This study intends to explore evolution of MSRV expression by analyzing the levels of MSRV transcripts in blood, as well as the levels of the MSRV-Env protein in serum of MS patients. The study will be conducted over one year in four cohorts of patients with different forms of MS (remitting-relapsing MS i.e. RRMS, primary-progressive MS i.e. PPMS and secondary-progressive MS i.e. SPMS) and in clinically isolated syndrome (CIS) patients who have suffered a single clinical event but do not comply with diagnosis criteria for definite MS. The MSRV RNA and MSRV-Env protein levels will be correlated with the clinical evolution of patients and with the reverse transcriptase activity, inflammatory markers assessed by cytokines levels. A control group of healthy subjects will be included (the study, GN-E-003, is performed in parallel and is part of another dedicated protocol).

Inclusion Criteria:

• Signature of an informed consent;
• Male or female between 18 and 60 years of age;
• Patients with PPMS (Revised McDonald criteria 2010) or patients with SPMS or CIS or patients with RRMS (Revised McDonald criteria 2010) ideally without IFN beta therapy at the T0 visit for RRMS patient only.

Exclusion Criteria:

• Positive serology for hepatitis B or C or HIV;
• Acute infection at inclusion;
• Severe psychiatric disorder;
• Autoimmune disease other than MS;
• Pregnancy or breastfeeding;
• Heavy smokers i.e. more than 10 cigarettes per day;
• History of alcohol or drug abuse in the last 3 years;
• Participation in a clinical trial (within the last 3 months).

Patients coming to the Hospital for regular visits.