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Progressive multifocal leukoencephalopathy (PML) is a rare, devastating demyelinating disease of the CNS caused by the JC virus (JCV) that occurs in patients with compromised immune systems. Detection of PML in systemically immunocompetent patients with multiple sclerosis treated with natalizumab points to a role for this drug in the pathophysiology of PML. Emerging knowledge of the cellular and molecular biology of JCV infection and the pathogenesis of PML—including interplay of this common virus with the human immune system and features of natalizumab that might contribute to PML pathogenesis—provides new opportunities to monitor viral status and predict risk of JCV-associated disease. In the absence of an effective treatment for PML, early detection of the disease in patients with multiple sclerosis who are receiving natalizumab or other immunomodulatory treatments is vital to minimize CNS injury and avoid severe disability. Frequent MRI, stratified along a clinical and virus-specific immune risk profile, can be used to detect presymptomatic PML. Improved approaches to PML risk stratification are needed to guide treatment choices and surveillance of patients with multiple sclerosis.

Progressive multifocal leukoencephalopathy (PML) is an opportunistic infectious demyelinating disease of the central nervous system caused by JC polyomavirus predominantly affecting immunocompromised individuals. Nowadays, HIV, hematological malignancies and iatrogenic immune suppression account for most PML cases. For unknown reasons, spinal cord is classically protected from PML lesions. Here, we report the course of a patient harboring spinal cord lesions in the context of PML with immune reconstitution inflammatory syndrome and review the eight other cases reported in the literature so far. Then, we discuss the evolving spectrum of PML over recent years, potentially making its diagnosis more challenging.

The main aim of the study is to evaluate the efficacy and safety profile of ocrelizumab (OCR), rituximab (RTX), and cladribine (CLA), employed as natalizumab (NTZ) exit strategies in relapsing–remitting multiple sclerosis (RRMS) patients at high-risk for progressive multifocal leukoencephalopathy (PML). This is a multicentre, retrospective, real-world study on consecutive RRMS patients from eleven tertiary Italian MS centres, who switched from NTZ to OCR, RTX, and CLA from January 1st, 2019, to December 31st, 2019. The primary study outcomes were the annualized relapse rate (ARR) and magnetic resonance imaging (MRI) outcome. Treatment effects were estimated by the inverse probability treatment weighting (IPTW), based on propensity-score (PS) approach. Additional endpoint included confirmed disability progression (CDP) as measured by Expanded Disability Status Scale and adverse events (AEs). Patients satisfying predefined inclusion and exclusion criteria were 120; 64 switched to OCR, 36 to RTX, and 20 to CLA. Patients from the 3 groups did not show differences for baseline characteristics, also after post hoc analysis. The IPTW PS-adjusted models revealed that patients on OCR had a lower risk for ARR than patients on CLA (ExpBOCR 0.485, CI 95% 0.264–0.893, p = 0.020). This result was confirmed also for 12-month MRI activity (ExpBOCR 0.248 CI 95% 0.065–0.948, p = 0.042). No differences were found in other pairwise comparisons (OCR vs RTX and RTX vs CLA) for the investigated outcomes. AEs were similar among the 3 groups. Anti-CD20 drugs were revealed to be effective and safe options as NTZ exit strategies. All investigated DMTs showed a good safety profile.

Eight patients with progressive multifocal leukoencephalopathy associated with chronic lymphocytic leukemia, HIV infection, lymphoma, or idiopathic lymphopenia received pembrolizumab. Five patients had clinical improvement or stabilization of PML, reduction in lesion size on MRI, and decreased JC viral load. Three showed no clinical benefit.

