The researchers reviewed clinical records collected between 2014 and 2024 from a source database of 518 unique people with multiple sclerosis. Fifty-nine had symptom onset at age 50 or older, the threshold used to define late-onset multiple sclerosis in the study. Three were excluded from the main analysis: two had clinically isolated syndrome and one had an unspecified phenotype, leaving 56 patients with relapsing-remitting, primary progressive or secondary progressive multiple sclerosis. The investigators extracted symptoms, magnetic resonance imaging lesion locations, comorbidities, baseline and five-year disability scores, and initial and current disease-modifying therapies. Because the Expanded Disability Status Scale is ordinal and the sample was small, they used nonparametric and exact statistical tests.

Pyramidal or motor symptoms were the most common early clinical manifestations, reported in 83.9% of the entire cohort. They occurred in every patient with progressive multiple sclerosis and in 76.3% of those with relapsing-remitting disease, a statistically significant difference with a p-value of 0.045. Bowel and bladder dysfunction was also more frequent in the progressive group, affecting 72.2% of progressive cases and 42.1% of relapsing-remitting cases, with a p-value of 0.035 by chi-square testing and 0.047 by Fisher’s exact test. Other frequently recorded symptoms included sensory symptoms and cerebellar or balance problems, each present in 71.4% of patients, as well as brainstem symptoms, reported in 62.5%. Cerebral symptoms appeared only in the relapsing-remitting group, but this result was based on eight patients and was flagged by the researchers as requiring caution.

Magnetic resonance imaging data for the brain, spinal cord and optic nerves were available for all 56 patients, and the cohort had lesion involvement in several central nervous system regions. Periventricular lesions were the most common finding, present in 94.6% of the cohort, followed by juxtacortical lesions in 87.5% and spinal cord lesions in 82.1%. Infratentorial lesions occurred in 75.0% and optic nerve involvement in 50.0%. All 18 patients with progressive disease had periventricular, infratentorial and spinal cord lesions recorded, compared with 92.1%, 63.2% and 73.7%, respectively, among the 38 patients with relapsing-remitting disease. The distributions showed that late-onset multiple sclerosis could involve multiple anatomical pathways, while also illustrating why imaging findings in older adults require caution because vascular, degenerative, metabolic and other inflammatory conditions may produce overlapping clinical or radiological features.

Disability scores documented at baseline and five years showed a pronounced separation between relapsing-remitting and progressive phenotypes. The median baseline Expanded Disability Status Scale score was 2.00, with an interquartile range of 1.50 to 3.00, in the relapsing-remitting group and 3.75, with an interquartile range of 3.12 to 5.88, in the progressive group. The difference was statistically significant, with a p-value below 0.001. Five-year scores were available for 39 of the 56 patients, including 25 of 38 patients with relapsing-remitting disease and 14 of 18 with progressive disease. Their median five-year scores were 3.00 and 6.00, respectively, again a significant difference with a p-value below 0.001. A three-group analysis found an overall difference among relapsing-remitting, primary progressive and secondary progressive disease, with secondary progressive multiple sclerosis showing a higher score than relapsing-remitting disease after Bonferroni adjustment.

Although absolute disability was consistently greater in the progressive group, the amount of change over five years did not differ significantly between the phenotypes. The median change in Expanded Disability Status Scale score was 1.00 point in progressive disease and 0.50 point in relapsing-remitting disease, with a p-value of 0.377. The investigators emphasized that this null comparison must not be interpreted as evidence that the two groups progress at equivalent rates. Progressive patients began with substantially higher scores, and the available follow-up represented only two assessment points rather than a detailed trajectory. Sixteen of the 17 patients lacking a five-year score had an age-derived disease duration shorter than five years, so missing follow-up was strongly associated with shorter observed disease duration.

A sensitivity analysis excluding patients whose age-derived disease duration was under five years did not materially change the pattern. Among the 34 retained patients, the progressive group continued to have higher baseline disability, with a median score of 4.00 versus 2.00 for relapsing-remitting disease, and higher five-year disability, with medians of 6.00 and 3.00. Change in score again did not differ significantly, with medians of 1.00 and 0.50 and a p-value of 0.524. The findings therefore suggest that the greater five-year disability observed in progressive late-onset multiple sclerosis was largely already present at the beginning of observation. They do not establish that progressive and relapsing-remitting phenotypes accumulate disability at the same rate, particularly given the modest sample and incomplete longitudinal data.

