This is a phase II multicenter open-label, single-arm prospective study to evaluate the efficacy of prophylactic emicizumab administered on a scheduled basis to prevent bleeds in patients with acquired hemophilia A (AHA).

Patients with AHA who are eligible will receive two loading doses of the study drug, emicizumab (6mg/kg on day 1 and 3 mg/kg on day 2) followed by once weekly subcutaneous emicizumab (1.5 mg/kg). Immunosuppression will be given concurrently as per investigator discretion. The primary endpoint (bleed rate) will be assessed after 12 weeks on study drug. If partial remission of the AHA has not been achieved, an additional 12 weeks of study drug may be given. A historical cohort and a study conducted in parallel in Germany (NCT04188639) will serve as control groups for evaluation of secondary endpoints provided the study cohort are comparable.

Inclusion Criteria:

• Signed Informed Consent/Assent Form
• Age ≥18 years at time of signing Informed Consent Form
• Ability to comply with the study protocol, in the investigator's judgment
• Diagnosis of AHA based on a reduced FVIII activity (<50 %) and positive FVIII inhibitor (>0.6 BU/ml) at screening (local laboratory)
• Current bleeding due to AHA at the time of screening
• Plan to be adherent to emicizumab prophylaxis during the study
• For women of childbearing potential who meet the following criteria:
• Refrain from heterosexual intercourse or use contraceptive methods that result in a failure rate of <1% per year during the study period A woman with ≥ 12 continuous months of amenorrhea with no identified cause other than menopause and has not undergone surgical sterilization (removal of ovaries and/or uterus). use of combined oral or injected hormonal contraceptive, bilateral tubal ligation, male sterilization, hormone- releasing intrauterine devices, and copper intrauterine devices.

Exclusion Criteria:

• Congenital hemophilia A
• Treatment with aPCC within the last 24 hours before first study treatment or planned treatment with aPCC during the course of the study
• Known positive lupus anticoagulant at the time of screening
• Severe uncontrolled infection at the time of screening
• Signs of active disseminated intravascular coagulation at the time of screening -
• Emicizumab ⎯ AHA Emi Version 1.0 20
• Current treatment for thromboembolic disease or signs of current thromboembolic disease at time of screening
• Patients who are at high risk for TMA (e.g., have a previous medical or family history of TMA), in the investigator's judgment
• Known severe congenital or acquired thrombophilia
• Life expectancy <3 months at the time of screening
• Other conditions that substantially increase risk of bleeding or thrombosis by the discretion of the investigator
• Contraindications according to the Investigator's Brochure of emicizumab
• Current treatment with emicizumab at time of screening
• History of clinically significant hypersensitivity associated with monoclonal antibody therapies or components of the emicizumab injection by the discretion of the investigator
• Concurrent disease, treatment, or abnormality in clinical laboratory tests that could interfere with the conduct of the study, may pose additional risk, or would, in the opinion of the local investigator, preclude the patient's safe participation in and completion of the study
• Addiction or other diseases that preclude the patient from appropriately assessing the nature and scope as well as possible consequences of the clinical study by the discretion of the investigator
• Pregnant or breast-feeding women
• Would refuse treatment with blood or blood products, if necessary.
• Subject is in custody by order of an authority or a court of law
• Treatment with any of the following:
• An investigational drug to treat or reduce the risk of hemophilic bleeds within 5 half-lives of last drug administration before Study Day 1
• A non-hemophilia-related investigational drug within the last 30 days or 5 half-lives- before Study Day 1, whichever is longer
• An investigational drug concurrently
• History of clinically significant hypersensitivity associated with monoclonal antibody therapies or components of the emicizumab injection

All of the individual participant data collected during the trial will be shared with the research group of the parallel European study (NCT04188639). Data will be shared at the end of the study for analysis for a period of 2 years.

Data will be shared with the research group of the parallel European study (NCT04188639) at the end of the study and will be available for 2 years.

Only researchers of this or the parallel trial (NCT04188639) will have access to this data.