Background Replacement therapy is the most common treatment for reduction of bleeding and control of episodic bleeding in individuals with hemophilia. Despite the proven effectiveness of factor replacement therapy, repeated intravenous administration is a heavy burden to individuals with hemophilia. Objectives To reduce the burden, therapeutic agents that can be subcutaneously administered need to be developed, and an anti–tissue factor pathway inhibitor (TFPI) antibody may be a suitable candidate for this purpose. Methods MG1113 is an IgG4 monoclonal antibody that binds to Kunitz‐2 domain (KD2) of TFPI. To confirm the coagulation potential of MG1113, several tests were conducted using factor VIII (FVIII)‐ or IX (FIX)‐deficient plasma. For the ex vivo spiking test, platelet‐poor plasma samples from 14 individuals with hemophilia were spiked with MG1113. The in vivo efficacy was determined using blood loss tests, modified prothrombin time (mPT), and free TFPI quantification after intravenous or subcutaneous administration of MG1113 into hemophilia A (HA)‐induced rabbits. Results Radiographic crystallography demonstrated the specific binding site between MG1113 and KD2. In FVIII‐deficient plasma and the plasma of individuals with hemophilia, peak thrombin and endogenous thrombin levels were increased by MG1113 in a concentration‐dependent manner. Rotational thromboelastometry assay revealed that clotting time, clot formation time, and maximum clot firmness were normalized in MG1113‐treated blood of patients. Intravenous or subcutaneous injection of MG1113 into HA‐induced rabbits resulted in rebalancing of blood loss, mPT, and free TFPI levels. Conclusions These results indicate that subcutaneous administration of MG1113 neutralizes the function of TFPI and regulates bleeding in individuals with hemophilia.
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