Systemic responses to intravenous rAAV administration in boys with Duchenne muscular dystrophy

Systemic gene therapies utilizing recombinant adeno-associated virus (rAAV) are in the clinic for the treatment of rare monogenic diseases. This includes delandistrogene moxeparvovec for Duchenne muscular dystrophy (DMD), which uses AAVrh74 vector to deliver a micro-dystrophin transgene to striated muscle. While there have been cases of transformative benefits incurred from rAAV therapies, serious adverse events and mortalities have occurred. This study aimed to investigate short-term rAAV dynamics and long-term systemic responses to intravenous rAAV in the phase 1/2a delandistrogene moxeparvovec clinical trial (NCT03375164), which represents the most promising cases of micro-dystrophin gene therapy for DMD.

Plasma and urine specimens from NCT03375164 were analyzed for rAAV using digital PCR and immunoblotting. The integrity and transduction competency of specimen-derived rAAV was evaluated in vitro. Systemic responses to rAAV treatment were investigated using the SomaScan proteomics platform. Preclinical antiviral responses to rAAV were assayed by real-time PCR in the livers of D2. mdx mice 1 week following systemic treatment with rAAV.

Digital PCR revealed high rAAV content in the plasma at Day 1 following treatment, which substantially reduced by Day 7. Urinary rAAV content was low and variable in all samples tested. The majority of detected vector genomes were packaged in AAVrh74 particles in these specimens, and the vector contained in Day 1 plasma samples was confirmed to be transduction competent. SomaScan data revealed highly significant changes in 99 circulating proteins, which include markers associated with immune activation, interferon responses, complement pathways, and organ injury. Most traditional markers of muscle damage were not changed across the time course, with the limitation that no healthy or untreated DMD samples were analyzed. Features of antiviral and interferon-associated responses were identified in D2. mdx mice.

Systemic rAAV treatments result in high levels of circulating and transduction-competent vector early after treatment in DMD boys and result in wide-spread activation of immune-associated markers. These findings will provide insights for future investigational study design and efforts to improve safety of rAAV gene therapies.