety of AB1793, a novel human anti-human CD154 mAb, in Cynomolgus renal transplant recipients. Methods. AB1793 (human immunoglobulin-G1:kappa) was derived from a hybridoma generated after immunization of human immunoglobulin transgenic mice (HuMAb-Mouse, Medarex Inc., Annandale, NJ). Cynomolgus monkey recipients of major histocompatibility complex-mismatched, life-supporting renal allografts were treated repeatedly with intravenous AB1793 for a 3-month period posttransplantation. Graft function was monitored by serum creatinine, and rejection was confirmed histologically. Results. AB1793 binds to human, Cynomolgus and Rhesus monkey CD154; it inhibits dose dependently in vitro CD154:CD40 binding and human mixed lymphocyte reaction. AB1793 is comparable to the mouse antihuman CD154 mAbs 5c8 and 24-31 with respect to affinity, inhibitory capacity, and species specificity; however, AB1793 binds to a different CD154 epitope. With 20 mg/kg of A131793, five of nine recipients showed substantially prolonged graft survival after cessation of treatment, whereas four of nine recipients were killed because of high serum creatinine while still receiving treatment. AB1793 treatment was associated with episodes of severe acute tubular necrosis (which was unrelated to rejection and responded to fluid and diuretic treatment) and a decrease in platelet numbers. Chronic and acute thromboembolic vascular lesions with hemorrhages were observed in the lung and brain of two allograft recipients. None of these side effects were observed in animals that underwent autotransplantation, thus excluding direct toxicity of AB1793. Conclusions. AB1793 treatment effectively prevents graft rejection in Cynomolgus monkeys. Evidence for rare thromboembolic events, as also previously observed with different anti-human CD154 mAbs, suggests that thromboembolic complications may be a class effect of anti-CD154 mAbs, unrelated to their epitope specificity.