Understanding Treatment Outcomes and Immunologic Mechanisms in Altuviiio Immune Tolerance Induction

The goal of this clinical trial is to learn how well Altuviiio (efanesoctacog alpha) works for Immune Tolerance Induction (ITI) while using Hemlibra (emicizumab) to prevent bleeds. Participants will be given Altuviiio for their ITI therapy and also be treated with Hemlibra as standard of care prophylaxis to prevent bleeding. The research doctor will decide how much and how often the participant will get Hemlibra. Participants will need to attend visits for checkups and tests. These visits are divided into 4 periods: 1. A screening period - 1 visit up to 8 weeks before the Treatment Period starts 2. ITI Treatment Period - 1 Baseline Visit plus Interim visits that occur every 4 weeks for up to 52 weeks. (Some of the interim visits may be done via phone) 3. Tapering Period - 5 visits at weeks 2, 4, 8, 12 and 16 4. Ongoing Monitoring Period - 4 visits at weeks 20, 30, 40 and 50

Inclusion Criteria: 1\) severe hemophilia A (congenital) 2) history of high titer inhibitor (≥ 5 BU) 3) peak inhibitor titer (pre-ITI) \< 1,000 3) age \< 18 y/o at the time of study enrollment 4) undergoing initial ITI course 5) current or planned concomitant use of emicizumab Exclusion Criteria: 1. von Willebrand disease or a known second bleeding diathesis besides SHA 2. prior course of ITI 3. inhibitor present for \> 2 years without prior attempts at eradication 3\) personal history of unprovoked thrombosis 4) known contraindication, intolerance, or allergy to either of the investigational agents of study 5) inability or unwillingness to provide informed consent and/or assent 6) inability to speak or read English 7) Any other condition, that in the opinion of the investigator, would negatively impact the safety of the participant