Quantification of neutralizing antibodies to human type I interferons using division-arrested frozen cells carrying an interferon-regulated reporter-gene.

Development of neutralizing antibodies (NAbs) to interferons (IFNs) can reduce the clinical response to IFN therapy. As current cell-based assays for quantifying NAbs have limitations, a highly sensitive and reproducible assay was developed, using division-arrested frozen human U937 cells transfected with the luciferase reportergene controlled by an IFN-responsive chimeric promoter, which allows IFN activity to be determined with precision within hours. Assay-ready PIL5 cells can be stored frozen for >3 years without loss of IFN sensitivity or the need for cell propagation. The assay is highly IFN sensitive (detecting <1.0 IU/mL), reproducible (SE ± 15%) over concentrations from <1.0 to 100 IU/mL and able to measure different IFN subtypes and their pegylated variants. The use of this assay has shown that NAbs from patients treated with IFN-α2 exhibited markedly lower titers against 10 LU/mL of low specific activity IFNs, namely, IFN-α1, PEG-IntronTM (Schering-Plough, Levallois-Perret,France), or PegasysTM...