AAN position conclusions on Nabs

Treatment of MS with IFNß (Avonex, Betaseron, or Rebif) is associated with the production of NAbs to the IFNß molecule (Level A).
It is probable that the presence of NAbs, especially in persistently high titers, is associated with a reduction in the radiographic and clinical effectiveness of IFNß treatment (Level B).
It is probable that the rate of NAb production is less with IFNß-1a treatment compared to IFNß-1b treatment (Level B). However, because of the variability of the prevalence data, and because NAbs disappear in the majority of patients even with continued treatment (especially in those with low-titer NAbs), the magnitude and persistence of any difference in seroprevalence between these forms of IFNß is difficult to determine.
It is probable that the seroprevalence of NAbs to IFNß is affected by one or more of the following: its formulation, dose, route of administration, or frequency of administration (Level B). Regardless of the explanation, it seems clear that IFNß-1a (as it is currently formulated for IM injection) is less immunogenic than the current IFNß preparations (either IFNß-1a or IFNß-1b) given multiple times per week subcutaneously (Level A). Because NAbs may disappear in many patients with continued therapy, the persistence of this difference is difficult to determine (Level B).
Although the finding of sustained high-titer NAbs (>100 to 200 NU/mL) has been associated with a reduction in the therapeutic effects of IFNß on radiographic and clinical measures of MS disease activity, there is insufficient information on the utilization of NAb testing to provide specific recommendations regarding when to test, which test to use, how many tests are necessary, and which cutoff titer to apply (Level U).