The clinical effect of neutralizing antibodies against interferon-beta is independent of the type of interferon-beta used for patients with relapsing-remitting multiple sclerosis.

OBJECTIVE: To establish whether the clinical effect of neutralizing antibodies (NAbs) against interferon-beta (IFN beta) depends on the type of IFNbeta (1a or 1b) used for treatment of patients with relapsing-remitting multiple sclerosis (MS).
INTRODUCTION: NAbs against IFN beta-1b appear faster and may be more evenly distributed on IgG subclasses, whereas NAbs against IFN beta-1a develop more slowly and may be devoid of IgG3. This might cause different clinical responses to NAbs. DESIGN/PATIENTS: All Danish MS-patients who had started first-time treatment with IFNbeta-1a 22 microg s.c tiw (Rebif22) or IFN beta-1b 250 microg s.c. qod (Betaferon) before January 1st 2003 were included. Relapses were recorded at bi-annual visit.
METHODS: We measured NAbs every 12 months using a clinically validated cytopathic effect assay. A blood sample with a neutralizing capacity of 20% or more was considered as NAb-positive. We used a mixed logistic regression analysis in which NAb-status (three levels), IFN beta-preparation, and time since treatment started were included as explanatory variables, and relapse rate as response variable.
RESULTS: In 1,309 patients, who were observed for 21,958 months, 32.3% were classified as NAb-positive. The odds-ratio (OR) for relapses in NAb-positive months compared with NAb-negative months was 1.25; P = 0.02. The risk of relapses was higher with Betaferon than with Rebif22 (OR 1.26; P < 0.01). The effect of NAb-level on relapses was independent of whether the patients were treated with Betaferon or Rebif22 (P = 0.89) and of time (P = 0.80).
CONCLUSION: NAbs caused by IFNbeta-1a s.c. do not differ from NAbs caused by IFNbeta-1b in their detrimental clinical effect.