Measuring and evaluating interferon b-induced antibodies in patients with multiple sclerosis

Antidrug Antibodies Against Biological Treatments for Multiple Sclerosis

The development of antidrug antibodies (ADAs) is a major problem in several recombinant protein therapies used in the treatment of multiple sclerosis (MS). The etiology of ADAs is multifaceted. The predisposition for a breakdown of immune tolerance is probably genetically determined, and many factors may contribute to the immunogenicity, including structural properties, formation of aggregates, and presence of contaminants and impurities from the industrial manufacturing process. ADAs may have a neutralizing capacity and can reduce or abrogate the bioactivity and therapeutic efficacy of the drug and cause safety issues. Interferon (IFN)-β was the first drug approved for the treatment of MS, and-although it is generally recognized that neutralizing antibodies (NAbs) appear and potentially have a negative effect on therapeutic efficacy-the use of routine measurements of NAbs and the interpretation of the presence of NAbs has been debated at length. NAbs appear after 9-18 months of therapy in up to 40% of patients treated with IFNβ, and the frequency and titers of NAbs depend on the IFNβ preparation. Although all pivotal clinical trials of approved IFNβ products in MS exhibited a detrimental effect of NAbs after prolonged therapy, some subsequent studies did not observe clinical effects from NAbs, which led to the claim that NAbs did not matter. However, it is now largely agreed that persistently high titers of NAbs indicate an abrogation of the biological response and, hence, an absence of therapeutic efficacy, and this observation should lead to a change of therapy. Low and medium titers are ambiguous, and treatment decisions should be guided by determination of in vivo messenger RNA myxovirus resistance protein A induction after IFNβ administration and clinical disease activity. During treatment with glatiramer acetate, ADAs occur frequently but do not appear to adversely affect treatment efficacy or result in adverse events. ADAs occur in approximately 5% of patients treated with natalizumab within 6 months of therapy, and persistent NAbs are associated with a lack of efficacy and acute infusion-related reactions and should instigate a change of therapy. When using the anti-CD20 monoclonal antibodies ocrelizumab and ofatumumab in the treatment of MS, it is not necessary to test for NAbs as these occur very infrequently. Alemtuzumab is immunogenic, but routine measurements of ADAs are not recommended as the antibodies in the pivotal 2-year trials at the population level did not influence lymphocyte depletion or repopulation, efficacy, or safety. However, in some individuals, NAbs led to poor lymphocyte depletion.

Immunogenicity of Human Interferon-Beta-Containing Pharmaceuticals

Multiple sclerosis is a severe autoimmune disease with inflammatory component that continues to be resistant to treatment. One of the approaches retarding its progression is based on using nonspecific therapy with human interferon-beta (IFN-β)-containing pharmaceuticals. Neutralizing antibodies (NAbs) against genetically engineered pharmaceuticals developed by the patient's immune system, which reduce their therapeutic and biological activity, pose a serious problem. Cell lines sensitive to IFN-β activity also quantifying NAb level are applied because direct measurement of IFN-β antiviral activity is complicated. This study was aimed at standardization and validation of a reporter cell system for measuring anti-human IFN-β NAb titers, and evaluation data were obtained with samples from 33 patients with multiple sclerosis.

Qualitative and quantitative analysis of antibody response against IFNβ in patients with multiple sclerosis

To date, inter-and intra-laboratory consistency of binding assays for measuring anti-interferon (IFN)β antibodies has not been assessed. In this investigation, two independent laboratories tested a library of 80 serum specimens obtained from multiple sclerosis (MS) patients treated with IFNβ. For binding antibodies (BAbs) evaluations, each laboratory used both a capture-ELISA (cELISA) and an enzyme-immuno-assay (EIA), which is commercially available. Samples were also tested for neutralizing antibodies (NAbs). Data demonstrated good intra-laboratory reliability (rpearson≥0.86), and a good overall agreement between the results obtained from the two centers, using both the cELISA (69/80 of observed agreements) and the EIA (67/80). Accordingly, kappa coefficients (K) showed good concurrence (K ≥ 0.651). There was also substantial agreement between cELISA and EIA measurements, as performed in both centers (Orbassano, 66/80, K = 0.631; Basel, 70/80, K = 0.717). However, by comparing NAbs and BAbs titers obtained with both assays, we found that a high degree of BAb-negative samples were positive in NAb-assay. Thus, our study does not support the usefulness of ELISA-based BAb assays as a screening tool for NAbs. Otherwise, BAb-assays can be used as a confirmation test, indicating that the decrease of the biological effects is due to antibodies. In this context, both ELISA-based assays are equally reliable techniques.

