The purpose of this study is to evaluate long-term safety and efficacy of ublituximab therapy in participants with relapsing multiple sclerosis (RMS).

TG1101-RMS303 is an open-label, single-arm extension study designed to evaluate long-term safety and efficacy of ublituximab in participants with RMS. Participants who complete the 96-week, double-blind treatment period of TG1101-RMS301 (RMS301 [NCT03277261]) or TG1101-RMS302 (RMS302 [NCT03277248]) are eligible for participation in this Open Label Extension (OLE) study. Participants may also be eligible for TG1101-RMS303 if they have completed Week 208 of TG1101-RMS201E (RMS201E [NCT03381170]) (United States of America [USA] participants only).

Inclusion Criteria:

Participants must meet the following criteria:

1. Complete the 96-week double-blind TG1101-RMS301 (NCT03277261) or TG1101-RMS302 (NCT03277248) study or complete the final Week 208 visit of the TG1101-RMS201E (NCT03381170) study
2. Investigator believes may benefit from treatment with ublituximab
3. Are able and willing to provide written informed consent (e.g., before the first infusion) and to comply with the study protocol
4. Female participants of child-bearing potential, and male partners must consent to use a medically acceptable method of contraception from consent, throughout the study period, and for 20 weeks after the last dose of ublituximab

Exclusion Criteria:

Participants who meet any of the following exclusion criteria are not to be enrolled to this study:

1. Any significant or uncontrolled medical condition or treatment-emergent, clinically significant laboratory abnormality such as:

   1. Absolute neutrophil count < 1.5 x 10e3/µL
   2. Hematocrit < 24%
   3. Platelet count < 150,000 cell/mm^3
   4. Hypogammaglobulinemia immunoglobulin G (IgG) < 4.0g/L

2. Active infection

3. Ongoing pregnancy (female participants)

4. Participants who discontinued ublituximab treatment or withdrew consent from the TG1101-RMS301 or TG1101-RMS302 study during the 96-week evaluation period or prior to completing the final Week 208 visit of the TG1101-RMS201E study

5. Participants who have started any disease modifying therapy (DMT), stem cell transplantation, or participation in any other interventional clinical trial after completion of the 96-week visit in the TG1101-RMS301, TG1101-RMS302, or after completing the final Week 208 visit of the TG1101-RMS201E study

6. Participants who have had a confirmed multiple sclerosis (MS) relapse within the past 30 days prior to Week 1 Day 1 (W1D1). Following a relapse, participants must be neurologically stable for at least 30 days prior to screening or W1D1 of the OLE

7. Participants with unstable disease activity

8. Presence of malignancy, except for surgically excised basal or squamous cell skin lesions

9. Vaccination with live virus within 2 months of randomization