Treatment patterns differed sharply by phenotype and changed between the initial and current assessments. Among active disease-modifying therapy users, initial anti-CD20 treatment was recorded in 19.4% of patients with relapsing-remitting disease, 88.9% of those with primary progressive disease and 42.9% of those with secondary progressive disease. At the current assessment, anti-CD20 therapy was used by 38.9% of active-treated relapsing-remitting cases, all nine primary progressive cases and 83.3% of active-treated secondary progressive cases. High-efficacy therapy was also more common in progressive phenotypes, whereas platform or moderate-efficacy treatment predominated in relapsing-remitting disease. Among 33 patients initially receiving platform or moderate therapy, 11 were receiving high-efficacy treatment at the current assessment, while all 19 initially classified in the high-efficacy group remained in that category.

Patients receiving anti-CD20 therapy had higher observed disability than those receiving other active therapies. Those starting with anti-CD20 treatment had a median baseline score of 3.50, compared with 2.00 for other active treatments, while patients currently receiving anti-CD20 therapy also had higher baseline and five-year scores than comparable patients on other active therapies. High-efficacy treatment groups likewise had higher five-year scores than the platform or moderate-efficacy group, with a median of 4.50 versus 2.50 and an adjusted p-value of 0.027. These are treatment associations, not evidence that anti-CD20 or high-efficacy therapy worsened outcomes. In routine care, clinicians may direct more intensive treatment toward patients with progressive disease, greater baseline disability or evidence of inflammatory activity, creating confounding by indication. Treatment exposure was also not fully aligned with the timing of disability assessments, and relapse activity, adherence, switching dates and adverse events were not systematically evaluated.

The study offers a detailed but geographically limited view of contemporary tertiary-care practice, rather than a nationally representative assessment of late-onset multiple sclerosis. Its retrospective design, single center and small progressive subgroups limited statistical power and adjustment for confounders. Diagnostic heterogeneity was possible because the study period spanned revisions of the McDonald criteria, MRI findings came from routine radiology reports rather than centralized image review, and five-year scores were unavailable for some participants. There was also no adult-onset comparison group, meaning the results cannot determine whether the observed features are unique to late-onset disease or mainly reflect the distinction between progressive and relapsing-remitting phenotypes. Multiple exploratory comparisons further argue against treating borderline findings as definitive. The authors positioned the findings as a replication and extension of established observations: late-onset multiple sclerosis, particularly its progressive forms, can carry a substantial motor, sphincter and disability burden, and geographically diverse cohorts are needed to define how that burden and contemporary treatment selection vary across healthcare systems.

Subject of Research: Clinical symptoms, disability outcomes, MRI findings and treatment patterns in late-onset multiple sclerosis

Article Title: Clinical characteristics, disability outcomes, and disease-modifying therapy patterns in late-onset multiple sclerosis: a single-center retrospective cohort study

Article References: Alomar, R., Polunosika, E., Karelis, G., & Pastare, D. (2026). Clinical characteristics, disability outcomes, and disease-modifying therapy patterns in late-onset multiple sclerosis: a single-center retrospective cohort study. Frontiers in Neurology, 17, Article 1966162. https://doi.org/10.3389/fneur.2026.1966162

Image Credits: AI Generated

DOI: 10.3389/fneur.2026.1966162

Keywords: late-onset multiple sclerosis, progressive multiple sclerosis, disability outcomes, Expanded Disability Status Scale, disease-modifying therapy, anti-CD20 therapy, MRI lesions, Latvian cohort, retrospective cohort study, Clinical, characteristics, disability

The study, published as a letter to the editors in the Journal of Neurology, comes from the Neurology Unit and Multiple Sclerosis Center at IRCCS Ospedale San Raffaele in Milan, with co-first authors Veronica Marino and Lucia Moiola and co-senior authors Simone Guerrieri and Massimo Filippi. The team conducted a retrospective, real-world comparison of patients with multiple sclerosis who discontinued natalizumab and were subsequently switched either to ocrelizumab, an intravenous anti-CD20 monoclonal antibody, or to ofatumumab, a subcutaneously injected antibody of the same class. The work was approved by the institutional ethics committee at San Raffaele and conducted in accordance with the Helsinki Declaration, with patients providing dedicated informed consent for inclusion in the Italian Multiple Sclerosis and Related Disorders Register.

To understand why this comparison matters, it helps to look at the biology. Both ocrelizumab and ofatumumab belong to a class of drugs that target the CD20 molecule, a protein found on the surface of most B cells, the immune cells that are central players in the inflammatory attacks of relapsing multiple sclerosis. By binding CD20, these antibodies deplete circulating B cells, quieting the autoimmune storm. Yet the two drugs are not identical twins. Ocrelizumab is delivered by intravenous infusion every six months and is approved for both relapsing and primary progressive forms of the disease. Ofatumumab is self-injected under the skin once a month and binds a slightly different region of the CD20 molecule, a difference in epitope that influences how the antibody interacts with its target and with the immune system more broadly.

