Neutralizing antibodies to interferon beta in multiple sclerosis: analytical evaluation for validation of a cytopathic effect assay.
BACKGROUND: Recent guidelines have recommended the use of validated assays for the measurement of neutralizing antibodies (NABs) to interferon beta (IFNbeta) in patients with multiple sclerosis (MS). In an attempt of validation, we studied the analytical performance of a bioassay based on antiviral cytopathic effect (CPE) using WISH cells and the vesicular stomatitis virus (WISH/VSV CPE). METHODS: NAB titres measured with the WISH/VSV CPE assay in 63 sera from IFNbeta-treated MS patients were compared to those obtained with the reference CPE method using A549 cells and the encephalomyocarditis virus. Binding antibodies (BABs) were measured using a capture ELISA as a screening test for NABs. RESULTS: No false-negative BAB was obtained in our patients. The between-run coefficients of variation (CVs) determined with log10 titres of the NIH anti-IFNbeta (G038-501-572) yielded good results (<or=10.4%) and within-run variability was excellent (CV<or=2%). The log10 titres obtained with both CPE assays were highly correlated (r=0.969 and r=0.884 for anti-IFNbeta-1a and anti-IFNbeta-1b, respectively). The same patients were found NAB-positive with both CPE assays. CONCLUSION: Because of its good precision, sensitivity and excellent correlation with the reference CPE method, the WISH/VSV CPE bioassay can be used in the follow-up of IFNbeta-treated MS patients.