Persistence of neutralizing antibodies after discontinuation of IFNβ therapy in patients with relapsing-remitting multiple sclerosis

Objective The main objective was to follow serum levels of neutralizing antibodies (NABs) against interferon-beta (IFNβ) after discontinuation of IFNβ therapy.

Background A large proportion of patients treated with recombinant IFNβ for multiple sclerosis (MS) develop therapy-induced NABs. Knowledge of persistence of NABs after discontinuation of therapy is limited. Design/patients: A retrospective follow-up study of patients treated in Denmark for relapsing-remitting (RR) MS with IFNβ for at least 12 months. NAB-positive patients, who discontinued therapy, were followed up with measurements of NABs.

Methods We measured NAB-neutralizing capacity and NAB titres a.m. Kawade using a clinically validated cytopathic effect assay.

Results Thirty-seven patients were included. Mean follow-up time was 22 months. Of the 29 patients with a NAB titre at or above 25 prior to termination of therapy, only three patients reverted to a titre below 25. Of these, two had a titre below 200 and one patient a titre of 600 at the last examination before treatment stop. The longest post-treatment follow-up during which a patient maintained NAB positivity was 59 months.

Conclusion NABs against IFNβ, especially with high titres, tend to persist for a long time after discontinuation of IFNβ therapy. NABs should always be measured before reinstitution of IFNβ treatment in NAB-positive patients.

Registers of multiple sclerosis in Denmark

There are two nationwide population-based registers for multiple sclerosis (MS) in Denmark. The oldest register is The Danish Multiple Sclerosis Registry (DMSR), which is an epidemiological register for estimation of prevalence and incidence of MS and survival, and for identifying exposures earlier in life that may affect the risk of MS. This register has no systematic follow-up data except for survival. The DMSR has over the years published nationwide incidence- and prevalence data from Denmark and has been involved in a number of 'historical prospective' studies to elucidate the association between a number of different environmental exposures in the past and the subsequent risk of MS. Some of these studies have been able to exonerate suspected risk factors. The other register, the nationwide Danish Multiple Sclerosis Treatment Register, is a follow-up register for all patients who have received disease-modifying treatments since 1996. It has, in particular, contributed to the knowledge of the role of antibodies against the biological drugs used for the treatment of MS.

BAb and MxA as functional biomarkers in routine clinical laboratories for the determination of anti-IFN-beta antibodies and their bioactivity levels in multiple sclerosis patients

In MS patients under IFNβ treatment to seek alternative treatments timely is important that anti-IFNβ antibodies and/or in vivo biologic activity loss detection in these. The most common diagnostic markers used for this purpose are BAb, Nab, and MxA. In this article, we aimed to establish the availability and feasibility of the correlation between BAb and MxA gene expression (mRNA) levels using evaluation of responses to IFNβ treatment for MS patients with a routine laboratory follow-up strategy in a major Turkish MS center. Bab seropositivity was determined in blood samples of 218 MS patients treated with different IFNβ preparations and MxA mRNA levels were measured in 128 patients among the total population. BAb seropositivity ratios to im INF-β 1a, scINF-β 1a, and sc INF-β 1b were 21.4%, 28.6%, and 70.4%, respectively (total 40%), and total loss of bioactivity (MxA mRNA) were 9.3%, 9.5%, and 11.6%, respectively (total 10.2%). The correlation between high BAb titers and low MxA mRNA levels was highly significant (P = 0.00003). Our data indicate that there is a good correlation between especially high BAbs levels and diminished MxA mRNA levels.

Correlation between anti-interferon-β binding and neutralizing antibodies in interferon-β-treated multiple sclerosis patients

BACKGROUND AND PURPOSE

Measurements of binding antibodies (BAbs), neutralizing antibodies (NAbs) and MX1 mRNA expression are used to analyse the immunological reactions in patients with MS treated with IFN-β. The correlations between these are yet not fully understood.

METHODS

We measured BAbs and NAbs to IFN-β in 110 serum samples from 83 patients with MS treated with IFN-β, and in a subgroup, antibody titre was compared with corresponding expressions of MX1 mRNA. The methods used were capture ELISA assay, luciferase reporter gene assay and mRNA RT-PCR for MX1 gene expression.

