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

Neuromyelitis optica spectrum disorder has long been distinguished from multiple sclerosis by its serological signature. In 2004, Lennon and colleagues identified a serum autoantibody that marks the disease and separates it clearly from multiple sclerosis, an antibody directed against aquaporin-4, a water channel protein abundantly expressed on astrocytes at the blood-brain barrier and within the central nervous system parenchyma. The binding of these pathogenic immunoglobulin G antibodies to aquaporin-4 triggers complement activation, inflammatory injury to astrocytes, and secondary damage to neurons and oligodendrocytes. Because the antibody is produced by B lineage cells, the logical therapeutic strategy has been to deplete the cells that generate it.

That strategy has been validated repeatedly. Rituximab, a chimeric monoclonal antibody targeting CD20 on the surface of pre-B cells and mature B cells, entered clinical practice on the strength of open-label series and was later tested in the RIN-1 study, a multicentre, randomised, double-blind, placebo-controlled trial published in The Lancet Neurology in 2020, which established its safety and efficacy in the disorder. Inebilizumab, a humanized anti-CD19 antibody with a broader reach across the B cell lineage because it also targets plasma cell precursors, demonstrated benefit in the N-MOmentum phase 2/3 trial reported in The Lancet in 2019. Complement inhibition with eculizumab, reported in the New England Journal of Medicine in 2019, provided an alternative downstream approach by blocking the terminal complement pathway that the pathogenic antibodies engage.

Now obinutuzumab β, a glycoengineered type II anti-CD20 monoclonal antibody, has produced remarkable results in a phase 3 randomized controlled trial described by Wu and colleagues in Nature Medicine. Unlike type I anti-CD20 antibodies such as rituximab, type II antibodies like obinutuzumab engage CD20 in a manner that promotes direct cell death through non-apoptotic mechanisms and mediates more efficient depletion of certain B cell compartments, including tissue-resident populations that are less accessible to complement-dependent mechanisms. The glycoengineering of the Fc region enhances affinity for activating Fc gamma receptors on effector cells, sharpening antibody-dependent cellular cytotoxicity. These pharmacological distinctions matter, because the depth of depletion achieved within different B cell niches may determine how thoroughly autoantibody production is suppressed.

This is precisely the distinction Nakashima highlights in his analysis. The pathogenic anti-aquaporin-4 antibodies in neuromyelitis optica spectrum disorder are secreted by plasmablasts and plasma cells, differentiated descendants of B cells that express little or no surface CD20 and are therefore invisible to all anti-CD20 therapies. Yet clinical experience shows that depleting CD20-positive B cells nevertheless suppresses disease activity in most patients, implying that the continuously replenished pool of CD20-positive B cells is essential for sustaining the plasmablast population that secretes the pathogenic antibody. Fundamental work by Chihara and colleagues, published in the Proceedings of the National Academy of Sciences in 2011, showed that interleukin-6 signaling promotes anti-aquaporin-4 autoantibody production from plasmablasts, suggesting that the survival and differentiation of antibody-secreting cells depend on signals delivered by the surrounding B cell and immune milieu that anti-CD20 therapy disrupts.

The deeper-versus-broader framing also captures a paradox that clinicians have observed since the earliest rituximab era. Nakashima himself reported, in the Journal of Clinical Neuroscience in 2011, transient increases in anti-aquaporin-4 antibody titers following rituximab treatment, associated with elevated serum levels of BAFF, a B cell activating factor belonging to the tumour necrosis factor family. When B cells are depleted, BAFF levels rise because the cytokine is no longer consumed by its targets, and this surge can paradoxically promote the differentiation of surviving precursors towards antibody-secreting cells. Perumal and colleagues documented disease exacerbation after rituximab induction in a subset of patients, a phenomenon plausibly linked to these humoral dynamics. Any new depleting agent must therefore be evaluated not only for how deeply it depletes circulating B cells but also for how it perturbs the regulatory cytokine networks that govern reconstitution.

