Use of plasmapheresis to lower anti-AAV antibodies in nonhuman primates with pre-existing immunity to AAVrh74.

Patients with pre-existing immunity to adeno-associated virus (AAV) are currently unable to receive systemic gene transfer therapies. In this nonhuman primate study, we investigated the impact of immunosuppression strategies on gene transfer therapy safety and efficacy and analyzed plasmapheresis as a potential pretreatment for circumvention of pre-existing immunity or redosing. In part 1, animals received delandistrogene moxeparvovec (SRP-9001), an AAVrh74-based gene transfer therapy for Duchenne muscular dystrophy. Cohort 1 (control, n = 2) received no immunosuppression; cohorts 2-4 (n = 3 per cohort) received prednisone at different time points; and cohort 5 (n = 3) received rituximab, sirolimus, and prednisone before and after dosing. In part 2, cohorts 2-4 underwent plasmapheresis before redosing; cohort 5 was redosed without plasmapheresis. We analyzed safety, immune response (humoral and cell-mediated responses and complement activation), and vector genome distribution. After 2 or 3 plasmapheresis exchanges, circulating anti-AAVrh74 antibodies were reduced, and animals were redosed. Plasmapheresis was well tolerated, with no abnormal clinical or immunological observations. Cohort 5 (redosed with high anti-AAVrh74 antibody titers) had hypersensitivity reactions, which were controlled with treatment. These findings suggest that plasmapheresis is a safe and effective method to reduce anti-AAV antibody levels in nonhuman primates prior to gene transfer therapy. The results may inform human studies involving redosing or circumvention of pre-existing immunity.

Evaluation of the Lipid-binding Properties of Recombinant Dystrophin Spectrin-like Repeat Domains R1-3.

Recombinant micro-dystrophin genes are designed to treat Duchenne muscular dystrophy (DMD) by retaining dystrophin domains believed to play key functional roles while fitting the packaging capacity of adeno-associated virus vectors. Domains R1-3 are important for muscle force generation and for association with the sarcolemma, but the nature of this interaction is not fully understood. We measured lipid-binding affinity of 3 peptides containing different spectrin-like repeat modules (R1-3; R1-2; and R1, 2, 22). Lipid-binding affinity was highest with R1-3, suggesting that the complete R1-R3 region could be beneficial and should be considered for inclusion in micro-dystrophin constructs.