Anti-Interferon Beta Antibody Titers Strongly Correlate Between Two Bioassays and In Vivo Biomarker Expression, and Indicates That a Titer of 150 TRU/mL Is a Biologically Functional Cut-Point

Abstract

Interferon beta (IFNβ) is used as a first-line treatment in relapsing-remitting multiple sclerosis (MS). The occurrence of neutralizing antidrug antibodies (NAbs) against IFNβ may reduce treatment response. Therefore, clinical monitoring of NAbs is currently executed using bioassays, but several bioassays are available and it is unclear how well their readouts correlate. We made a comparison between 2 bioassays; myxovirus resistance protein A (MxA) gene expression assay (MGA) and iLite™ anti-Human IFNβ bioassay, to measure IFNβ-specific NAb titers in 44 MS patients. We further studied how NAb titers affected in vivo transcription of IFN-induced genes myxovirus resistant 1 (MX1) and C-X-C motif chemokine 10 (CXCL10), in addition to serum CXCL10 protein levels. There were significant correlations between NAb titer levels measured with MGA and iLite (Spearman r=0.9368). MX1 and CXCL10 gene expression was strongly induced by IFNβ and NAb positivity significantly reduced this expression. A NAb titer of 150 TRU/mL was observed to be a biological cut-point applicable to both assays, since MX1 and CXCL10 expression was greatly reduced or blocked in patients above this titer level. In conclusion, NAb titers measured with the MGA and iLite bioassays are comparable, but the threshold for positivity in both assays does not correspond to the biologically functional cut-point.

Occurrence of Anti-Drug Antibodies against Interferon-Beta and Natalizumab in Multiple Sclerosis: A Collaborative Cohort Analysis

“…The ADA assay methods which have changed across time in Sweden and Austria were associated with ADA occurrence, suggesting a difference in the sensitivity of the assays as previously reported [18]. The MPA method detected a higher rate of ADA with 20% (95% CI 14.7–25.1) of the patients who developed ADA before 18 months of therapy in Austria and 30.3% (95% CI 18.6–36.1) in Sweden, while 7% (95% CI 1.3–10.7) developed ADA with the MGA method in Austria and 8.4% (95% CI 6.9–10.6) in Sweden.…”

“…We cannot assess the effect of change in IFNβ-1a s.c. formulation as its date is too close to the date of change in type of assay used. Nevertheless when we adjusted on the type of IFNβ treatment in the multivariate analyses, differences between the assay methods in terms of ADA development remained significant, suggesting that assay methods may differ in sensitivity of ADA detection as previously reported [18]. …”

“…In a recent publication a strong correlation of NAb titers was found on a series of 118 serum samples titrated with the MPA and the MGA assay in the Swedish central laboratory [12]. There were also significant correlations between NAb titer levels measured with MGA and iLite [18]. For the three assays, titers were adjusted using the Kawade formula [19].…”

Antidrug Antibodies: B Cell Immunity Against Therapy

“…It is the high‐titre nADA that are responsible for the blocking of the biological effect of IFN‐ β . This blocking is titre dependent, and the biological threshold can be determined by pharmacodynamic studies correlating the intended gene expression stimulation of the drug with levels of nADA . Neutralizing ADA are measured in bioassays in which the stimulation of the cells with IFN‐ β is blocked by the addition of patients' serum and thus mimicking the biological significance of nADA.…”

Evaluation of the impact of neutralizing antibodies on IFNβ response

“…Each laboratory should establish its own threshold. Using two different assays for NAbs quantification Hermanrud and collaborators [37] found that a titer over 150 was associated with loss of IFNβ biological activity.…”