 As has been seen with other recombinant protein molecules, the use of injectable recombinant proteins may result in the development of neutralising antibodies NAbs. Antibodies are considered neutralising by their ability to inhibit the biological effect of interferon in a bioassay system. EMD Serono has actively pursued improvements in the formulation of interferon IFN beta-1a to reduce aggregate levels and to develop a formulation that is HSA-free. Reducing aggregates should reduce antigenicity of the product while removal of HSA may have an unpredictable effect on antigenicity. EMD Serono will conduct a study to assess the immunogenicity and safety of the new HSA-free formulation, manufactured using IFN-ß-1a drug substance produced by a new clone from the FBS-free process. 