Dysregulated B cell differentiation towards antibody-secreting cells is now recognised as a hallmark of the disease, as Hoshino and colleagues described in the Journal of Neuroinflammation in 2022. In patients with neuromyelitis optica spectrum disorder, the balance between naïve B cells, memory compartments, and plasmablasts is shifted, with expanded populations of antibody-secreting cells circulating in the blood and correlating with disease activity. This pathobiology explains why broader depletion strategies, such as those targeting CD19 across a wider span of B cell differentiation including plasmablast precursors, and deeper depletion strategies, such as those using type II anti-CD20 antibodies with enhanced effector function, both hold mechanistic appeal. The phase III results with obinutuzumab β suggest that the depth and character of depletion may translate directly into clinical protection against relapse, the outcome that matters most in a disease where each attack can leave permanent, disabling neurological damage.

The clinical stakes of these distinctions are considerable. Neuromyelitis optica spectrum disorder disproportionately affects women and shows a striking predilection for populations in East Asia, and attacks of optic neuritis and transverse myelitis can cause irreversible blindness and paralysis. Since the identification of the aquaporin-4 antibody, a growing therapeutic armamentarium has emerged, encompassing B cell depletion, complement inhibition, and blockade of the interleukin-6 receptor, each intercepting the autoimmune cascade at a different point. The demonstration that obinutuzumab β achieves striking efficacy adds a potent new option, but it also invites head-to-head comparisons that have not yet been performed, leaving open the question of whether deeper depletion of conventional B cell compartments truly outperforms broader depletion that extends into the plasmablast lineage.

Longer-term considerations also come into focus as depleting therapies mature. Repeated courses of B cell depletion carry implications for humoral immunity, vaccine responses, and infection risk, and the dynamics of B cell reconstitution after obinutuzumab β, with its enhanced potency, may differ meaningfully from those seen after rituximab or inebilizumab. Monitoring strategies based on circulating CD19 and CD27-positive cell counts, serum BAFF levels, and anti-aquaporin-4 antibody titers may ultimately allow clinicians to individualise retreatment intervals, depleting deeply enough to prevent relapse while avoiding the prolonged immunosuppression that extended courses might otherwise impose. Biomarker-driven personalisation of this kind remains aspirational, but the mechanistic groundwork laid over the past two decades makes it increasingly plausible.

What the phase III obinutuzumab β trial ultimately delivers, in Nakashima’s assessment, is both a confirmation and a challenge. The confirmation is that B cell depletion remains the most reliable therapeutic principle yet discovered for aquaporin-4-IgG-positive neuromyelitis optica spectrum disorder, capable of preventing the relapses that define the disease’s destructive course. The challenge is to move beyond the blunt question of whether B cells should be depleted and toward the precise one of which subpopulations sustain the autoimmune process, and how the depth, breadth, and timing of depletion can be tuned to maximize benefit while minimizing risk. As next-generation antibodies push the limits of what depletion can achieve, the field is converging on a richer, more granular understanding of B cell biology in neuroimmunological disease, one in which the architecture of the humoral immune response, rather than its mere suppression, becomes the true target of therapy.

Subject of Research: B cell depletion therapy for aquaporin-4-IgG-positive neuromyelitis optica spectrum disorder

Article Title: Deeper versus broader B cell depletion in neuromyelitis optica spectrum disorder

Article References: Nakashima, I. (2026). Deeper versus broader B cell depletion in neuromyelitis optica spectrum disorder. Nature Reviews Neurology. https://doi.org/10.1038/s41582-026-01269-w

Image Credits: AI Generated

DOI: 10.1038/s41582-026-01269-w

Keywords: neuromyelitis optica spectrum disorder, B cell depletion, obinutuzumab beta, aquaporin-4 antibody, anti-CD20 therapy, plasmablasts, rituximab, inebilizumab, neuroimmunology, phase III trial, BAFF, autoantibody