Hemophilia A (HA) is a common hereditary bleeding disorder caused by deficiency or dysfunction of factor (F)VIII. Regular prophylaxis with FVIII products has markedly improved the quality of life for people with severe HA (PwHA) 1. Recent studies reported that approximately 15% of PwH in the United States have cardiovascular diseases (CVDs) 2, and the prevalence of atrial fibrillation (AF) in Europe increases from 0.84% to 3.4% in those aged over 60 years 3. Direct oral anticoagulants (DOACs), such as dabigatran and FXa inhibitors, are widely used for thromboembolic disorders and are generally safer and more effective than warfarin 4. However, vitamin K antagonists (VKAs) remain essential for patients with mechanical heart valves or certain pediatric cases 5. Current guidelines recommend maintaining FVIII or FIX activity (FVIII:C or FIX:C) above 20%–30% in PwH on anticoagulant therapy 6. Emicizumab (Hemlibra), a bispecific antibody bridging FIX(a) and FX, mimics FVIIIa cofactor function. Its trough plasma concentration (∼50 µg/mL) corresponds to 10–15 IU/dL FVIII:C previously identified using an acquired HA primate model 7. Recently, Mim8 (Novo Nordisk A/S, Bagsværd, Denmark), which exhibits higher potency in preclinical studies, was developed as the next-generation bispecific antibody 8, and is currently undergoing clinical trials. We previously demonstrated that the hemostatic activity of emicizumab is substantially reduced during warfarin treatment 9. However, the coagulation potential in PwHA receiving Mim8 under warfarin therapy remains to be investigated. We hypothesized that Mim8 may provide sufficient hemostatic function even under warfarin therapy. Therefore, we investigated the impact of warfarin on Mim8-mediated coagulation using rotational thromboelastometry (ROTEM) and thrombin generation assay (TGA). One severe PwHA (FVIII:C 20% even under oral warfarin therapy (INR 1.6–2.4). Thrombin generation assay (TGA) in FVIII-depleted samples with Mim8 or emicizumab under various INR conditions. The coagulation function of plasma samples from a PwHA receiving oral warfarin therapy and FVIII product supplementation was analyzed at INR 1.6, 2.4, and 3.1 by TF and ellagic acid-triggered TGA. FVIII-depleted samples obtained by the addition of anti-FVIII polyclonal antibody were incubated with either Mim8 (5 µg/mL) or emicizumab (50 µg/mL) for 15 min at room temperature. In sample with INR 1.6, the TG potential of the raw sample, in which the FVIII inhibitor titer (Bethesda) was adjusted to approximately 2 BU/mL (corresponding FVIII:C 26 IU/dL), was also evaluated. Thrombin generation curves are shown (red; Raw sample, green; Mim8 5 µg/mL, blue; Emi 50 µg/mL, Black; Raw sample spiked with anti-FVIII inhibitor at 2 BU/mL). INR; International normalized ratio, Emi; Emicizumab. In the present study, we demonstrated that Mim8 could maintain a higher coagulation potential under warfarin treatment, possibly due to its enhanced FIXa-mediated activation of FX 10, whereas emicizumab-induced coagulation was markedly reduced. To our knowledge, this is the first report evaluating Mim8-mediated coagulation under VKAs therapy. Warfarin inhibits the γ-carboxylation of VK-dependent coagulation factors (FII, FVII, FIX, and FX), leading to a decreased prothrombinase activity and thrombin generation. Because the cofactor activity of emicizumab depends on the availability of FIX(a) and FX, its hemostatic potential is markedly influenced by warfarin-induced depletion. In contrast, Mim8 appears to compensate for this reduction more effectively because of its enhanced FIXa-dependent activity compared with emicizumab. In this context, Mim8 may maintain sufficient coagulation potential equivalent to FVIII:C >20% even under warfarin therapy (INR 1.6–2.4). However, at INR 3.1, the coagulation function of Mim8 was comparable to that of emicizumab and lower than that of the raw sample (FVIII:C 27 IU/dL). At such high INR, the characteristic advantage of Mim8 - its strong FIXa-dependent activity—may not be fully exerted because of the markedly reduced FIX levels. Consequently, Mim8-induced coagulation potential may be reduced compared with that observed with FVIII:C of 27 IU/dL. Therefore, the hemostatic advantage of Mim8 might not be maintained beyond INR 3.0. From a clinical perspective, these findings have potential implications for the management of PwHA who require long-term anticoagulation. As life expectancy in PwHA continues to increase, the coexistence of hemophilia and cardiovascular comorbidities, such as AF and ischemic heart disease, is expected to become more common. In such settings, achieving an appropriate balance between bleeding risk and prevention of thromboembolic events remains a major clinical challenge. Although current recommendations suggest maintaining FVIII activity above 20%–30% during anticoagulant therapy, evidence supporting these thresholds in patients receiving non-factor therapies is limited. In this single-case observation, Mim8 was associated with a higher coagulation potential than emicizumab under warfarin therapy, particularly within the INR range of 1.6–2.4. This observation suggests that Mim8-treated patients may maintain a relatively preserved global coagulation potential under vitamin K antagonist therapy without additional factor supplementation in selected clinical situations. However, considering the limited data, careful clinical and laboratory monitoring remains essential, especially at higher INR levels. Several limitations should be addressed. First, the present data were derived from a single PwHA; therefore, firm conclusions cannot be drawn. Future studies with larger numbers of patients and various anticoagulant treatments, including DOACs, are needed to clarify safe and effective antithrombotic management for PwHA receiving next-generation FVIII-mimetic therapies. Furthermore, some data discrepancies were observed between ROTEM and TGA results. Nevertheless, both assays provide novel insight into the potential use of Mim8 in PwHA under warfarin therapy. Further clinical evaluation is warranted to determine whether Mim8 could provide sufficient coagulation function under antithrombotic management. Yuto Nakajima designed all experiments, interpreted the data, prepared figures, wrote and edited the manuscript and approved the final version to be published. Tomofumi Yoshimoto and Hiroaki Yaoi and Kenichi Ogiwara supported clinically. Keiji Nogami designed the research, supported the data, interpreted the data, wrote the paper, and edited the manuscript. This research was supported by research funding from Novo Nordisk, and partly by a Grant-in-Aid for Scientific Research (KAKENHI) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) to KN (24K10935) and YN (25K19236). This study was approved by the Medical Research Ethics Committee of Nara Medical University (No. 4071). Written informed consent was obtained from the participant in accordance with institutional ethical guidelines and the Declaration of Helsinki. Yuto Nakajima has received a grant from Takeda Pharmaceutical Co and Novo Nordisk A/S. Tomofumi Yoshimoto has no conflict of interest to disclose. Hiroaki Yaoi has received a grant from Novo Nordisk A/S. Kenichi Ogiwara taught a course endowed by CSL Behring and has received a grant from Novo Nordisk A/S and personal fees from Chugai Pharmaceutical Co., Ltd. and CSL Behring. Keiji Nogami has received grants, personal fees, and non-financial support from Chugai Pharmaceutical Co., Ltd.; personal fees from F. Hoffmann-La Roche Ltd.; and grants and personal fees from Sysmex Co., Takeda Pharmaceutical Co., Sanofi S. A., CSL Behring Co., KM Biologics Co., Novo Nordisk A/S, Bayer AG and is an inventor of patents relating to emicizumab. The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.
Nakajima et al. (Thu,) studied this question.