Effects of Oral Cladribine on Remyelination and Inflammation in Multiple Sclerosis Patients

Inclusion criteria: Participants who meet all of the following criteria will be included: * Consent to participate in the study by signing the ICF; * Age between 18 and 55 years, inclusive; * Relapsing-remitting multiple sclerosis diagnosed according to 2017 revised McDonald's criteria; * Highly active disease, defined as 1) occurrence of ≥2 relapses within 12 months prior to study enrolment, regardless of whether or not treatment with another disease-modifying drugs (DMD) was present; or 2) occurrence of ≥1 relapse in the previous 12 months during treatment with another DMD, together with ≥1 gadolinium-enhanced T1 lesion or ≥9 T2/FLAIR lesions on MRI performed during the same period; * Disease duration (time since first relapse) ≤4 years; * EDSS score ≤5.0; * Eligibility for treatment with cladribine tablets, according to the label approved in Brazil; * For women or men of childbearing potential: agreement to use effective contraceptive method as recommended in cladribine tablets label. Exclusion criteria: Participants who meet any of the following criteria will be excluded: * Contraindications to the use of cladribine tablets (as per the label), including (but not limited to) baseline lymphopenia (\<1,000 cells/ mm³), active neoplasm or neoplasm within the last 5 years, active infections (especially tuberculosis, hepatitis B or C and HIV), latent tuberculosis without proper treatment, moderate to severe renal or hepatic impairment, use of immunosuppressants or immunosuppression for another cause; * Pregnancy or lactation; * Presence of other medical conditions or current or previous use of another therapy capable of interfering with neurological, neuropsychological, radiological or laboratory evaluation, as per investigator's judgment; * Contraindications to MRI or gadolinium use; * Inability to adhere to study procedures, as per investigator's judgment.