Depending upon the clinical course of their MS, subjects will then proceed from the ITP to either the Maintenance Treatment Period (with open-label interferon-beta treatment) or LTFU period (with either open-label low-dose cladribine or no additional treatment (if no progression to MS has been noted after the initial treatment period). The single primary endpoint for the overall study, which will be determined during the ITP, is time to conversion to MS (from randomization), according to the Poser criteria.