Global Seroprevalence of Pre-existing Immunity Against AAV5 and Other AAV Serotypes in People with Hemophilia A

Abstract

Adeno-associated virus (AAV)-mediated gene therapy may provide durable protection from bleeding events and reduce treatment burden for people with hemophilia A (HA). However, pre-existing immunity against AAV may limit transduction efficiency and hence treatment success. Global data on the prevalence of AAV serotypes are limited. In this global, prospective, noninterventional study, we determined the prevalence of pre-existing immunity against AAV2, AAV5, AAV6, AAV8, and AAVrh10 among people ≥12 years of age with HA and residual FVIII levels ≤2 IU/dL. Antibodies against each serotype were detected using validated, electrochemiluminescent-based enzyme-linked immunosorbent assays. To evaluate changes in antibody titers over time, 20% of participants were retested at 3 and 6 months. In total, 546 participants with HA were enrolled at 19 sites in 9 countries. Mean (standard deviation) age at enrollment was 36.0 (14.87) years, including 12.5% younger than 18 years, and 20.0% 50 years of age and older. On day 1, global seroprevalence was 58.5% for AAV2, 34.8% for AAV5, 48.7% for AAV6, 45.6% for AAV8, and 46.0% for AAVrh10. Considerable geographic variability was observed in the prevalence of pre-existing antibodies against each serotype, but AAV5 consistently had the lowest seroprevalence across the countries studied. AAV5 seropositivity rates were 51.8% in South Africa (n = 56), 46.2% in Russia (n = 91), 40% in Italy (n = 20), 37.2% in France (n = 86), 26.8% in the United States (n = 71), 26.9% in Brazil (n = 26), 28.1% in Germany (n = 89), 29.8% in Japan (n = 84), and 5.9% in the United Kingdom (n = 17). For all serotypes, seropositivity tended to increase with age. Serostatus and antibody titer were generally stable over the 6-month sampling period. As clinical trials of AAV-mediated gene therapies progress, data on the natural prevalence of antibodies against various AAV serotypes may become increasingly important.

Keywords: adeno-associated virus; antibody; gene therapy; hemophilia A; seropositivity.

Figure 1.

Seropositivity for (A) the global population, (B) using the global HA weighted average, and by country for (C) AAV2, (D) AAV5, (E) AAV6, (F) AAV8, and (G) AAVrh10. Data are for adults and adolescents on day 1. Samples from Brazil were only tested using the AAV5 assay, not RUO assays. Global HA weighted average was calculated by multiplying the percentage of participants who tested positive in each country by the number of people with HA in that country, per 2018 WFH survey, divided by the total number of people with HA in all countries in this study, per 2018 WFH survey. AAV, adeno-associated virus; CI, confidence interval; HA, hemophilia A; RUO, research-use-only; WFH, World Federation of Hemophilia.

Figure 2.

AAV serotype positivity by age group. Data are for the global population on day 1.

Figure 3.

Individual participant titers on day 1. Data are dilution titers from day 1 for individual participants in the global population. Participants with negative titers are shown as 1. Participants with positive titer results and a titer <20, the MRD, are shown as 20. Width is representative of the number of points at a particular value. Mean (SD) values are for participants with quantifiable titers only: AAV2, n = 294; AAV5, n = 188; AAV6, n = 247; AAV8, n = 227; AAVrh10, n = 233. MRD, minimum required dilution; SD, standard deviation.

Figure 4.

For all serotypes over 6 months, (A) percent of positive participants and (B) mean antibody titers in positive participants. Data are for all participants in the global population with valid assay results for the relevant time point. Titer was only evaluated in seropositive participants. Note that titers cannot be directly compared across serotypes, as assays have varying sensitivity.