An Open-label Study to Assess the Safety, Efficacy, and Cellular Kinetics of YTB323 in Relapsing Multiple Sclerosis

All participants in this study will receive YTB323. Both the participant and the study doctor will know the participant is getting YTB323. Participants will be given one dose of YTB323. Different groups of participants may receive a higher dose of YTB323, if proven to be safe for every participant at the lower dose. Participants are in this study for 2 years and will be followed for an additional 13 years in a long-term follow up study. The main question this trial is designed to answer: Is YTB323 treatment safe for participants with relapsing MS?