Abstract Number: OC 60.4
Meeting: ISTH 2021 Congress
Background: Milvexian (formerly known as BMS-986177/JNJ-70033093) is a FXIa inhibitor in clinical development and has demonstrated robust antithrombotic activity in preclinical models of arterial and venous thrombosis while not increasing bleeding time. Although in clinical studies we anticipate FXIa inhibition will reduce thromboembolic events without significantly increasing bleeding risk, it is prudent to develop an effective means to rapidly and completely neutralize milvexian for patients needing urgent surgery and patients with life-threatening bleeding.
Aims: To generate antibodies to milvexian and characterize their Fab fragments.
Methods: Antibodies to milvexian were generated by immunizing transgenic mice which express human immunoglobulins. By screening the hybridoma supernatants, a lead antibody was identified and selected for affinity maturation by in vitro mRNA display. BMS-986341/JNJ-77906998 (BMS-341/JNJ-6998) was selected for further characterization and expressed in mammalian cells as an antigen-binding fragment (Fab). The affinity and rate constants for the binding of BMS-341/JNJ-6998 to milvexian were determined in competitive binding studies employing kinetic exclusion assay (KinExA). The ability of BMS-341/JNJ-6998 to neutralize the anticoagulant activity of milvexian was measured in human plasma using the activated partial thromboplastin time (aPTT) assay. Unbound milvexian was measured following ultrafiltration.
Results: BMS-341/JNJ-6998 rapidly bound to milvexian with an association rate constant of 9×105 M-1 s-1. The BMS-341/JNJ-6998:milvexian complex dissociated very slowly with a rate constant of ≤4×10-6 s-1 and a half-life for dissociation of ≥47 hours. The equilibrium constant for dissociation is 0.13 pM. In human plasma, BMS-341/JNJ-6998 neutralized the anticoagulant activity of milvexian in a concentration-dependent manner. At a one-to-one molar ratio of BMS-341/JNJ-6998 to milvexian the aPTT was restored to baseline and the free concentration of milvexian was below the limit of detection.
Conclusions: BMS-341/JNJ-6998 is a fully human antibody Fab with very high affinity for milvexian. In vitro studies in human plasma demonstrate that BMS-341/JNJ-6998 completely neutralizes milvexian to restore normal coagulant activity.
To cite this abstract in AMA style:Wu Y, Schneeweis L, Pinckney J, Terragni C, Mai S, An Y, Gordon J, Kozhich A, Dilger AK, Ewing WR, Nandi P, Luettgen JM. Discovery and in vitro Characterization of an Antibody Fragment (Fab) which Neutralizes Milvexian (BMS-986177/JNJ-70033093) [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 1). https://abstracts.isth.org/abstract/discovery-and-in-vitro-characterization-of-an-antibody-fragment-fab-which-neutralizes-milvexian-bms-986177-jnj-70033093/. Accessed September 24, 2021.
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