A Study to Evaluate the Safety, Tolerability, Efficacy, and Drug Levels of CC-97540 in Participants With Relapsing Forms of Multiple Sclerosis, Progressive Forms of Multiple Sclerosis or Refractory Myasthenia Gravis (MG) (Breakfree-2)

Other illness

• Cohorts 1 and 2: Participants that cannot complete the 9-Hole Peg Test (9-HPT) in at least 1 hand in \<240 seconds unless extenuating medical conditions unrelated to MS prohibit this.
• Presence of other confounding peripheral nervous system disorders or other disorders that may impact muscle strength (eg, myositis) or cause weakness, stroke, chronic inflammatory demyelinating polyradiculoneuropathy, Lambert-Eaton myasthenic syndrome.

Other

• Participants that cannot perform a Timed 25-Foot Walk Test (T25FWT) in \< 150 seconds.
• Other protocol-defined Inclusion/Exclusion criteria apply.

• \- Relapsing forms of Multiple Sclerosis (RMS) - Cohort 1.
• Participants must have an Expanded Disability Status Scale (EDSS) of ≥ 3.0 and ≤ 5.5.
• Participants must have a diagnosis of Multiple Sclerosis (MS) with relapsed/refractory MS or conversion to active secondary progressive multiple sclerosis (aSPMS), and worsening of disease within 12 months prior to Screening and while on treatment with a high-efficacy DMT for at least 6 months.
  • \- Progressive forms of MS - Cohort 2.
• Participants must have an EDSS ≥ 3.0 and ≤ 6.0.
• Participants must have a diagnosis of primary progressive multiple sclerosis (PPMS) that is treatment-resistant or diagnosis of inactive secondary progressive multiple sclerosis (iSPMS).
  • \- Myasthenia Gravis - Cohort 3
  • i)MGFA classification of II-IV at screening
• Documentation of autoantibodies against AChR or MuSK (historical or at Screening)
• Refractory disease defined as disease activity on at least 2 immunosuppressants, including steroids, NSIs, or biologics.
• Has had thymectomy, only if indicated according to current guidelines.