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

Abstract

Background:

The biosimilar drug of natalizumab was marketed with a new anti-John Cunningham virus (JCV) assay (Immunowell^TM).

Objectives:

To compare the performance of the Immunowell^TM JCV assay to Stratify^TM, 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 Stratify^TM and 61.4% with Immunowell^TM. 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 Immunowell^TM. According to index value cutoffs, 42.9% of the results showed discordances, with a systematic higher risk estimate for Immunowell^TM. Most of them (83/111) were negative with Stratify^TM and at low risk of progressive multifocal leukoencephalopathy (PML) (<0.8) with Immunowell^TM. Eighteen were upgraded to intermediate risk (0.8–1.4) and 10 to high risk (⩾1.4).

Conclusions:

The Immunowell^TM 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.