In studies presented at the annual ACTRIMS/ECTRIMS meeting, patients with relapsing-remitting multiple sclerosis (MS) treated with three commercially available interferon beta formulations yielded similar clinical outcomes.^1,2 However, one formulation, intramuscular (IM) interferon beta-1a (Avonex) was associated with a significantly lower incidence of neutralizing antibodies.¹ Furthermore, in the same study, the development of neutralizing antibodies was shown to diminish the clinical benefit of interferon beta therapy.¹

Per Soelberg Sorensen, MD, Professor of Neurology and Director of the Copenhagen Multiple Sclerosis and Neuroscience Center, Copenhagen University Hospital, Copenhagen, Denmark, stated "Neutralizing antibodies do matter" in the long-term efficacy of interferon beta in MS treatment.¹ In fact, lack of response to interferon beta therapy should raise the suspicion of neutralizing antibodies, and if confirmed, such patients should be considered for alternative therapy, he suggested.

As background, Dr. Sorensen said the frequency with which interferon beta therapy for MS induces neutralizing antibodies has reportedly varied from 2% to 42% in different clinical trials and has depended on the specific interferon beta formulation investigated and the dose administered. Initially, studies found no relation between the development of neutralizing antibodies and the clinical efficacy of interferon beta, but re-evaluation of preliminary findings and more prolonged observation of patients subsequently revealed that neutralizing antibodies contribute to the lack of therapeutic response from interferon beta in some patients with MS.

"For example, the 2-year data from the PRISMS study (in patients receiving subcutaneous (SC) interferon beta-1a (Rebif) three times weekly) showed no difference in annualized relapse rate for patients with or without neutralizing antibodies, but the data at 3 and 4 years showed a significant difference," Dr. Sorensen stated. At 3 and 4 years^[3], annualized relapse rate was 0.50 for neutralizing antibody-negative patients and 0.81 for patients who developed neutralizing antibodies (P = 0.002), he noted.

To determine how neutralizing antibodies affect the long-term clinical course of interferon beta therapy, the Danish National Interferon Beta Project followed 467 patients with MS treated with different interferon beta formulations for up to 5 years. The project also aimed to set standards for defining neutralizing antibody-positive status, determining the appropriate assay sensitivity, and identifying factors that might produce the occurrence of neutralizing antibodies.

Measurements of neutralizing antibodies were performed every 6 months in a blinded fashion using antiviral neutralization (A549/EMC) bioassays with high [3 LU/mL], median [10 LU/mL] and low [100 LU/mL] sensitivity. Rather than antibody titers, the project used the more accurate "neutralizing capacities" as cut-off values for the definition of neutralizing antibody positivity. The neutralizing capacity is defined as the extent of interferon beta neutralization by neutralizing antibodies in a given sample.

The bioassay used in the present study is only employed in investigational settings, but for reference, a high sensitivity assay (3 LU/mL) is similar to a 1:20 titer, he explained. A 1:20 titer is the level at which neutralizing antibodies have been shown to affect clinical and magnetic resonance imaging (MRI) outcomes in several studies.^3-5 As would be expected, the percentage of neutralizing antibodies was dependent on the sensitivity of the assay.

The lowest proportion of neutralizing antibodies was seen in patients treated with Avonex 30 mcg once weekly (Table 1). The low proportion observed with Avonex was consistent over the course of the study, while the highest proportion was initially observed with interferon beta-1b (Betaferon). At 36 months, the highest proportion was observed with subcutaneous Rebif 22 mcg three times weekly, Dr. Sorensen reported.

More Relapses in Neutralizing Antibody-Positive Patients

"We observed a significantly higher relapse rate during neutralizing antibody-positive periods compared with neutralizing antibody-negative periods," Dr. Sorensen reported. "The time to first relapse was significantly longer in neutralizing antibody-negative patients compared with neutralizing antibody-positive patients."

The odds ratio for the higher relapse rate was 1.55 (range, 1.25-1.94; P<0.01) in neutralizing antibody-positive patients, as determined by both the low- and medium-sensitivity bioassays. With the low-sensitivity bioassay, the yearly relapse rate was 0.73 for neutralizing antibody-positive and 0.48 for neutralizing antibody-negative patients; with the medium-sensitivity bioassay, the rates were 0.67 and 0.44, respectively.

Differences were less with the high-sensitivity assay, which picked up inconsequential antibody loads, he explained. "Very low concentrations of neutralizing antibodies do not influence the odds ratio for relapses," he noted. Future investigations will use the lowest cut-off value for neutralizing capacity (≥20%) for the definition of neutralizing antibody positivity. Time to first relapse was also influenced by neutralizing antibody positivity. The time to first attack occurred an average of 177 days earlier in the neutralizing antibody-positive patients, he reported. There was no difference between the groups, however, in mean Expanded Disability Status Scale (EDSS) or time to sustained progression, although a clear trend was demonstrated beginning at year 3.

There were no pre-clinical features that were predictive of the development of neutralizing antibodies, although there was a trend for greater development of neutralizing antibodies in patients with a short duration of disease and a high progression index, stated Dr. Sorensen.

While some patients develop neutralizing antibodies that ultimately disappear, Dr. Sorensen pointed out that neutralizing antibodies generally persist. "In our study, 80% of patients who were neutralizing antibody-positive at 12 months were still positive at 2 years; 70% were still positive at 3 years; and 60% were still positive at 4 years," he noted.

