Inebilizumab Shows Lasting Protection Against NMOSD Attacks Regardless of Prior Immunosuppressant Use

People living with neuromyelitis optica spectrum disorder (NMOSD) now have clearer evidence that switching to a modern targeted therapy works well even after years on older immunosuppressant drugs. A new post hoc analysis of the pivotal N-MOmentum trial, published in Annals of Clinical and Translational Neurology, reports that the monoclonal antibody inebilizumab provided similarly strong protection against debilitating attacks whether or not participants had previously been treated with oral immunosuppressants such as azathioprine or mycophenolate mofetil. The findings carry real weight for clinical practice, because many patients worldwide still begin their treatment journey with these older, off-label medications before eventually transitioning to approved antibody therapies.

NMOSD is a rare, autoimmune inflammatory disorder of the central nervous system that predominantly targets the optic nerves and spinal cord. In most patients, the disease is driven by pathogenic immunoglobulin G antibodies directed against aquaporin-4 (AQP4), a water channel protein abundantly expressed on astrocytes. Each relapse can leave permanent neurological damage, ranging from irreversible vision loss to paralysis, which is why suppressing the underlying B-cell–driven immune attack is the central goal of long-term management. Before targeted therapies earned regulatory approval, clinicians commonly prescribed oral immunosuppressants (ISTs) such as azathioprine, mycophenolate mofetil, and methotrexate off-label to keep the disease at bay.

Those older drugs have well-recognized shortcomings. Comparative studies have associated oral ISTs with a greater frequency of relapses and a shorter time to relapse after treatment initiation compared with approved monoclonal antibodies. They are also linked to gastrointestinal and hematologic side effects and a high frequency of infections, problems that accumulate over years of continuous use. Inebilizumab, by contrast, is a humanized, affinity-optimized, glycoengineered monoclonal antibody that targets CD19, a marker expressed broadly across the B-cell lineage, depleting the cells responsible for producing the pathogenic AQP4 antibodies. The randomized, placebo-controlled N-MOmentum trial demonstrated its efficacy in AQP4-seropositive NMOSD and led to regulatory approval.

A key question remained, however. Many participants entering N-MOmentum had years of prior IST exposure, and it was unclear whether that treatment history might blunt or otherwise alter the drug’s long-term efficacy and safety. To investigate, researchers analyzed 202 of the 213 AQP4-seropositive participants from the randomized controlled period (RCP) and 197 of the 201 from the open-label period (OLP), splitting them roughly evenly between those with prior IST treatment and those who were IST-naïve. Only ISTs taken before day 1 of the trial were considered; ISTs were prohibited once the trial began.

The randomized portion of the trial delivered an unambiguous message. Participants on inebilizumab experienced far fewer adjudicated NMOSD attacks than those on placebo, and the magnitude of benefit was essentially identical in both subgroups. Among participants with prior IST use, the hazard ratio for attack was 0.21 (95% confidence interval 0.09–0.48), while among IST-naïve participants it was 0.23 (0.09–0.59). NMOSD-related inpatient hospitalizations were also less frequent with inebilizumab in the prior-IST group. Worsening on the Expanded Disability Status Scale (EDSS) was significantly less common with inebilizumab versus placebo in both groups: 19.2% versus 43.5% among those with prior IST exposure, and 13.6% versus 28.0% among those who were IST-naïve, both comparisons reaching nominal statistical significance.

Because the randomized controlled period lasted only about 28 weeks, the research team turned to modeling to assess long-term outcomes over years rather than months. In the any-INEB population, the adjusted annualized attack rate was 0.11 (0.07–0.17) for participants with prior IST use and 0.08 (0.05–0.14) for those without, a difference so small it is unlikely to matter clinically. A high probability of remaining attack-free persisted through week 286 of treatment in both groups, and EDSS scores actually improved during the open-label extension regardless of treatment history. NMOSD-related hospitalizations were equal in number across the two subgroups during long-term follow-up.

The most striking results emerged when inebilizumab was compared against synthetic historical comparator groups built from published Kaplan–Meier survival curves of patients treated with azathioprine or other broad-spectrum ISTs, or with placebo. Using a time-varying spline model with two internal knots, selected through formal information-criterion testing and visual fit assessment, the researchers found the time to NMOSD attack was significantly longer with inebilizumab than with azathioprine or other ISTs (hazard ratio 0.29; p < 0.001) and than with placebo (hazard ratio 0.15; p < 0.001). The modeled four-year attack-free probability was 77% for inebilizumab, 36% for azathioprine or other ISTs, and just 12% for placebo. Notably, the widening gap over time suggests inebilizumab’s relative advantage may grow the longer patients stay on treatment.

Safety outcomes were reassuringly similar across subgroups. Through the open-label period, roughly 92% of participants in both groups experienced at least one treatment-emergent adverse event, but drug-related events were somewhat more common among IST-naïve participants, 46.6% versus 30.9%. Infections, the adverse event category of greatest concern for a B-cell–depleting therapy, occurred at nearly identical rates in both groups, affecting 72.3% of those with prior IST use and 76.7% of those without, and were not increased by prior immunosuppressant exposure. Opportunistic infections were rare, one case in each group, no anaphylactic reactions were reported, and deaths were similarly uncommon.

The authors caution that this was a post hoc, exploratory analysis with limitations. Subgroup sample sizes were modest, randomization was not stratified by duration of IST history, and p values were not adjusted for multiple comparisons, so all statistical results are nominal. The synthetic historical comparators, reconstructed by digitizing published survival curves, introduce approximation error and cannot fully control for differences in study populations and designs across the source studies. These constraints mean the long-term comparative estimates should be interpreted as suggestive rather than definitive evidence from head-to-head trials, which have never been conducted.

Even so, the practical implications for patients and clinicians are substantial. Switching from off-label immunosuppressants to immunotherapies generally requires an overlapping treatment period to avoid triggering an attack upon discontinuation of the old drug, and many providers overlap ISTs for up to six months, although concurrent inebilizumab and IST use is not recommended as a routine regimen. The new analysis supports inebilizumab treatment for patients with AQP4-seropositive NMOSD regardless of whether they previously received first-line immunosuppressants, with sustained reductions in attack risk, stabilized or improved disability scores, and a safety profile consistent with the overall trial population. For the many patients still managed with older oral agents, the data offer a quantitative basis for a confident transition to targeted B-cell depletion.

Subject of Research: Long-term efficacy and safety of inebilizumab in AQP4-seropositive NMOSD patients with or without prior immunosuppressant use

Article Title: Efficacy of Inebilizumab in N‐MOmentum Trial Participants With or Without Prior Immunosuppressants

Article References: Cree, B. A. C., Suero, B., Walsh, S., Marignier, R., Lindsey, J. W., Kim, H. J., She, D., Cimbora, D., Cavida, D., & Paul, F. (2026). Efficacy of Inebilizumab in N‐ MOmentum Trial Participants With or Without Prior Immunosuppressants. Annals of Clinical and Translational Neurology, 13(9), 1930-1936. https://doi.org/10.1002/acn3.70426

Image Credits: AI Generated

DOI: 10.1002/acn3.70426

Keywords: inebilizumab, NMOSD, N-MOmentum trial, aquaporin-4, CD19 B-cell depletion, azathioprine, mycophenolate mofetil, immunosuppressants, clinical trial, neuroimmunology, EDSS, autoimmune disease