The main purpose of this study is to evaluate if obe-cel is safe or causes any side effects in adults with refractory progressive MS. The study also plans to assess if obe-cel can show early signs of efficacy in MS. The trial includes only 1 group of participants (single-arm). The study population comprises participants with progressive forms of MS, not responsive to highly effective therapies.

Upon confirmation of study eligibility, participants will receive chemotherapy (used here for lymphodepletion) over 1 to 3 days in preparation for receiving a single obe-cel infusion.

Participants will be checked closely in the 28 days following obe-cel treatment. After this, participants will be monitored to evaluate safety and efficacy up to 24 months.

This is a Phase 1 study to determine the safety, tolerability, and preliminary efficacy of obe-cel in participants with refractory progressive forms of multiple sclerosis.

The study comprises 3 periods:

Screening Period: From Day -30 to enrolment Treatment Period: From day of enrolment to End of Treatment (EOT) or Day 1 - Participants will be evaluated to confirm eligibility for lymphodepletion, and thereafter receive lymphodepletion to enhance treatment efficacy and cluster of differentiation (CD)19 chimeric antigen receptor (CAR) T cell survival.

Obe-cel Administration: If the participant's eligibility for receiving obe-cel infusion is confirmed, the participant is to receive a single obe-cel infusion on Day 1.

Post treatment Period: From Day 1 to End of Study all participants will be followed up for efficacy and safety evaluation.

Inclusion Criteria:

• Willing and able to give written informed consent for participation in the study.
• Ability and willingness to adhere to the protocol's Schedule of Activities and other requirements.
• Participants must be 18 to 60 years of age inclusive at the time of signing the informed consent form.
• A female participant is eligible to participate if she is not pregnant or breastfeeding.
• Current diagnosis of PMS.
• Must have been treated previously with 2 disease-modifying therapies.

Exclusion Criteria:

• Any medications prohibited by the protocol.
• Highly active multiple sclerosis.
• Diagnosis of another autoimmune central nervous system condition.
• Active or uncontrolled fungal, bacterial, viral infection.
• History of malignant neoplasms unless disease-free for at least 24 months.
• History of heart, lung, kidney, liver transplant or hematopoietic stem cell transplant.