The purpose of this study is to assess the safety and tolerability of single ascending doses, as well as of repeated administrations of GNbAC1 in MS patients.

Scientific research has shown that the expression of genes of a virus which is integrated in the Human genetic material, the Multiple Sclerosis associated RetroVirus (MSRV) could play a critical role in the causation of multiple sclerosis.

GNbAC1 is an experimental medication, which neutralizes (i.e. inactivates) a protein of MSRV that might contribute to the development or deterioration of multiple sclerosis.

Inclusion Criteria:

• Male or female patients (if female, neither pregnant nor breast-feeding, should be post-menopausal or surgically sterile, or should use two highly effective method of contraception such as oral contraception plus mechanical barrier); Male subjects with partners of childbearing potential have to use adequate contraception during the study. Contraception methods should be followed during the study and up to 3 months after the last study drug administration. Female subjects who are women of childbearing potential (WOCBP) will have to be tested negative with a pregnancy test (serum or urine) at screening and Day 1 and before each repeated administrations of GNbAC1.
• Between 18 and 65 years of age;
• Patients with Primary Progressive MS (PPMS) according to the Revised McDonald criteria 2010 or patients with Secondary Progressive MS (SPMS) or patients with Relapsing-Remitting MS(RRMS)according to the Revised McDonald criteria 2010 who cannot be treated with available treatments for MS due to intolerance, non response or refusal of treatment;
• Score ≤ 6.5 on the Expanded Disability Status Scale (EDSS);
• Body weight between 40 and 100kg.

Exclusion Criteria:

• Positive serology for viral hepatitis and HIV;
• Disease other than MS that could better explain his/her signs and symptoms;
• Previously treated with cladribine, lymphoid irradiation or depleting antibodies;
• Usage in the last 3 months of interferon beta or glatiramer acetate;
• Any usage in the last 6 months of mitoxantrone, cytotoxic immunosuppressive therapy, natalizumab, fingolimod or immunoglobulin;
• Usage within 30 days prior to baseline of oral or systemic corticosteroids or ACTH;
• Inadequate liver function;
• Severe renal impairment;
• Severe psychiatric disorder;
• Known inability to undergo an MRI scan;
• Having participated in another clinical study within 6 months prior to study baseline except for patients who have participated or who are currently participating in an interventional study without any study drug intake.
• Pregnancy or breastfeeding
• Female subjects considering becoming pregnant during the study