Incorporation of an interferon-β neutralizing antibody assay into routine clinical practice

Incorporation of routine clinical testing for neutralizing antibodies (NAbs) to interferon (IFN)-β has remained problematic. With increasing treatment choice for patients, routine NAb testing should be incorporated to aid therapeutic decisions.

We sought to improve interpretation of NAb results by combining the luciferase NAb assay (luciferase gene expression assay under control of interferon-stimulated response element) and in-vivo biomarker (myxovirus A protein, MxA) induction in patients with MS.

Blood samples (serum and PAXGene(®) for RNA) were obtained pre-injection and 12 hours post-injection of IFN-β from 144 subjects. Sera were tested for NAbs using the luciferase assay. MxA expression was quantified by real-time polymerase chain reaction (PCR).

26% of samples were NAb positive (titre > 20 NU). There was no difference in NAb titres in the pre- or post-dose sera (p = 0.643). MxA expression was inhibited in a dose-dependent fashion in NAb positive samples. Mean MxA level post-IFN-β: NAb negative 2330 (95% CI 1940-2719), NAb 20-99 NU 1533 (95% CI 741-2324), NAb 100-600 NU 832 (186-1478) and NAb > 600 NU 101 (95% CI 0-224). NAb titre and MxA level correlated strongly: MxA pre- (Spearman r = -0.72, p < 0.0001), MxA post- (Spearman r = -0.79, p < 0.0001) and MxA induction (Spearman r = -0.67, p = 0.0004).

A single, 12-hour post-injection sample should be used to test for NAbs using the luciferase assay and IFN-β bioactivity (MxA) in the clinical setting.