Those pharmacological distinctions translate into different clinical profiles. Ofatumumab’s subcutaneous route produces rapid and sustained B-cell depletion with a more continuous exposure, while ocrelizumab’s intermittent infusions create a pulsatile pattern of depletion and repopulation. Previous research, including pharmacokinetic and pharmacodynamic analyses of the pivotal OPERA and ORATORIO trials for ocrelizumab and the phase 2 APLIOS study of subcutaneous ofatumumab, has documented these characteristics. A recent comparative analysis published in Annals of Neurology in 2025 suggested that treatment outcomes can differ between patients receiving the two agents, adding urgency to the question of which drug is the better landing spot for patients stepping down from natalizumab.

The natalizumab discontinuation problem is well known to specialists. Natalizumab works by blocking the trafficking of immune cells across the blood-brain barrier, and when it is stopped, that barrier traffic resumes, sometimes with a vengeance. Systematic reviews and meta-analyses have documented post-natalizumab disease reactivation, including severe rebound phenomena in which patients experience bursts of new relapses and magnetic resonance imaging activity within weeks to months of the last infusion. Risk factors for reactivation after cessation have been identified in large cohort studies, and the timing of the switch is critical. A prolonged gap between stopping natalizumab and starting the next therapy leaves a window in which the disease can flare, while certain successor drugs, particularly those with slower onset, may not close that window quickly enough.

Against that backdrop, anti-CD20 agents have emerged as favored switch options, because they act on a different arm of the immune response and can maintain disease control across the transition. Several earlier studies, including pilot work on switching to ocrelizumab from natalizumab given at extended interval dosing in patients at high risk of progressive multifocal leukoencephalopathy, have reported favorable outcomes over follow-up periods as long as 96 weeks. But head-to-head real-world data comparing ocrelizumab and ofatumumab specifically in the post-natalizumab setting had been lacking, leaving clinicians to extrapolate from trials that enrolled different populations. The Milan study was designed to fill that gap using the kind of messy, unselected patient data that randomized trials rarely capture.

The retrospective design has both strengths and limits that readers should keep in mind. On the strength side, real-world cohorts reflect the full spectrum of patients seen in clinic, including those with comorbidities, atypical disease courses, and prior treatment histories that trial populations often exclude. The San Raffaele center is one of the largest multiple sclerosis referral hubs in Italy, and its registry-based approach allows researchers to track outcomes such as relapse rates, magnetic resonance imaging activity, and safety events under routine clinical conditions. On the limit side, retrospective comparisons cannot fully control for why clinicians chose one drug over the other, and such selection bias can color the results. The authors acknowledge the inherent constraints of this design, and the findings should be read as hypothesis-generating evidence that complements, rather than replaces, randomized trials.

Safety is a central concern in any switch strategy. Anti-CD20 therapies deplete B cells broadly, and while they have accumulated a substantial safety record since ocrelizumab’s approval, questions remain about infection risk, hypogammaglobulinemia over the long term, and the theoretical concern that B-cell depletion could modulate the immune response to the JC virus itself. The risk stratification for progressive multifocal leukoencephalopathy relies on anti-JC virus antibody testing using second-generation assays such as the STRATIFY JCV DxSelect, which supports clinical decisions about when natalizumab must be abandoned. The Milan team evaluated safety alongside efficacy in both switch groups, providing clinicians with a side-by-side view of how patients tolerate each transition in everyday practice.

The broader significance of the study lies in the evolution of multiple sclerosis treatment. The field has moved decisively toward high-efficacy therapies earlier in the disease course, and natalizumab, once a flagship of that movement, is increasingly managed with extended interval dosing to reduce infection risk before ultimately being withdrawn in patients who accumulate risk factors. As the population of patients needing a post-natalizumab home grows, the choice between intravenous ocrelizumab and subcutaneous ofatumumab becomes a practical fork in the road, influenced by efficacy signals, safety profiles, dosing convenience, patient preference, and health system logistics. Real-world comparisons like this one give neurologists evidence grounded in clinical reality rather than idealized trial conditions.