RESULTS

There were significant correlations between binding, neutralizing and MX1 results. Cut-off values are suggested for the definition of samples of BAbs and NAbs as negative, positive and grey zones. Naturally occurring groups of low and high antibody titres were identified by the correlation between BAbs and NAbs, probably as a result of an immunological maturation process of antibodies. The low-titre group had lower correlations between BAbs and NAbs than the high-titre group.

CONCLUSIONS

High correlation is demonstrated between the results obtained by the three methods, and we suggest the possibility of using ELISA measurements of BAbs to identify patients with high titres of anti-IFN-β antibodies that block the biological response to IFN-β. Ιn patients with low titres, we suggest to supplement ELISA with measurement of MX1 mRNA to establish whether the bioavailability of IFN-β is preserved.

Neutralizing antibodies against interferon-Beta

The development of neutralizing antibodies (NAbs) is a major problem in multiple sclerosis (MS) patients treated with interferon-beta (IFN-ß). Whereas binding antibodies (BAbs) can be demonstrated in the vast majority of patients, only a smaller proportion of patients develop NAbs. The principle in NAb in vitro assays is the utilization of cultured cell lines that are responsive to IFN-ß. The cytopathic effect (CPE) assay measures the capacity of NAbs to neutralize IFN- ß's protective effect on cells challenged with virus and the MxA induction assay measures the ability of NAbs to reduce the IFN-ß-induced expression of MxA, either at the mRNA or the protein level. A titer of >20 neutralizing units/ml traditionally defines NAb posi-tivity. NAbs in high titers completely abrogate the in vivo response to IFN-ß, whereas the effect of low and intermediate titers is unpredictable. As clinically important NAbs appear only after 9-18 months IFN- ß0 therapy, short-term studies of two years or less are unsuitable for evaluation of clinical NAb effects. All long-term trials of three years or more concordantly show evidence of a detrimental effect of NAbs on relapses, disease activity on MRI, or on disease progression. Persistent high titers of NAbs indicate an abrogation of the biological response and, hence, absence of therapeutic efficacy, and this observation should lead to a change of therapy. As low and medium titers are ambiguous treatment decisions in patients with low NAb titres should be guided by determination of in vivo mRNA MxA induction and clinical disease activity.

Critical review: assessment of interferon-β immunogenicity in multiple sclerosis

This review discusses type I interferon (IFN) immunogenicity with focus on methods of detection of anti-IFN antibodies in patients treated with human recombinant IFN-β. Pitfalls involved in the clinical use of various types of assays for binding antibodies and neutralizing antibodies against IFN-β are presented, and the widely held distinction between binding antibodies and neutralizing antibodies is questioned both in terms of detection and clinical importance. The article also addresses important bioavailability and pharmacokinetic issues occurring with prolonged use of protein drugs. The rationale for individualized or personalized medicine, ie, optimizing therapies according to individual needs rather than using standardized trial-and-error regimens to all patients, is highlighted.

Breakthrough disease during interferon-β therapy in MS

Background: Disease activity is highly variable in patients with multiple sclerosis (MS), both untreated and during interferon (IFN)-β therapy. Breakthrough disease is often regarded as treatment failure; however, apart from neutralizing antibodies (NAbs), no blood biomarkers have been established as reliable indicators of treatment response, despite substantial, biologically measurable effects. We studied the biologic response to treatment in a cohort of NAb-negative patients to test whether difference in responsiveness could segregate patients with and without breakthrough disease during therapy.

Methods: Gene expression in blood cells from 23 patients with relapsing-remitting MS was analyzed by microarray and PCR. Samples were collected pretreatment and 9–12 hours after IFNβ injection at 3 and 6 months' treatment. Definition of breakthrough disease was based on the occurrence of relapses, disability progression, or subclinical activity on 3T MRI at 3 and 6 months.

Results: Sixteen patients had breakthrough disease and 7 patients were stable. Microarray and PCR showed marked effects of IFNβ on gene expression profiles, but biologic responses did not differ between patients with breakthrough disease and stable patients. However, pretreatment variables did differ: patients with breakthrough disease had lower baseline IL10 expression, more gadolinium-enhancing lesions, and a higher number and volume of T2 lesions.

Conclusions: Breakthrough disease during interferon (IFN)-β treatment is not paralleled by differences in biologic responsiveness to treatment in NAb-negative patients; most likely, the spontaneously occurring variation in underlying disease activity between patients causes the varying level of breakthrough disease observed in IFNβ-treated patients with multiple sclerosis.

