A specific blood cell type called HLA-DR2 may be required in order for RTL1000 to work. For that reason, all subjects will be tested for HLA-DR2 and only those subjects who test positive (about 50%) will undergo further tests to determine if they meet inclusion and exclusion criteria.

Inclusion criteria:

• Fulfill McDonald criteria for multiple sclerosis
• Confirmed diagnosis of chronic progressive or relapsing-remitting multiple sclerosis
• EDSS score of 0.0 to 6.5
• No clinical exacerbations within the 8 weeks before administration of RTL1000
• HLA-DR2 positive, as confirmed by study reference laboratory
• Negative serum pregnancy test within 7 days of administration of RTL1000 and negative urine pregnancy test on Day 0 for all women of childbearing potential
• Agreement of sexually active men and women of childbearing potential to practice a medically-approved form of contraception
• Capable of and willing to provide written informed consent

Exclusion Criteria:

• Exposure to alemtuzumab or dacluzimab any time in the 6 months before administration of RTL1000
• Exposure to natalizumab or other drugs targeting alpha-4 integrin in the 6 months before RTL1000 administration or more than 3 doses of natalizumab or these drugs at any time.
• Any prior exposure to RTL1000
• Exposure to other MS disease-modifying drugs (e.g., recombinant interferon beta and glatiramer acetate), immunosuppressant agents, or systemic corticosteroids (other than replacement doses) within the 4 weeks prior to RTL1000 administration
• Exposure to chemotherapeutic immunosuppressants, including azathioprine, mycophenolate mofetil, methotrexate, cladribine, mitoxantrone, or cyclophosphamide, during the six months prior to administration of RTL1000
• Total lymphoid irradiation or bone marrow transplantation at any time
• Known or suspected allergy to gadolinium
• Contraindication to MRI (e.g., subject has a pacemaker or other contraindicated implanted metal devices or has claustrophobia that cannot be medically managed)
• Clinically significant abnormalities in laboratory findings for hematologic, hepatic, and renal function at screening.
• Significant medical diseases or conditions, including poorly controlled hypertension, cardiovascular disease, inflammatory disorders, immunodeficiency (e.g., HIV infection), renal failure, liver dysfunction, cancer (except treated basal cell carcinoma), or active infection.
• History of, or current, psychiatric illness likely to interfere with ability to comply with protocol requirements or give informed consent
• History of alcohol or drug abuse likely to interfere with ability to comply with protocol requirements
• Pregnancy or lactation