For patients and clinicians alike, the message from Milan is one of cautious reassurance paired with continued vigilance. Switching from natalizumab to either anti-CD20 agent appears to be a viable strategy for maintaining disease control, but the details of timing, monitoring, and individual risk profiling remain decisive. The study’s data are held at IRCCS Ospedale San Raffaele and are available upon reasonable request to the corresponding author, an approach that supports transparency and further analysis by the research community. As longer follow-up accumulates and more centers contribute their own switch cohorts, the evidence base will mature, helping to convert one of neurology’s trickiest transitions from an act of clinical judgment into an evidence-based protocol.

Subject of Research: Comparison of ocrelizumab and ofatumumab as post-natalizumab switch therapies in multiple sclerosis

Article Title: Ocrelizumab versus ofatumumab efficacy and safety after natalizumab discontinuation in multiple sclerosis: a retrospective real-world comparison

Article References: Marino, V., Moiola, L., Zanetta, C., Rubin, M., Rossi, L., Margoni, M., Nozzolillo, A., Gattuso, I., Viti, V., Petza, E., Rocca, M. A., Guerrieri, S., & Filippi, M. (2026). Ocrelizumab versus ofatumumab efficacy and safety after natalizumab discontinuation in multiple sclerosis: a retrospective real-world comparison. Journal of Neurology, 273(10), Article 577. https://doi.org/10.1007/s00415-026-14124-1

Image Credits: AI Generated

DOI: 10.1007/s00415-026-14124-1

Keywords: multiple sclerosis, natalizumab, ocrelizumab, ofatumumab, anti-CD20 therapy, B-cell depletion, progressive multifocal leukoencephalopathy, JC virus, drug switching, real-world evidence, disease reactivation, neuroimmunology

Ocrelizumab is a humanized monoclonal antibody that binds to the CD20 protein found on the surface of B cells, marking them for destruction and dramatically reducing the immune attacks on the nervous system that drive multiple sclerosis. Approved after landmark trials showed clear benefits in both relapsing and primary progressive forms of the disease, it has become one of the most prescribed high-efficacy therapies in neurology. Like all immunotherapies, however, it reshapes the immune system in ways that are still being mapped. Infections, infusion reactions, and a theoretical concern about certain malignancies have long been part of its safety profile. The new study suggests that the lung, an organ densely populated by immune surveillance cells, may occasionally become collateral damage in the altered immunological landscape that follows B-cell depletion.

Organizing pneumonia is not an infection at all, despite its name. It is a form of interstitial lung disease in which the tiny air sacs of the lung and their surrounding tissue become inflamed and then filled with plugs of loose connective tissue, a process pathologists describe as granulation tissue extending into the alveolar spaces. It can arise without any identifiable cause, in which case it is called cryptogenic, or it can be secondary to drugs, infections, radiation, or autoimmune disease. Patients typically develop a persistent fever, a dry cough, and breathlessness that fail to respond to antibiotics, which is precisely the pattern that should alert clinicians to look for something other than bacterial pneumonia. On chest computed tomography, the signature findings are patchy ground-glass opacities, areas of consolidation, and sometimes the striking reversed halo sign, in which a ring of denser tissue surrounds a clearer center.

The Milanese team, led by Enrico Petza and senior author Massimo Filippi, retrospectively collected clinical, radiological, laboratory, treatment, and outcome data from multiple sclerosis patients at their center who developed organizing pneumonia while on ocrelizumab. The five identified patients, three of them women, had a median age of 54 years, with ages ranging from 27 to 64. The condition did not appear early in treatment. On average, patients had been receiving ocrelizumab for about 5.1 years before symptoms emerged, with a standard deviation of 2.9 years, and the lung disease declared itself a mean of 10.8 weeks, with a standard deviation of 10.4 weeks, after the most recent infusion. That long latency is clinically important, because it means neither patient nor physician is likely to connect a fever appearing months after a routine infusion with the drug that caused it.

The clinical picture in all five cases was strikingly uniform. Each patient presented with a persistent fever that refused to yield to antibiotics, and some also had a nonproductive cough. Chest CT scans consistently revealed patchy ground-glass opacities and consolidations, the radiological hallmarks of organizing pneumonia. Treatment followed the standard approach for the condition: all patients received prednisone at doses of 0.5 to 1 milligram per kilogram of body weight per day, continued for a median of 30 days with a range of 15 to 60 days, followed by a gradual tapering of the dose. Corticosteroids suppress the inflammatory process and usually produce a prompt clinical response, and indeed the patients initially improved. Ocrelizumab was discontinued in every case, a decision that reflects the seriousness with which the treating neurologists viewed the association.