Treatment with azathioprine and cyclic methylprednisolone has little or no effect on bioactivity in anti-interferon beta antibody-positive patients with multiple sclerosis

Background

It is unknown whether immunosuppression of patients who have developed interferon-β (IFN-β) neutralizing antibodies (NAbs) hastens disappearance of NAbs in the blood.

Objective

We wanted to test whether immunosuppression with cyclic methylprednisolone (MP) in combination with azathioprine (AZA) for 6 months accelerates recovery of IFN-β bioactivity in patients with multiple sclerosis (MS) with abolished in-vivo myxovirus resistance protein A (MxA) mRNA response to IFN-β.

Methods

We included 13 patients with MS with NAbs and a low IFN-β bioavailability detected by the MxA-mRNA response in a descriptive, non-randomized trial. Another 14 NAb-positive patients with a low MxA-mRNA response served as controls. The primary outcome was the fraction of patients who regained an MxA-mRNA response to IFN-β. NAbs were measured by means of a clinically validated cytopathic effect assay and a new reporter gene assay. The in-vivo MxA-mRNA response was measured by real-time polymerase chain reaction.

Results

A total of 11 patients in the treatment group completed the trial. In all, two of these 11 patients regained an in-vivo MxA-mRNA response as compared to one of 14 patients in the control group.

Conclusion

Treatment with AZA and cyclic MP for 6 months has little or no effect on IFN-β bioactivity in NAb-positive patients with MS.

Interferon-beta bioactivity measurement in multiple sclerosis: feasibility for routine clinical practice

BACKGROUND

Neutralising antibodies (NAb) to interferon beta (IFN beta) are associated with a reduced bioactivity and efficacy of IFN beta in multiple sclerosis (MS). Unclear is how to apply IFN beta bioactivity measurements (quantification of Myxovirus resistance protein A (MxA) mRNA) in clinical practice.

OBJECTIVES

To evaluate value and feasibility of IFN beta bioactivity measurement with a single MxA mRNA measurement for screening and a second measurement before and after IFN beta administration for definite confirmation of IFN beta bioactivity status.

METHODS

In 79 MS patients MxA mRNA expression was determined 4 hours after IFN beta administration. If inadequate, MxA mRNA expression testing was repeated 3 months afterwards, comparing post- and pre injection samples to determine whether IFNb bioactivity was persistently lacking. MxA mRNA expression was compared to NA beta titres, determined by the cytopathic effect assay (CPE).

RESULTS

NAb titres correlated significantly with MxA mRNA expression and MxA mRNA induction. Of all screened patients, only one patient had adequate MxA mRNA expression and high NAb titres simultaneously. Of the biological non-responders at second measurement (21/55), 17 (81%) were high-titre NAb positive, 1 (5%) was low-titre NAb positive and 3 (14%) were NAb negative. Without considering the pre-injection measurement, two more NAb negative patients would have tested negative for IFN beta bioactivity, emphasizing the need of a pre-injection sample.

CONCLUSIONS

Our data suggest that for IFN beta bioactivity screening a single post-injection measurement seems reasonable. However, MxA induction measurement based on both pre- and post-IFN beta injection samples at second measurement is somewhat more precise in determining ultimate IFN beta bioactivity status.

The effect of beta-interferon therapy on myelin basic protein-elicited CD4+ T cell proliferation and cytokine production in multiple sclerosis

Interferon (IFN)-beta therapy has well-established clinical benefits in multiple sclerosis (MS), but the underlying modulation of cytokine responses to myelin self-antigens remains poorly understood. We analysed the CD4+ T cell proliferation and cytokine responses elicited by myelin basic protein (MBP) and a foreign recall antigen, tetanus toxoid (TT), in mononuclear cell cultures from fourteen MS patients undergoing IFN-beta therapy. The MBP-elicited IFN-gamma-, TNF-alpha- and IL-10 production decreased during therapy (p<0.007-0.03), while the IL-6 production increased (p<0.03). No significant change was observed in the MBP-induced CD4+ T cell proliferation, or in the production of IL-4, IL-5 and brain-derived neurotrophic factor. In comparison, IFN-beta therapy reduced IFN-gamma and IL-4 responses to TT (p<0.003 and p<0.04). Thus, IFN-beta inhibits IFN-gamma production in general, presumably alleviating the detrimental influence of IFN-gamma in MS. However, the increase in proinflammatory IL-6 and the decrease in anti-inflammatory IL-10 responses suggest that IFN-beta has more diverse effects than previously assumed.

