All in all, this indicates that IFNβ treatment in MS, i.e. using a biosimilar to an endogenous protein component of immune regulation (27), may be harmful in the long-term if neutralizing antibodies are induced, in parallel to what has previously been reported for treatment with human recombinant erythropoietin (29, 30). The gene discussed is EPO; the disease is myeloid sarcoma.