Japan Approves Tanabe Pharma's Inebilizumab for Myasthenia Gravis

Japan's Ministry of Health, Labour and Welfare has approved an additional indication for inebilizumab (Uplizna), administered by intravenous infusion at a 100 mg dose, to treat generalized myasthenia gravis (gMG) in patients who do not respond adequately to corticosteroids or non-steroidal immunosuppressants, Tanabe Pharma announced September 16, 2026.¹ Inebilizumab is now the only treatment approved in Japan for gMG with a mechanism of action that targets CD19-positive B cells, according to the company.¹

What did the MINT trial show?

Approval was based on data from the myasthenia gravis inebilizumab trial (MINT; NCT04524273), a randomized, double-blind, placebo-controlled trial that enrolled 238 adults with gMG, including 190 who were acetyl choline receptor antibody (AChR)-positive and 48 who were muscle-specific kinase (MuSK)-positive.¹^,² At week 26, inebilizumab showed a 1.9-point difference in Myasthenia Gravis Activities of Daily Living (MG-ADL) score compared with placebo (-4.2 vs -2.2; P<.0001), the trial's primary endpoint.¹ In an exploratory analysis of the AChR-positive subgroup, benefits continued through week 52, the longest randomized-controlled period for a phase 3 gMG trial, with a 2.8-point MG-ADL difference favoring inebilizumab (-4.7 vs -1.9; 95% confidence interval, -3.9 to -1.7).¹ MINT was the largest phase 3 biologic study to include both AChR-positive and MuSK-positive patients and the first to successfully incorporate a steroid taper into its protocol; by week 26, 87.4% of patients on inebilizumab and 84.6% on placebo had reduced their steroid dose to 5 mg or less per day.¹

How does inebilizumab work, and how does it differ from other gMG therapies?

Inebilizumab is a humanized monoclonal antibody that causes targeted, sustained depletion of CD19-positive B cells, including plasmablasts and some plasma cells, thereby suppressing production of pathogenic IgG autoantibodies; its precise mechanism of therapeutic effect is not fully understood. gMG is thought to be primarily driven by AChR and MuSK autoantibodies produced by these CD19-positive B cell populations.¹ Unlike anti-CD20 B-cell-depleting therapies such as rituximab, which target naive and memory B cells, inebilizumab's CD19 target is expressed throughout B-cell development, including on a subset of plasma cells that anti-CD20 agents do not reach.³ After 2 initial infusions, patients require only 1 maintenance dose of inebilizumab every 6 months.¹

Why is a new treatment option significant for gMG?

gMG is a rare, chronic, B-cell-mediated autoimmune disorder that impairs neuromuscular communication, causing fluctuating muscle weakness, trouble breathing, difficulty swallowing, and impaired speech and vision.¹ A 2018 nationwide epidemiological survey in Japan estimated approximately 29,000 people had myasthenia gravis, a prevalence of 23.1 per 100,000, with a median age at onset of 59 years and about 80% of cases classified as generalized.¹ Other approved treatments for gMG in Japan include corticosteroids, nonsteroidal immunosuppressants, and other targeted therapies, though disease control can remain difficult for patients who do not respond adequately to first-line options.

What's next for inebilizumab in Japan?

This is inebilizumab's third approved indication in Japan, following initial approval in March 2021 for prevention of relapse in neuromyelitis optica spectrum disorder and an additional indication in November 2025 for suppression of relapse in IgG4-related disease.¹ The drug is developed in collaboration with Amgen, its licensor.¹

MINT's primary endpoint analysis reflects the combined AChR-positive and MuSK-positive population. The week 52 AChR-positive subgroup data are described as exploratory rather than confirmatory, and the trial's optional 3-year open-label extension has not yet been reported.

References

1. Tanabe Pharma. Tanabe Pharma receives approval in Japan for additional indication of generalized Myasthenia Gravis: anti-CD19 monoclonal antibody UPLIZNA for I.V. infusion 100 mg. Press release. Published September 16, 2026. Accessed September 16, 2026. https://www.tanabe-pharma.com/en/news/rel_260916/main/0/link/e_rel_260916.pdf
2. Myasthenia gravis inebilizumab trial (MINT). ClinicalTrials.gov. NCT04524273. Updated May 15, 2026. Accessed September 16, 2026. https://clinicaltrials.gov/study/NCT04524273
3. Yi JS, Guptill JT, Stathopoulos P, Nowak RJ, O'Connor KC. B cells in the pathophysiology of myasthenia gravis. Muscle Nerve. 2018;57(2):172-184. doi:10.1002/mus.25973