Study is being terminated due to a business decision.

This is a gene transfer therapy study evaluating the safety of delandistrogene moxeparvovec and delandistrogene moxeparvovec dystrophin expression in association with imlifidase, in participants with DMD with pre-existing antibodies to rAAVrh74 over a period of 104 weeks.

Inclusion Criteria:

• Ambulatory per protocol specified criteria.
• Has a definitive diagnosis of DMD prior to Screening based on documentation of clinical findings and confirmatory genetic testing.
• Ability to cooperate with motor assessment testing.
• Has elevated rAAVrh74 antibody titers per protocol-specified requirements.
• A pathogenic frameshift mutation, nonsense mutation or premature stop codon or pathogenic variant in the DMD gene that is expected to lead to absence of dystrophin protein.
• Stable daily dose of oral corticosteroids for at least 12 weeks prior to Screening, and the dose is expected to remain constant throughout the study (except for modifications to accommodate changes in weight).

Exclusion Criteria:

• Previous treatment with imlifidase.
• Presence of any other clinically significant illness, including cardiac, pulmonary, hepatic, renal, hematologic, immunologic, or behavioral disease, or infection or malignancy or concomitant illness or requirement for chronic drug treatment that in the opinion of the Investigator creates unnecessary risks for receiving the study drugs or a medical condition or extenuating circumstance that, in the opinion of the Investigator, might compromise the participant's ability to comply with the protocol required testing or procedures or compromise the participant's wellbeing, safety, or clinical interpretability.
• Exposure to gene therapy, investigational medication, or other protocol-specified treatment within the protocol specified time limits.
• Abnormality in protocol-specified diagnostic evaluations or laboratory tests.

Note: Other inclusion or exclusion criteria could apply.