Comparative study of four different assays for the detection of binding antibodies against interferon-beta

BACKGROUND

Binding antibodies (BAB) against interferon-beta (IFNbeta) are often determined as screening assays before performing an expensive and elaborate neutralizing antibody (NAB) test.

METHODS

In this study, we compared four BAB tests, a western blot (WB), a direct binding enzyme-linked immunosorbent assay (ELISA) (dELISA), a capture ELISA (cELISA), and a commercial enzyme immuno-assay (EIA) in 325 multiple sclerosis patients with and without neutralizing antibodies to evaluate the sensitivity and specificity to detect NAB by receiver operating characteristics analysis.

RESULTS

The area under the curve (AUC) values were 0.907 for the dELISA, 0.925 for the cELISA, and 0.776 for the EIA (P < 0.0001 for all). At a sensitivity of 95%, the specificity was approximately 30% in the dELISA, 55% in the cELISA, and 13% in the EIA. The WB as a qualitative BAB detection method had a given sensitivity of 97% and a specificity of 55%. There was a strong and significant correlation between high NAB titers (>500 neutralizing units [NU]) and titers obtained by all quantitative BAB assays. However, low to medium NAB titers (20-500 NU) did not significantly correlate with BAB titers.

CONCLUSION

We conclude that the cELISA seems to be most suitable for NAB screening, but BAB titers cannot reliably predict NAB titers.

Glatiramer acetate: evidence for a dual mechanism of action

Glatiramer acetate is a disease-modifying drug approved for the treatment of relapsing-remitting multiple sclerosis. Since its discovery almost four decades ago, and in particular since the observation of its beneficial clinical effects in the late 1980s and early 1990s, numerous data have been generated and contribute pieces of a puzzle to help explain the mechanism of action of glatiramer acetate. Two major themes have emerged, namely (i) the induction of glatiramer acetate-reactive TH2 immunoregulatory cells, and (ii) the stimulation of neurotrophin secretion in the central nervous system that may promote neuronal repair.

Using measurements of neutralizing antibodies: the challenge of IFN-? therapy

Although the occurrence of neutralizing antibodies (NAbs) to interferon (IFN)-beta has been acknowledged since the pivotal trials of IFN-beta in multiple sclerosis (MS), the effect of these antibodies has for several reasons been debated. The main reason for the controversies has been insufficient knowledge of the fact that clinically relevant NAbs do not appear until 12-18 months after initiation of IFN-beta therapy which make studies of 2 years or less unsuited to assess the clinical relevance of NAbs. Further, changes in NAb affinity occur and contribute to increase NAb effects by time. The present paper reviews our current knowledge of NAbs and stresses the importance of using measurements of NAbs routinely. It is concluded that NAb titres are important for the biological response to IFN-beta. Patients with low or intermediate titres may have preserved a full or partial biological response and might still benefit from IFN-beta therapy. However, persistent high titres of NAbs indicate an abrogation of the biological response and, hence, absence of therapeutic efficacy, and this observation should lead to a change of therapy. The application of the existing information about NAbs in clinical practice would lead to improved efficacy of IFN-beta treatment for the benefit of patients with MS.

An association between autoreactive antibodies and anti-interferon-beta antibodies in multiple sclerosis

