This study looks at whether and how much BRIUMVI™ (also known as Ublituximab) shows up in breast milk. BRIUMVI™ is a medicine used to treat relapsing forms of multiple sclerosis (RMS), which is a disease where the body's immune system attacks the brain and spinal cord. The study is for mothers who are already taking BRIUMVI™ and want to keep breastfeeding their babies. Multiple sclerosis has different types, like relapsing-remitting (RRMS), where symptoms come and go, and secondary progressive (SPMS), where it slowly gets worse.

**Key Points to Consider:**

• The study requires mothers to pump breast milk for a day after taking BRIUMVI™ through an IV.
• Mothers should plan to feed their babies breast milk during the study and not wean them.
• Participants must not have infections or take drugs that could harm the baby through breast milk.

The study is important for understanding if BRIUMVI™ is safe for babies when breastfeeding. Participants should be willing and able to provide breast milk samples and ensure their babies meet growth requirements.