The overall goal of this study is to elucidate a mechanism by which vancomycin modulates the gut-brain axis in multiple sclerosis (MS). The gut microbiome plays an important role in autoimmunity, including MS. However, the identity of gut microbes modulating neuroinflammation in MS and their mechanisms of action remain obscure. Hence, here the research team proposes to investigate the effects of vancomycin on the gut microbiota composition, peripheral immune function, and brain MRI lesions in MS patients.

Inclusion Criteria:

• aged 18 - 50
• newly diagnosed MS (2017 McDonald criteria), CIS or RIS patients, who have experienced symptoms no earlier than the past year
• treatment naive
• able to understand the risks, benefits, and alternatives of participation and give meaningful consent

Exclusion Criteria:

• antibiotic use within the past 90 days;
• pre- or probiotic use within past month or corticosteroids use within the past month;
• use of tobacco products within the past 1 month;
• history of treatment with immunosuppressants;
• history of gastroenteritis within the past month or diagnosis with a chronic infectious disease, i.e. hepatitis B, C or HIV;
• pregnancy or less than 6 months postpartum;
• irritable bowel syndrome and other bowel dysfunction such as constipation;
• history of bowel surgery;
• inflammatory bowel disease, rheumatoid arthritis, systemic lupus erythematosus, diabetes and any other auto-immune illness;
• diagnosis with another neurological disease, behavioral or psychiatric conditions that would be incompatible with a safe and successful participation in the study (such as severe major depression, schizophrenia and presence of psychotic symptoms);
• eating disorders such as anorexia nervosa, bulimia, or binge eating syndrome;
• travel outside of the country within the past month;
• contraindication to vancomycin including estimated glomerular filtration rate of <60ml/min, impaired hearing or known allergy.
• Contraindication to MRI such as implanted metallic objects

The investigator is not developing the product. The study has been exempted from an IND by the FDA, since it entails the off-label use of a marketed drug.

The research team will be blinded to the treatment group (placebo/vancomycin).