Should we measure the bioavailability of interferon β in vivo in patients with multiple sclerosis?

MicroRNA-29b variants and MxA expression change during interferon beta therapy in patients with relapsing-remitting multiple sclerosis

BACKGROUND

Multiple sclerosis is a chronic inflammatory demyelinating disease of the central nervous system (CNS) characterized by immune-mediated demyelination and axonal injury. Myelin-reactive IFN-γ-producing Th1 cells has been shown to play an important role in the development of MS. MicroRNAs (miRNAs) are a new class of small non-coding RNA molecules about 22 nucleotides long which regulate gene expression post-transcriptionally by binding to 3' UTR of their mRNA targets, and resulting in degradation or transcriptional repression of the targeted mRNA. Accumulating evidence supports that miRNA dysregulation is linked to the pathogenesis of autoimmune diseases that include MS. miR-29b expression has been shown to be upregulated in memory CD4+T cells from relapsing-remitting MS (RR-MS) patients, which may reflect chronic Th1 inflammation. Interferon beta (IFN-β) benefits patients with MS and reduces symptoms of the RR-MS. MxA is induced by type I interferon and predicts IFN-β response in MS patients. The aim of this study was to evaluate miR-29b variants and MxA expression and serum IFN-γ level in responders and non-responders to IFN-β treatment.

METHODS

A total of 70 IFN-β treated RR-MS patients including 35 responders and 35 non-responders were enrolled. We analyzed the expression level of miR-29b variants and MxA using the peripheral blood of MS patients treated with IFN-β for more than one year. Real-time RT-PCR was performed to analyze miR-29b variants and MxA expression one year after initiation of IFN-β therapy. Serum cytokine level was measured by ELISA.

RESULTS

The results indicated that the expression level of miR-29b-3p changed related to IFN-β response. Moreover, miR-29b-5p was downregulated under IFN-β treatment in responders versus non-responders. MxA level was significantly decreased in the responders. There was no change in IFN-γ level following treatment with IFN-β in the MS patients.

CONCLUSIONS

Our results might provide fundamentals for the development of new markers of the biological effects of IFN-β therapy.

MxA mRNA quantification and disability progression in interferon beta-treated multiple sclerosis patients

Even though anti-interferon beta (IFNβ) antibodies are the main determinants of IFNβ bioactivity loss and Myxovirus-resistance protein A (MxA) is the most established marker of IFNβ biological activity in IFNβ-treated multiple sclerosis patients, their usefulness in the routine clinical practice is still debated. Therefore, 118 multiple sclerosis patients naïve for treatment were enrolled for a 3-year longitudinal observational study mimicking the conditions of a real-world setting. In order to evaluate the kinetics of bioactivity loss in blood samples obtained every 6 months after therapy initiation, MxA and interferon receptor isoform/subunit mRNA were quantified by real-time PCR, anti-IFNβ binding antibodies were detected by radioimmunoprecipitation, and neutralizing antibodies by cytopathic effect inhibition assay. Clinical measures of disease activity and disability progression were also obtained at all time points. We found that, at the individual-patient level, the response to IFNβ therapy was extremely heterogeneous, including patients with stable or transitory, early or late loss of IFNβ bioactivity, and patients with samples lacking MxA mRNA induction in spite of absence of antibodies. No interferon receptor isoform alterations that could explain these findings were found. At the group level, none of these biological features correlated with the measures of clinical disease activity or progression. However, when MxA mRNA was evaluated not at the single time point as a dichotomic marker (induced vs. non-induced), but as the mean of its values measured over the 6-to-24 month period, the increasing average MxA predicted a decreasing risk of short-term disability progression, independently from the presence of relapses. Therefore, a more bioactive treatment, even if unable to suppress relapses, reduces their severity by an amount that is proportional to MxA levels. Together with its feasibility in the routine laboratory setting, these data warrant the quantification of MxA mRNA as a primary tool for a routine monitoring of IFNβ therapy.

Variability in detection and quantification of interferon β-1b-induced neutralizing antibodies

BACKGROUND

Interferon-beta (IFNB) therapy for multiple sclerosis can lead to the induction of neutralizing antibodies (NAbs) against IFNB. Various methods are used for detection and quantification of NAbs.

METHODS

Blood samples from 125 IFNB-1b-treated patients, which were tested NAb negative or NAb positive after conclusion of a clinical study, were retested three years after first being assessed in four different laboratories that offer routine NAb testing to practicing neurologists. The myxovirus protein A (MxA) induction assay, the cytopathic effect (CPE) assay (two laboratories), or the luciferase assay were used. Intra- and inter-laboratory agreement between assays with respect to NAb detection and NAb titer quantification were evaluated.

RESULTS

High agreement for NAb detection (kappa coefficient, 0.86) and for titer levels was observed for the intra-laboratory comparison in the laboratory using the MxA induction assay performed three years ago and now. A similarly high agreement for NAb detection (kappa coefficient, 0.87) and for titer quantification was noted for the MxA assay of this laboratory with one of two laboratories using the CPE assay. All other inter-laboratory comparisons showed kappa values between 0.57 and 0.68 and remarkable differences in individual titer levels.

CONCLUSIONS

There are considerable differences in the detection and quantification of IFNB-induced NAbs among laboratories offering NAb testing for clinical practice using different assay methods. It is important that these differences are considered when interpreting NAb results for clinical decision-making and when developing general recommendations for potentially clinically meaningful NAb titer levels.