The follow-up data, however, reveal a more troubling story than the initial recovery might suggest. Over a median follow-up of 29 months, ranging from 4 to 47 months, four of the five patients experienced respiratory relapses, and residual radiological abnormalities persisted in their lungs despite treatment. Only one patient eventually restarted a disease-modifying therapy, beginning ozanimod, a sphingosine-1-phosphate receptor modulator, two years after the onset of the lung disease. The reluctance to re-expose these patients to immunotherapy is understandable, but it leaves them vulnerable to renewed multiple sclerosis activity, creating a genuine therapeutic dilemma. The persistence of lung changes on imaging also raises questions about whether organizing pneumonia associated with B-cell depletion follows a more indolent course than the idiopathic form of the disease.

To place their five cases in context, the researchers conducted a literature review and identified 17 previously reported cases of organizing pneumonia in ocrelizumab-treated patients. Descriptive comparison showed substantial consistency between the Milanese cohort and the published cases, in terms of timing, presentation, imaging findings, and response to corticosteroids. Earlier reports included patients whose lung disease followed COVID-19 infection during anti-CD20 therapy, complicating the picture, since viral infection itself can trigger secondary organizing pneumonia. But the accumulation of cases without any infectious trigger, occurring years into treatment and weeks after infusions, strengthens the argument that ocrelizumab itself can be the inciting agent. The pattern also echoes what has been described with rituximab, an older anti-CD20 antibody used in lymphoma and rheumatoid arthritis, which has been linked to organizing pneumonia in multiple published reports.

Why would depleting B cells inflame the lung? The authors point out that the mechanism remains unclear and call for further studies to clarify the potential role of CD20-positive lymphocyte depletion in the pathogenesis of organizing pneumonia. Several hypotheses are plausible. B cells are not merely antibody producers; they regulate other immune cells, present antigens, and secrete cytokines that maintain immune homeostasis in tissues. Removing them may disturb the delicate balance of immune surveillance in the lung, allowing aberrant repair processes to take hold. Alternatively, the timing of the lung injury weeks after infusion could reflect the repopulation phase, when immature B cells return and the immune system recalibrates. It is also possible that a subclinical infection, undetected in an immunologically altered host, seeds the inflammatory cascade. Disentangling these possibilities will require immunological studies of affected lung tissue and longitudinal immune monitoring of treated patients.

For clinicians, the practical message is vigilance. A multiple sclerosis patient on ocrelizumab who develops weeks of unexplained fever with a dry cough, especially when antibiotics fail, should undergo chest imaging, and the radiologist should be told to consider organizing pneumonia among the differential diagnoses. Early recognition matters because corticosteroids are effective and because continuing the offending drug may prolong or worsen the lung injury. The authors note that the condition remained rare, affecting fewer than one in a hundred patients at their center, and nothing in the study undermines the substantial efficacy that ocrelizumab has demonstrated in randomized trials. But rare complications of very common drugs translate into real numbers of affected people, and the long latency between treatment and disease makes spontaneous reporting and pooled surveillance essential.

The study also highlights a broader theme in modern neuroimmunology: as high-efficacy immunotherapies transform the prognosis of multiple sclerosis, the frontier of care is shifting toward the fine print of long-term safety. Interstitial lung disease has now been reported as a late occurrence in ocrelizumab-treated patients in other journals as well, suggesting that the signal is no longer anecdotal. Larger registries, systematic pulmonary follow-up, and mechanistic research into how B-cell depletion reshapes lung immunity will be needed to identify who is at risk and whether monitoring or prophylactic strategies can prevent the disease. For now, the Milanese case series offers clinicians a clear template of what to watch for, and it offers patients the reassurance that when the condition is caught, effective treatment exists, even if the road to full recovery can be longer than anyone would like.

Subject of Research: Organizing pneumonia associated with ocrelizumab treatment in multiple sclerosis patients

Article Title: Ocrelizumab-related organizing pneumonia in multiple sclerosis: insights from a case series and literature review

Article References: Petza, E., Guerrieri, S., Marino, V., Gattuso, I., Rubin, M., Nozzolillo, A., Rocca, M. A., Moiola, L., & Filippi, M. (2026). Ocrelizumab-related organizing pneumonia in multiple sclerosis: insights from a case series and literature review. Journal of Neurology, 273(10), Article 600. https://doi.org/10.1007/s00415-026-14130-3

Image Credits: AI Generated

DOI: 10.1007/s00415-026-14130-3

Keywords: multiple sclerosis, ocrelizumab, organizing pneumonia, interstitial lung disease, anti-CD20 therapy, B-cell depletion, corticosteroids, chest CT, drug safety, neuroimmunology, case series, Journal of Neurology

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