First-in-Class B-Cell Depleting Agent Promising for MG

SAVANNAH, Georgia — Inebilizumab, a first-in-class anti-CD19 B-cell depleting agent, demonstrated both safety and superior efficacy compared with placebo in patients with seropositive generalized myasthenia gravis (gMG), new phase 3 data showed.

“Based on these results, we have demonstrated that targeting B cells, including the antibody-secreting cells, is beneficial, and there is likely a role for this kind of therapeutic strategy for patients with myasthenia gravis,” senior investigator Richard Nowak, MD, told Medscape Medical News.

The findings were published and presented here on October 15 at the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) 2024.

Largest Cohort of Muscle-Specific Kinase (MuSK) Antibody–Positive Disease

The Myasthenia Gravis INebilizumab Trial study enrolled 238 participants, 60.8% women, mean age 47.5 years, from 79 sites in 18 countries. The participants were divided into two cohorts: 190 acetylcholine receptor (AChR) autoantibody–positive patients and 48 MuSK autoantibody–positive patients.

“This is the largest enrolled cohort of MuSK antibody–positive disease in a placebo-controlled trial to date,” said Nowak, director of the Yale Myasthenia Gravis Clinic and associate professor of neurology at Yale School of Medicine, in New Haven, Connecticut.

Both groups had similar gMG duration (mean 6.7 and 5.2 years for AChR+ and MuSK+ patients, respectively) and disease severity based on Myasthenia Gravis Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) baseline score. In addition, more than 80% of participants were on a prednisone equivalent dose > 5 mg daily at study entry.

Participants were randomly assigned to receive intravenous (IV) inebilizumab or IV placebo for 52 weeks (AChR+ group) or 26 weeks (MuSK+ group). In addition, study participants who were taking corticosteroids were tapered down starting at week 4 to prednisone 5 mg per day by week 24.

The trial met its primary endpoint, with a statistically significant change from baseline in MG-ADL and with a reduction of 4.2 points for inebilizumab vs 2.2 for placebo (P

“You can see that the trend is actually going toward separation of the two groups after week 8 in the combined population,” said Nowak. Key secondary endpoints also showed statistically significant and clinically meaningful change from baseline compared with placebo.

This included a statistically significant change in QMG score inebilizumab compared with placebo for the combined population, a reduction of 4.8 vs 2.3 points, respectively, at week 26 (P = .0002).

In addition, both MG-ADL and QMG scores in the AChR+ subgroup were superior for inebilizumab vs placebo at week 26, with reductions of 4.2 vs 2.4, and 4.4 vs 2.0; P = .0015 and P = .0011, respectively.

In the MuSK+ subgroup, inebilizumab-treated patients had better MG-ADL scores than placebo-treated patients, with reductions of 3.9 vs 1.7 points, respectively, at week 26, although this difference did not meet statistical significance.

“There were no increased safety incidents in the inebilizumab-treated patients versus placebo, and a similar percentage of safety incidents in the AChR–positive and MuSK–positive groups. There were three deaths reported, all likely related to myasthenic crisis,” he said.

Nowak told Medscape Medical News that inebilizumab is “unique from the other currently FDA-approved medications for myasthenia gravis in that it’s targeting the upstream immunopathogenic mechanism of disease, specifically B cells — and B cells that are actually antibody-secreting cells.”

“It is targeting the factories of autoantibody production, whereas an FcRn antagonist, for example, is not targeting those factories but rather targeting what’s being produced — the immunoglobulins, IgGs in general,” he added.

Nowak added that what is particularly exciting about the drug is that the schedule is not very frequent. It begins with an initial IV infusion, followed by a second infusion 2 weeks later and a third infusion 6 months after that, so that patients are treated approximately every 6 months. This is in contrast to some other targeted therapies, where failing to address the underlying factors driving immunopathogenesis necessitates more regular and frequent medication administration.

New, Novel, Exciting

Commenting on the research for Medscape Medical News, Neelam Goyal, MD, who chaired the session, said, “It’s definitely new, novel, interesting, exciting.”

Goyal, clinical professor of neurology and neurological sciences at Stanford University School of Medicine in Palo Alto, California, also noted that while B-cell depletion has shown some previous success in MG, it was with rituximab, a CD20 B-cell depleting agent.

She noted that unlike rituximab, which targets CD20, inebilizumab targets CD19, although both medications lead to B-cell depletion. Rituximab has proven effective for MUSK–positive MG, which accounts for approximately 5% of cases.

However, Goyal noted that the results for AChR–positive MG have been mixed — “the BeatMG trial was negative and the RINOMAX trial was positive. So, I think this is really interesting. It is exciting, and this drug is already on the market.”

She added that although inebilizumab is already US Food and Drug Administration-approved for the treatment of neuromyelitis optica, it still faces approval and indication hurdles for MG.

The future of this drug in the management algorithm for MG remains uncertain. Goyal noted that it’s “quite costly,” and although its benefits are evident — particularly for FcRn and complement inhibitors — some early data from chimeric antigen receptor T-cell therapy studies appear significantly more impressive.

Nowak disclosed research support from the National Institutes of Health, Genentech Inc., Alexion Pharmaceuticals, Inc., argenx, Annexon Biosciences, Inc., Ra Pharmaceuticals, Inc. (now UCB S.A.), the Myasthenia Gravis Foundation of America, Inc., Momenta Pharmaceuticals, Inc. (now Janssen), Immunovant, Inc., Grifols, S.A., and Viela Bio, Inc., Horizon Therapeutics (now Amgen, Inc.). Served as a consultant and advisor for Alexion Pharmaceuticals, Inc., argenx, Cabaletta Bio, Inc., Cour Pharmaceuticals, Ra Pharmaceuticals, Inc. (now UCB S.A.), Immunovant, Inc., Momenta Pharmaceuticals, Inc. (now Janssen), and Viela Bio, Inc. (Horizon Therapeutics, now Amgen, Inc.).

Goyal disclosed consultant, advisory, or grant support from argenx, UCB, Alexion, and Janssen. The study was funded by Amgen, Inc.