AKATSUKI 48-Week Interim Analysis: Emicizumab and Immune Tolerance Induction in People with Hemophilia A and Factor VIII Inhibitors

Background: Immune tolerance induction (ITI) therapy, for the eradication of factor (F)VIII inhibitors, is indicated for people with hemophilia A (PwHA) with FVIII inhibitors. There are limited data regarding the safety of emicizumab treatment in combination with ITI, particularly regarding thrombotic events (TEs). This study, conducted in Japan, aims to evaluate the safety profile of emicizumab during and immediately after ITI.

Methods: AKATSUKI is a Phase IV, open-label, non-randomized, interventional, multicenter study; the methods have been previously published (Matsushita et al. BMJ Open 2022). PwHA with FVIII inhibitors received an approved dose of emicizumab and ITI therapy. Any standard half-life (SHL) FVIII concentrate could be used for ITI, with a dosing regimen of 50IU/kg, three times a week; when using an extended half-life (EHL) FVIII concentrate, 50IU/kg twice a week was permitted. Those who achieved ITI partial success received prophylaxis with emicizumab and a FVIII concentrate starting from the date of their next study visit following investigator confirmation of partial success. Any FVIII concentrate could be used for post-ITI maintenance therapy, given as 50IU/kg once a week for the first 24 weeks followed by 50IU/kg once every 2 weeks for the next 24 weeks, followed by discontinuation of the FVIII concentrate at the investigator’s discretion. The primary endpoint was evaluation of adverse events (AEs), with a key focus on TEs, and abnormal laboratory values over time during and immediately after ITI. The main secondary endpoints included number of treated bleeds and the proportion of participants meeting ITI success criteria. Partial success was achieved on the same date that the participant’s blood sample showed normal FVIII recovery in addition to the participant receiving a negative FVIII inhibitor titer. Normalized FVIII recovery was defined as a FVIII recovery rate of ≥66% of the predicted value on two consecutive occasions ≥2 weeks apart, and a negative FVIII inhibitor titer was defined as achieving FVIII inhibitor levels of <0.6 BU/mL on two consecutive occasions ≥2 weeks apart.

Results: Twelve participants, all of whom were male (median [range] age 2.5 [1–54] years) were included in this interim analysis (evaluation period, median [range]: 437.5 days [224–749]. Data cut-off date: December 22, 2022). Prior to the study, participants had received emicizumab (n=11), ITI (n=9), or both (n=7), and the median (range) duration of ITI in combination with emicizumab was 203.0 (7–1,002) days. Three participants used a SHL FVIII product for their ITI treatment regimen, and nine participants used an EHL FVIII product. Additional baseline characteristics are presented in Table 1.

Overall, 30 AEs occurred, none of which were considered emicizumab- or FVIII concentrate-related. Two participants each experienced one serious AE: one case of pneumonia, initially caused by transmission of a viral infection, and one wound hemorrhage, which was recorded as accidental; both recovered. No participants experienced a TE. Three participants reported a total of 10 treated bleeds, all of which were categorized as traumatic and were treated with recombinant activated FVII. At data cut-off, one participant had achieved partial ITI success, having reached a negative inhibitor titer at Week 5 and normalized FVIII recovery by Week 17. This participant was then treated with emicizumab and FVIII concentrate (50IU/kg once a week). No bleeds or AEs were reported for this participant during the observational period. The changes in FVIII inhibitor titer across the study for all participants are presented in Figure 1.

Conclusions: At this 48-week interim analysis, no new safety concerns or TEs were reported in PwHA receiving emicizumab and ITI. This study continues to evaluate the safety of emicizumab in conjunction with, and following, ITI therapy in PwHA with FVIII inhibitors.