Cladribine Tablets After Treatment With Natalizumab (CLADRINA)

This will be an open label, single arm, multicenter, collaborative phase 4 research study, designed to generate hypotheses regarding the transition to cladribine tablets after treatment with natalizumab in patients with relapsing forms of multiple sclerosis MS, to include relapsing-remitting multiple sclerosis (RRMS) and active secondary progressive multiple sclerosis (SPMS). The total duration of this interventional study will be 2 years, but patients who require additional time (up to 6 months) for recovery of Absolute lymphocyte count (ALC) to 800 cells/ul prior to the second treatment course will be followed for up to 6 additional months in order to have a full second year of follow up after initiation of the second year's treatment course (for a total study duration of up to 30 months in some patients). A total of 40 study participants with relapsing forms of MS, to include RRMS and active SPMS, who meet the criteria for treatment with cladribine tablets as per the approved United States Prescribing Information (USPI) are planned to be enrolled at up to three centers in the United States. All study participants will receive treatment with cladribine 10 mg tablets during year 1 and year 2 according to the approved USPI (EMD Serono, 2019). Cladribine 10 mg tablets will be provided as commercial material. Treatment with cladribine tablets is intended to be initiated approximately 14 days after the last infusion of natalizumab (e.g., a 14-day "washout"), with a maximum permissible washout period of no more than four weeks. After successful completion of the study, all participants in CLADRINA will be offered to participate in the CLADRINA 2-Year Extension study. During this extension trial, there will be no intervention. Patient will be followed for an additional 24 months, and their clinical and paraclinical disease activity will be assessed through neurological examinations, EDSS scores, brain MRI, and biological markers.