A novel bioassay for the determination of neutralizing antibodies to IFN-beta 1b

We have adapted the new MxA gene-induction bioassay to measure neutralizing antibodies to interferon-beta 1b (IFN-beta 1b, the active ingredient in Be taseron(R) in sera from patients treated with Betaseron(R). This antibody a ssay has been validated to quantify neutralizing titers of 1:20 and above, with a precision of +/-0.20 in log(10). We have used this MxA gene-inductio n antibody assay to reinvestigate serum samples from multiple sclerosis (MS ) patients treated with Betaseron(R). The titers measured were closely comp arable to those obtained in antiviral assays. Data obtained by both methods show that neutralizing antibodies may appear and subsequently disappear ov er time in the sera of some patients treated with Betaseron(R). Sera from s ome patients contain binding antibodies to IFN-ss 1b. It was shown that bin ding antibody titers do not correlate quantitatively or qualitatively with neutralizing antibody titers, and indeed, a number of patients develop high levels of binding antibodies but never form measurable levels of neutraliz ing antibodies.