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Evaluation of binding and neutralizing antibodies to interferon beta-1b in multiple sclerosis patients receiving treatment : development and validation of a new Elisa compared to existing antibody detection techniques and the search for a clinical correlate Paszner, Beatrix M.

Abstract

In recent years interferon beta has gained widespread use as a first line treatment for relapsingremitting Multiple Sclerosis (MS). Treatment with interferons can lead to the development of antibodies. Lack of standardization in the measurement of antibodies has made comparison of antibody data, particularly with reference to cut-off points and determination of positivity, impossible. As a result, the frequency of antibody formation to interferon beta in MS patients has been reported to be as low as 5% and as high as 64%. The assays available for antibody detection are divided into 2 classes: binding antibody assays, usually in the form of an enzyme-linked immunosorbent assay (ELISA) and neutralizing antibody bioassays such as the antiviral neutralization bioassay and more recently, the MxA induction assay. In our studies we have developed an ELISA assay to compete with these neutralizing bioassays. However, a major problem in determining the validity of any of the antibody assays is the lack of a true gold standard. The antibody results as measured by ELISA were compared to those obtained previously from samples tested by both the antiviral and MxA induction assays for the detection of antibodies to interferon beta in patients who have received long-term treatment. The results from the assays were compared on a per patient basis, where positivity was determined for a single patient over the entire period of study using defined positivity criteria and on a per sample basis, where positivity was determined within a single sample only. These comparisons showed that the ELISA was both sensitive and specific for detecting antibody positivity. Due to a high number of ELISA binding antibody negative but neutralizing antibody positive results in samples with very low neutralizing antibody titres, we suggest a need to re-evaluate the titre cut-off point used by the neutralization bioassays, as they may be too low. Long-term follow-up of the antibody status of patients who had received treatment on average for >6 years, showed that sero-reversion of both binding (ELISA) and neutralizing (MxA induction assay) antibodies occurred. Finally, further work is required to prove that the measurement of antibodies (binding or neutralizing) is important on a clinical level. Although we appear to be able to reliably detect antibodies by each of the assay methods available, no clinical correlation has as yet been established with respect to the presence or absence of these antibodies. As a result, a study has been designed with the primary purpose of validating the use of the three assays in a clinical context. We cannot hope to establish antibody testing as a clinically relevant tool unless it can be related to some clinical effect. Until standardization and validation in these areas is achieved, no definitive conclusions surrounding the issue of the significance of antibodies can be made.

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