Treatment with natalizumab once every 4 weeks is approved for patients with relapsing-remitting multiple sclerosis, but is associated with a risk of progressive multifocal leukoencephalopathy. Switching to extended-interval dosing is associated with lower progressive multifocal leukoencephalopathy risk, but the efficacy of this approach is unclear. We aimed to assess the safety and efficacy of natalizumab once every 6 weeks compared with once every 4 weeks in patients with relapsing-remitting multiple sclerosis. We did a randomised, controlled, open-label, phase 3b trial (NOVA) at 89 multiple sclerosis centres across 11 countries in the Americas, Europe, and Western Pacific. Included participants were aged 18–60 years with relapsing-remitting multiple sclerosis and had been treated with intravenous natalizumab 300 mg once every 4 weeks with no relapses for at least 12 months before randomisation, with no missed doses in the previous 3 months. Participants were randomly assigned (1:1), using a randomisation sequence generated by the study funder and contract personnel with interactive response technology, to switch to natalizumab once every 6 weeks or continue with once every 4 weeks. The centralised MRI reader, independent neurology evaluation committee, site examining neurologists, site backup examining neurologists, and site examining technicians were masked to study group assignments. The primary endpoint was the number of new or newly enlarging T2 hyperintense lesions at week 72, assessed in all participants who received at least one dose of assigned treatment and had at least one postbaseline MRI, relapse, or neurological examination or efficacy assessment. Missing primary endpoint data were handled under prespecified primary and secondary estimands: the primary estimand included all data, regardless of whether participants remained on the assigned treatment; the secondary estimand classed all data obtained after treatment discontinuation or study withdrawal as missing. Safety was assessed in all participants who received at least one dose of study treatment. Study enrolment is closed and an open-label extension study is ongoing. This study is registered with EudraCT, 2018-002145-11, and ClinicalTrials.gov, NCT03689972. Between Dec 26, 2018, and Aug 30, 2019, 605 patients were assessed for eligibility and 499 were enrolled and assigned to receive natalizumab once every 6 weeks (n=251) or once every 4 weeks (n=248). After prespecified adjustments for missing data, mean numbers of new or newly enlarging T2 hyperintense lesions at week 72 were 0·20 (95% CI 0·07–0·63) in the once every 6 weeks group and 0·05 (0·01–0·22) in the once every 4 weeks group (mean lesion ratio 4·24 [95% CI 0·86–20·85]; p=0·076) under the primary estimand, and 0·31 (95% CI 0·12–0·82) and 0·06 (0·01–0·31; mean lesion ratio 4·93 [95% CI 1·05–23·20]; p=0·044) under the secondary estimand. Two participants in the once every 6 weeks group with extreme new or newly enlarging T2 hyperintense lesion numbers (≥25) contributed most of the excess lesions. Adverse events occurred in 194 (78%) of 250 participants in the once every 6 weeks group and 190 (77%) of 247 in the once every 4 weeks group, and serious adverse events occurred in 17 (7%) and 17 (7%), respectively. No deaths were reported. There was one case of asymptomatic progressive multifocal leukoencephalopathy (without clinical signs) in the once every 6 weeks group, and no cases in the once every 4 weeks group; 6 months after diagnosis, the participant was without increased disability and remained classified as asymptomatic. We found a numerical difference in the mean number of new or newly enlarging T2 hyperintense lesions at week 72 between the once every 6 weeks and once every 4 weeks groups, which reached significance under the secondary estimand, but interpretation of statistical differences (or absence thereof) is limited because disease activity in the once every 4 weeks group was lower than expected. The safety profiles of natalizumab once every 6 weeks and once every 4 weeks were similar. Although this trial was not powered to assess differences in risk of progressive multifocal leukoencephalopathy, the occurrence of the (asymptomatic) case underscores the importance of monitoring and risk factor consideration in all patients receiving natalizumab. Biogen.

Three patients with progressive multifocal leukoencephalopathy who were treated with third-party–produced, cryopreserved, partially HLA-matched T cells specific for BK virus had clinical improvement or stabilization of PML and reduction in JC viral load.

Immune reconstitution has improved outcomes for progressive multifocal leukoencephalopathy (PML), a potentially lethal brain disease caused by JC virus (JCV). However, an antiviral treatment to control JCV is needed when immune reconstitution is delayed or not possible. On the basis of in vitro efficacy, this study evaluated the effect of mefloquine on PML and factors that may predict PML outcomes. This 38-week, open-label, randomized, parallel-group, proof-of-concept study compared patients with PML who received standard of care (SOC) with those who received SOC plus mefloquine (250 mg for 3 days, then 250 mg weekly). Patients randomized to SOC could add mefloquine treatment at week 4. The primary endpoint was change from baseline to weeks 4 and 8 in JCV DNA copy number (load) in cerebrospinal fluid (CSF). Exploratory analyses evaluated factors that might correlate with clinical outcome. The majority of enrolled patients were HIV positive. Preplanned interim data analyses suggested that the study was unlikely to successfully demonstrate a significant difference between groups; therefore, the study was terminated prematurely. There was no significant difference between groups in CSF JCV DNA loads or clinical/MRI findings. Decrease in CSF JCV DNA load from baseline to week 4 was associated with a better clinical outcome at 16 weeks, as measured by Karnofsky scores. This study found no evidence of anti-JCV activity by mefloquine. An early decrease of CSF JCV DNA load appears to be associated with a better clinical outcome.

