Cell-based reporter gene assay for therapy-induced neutralizing antibodies to interferon-beta in multiple sclerosis

Patients with therapy-induced neutralizing antibodies (NAbs) to interferon-beta (IFN-β) have reduced responses to IFN-β treatment, resulting in higher relapse rates, increased magnetic resonance imaging activity, and a higher risk of disease progression. A functional assay was employed for both screening and titering of IFN-β NAbs utilizing a human cell line transfected with a luciferase reporter gene responsive to IFN-β. This assay demonstrated 100% sensitivity and specificity compared with the traditional cytopathic effect (CPE) assay and normal donor specimens. Additionally, 183 patients with multiple sclerosis (MS) undergoing therapy with IFN-β were tested in the reporter gene assay. Percent positivity for NAbs to the IFN-β was as follows: Avonex (1α) 26.5%, Rebif (1α) 34.1%, and Betaseron (1β) 31.8%. The IFN-β reporter gene assay showed excellent correlation with the well-established CPE assay offering clear advantages. The 50% false-positivity rate typically seen in enzyme-linked immunosorbent assays could be eliminated by using a functional assay for both screening and titering. Results can be reported within 20 h, and the cell line is cryopreserved, eliminating the need to maintain live viral and cell cultures. The use of this functional assay should be a valuable tool for detecting and monitoring the presence of NAbs in IFN-β-treated patients with MS.