Open-label, Multi-center, Phase I/II Study to Assess Safety, Disease Progression and Cellular Kinetics Following YTB323 Administration in Participants With Non-active Progressive Multiple Sclerosis (PMS)

This study is testing a new cell therapy called YTB323 for people with progressive multiple sclerosis (MS) — the kind that slowly worsens over time without relapses. Researchers want to see if this treatment is safe and whether it can slow or stop disability progression. **You may be eligible if...** - You are 18–60 years old - You have been diagnosed with secondary progressive MS (SPMS) or primary progressive MS (PPMS) - Your MS has been getting worse in the past 2 years (disability increased) - You have not had a relapse in the last 2 years - You are able to walk, at least with assistance (disability score 3–6.5) - Your MS symptoms started no more than 15 years ago - You are up to date on recommended vaccines **You may NOT be eligible if...** - You have relapsing MS or actively inflamed (enhancing) lesions on MRI - You have had a prior stem cell transplant, gene therapy, or organ transplant - You have significant heart, lung, liver, kidney, or psychiatric conditions - You are pregnant or breastfeeding - You have an active or chronic infection (such as hepatitis B or C, or tuberculosis) - You are unable to have MRI scans or lumbar punctures Talk to your doctor to see if this trial is right for you.