Rituximab and Ocrelizumab in Serum With Multiple Sclerosis

This is a blood sample collection study looking at the levels of two multiple sclerosis (MS) medications — rituximab and ocrelizumab — in patients' blood over time. It is a sub-study connected to a larger MS trial, aimed at better understanding how these drugs behave in the body. **You may be eligible if...** - You are already enrolled in the OVERLORD-MS clinical trial (NCT04578639) - You are willing to visit the laboratory to have blood drawn at the scheduled time points **You may NOT be eligible if...** - You are not enrolled in the OVERLORD-MS trial - You are unwilling to come to the laboratory for scheduled blood draws Talk to your doctor to see if this trial is right for you.