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Comparative Study
. 2025 Jun;31(7):877-881.
doi: 10.1177/13524585251322683. Epub 2025 Jun 14.

Beyond the switch to the biosimilar of natalizumab: What is the impact of changing the JCV test?

Sandra Vukusic  1   2   3 , Florian Hubben  1   2 , Antoine Gavoille  1   4   5 , Yannis Malek  1   2 , Olivier Casez  6   7 , Laurent Kremer  8 , Thomas Palpacuer  9 , Romain Marignier  2   1   10   11 , Françoise Durand-Dubief  1 , Géraldine Androdias-Condemine  1 , Julie Pique  1   10 , Elisabeth Maillart  12 , Patrick Vermersch  13 , Jérôme de Seze  8
Affiliations
Comparative Study

Beyond the switch to the biosimilar of natalizumab: What is the impact of changing the JCV test?

Sandra Vukusic et al. Mult Scler. 2025 Jun.

Abstract

Background: The biosimilar drug of natalizumab was marketed with a new anti-John Cunningham virus (JCV) assay (ImmunowellTM).

Objectives: To compare the performance of the ImmunowellTM JCV assay to StratifyTM, the reference one.

Methods: We analyzed retrospectively serological results from patients with multiple sclerosis (MS) followed in four French MS centers and tested simultaneously in routine with both tests.

Results: Two hundred and fifty-nine patients were included. Results were positive in 23.6% with StratifyTM and 61.4% with ImmunowellTM. A binary discordance was found in 37.8%. Sensitivity and negative predictive value were 100%, with lower specificity (50.5%) and positive predictive value (38.4%) for ImmunowellTM. According to index value cutoffs, 42.9% of the results showed discordances, with a systematic higher risk estimate for ImmunowellTM. Most of them (83/111) were negative with StratifyTM and at low risk of progressive multifocal leukoencephalopathy (PML) (<0.8) with ImmunowellTM. Eighteen were upgraded to intermediate risk (0.8-1.4) and 10 to high risk (⩾1.4).

Conclusions: The ImmunowellTM JCV IgG assay is reliable to detect patients at risk of progressive multifocal leukoencephalopathy, but the high rate of discrepancy is challenging in deciding to continue on natalizumab or not.

Keywords: JCV serology; Multiple sclerosis; biosimilar; natalizumab; progressive multifocal leukoencephalopathy.

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Conflict of interest statement

Declaration of Conflicting InterestsThe author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: S.V. has received non-personal consulting and lecturing fees, travel grants, and unconditional research support from Biogen, Janssen, Merck, Novartis, Roche, Sandoz, and Sanofi.O.C. has received consulting fees from Biogen, Janssen, Merck, Novartis, Roche, and Sanofi, and support for attending meetings and/or travel from Merck, Novartis, and Janssen.L.K. has received consulting and lecturing fees, travel grants from Alexion, Biogen, Novartis, Merck, Roche, and Sanofi.R.M. has received personal fees from Horizon Therapeutics, Alexion, Roche, and UCB and non-financial support from Horizon Therapeutics, Merck, Biogen, and Roche, outside the submitted work.G.A-.C. has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Biogen, Jannsen, Merck, Novartis, Roche, and Sanofi-Genzyme.J.P. has received travel grants and personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Teva, Biogen, Novartis, Merck, Sanofi-Genzyme, Roche, Celgene-BMS, and Alexion.E.M. has received research support from Biogen and ARSEP foundation and personal fees for lectures and advisory boards from Biogen, Janssen, Merck, Novartis, Roche, Sanofi, and Teva.P.V. has received Honorarium, contributions to meeting from Biogen, Sanofi-Genzyme, Novartis, Teva, Merck, Roche, Imcyse, AB Science, Janssen, Ad Scientiam, and BMS and research supports from Novartis, Sanofi-Genzyme, and Merck.J.D.S. has received consulting and lecturing fees, travel grants, and unconditional research support from Biogen, Genzyme, Novartis, Roche, Sanofi Aventis, and Teva Pharma.F.H. has nothing to disclose.A.G. has nothing to disclose.Y.M. has nothing to disclose.T.P. has nothing to disclose.F.D-.D. has nothing to disclose.

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