Human type I Interferons (IFN-β, IFN-ɛ, IFN-κ, IFN-ω, and 12 subtypes of IFN-α) are a family of pleiotropic cytokines with antiviral, antiproliferative, and immunomodulatory activities. They signal through the same cell surface receptors, IFNAR1 and IFNAR2, yet evoking markedly differential potency. One differentiating factor of IFN-β from other type I interferons is the presence of a consensus sequence (NG) for deamidation. Comparing almost completely deamidated IFN-β-1a with untreated IFN-β-1a, this present study reports the increased activities in 3 in-vitro bioassays testing the antiviral, antiproliferative, and immunomodulatory properties, respectively, of the molecule. Deamidated IFN-β-1a has the potential to improve current therapies in multiple sclerosis, and its ability to potentiate the MHC-Class I expression suggests a clinical benefit in diseases where the downmodulation of the MHC-class I expression plays a role (eg, in immuno-oncology combination therapies or antiviral agents). The present study on IFN-β deamidation adds a new prospective on deamidation as part of a posttranslational modification code that allows the modulation of the biological properties of proteins. Moreover, it underlines the unique IFN-β-1a properties that differentiate this molecule from other members of the type I interferon family.