A Study Evaluating the Presence and Concentration of BRIUMVI™ (Ublituximab) in Breast Milk

This study measures how much of the multiple sclerosis drug ublituximab (brand name BRIUMVI) passes into breast milk, to help determine whether it is safe for breastfeeding mothers and their infants. **You may be eligible if...** - You have relapsing multiple sclerosis (including relapsing-remitting MS or active secondary progressive MS) - You have independently decided to take BRIUMVI before joining the study - You are currently breastfeeding or pumping breast milk - Your baby was born at 35 weeks gestation or later and is at a healthy weight **You may NOT be eligible if...** - You have an active infection that prevents breastfeeding - You have had breast surgery (implants, augmentation, reduction, or mastectomy) that significantly affects milk production - You have a breast infection or mastitis - You are using medications known to be harmful to infants through breast milk (such as tetracyclines or fluoroquinolones) - Your infant has a significant medical condition including heart, lung, or liver disease Talk to your doctor to see if this trial is right for you.