Previous estimates of risk of progressive multifocal leukoencephalopathy (PML) in patients with multiple sclerosis receiving natalizumab were stratified by three risk factors: anti-John Cunningham virus (JCV) antibodies in serum, previous immunosuppressant use, and treatment duration, which were estimated using population-based assumptions. We aimed to calculate PML risk estimates from patient-level risk-factor data and to stratify risk by concentrations of anti-JCV antibody in serum (anti-JCV antibody index). Data on natalizumab-treated patients were pooled from four large, observational, open-label studies: STRATIFY-2, STRATA, TOP, and TYGRIS. Data were analysed with and without imputation for missing values of anti-JCV antibody status and previous immunosuppressant use. For anti-JCV antibody-positive patients in this pooled cohort, cumulative PML risk with or without previous immunosuppressant use was estimated using Kaplan-Meier analysis. Annual PML risks (per 12 natalizumab infusions) for patients without PML in the preceding year were estimated using conditional probability based on the life table method. For anti-JCV antibody-positive patients without previous immunosuppressant use, risk estimates were further stratified using a probability distribution for anti-JCV antibody index values, separately for patients with or without PML. Anti-JCV antibody index cutoffs were selected via sensitivity and specificity assessments for identifying PML cases in an index cohort. 156 (<1%) of 37 249 patients in the pooled cohort had PML. We imputed missing values on anti-JCV antibody status (3912 patients) and on previous immunosuppresant use (544 patients) using a multiple imputation method. For anti-JCV antibody-negative patients (n=13 996), estimated PML risk was less than 0·07 per 1000 patients (95% CI 0·00–0·40). In anti-JCV antibody-positive patients (n=21 696), estimated cumulative PML probability over 6 years (72 infusions of natalizumab) was 2·7% (95% CI 1·8–4·0) in patients with previous immunosuppressant use and 1·7% (1·4–2·1) in those without. In patients without previous immunosuppressant use (n=18 616), estimated annual PML risks per 1000 patients, conditional on having no PML before that year, ranged from 0·01 (0·00–0·03) in year 1 (1–12 infusions) to 0·6 (0·0–1·5) in year 6 (61–72 infusions) for people with an index of 0·9 or less; from 0·1 (0·0–0·2) in year 1 to 3·0 (0·2–5·8) in year 6 for those with an index of more than 0·9 up to and including 1·5; and from 0·2 (0·0–0·5) in year 1 to 10·0 (5·6–14·4) in year 6 for those with an index of more than 1·5. Our risk estimates calculated from patient-level clinical data allow individualised annual prediction of risk of PML in patients receiving natalizumab for multiple sclerosis, supporting yearly benefit–risk re-evaluation in clinical practice. Further, our estimates are generally consistent with previously calculated estimates. Incorporating anti-JCV antibody index allows further risk stratification for anti-JCV antibody-positive patients who have not previously taken immunosuppressants. Biogen.

Treatment of multiple sclerosis with natalizumab is complicated by rare occurrence of progressive multifocal leukoencephalopathy (PML). Between July, 2006, and November, 2009, there were 28 cases of confirmed PML in patients with multiple sclerosis treated with natalizumab. Assessment of these clinical cases will help to inform future therapeutic judgments and improve the outcomes for patients. The risk of PML increases with duration of exposure to natalizumab over the first 3 years of treatment. No new cases occurred during the first two years of natalizumab marketing but, by the end of November, 2009, 28 cases had been confirmed, of which eight were fatal. The median treatment duration to onset of symptoms was 25 months (range 6–80 months). The presenting symptoms most commonly included changes in cognition, personality, and motor performance, but several cases had seizures as the first clinical event. Although PML has developed in patients without any previous use of disease-modifying therapies for multiple sclerosis, previous therapy with immunosuppressants might increase risk. Clinical diagnosis by use of MRI and detection of JC virus in the CSF was established in all but one case. Management of PML has routinely used plasma exchange (PLEX) or immunoabsorption to hasten clearance of natalizumab and shorten the period in which natalizumab remains active (usually several months). Exacerbation of symptoms and enlargement of lesions on MRI have occurred within a few days to a few weeks after PLEX, indicative of immune reconstitution inflammatory syndrome (IRIS). This syndrome seems to be more common and more severe in patients with natalizumab-associated PML than it is in patients with HIV-associated PML. Diagnosis of natalizumab-associated PML requires optimised clinical vigilance, reliable and sensitive PCR testing of the JC virus, and broadened criteria for recognition of PML lesions by use of MRI, including contrast enhancement. Optimising the management of IRIS reactions will be needed to improve outcomes. Predictive markers for patients at risk for PML must be sought. It is crucial to monitor the risk incurred during use of natalizumab beyond 3 years.

In patients treated with natalizumab, PML incidence was about 11 cases per 1000 patients with 25 to 48 months of treatment, prior immunosuppressant use, and anti–JC virus antibody–positive status. The incidence was estimated to be 0.09 cases or fewer per 1000 antibody-negative patients. Natalizumab (Tysabri, Biogen Idec and Elan Pharmaceuticals) is approved for the treatment of relapsing–remitting multiple sclerosis in more than 50 countries and also for the treatment of moderate-to-severe Crohn's disease in the United States. As of February 2012, approximately 100,000 patients have been treated with natalizumab worldwide (unpublished data). In the pivotal Natalizumab Safety and Efficacy in Relapsing Remitting Multiple Sclerosis trial (AFFIRM; ClinicalTrials.gov number, NCT00027300), natalizumab monotherapy decreased the risk of progression of disability by 42 to 54% and reduced the annualized rate of relapse by 68%. 1 Natalizumab treatment is associated with the risk of progressive multifocal leukoencephalopathy (PML), . . .