Multicenter assessment and longitudinal study of the prevalence of antibodies and related adaptive immune responses to AAV in adult males with hemophilia

Adeno-associated virus (AAV) based gene therapy has demonstrated effective disease control in hemophilia. However, pre-existing immunity from wild-type AAV exposure impacts gene therapy eligibility. The aim of this multicenter epidemiologic study was to determine the prevalence and persistence of preexisting immunity against AAV2, AAV5, and AAV8, in adult participants with hemophilia A or B. Blood samples were collected at baseline and annually for ≤3 years at trial sites in Austria, France, Germany, Italy, Spain, and the United States. At baseline, AAV8, AAV2, and AAV5 neutralizing antibodies (NAbs) were present in 46.9%, 53.1%, and 53.4% of participants, respectively; these values remained stable at Years 1 and 2. Co-prevalence of NAbs to at least two serotypes and all three serotypes was present at baseline for ~40% and 38.2% of participants, respectively. For each serotype, ~10% of participants who tested negative for NAbs at baseline were seropositive at Year 1. At baseline, 38.3% of participants had detectable cell mediated immunity by ELISpot, although no correlations were observed with the humoral response. In conclusion, participants with hemophilia may have significant preexisting immunity to AAV capsids. Insights from this study may assist in understanding capsid-based immunity trends in participants considering AAV vector-based gene therapy.