Induction of acquired factor IX inhibitors in cynomolgus monkey (Macaca fascicularis): A new primate model of hemophilia B

Inherited hemophilia dog and other transient hemophilic animal models have been used for evaluation of hemostatic agents for use in treatment of hemop hilia. We established the first nonhuman primate hemophilic model by immuni zing cynomolgus monkeys with human FIX (hFIX) in adjuvants. FIX activities of all three hFIX-immunized monkeys decreased transiently to less than 10% in accordance with prolongation of activated partial thromboplastin time (A PTT). Forty micrograms of human factor VIIa (hFVIIa) per kilogram body weig ht (that was reported to be clinically effective) was administered to the m onkey with the highest inhibitor titer to evaluate its usefulness as a hemo philia inhibitor model. Results of thromboelastography (TEG) after the inje ction demonstrated that the hemostatic effect of FVIIa in this model would be similar to that in hemophiliacs with inhibitors. The antibodies purified from the monkey's plasma by kFIX-immobilized gel were composed of two type s: Ca2+-dependent and -independent antibodies, with features of IgG(1) and IgG(4). Both types of antibodies reacted to cynomolgus FIX, and only Ca2+-d ependent antibodies also expressed inhibitory activity against cynomolgus F IX. Immunoblotting analyses of Ca2+-dependent antibodies using hFIX and its derivatives suggested that they recognized the Ca2+-dependent conformation related to the gamma -carboxyglutamic acid (Gla) domain. Comparison of FIX cDNA from human, cynomolgus monkey, and other species, and the results of immunization of various animals (goats, beagle dogs, rabbits, and rats) wit h hFIX in adjuvants strongly suggested that the development of acquired FIX inhibitors in the monkeys might be due to high cross-reactivity of the ant ibodies to molecular mimic antigens, hFIX, and cynomolgus FIX. (C) 2001 Els evier Science Ltd. All rights reserved.