Approximately 5-25% of interferon-beta (IFN-beta) treated multiple sclerosis (MS) patients develop anti-IFN-beta neutralizing antibodies (NAb) but the patient-specific variables associated with the risk of developing anti-IFN-beta antibodies are poorly understood. Anti-IFN-beta NAb are a subset of anti-IFN-beta binding antibodies (BAb) and all patients with NAb generally have high levels of associated BAb. The purpose of this research was to assess the association between autoreactive antibodies (ARAB) and the risk of developing anti-IFN-beta BAb in MS patients. This was a retrospective study that included consecutive patients diagnosed with clinically definite MS evaluated at our center and considered appropriate for IFN-beta therapy. The patients were tested for various subtypes of antiphospholipid antibodies (APLA) including anti-phosphatidylethanolamine (APE), anti-phosphatidylserine (APS), and anti-cardiolipin (ACA) antibodies, and other ARAB, antinuclear and anti-neutrophilic cytoplasmic antibodies, anti-thyroid peroxidase antibodies (ATA), anti-SS-A and anti-SS-B antibodies. BAb levels were assessed using a commercial binding ELISA assay. A total of 33 patients (mean age: 45.4 years, 85% female) were enrolled; 15 patients were negative and 18 patients were positive for BAb. APLA or ATA were present in 95% (17 of 18 patients) of patients positive for BAb. In comparison, APLA or ATA occurred in only 27% (four of 15 patients) of patients in the BAb negative group. The associations between the occurrence of BAb and the occurrence of high APLA or ATA were significant (chi2 = 13.4, P<0.001in Fisher exact test). The odds ratio for the association was 46.8 (with a 95% confidence interval range of 4.6-475). No significant correlations were found for other ARAB. The presence of autoreactive antibodies, particularly APLA and ATA is associated with increased risk of occurrence of IFN-beta BAb in MS patients on long-term IFN-beta therapy.

Measuring and management of anti-interferon beta antibodies in subjects with multiple sclerosis

Interferon Beta is well established as a first line agent to treat relapsing remitting Multiple Sclerosis. It frequently induces the formation of neutralising anti-Interferon Beta Antibodies (Nabs) which may abrogate the clinical efficacy of the drug. Numerous studies have shown a loss of bioactivity of the drug in the presence of Nabs. The focus has shifted to reliable quantification of Nabs and their appropriate incorporation into clinical practice. Here we review the development and persistence of Nabs, the effect on Interferon beta bioactivity, clinical and para-clinical autocome measures in trials, Nab assays and discuss management strategies to optimise the use of Interferon beta in relapsing remitting MS.

Are ex vivo neutralising antibodies against IFN-beta always detrimental to therapeutic efficacy in multiple sclerosis?

Neutralising antibodies (NAbs) against interferon (IFN)-beta reduce the treatment effect in multiple sclerosis (MS). However, data from pivotal trials of IFN-beta in MS suggest that NAb-positive patients may have a reduced relapse rate during the first six to 12 months of therapy. We collected clinical data and plasma samples for NAb measurements prospectively, every six months, in 468 patients treated with the same IFN-beta preparation for at least 24 months. NAbs were measured blindly with a cytopathic effect (CPE) assay. During treatment months 0-6, patients who became NAb-positive had significantly fewer relapses compared to patients who maintained the NAb-negative status, whereas the opposite was observed after month 6. This is in accordance with observations in randomised studies of the three different IFN-beta preparations, showing that patients who become NAb-positive have lower relapse rates during the first six or 12 months of therapy. We hypothesise that low affinity NAbs, present early after the start of IFN-beta therapy, though neutralising in vitro in sensitive assays increase the half-life of IFN-beta in vivo and, thereby, enhance the therapeutic effect. With affinity maturation, NAbs effectively prevent IFN-beta binding to its receptors also in vivo and, hence, abolish the treatment effect.

Neutralizing antibodies to interferon beta in multiple sclerosis: Analytical evaluation for validation of a cytopathic effect assay

BACKGROUND

Recent guidelines have recommended the use of validated assays for the measurement of neutralizing antibodies (NABs) to interferon beta (IFNbeta) in patients with multiple sclerosis (MS). In an attempt of validation, we studied the analytical performance of a bioassay based on antiviral cytopathic effect (CPE) using WISH cells and the vesicular stomatitis virus (WISH/VSV CPE).

METHODS

NAB titres measured with the WISH/VSV CPE assay in 63 sera from IFNbeta-treated MS patients were compared to those obtained with the reference CPE method using A549 cells and the encephalomyocarditis virus. Binding antibodies (BABs) were measured using a capture ELISA as a screening test for NABs.

RESULTS

No false-negative BAB was obtained in our patients. The between-run coefficients of variation (CVs) determined with log10 titres of the NIH anti-IFNbeta (G038-501-572) yielded good results (<or=10.4%) and within-run variability was excellent (CV<or=2%). The log10 titres obtained with both CPE assays were highly correlated (r=0.969 and r=0.884 for anti-IFNbeta-1a and anti-IFNbeta-1b, respectively). The same patients were found NAB-positive with both CPE assays.

CONCLUSION

Because of its good precision, sensitivity and excellent correlation with the reference CPE method, the WISH/VSV CPE bioassay can be used in the follow-up of IFNbeta-treated MS patients.