Dr. Sorensen emphasized the need to perform neutralizing antibody assays during treatment, "at a minimum" in patients with significant clinical activity, and to manage neutralizing antibody-positive patients differently. If the patient is neutralizing antibody-positive, you should think of changing treatment, he advised.

In addition, he suggested, "Frequency of neutralizing antibodies is one factor to consider when selecting an interferon beta."

Observational Trial Shows Interferon Beta Products are Equivalent

Maria Trojano, MD, of the University of Bari, Bari, Italy presented the results of a large observational study comparing three commercially available interferon beta formulations in 1,033 mildly disabled (EDSS 0-3.5) relapsing-remitting MS patients.² Relapse rate, EDSS, adverse events, presence of neutralizing antibodies, and treatment discontinuations were evaluated every 3 months. Twelve-month data were available for Betaferon (n = 234), Avonex (n = 219) and Rebif (n = 89), and 24-month data were available for Betaferon (n = 209) and Avonex (n = 169).

Each interferon beta formulation, independent of dose regimen, had similar effects on relapse rate, each reducing relapses at 12 and 24 months (P<0.001). At 12 months, relapse rates were equally reduced from baseline by 42% with Avonex (30 mcg IM once weekly), 43% with Rebif (22 mcg SC three times weekly), and 50% with Betaferon (250 mcg SC every other day) (P = 0.001). At 24 months, reductions in relapse rates were still statistically similar, 46% with Avonex and 54% with Betaferon, she reported.

Outcomes were also similar with regard to the proportion of patients who were relapse-free at 12 months (54.4 % for Avonex, 53.7% for Betaferon, and 49% for Rebif; P = 0.10) and 24 months (33% Avonex, 37% Betaferon, no 24-month data for Rebif). Changes in EDSS scores at 12 and 24 months were also comparable between the formulations (P = 0.17), Dr. Trojano reported.

However, two significant differences were observed in this study: a higher rate of adverse events associated with Betaferon and a lower incidence of neutralizing antibodies with Avonex.

The side effect profile was better with Avonex, at least in the early period, Dr. Trojano stated. "In general, Betaferon patients had a higher incidence of adverse events during the first 3 months of treatment compared with Avonex patients (P<0.05), and more patients discontinued treatment with Betaferon—10% vs 5% at 24 months."

The increase in adverse events with Betaferon was significant for arthralgias, asthenias, fevers, injection site reactions, leukopenia, anemia, and several laboratory parameters, such as elevated liver enzymes, primarily occurring in the early treatment period. Injection site reactions and anemia remained more frequent with Betaferon compared to the other formulations over the entire period of observation.

While Dr. Trojano does not consider these differences clinically meaningful, she said, "The more favorable efficacy/safety ratio of Avonex versus Betaferon in relapsing-remitting patients with low disability may improve patient compliance during long-term treatment."

The cumulative numbers of patients discontinuing treatment at 24 months were 10% with Betaferon, 7% with Rebif, and 5% with Avonex. Adverse events were given as the reason for treatment discontinuation in 41%, 28%, and 16% of those patients, respectively, she reported.

Consistent with studies from other investigators, the risk of developing neutralizing antibodies (titer ≥20 in at least two consecutive samples 3 months apart) was significantly less with Avonex (2.2%) compared to Betaferon (14.8%) and Rebif (6.7%)(P<0.00005).

Conclusion

In studies by European investigators at this meeting, the three commercially available interferon beta formulations yielded similar clinical outcomes in patients with relapsing-remitting MS. Avonex was associated with a more favorable adverse event profile as well as a lower incidence of neutralizing antibodies. In one large study, neutralizing antibodies were associated with an attenuation of clinical outcomes, confirming that neutralizing antibodies can affect treatment efficacy and should be considered a possible determining factor in MS patients who are not responding to interferon beta treatment.

References

1. Sorensen PS, Koch-Henriksen N, Ross C, et al. Neutralizing antibodies against interferon (IFN)-beta reduce the clinical effect in relapsing-remitting multiple sclerosis. Presented at the 7th Annual Meeting of the Americas Committee for Treatment and Research in Multiple Sclerosis and the 18th Congress of the European Committee for Treatment and Research in Multiple Sclerosis, September 18-21, 2002, Baltimore, Maryland. Abstract 24.
2. Trojano M, Paolicelli D, Ligouri M, et al. Interferon-b treatment in relapsing-remitting multiple sclerosis: results of an observational study in southern Italy. Presented at the 7th Annual Meeting of the Americas Committee for Treatment and Research in Multiple Sclerosis and the 18th Congress of the European Committee for Treatment and Research in Multiple Sclerosis, September 18-21, 2002, Baltimore, Maryland. Poster Presentation 311.
3. PRISMS-4: Long-term efficacy of interferon-b-1a in relapsing MS. PRISMS Study Group. Neurology. 2001;56:1628-1636.
4. Rice G for the PRISMS Study Group. Interferon-neutralizing antibodies reduce clinical and magnetic resonance imaging efficacy in multiple sclerosis patients treated with interferon b-1a (Rebif): observations from the PRISMS 4-year extension study [abstract]. Ann Neurol. 2000;48:477.
5. Neutralizing antibodies during treatment of multiple sclerosis with interferon beta-1b. The IFNB Multiple Sclerosis Study Group. Neurology. 1996;47:889-894.