Background: Adeno-associated virus (AAV) vectors have become the vehicle of choice for gene transfer therapy for Duchenne muscular dystrophy (DMD). The rAAVrh74 serotype, which efficiently transduces tissues impacted by DMD, including skeletal and cardiac muscle, was derived from Rhesus monkey and may have a lower risk of pre-existing antibodies. It was therefore selected to develop a DMD gene therapy expressing a functional, shortened dystrophin protein. Pre-existing antibodies to AAVs can limit therapeutic potential and pose safety concerns.
Objective: Here we sought to evaluate the prevalence of total binding antibodies (neutralizing and non-neutralizing) against rAAVrh74 in patients with DMD. Measuring total binding antibodies is more a comprehensive approach to assessing pre-existing immune response versus measuring neutralizing antibodies alone.
Methods: Eligible individuals were ?4 to <18 years old with genetically confirmed DMD and were excluded from the study if they lived with a person who had exposure to rAAVrh74 or other gene transfer therapy, or if they received prior treatment with gene transfer therapy. A single blood sample was obtained from each participant and anti-rAAVrh74 total binding antibodies were measured by enzyme-linked immunosorbent assay. Total binding antibody level <1:400 was defined as ‘not elevated’. Primary endpoint was the percentage of subjects with elevated total antibody titers to rAAVrh74.
Results: Overall, 86.1% (87/101) of study participants were seronegative, with pre-existing total antibody titers to rAAVrh74 <1:400. There was no association between seroprevalence and age observed in this limited study of individuals with DMD, aged ?4 to <18 years. In the 14 seropositive participants (13.9%), anti-rAAVrh74 antibody titers ranged from 1:400 to the upper limit of the assay of 1:3200.
Conclusions: The comprehensive approach of measuring total binding antibodies (both neutralizing and non-neutralizing) demonstrates that 86.1% of patients with DMD in this final data set were seronegative (<1:400) for anti-rAAVrh74 total binding antibodies.