Emicizumab (Hemlibra) is well tolerated and has substantial, clinically meaningful efficacy in pediatric patients with hemophilia A and factor VIII inhibitors, according to an analysis of data from the HAVEN 2 trial in this bispecific humanized monoclonal antibody.
Among those receiving once-weekly emicizumab prophylaxis, 77% had no treated bleeding events and 100% of evaluable target joints resolved in the HAVEN 2 study, which investigators say is the largest prospective study so far of bleed prevention in pediatric patients with hemophilia A and inhibitors.
Moreover, emicizumab resulted in a 99% reduction in bleeding rate versus previous bypassing agent prophylaxis, subsequent, according to an intraindividual comparison described in the report.
Based on these results, emicizumab stands to become the “next-generation standard of care” for pediatric patients with hemophilia A and factor VIII inhibitors, reported Guy Young, MD, of Children’s Hospital Los Angeles and University of Southern California Keck School of Medicine, and his coinvestigators.
“Despite a rapidly evolving treatment landscape in hemophilia, children have been largely excluded from recent trials of novel agents,” they said in the report, which appears in the journal Blood.
Before emicizumab, current treatment options for pediatric patients with factor VIII inhibitors were limited to immune tolerance induction, or use of bypassing agents with efficacy that “can be suboptimal and unpredictable,” said Dr. Young and colleagues.
“More effective prophylactic options with reduced treatment burden are needed,” they said.
Emicizumab works in hemophilia A by bridging activated factor IX and factor X, restoring the function of missing factor VIIIa, according to the report.
A total of 88 male pediatric patients with congenital hemophilia A were enrolled in HAVEN 2, an ongoing phase 3 multicenter study that is nonrandomized and open label. The median age of patients was 7 years (range, 1-15 years). Most participants (97%) had severe hemophilia A, 72% had previously undergone immune tolerance induction, and 75% were receiving treatment with prophylactic bypassing agents.
Most participants received 4 once-weekly loading doses of 3 mg/kg body weight of emicizumab subcutaneously, followed by a maintenance regimen of 1.5 mg/kg weekly.
The annualized bleed rate was 0.3, with 77% of participants having zero bleeding events, for the 65 participants in the trial who were under 12 and received emicizumab 1.5 mg/kg weekly, according to the report.
In the subset of those patients with target joints, the mean annualized bleed rate was 3.3 for the first 24 weeks, and 0 for the next 24 weeks; these findings suggest that bleed rates decrease over time with continuing emicizumab treatment “even in patients with a more severe phenotype,” the investigators wrote.
For 15 patients younger than 12 years of age receiving bypassing agent prophylaxis, emicizumab 1.5 mg/kg once weekly resulted in an annualized bleed rate of 0.3, compared to 21.1 for the prior bypassing agent, which translates into a 99% reduction in bleeding risk, according to investigators.
Annualized bleed rates for patients receiving emicizumab 3 mg/kg every 2 weeks or 6 mg/kg every 4 weeks were 0.2 and 2.2, respectively; hover, the numerically higher annualized bleed rate in the 6 mg/kg every-4-weeks group was based on 2 out of the 10 patients treated with that maintenance regimen, including one who had 6 target joint bleeds in the 24 weeks before enrolling in the study, and another who developed antidrug antibodies within the first 8 weeks of emicizumab treatment.
Out of 23 patients who had target joints and received emicizumab prophylaxis for at least 52 weeks, 100% (45 of 45) target joints resolved, according to the report.
“Notably, this is the first report of a treatment resolving target joints in an inhibitor population, which until now has only been reported when using factor VIII products in patients without inhibitors,” Dr. Young and colleagues said.
The most common of the 721 adverse events reported in HAVEN 2 were nasopharyngitis and injection-site reactions. Of 21 serious adverse events, only 1 (antidrug antibodies with neutralizing potential) was thought by investigators to be related to emicizumab.
The Food and Drug Administration (FDA) initially approved emicizumab in November 2017 on the basis of the HAVEN 2 pediatric trial, and on HAVEN 1, a randomized, multicenter, open-label, phase 3 trial including 109 adult and adolescent males with hemophilia A and FVIII inhibitors. The indication for emicizumab was expanded to include patients without inhibitors in October 2018, on the basis of the HAVEN 3 and HAVEN 4 randomized phase 3 trials.
Dr. Young reported disclosures related to Alnylam, Bayer, Bioverativ, CSL Behring, Genentech/Roche, Grifols, Kedrion, Novo Nordisk, Shire, Spark, and uniQure.
SOURCE: Young G, et al. Blood. 2019 Oct 10. doi: 10.1182/blood.2019001869.