Treatment of Participants With Primary or Secondary Progressive Multiple Sclerosis

Prior treatment

• Clinical relapse of MS in the 1 year prior to study entry.
• Prior treatment with CAR-T or gene therapy product directed at any target.
• Prior treatment with mitoxantrone, cladribine (or other chemotherapies), or alemtuzumab within 2 years prior to TRX319 dose.
• Prior treatment with CD20-depleting antibodies within 3 months and prior treatment with Bruton's tyrosine kinase inhibitor (BTKi) and sphingosine 1 phosphate (S1P) modulators within 1 month of TRX319 dose.
• Plan to or have received live, attenuated vaccines less than 4 weeks (28 days) prior to TRX319 infusion, and other vaccines less than 2 weeks (14 days) prior to TRX319 infusion.
• Previous or concurrent malignancy.
• Prior organ transplant, or allogeneic hematopoietic stem cell transplantation or recipient of peripheral blood products \< 3 years prior to TRX319 infusion.
• Major surgery within 4 weeks prior or planned within 4 weeks after TRX319 administration.

Other illness

• MS clinical stability on disease modifying therapy.
• Diseases other than MS to explain the first demyelinating event, including aquaporin 4 IgG or myelin oligodendrocyte glycoprotein-IgG seropositivity.
• Serologic status reflecting active hepatitis B or C infection.
• Positive serology for human immunodeficiency virus (HIV).
• History of progressive multifocal leukoencephalopathy.
• Untreated active, or active with documented completed treatment but without a negative chest X-ray that shows no evidence of active tuberculosis, or latent tuberculosis.
• Primary immunodeficiency as defined by a known genetic disorder.
• History of splenectomy.
• Impaired cardiac function or clinically significant cardiac disease.
• History of any other neurologic disorder or medical condition the Investigator considers would increase the risk for the participant, including seizure disorders.
• Life-threatening allergies, hypersensitivity, or documented intolerance to TRX319 drug product excipients.
• Serious and/or uncontrolled medical condition that, in the Investigator's judgment, would cause unacceptable safety risk, interfere with study procedures or results, or compromise compliance with the protocol.

Other

• Subjects that are pregnant, breast feeding or aim to become pregnant during the study period (Subjects must agree to use a highly effective method of contraception).

• Clinical diagnosis of MS with evidence of PPMS or SPMS according to 2025 McDonald criteria.
• Expanded Disability Status Scale (EDSS) range ≥ 2.5 to ≤ 6.5.
• Evidence of clinical disability progression within 2 years prior to enrollment.
• Documented presence of CSF-restricted OCBs and/or elevated IgG index and/or κ free light chain.
• Males and females ≥ 18 and ≤ 65 years of age at time of consent.
• Evidence of adequate organ function
• Women of child bearing potential have a negative pregnancy test at screening.
• Contraceptive use by all participants while on study.
• Participants must be able to understand, consent, and be willing and able to complete all specified procedures and visits.
• Positive varicella zoster virus titer. Participants who test seronegative for varicella zoster virus IgG antibodies need to complete vaccination ≥ 4 weeks prior to TRX319 infusion.
• Participants must be willing to refrain from donating blood for 1 year after TRX319 infusion.