Study to Assess Effects of Ublituximab in Pediatric Participants With Relapsing Forms of Multiple Sclerosis

Inclusion criteria

for Part A and Part B:

• Diagnosis of RMS.
• EDSS at screening: 0-5.5, inclusive.
• Neurologic stability for ≥ 30 days prior to screening, and between screening and Week 1 Day 1 (W1D1).

Inclusion criteria

for Part C:

• Participants must have completed Part A (Week 24 visit) or Part B (Week 96 visit) to be eligible for Part C.

Exclusion criteria

for Part A and B:

• Known presence or suspicion of other neurologic disorders that may mimic MS.
• Prior treatments:

• Systemic corticosteroids (>0.1 milligrams/kilogram/day [mg/kg/day], or >5 milligrams/day [mg/day] of prednisone equivalent) or adrenocorticotropic hormone (ACTH) within 30 days prior to the screening MRI scan (note: Topical, ophthalmic, or inhaled corticosteroids are permitted).
• High dose intravenous immunoglobulin (IVIG) or subcutaneous IG (SCIG) within 2 months prior to W1D1.
• Treatment with anti-CD20 or other B cell directed treatment at any time.
• Treatment with alemtuzumab, cladribine, cyclophosphamide, mitoxantrone at any time.

Additional Exclusion Criteria for Part B Only (Relevant to Fingolimod Treatment):

• Treatment with fingolimod or other sphingosine-1 phosphate-1 (S1P1) modulators at any time.
• The following antiarrhythmic drugs at Screening: Class Ia anti-arrhythmics.

Exclusion criteria

for Part C:

• If the absolute lymphocyte count (ALC) is outside the specified range the participant will not be eligible to receive ublituximab in Part C.

Note: Other protocol-specified inclusion/exclusion criteria may apply