Quantification and comparison of anti-AAV9 and anti-AAVrh74 antibodies in plasma and human milk: Implications for AAV-based gene therapy candidacy

Background The application of recombinant adeno associated virus (rAAV) in gene therapy is accepted as an effective strategy for the treatment of monogenic diseases. However, eligibility for such therapies is contingent upon the absence or minimal presence of antibodies against adeno-associated virus (AAV) capsid protein. While the passive transfer of maternal immunoglobulins in utero is well established, the potential impact of maternal antibodies transferred via breastfeeding remains less explored. Objective This study aims to quantify and compare the levels of anti-AAV9 and anti-AAVrh74 immunoglobulin G (IgG) and M (IgM) in both plasma and human milk from a group of healthy lactating mothers. Methods In this cross-sectional study, we analyzed plasma and human milk samples from healthy lactating mothers. We used an enzyme linked immunosorbent assay (ELISA) to determine the levels of circulating IgG and IgM antibodies against AAV9 and AAVrh74 capsids and compared their concentrations in the paired samples. Results Thirty-one paired plasma and human milk samples were analyzed. The median age at participation was 34 years (range: 25-43), median duration of breastfeeding at the time of sample collection was 7.5 months (range:0.7-33), and median body mass index was 23 Kg/m(2) (range: 19.7-35.4). Median anti-AAV9 IgG in plasma and human milk, were 183 U/mL (range: 29-7214) and 1 U/mL (range: 1-33), respectively. Median anti-AAVrh74 IgG, in plasma and human milk were 138 U/mL (range: 23-8725) and 1 U/mL (range: 1-27), respectively. The differences in anti-AAV9 and anti-AAVrh74 IgG levels between plasma and human milk were statistically significant (p < 0.0001). Additionally, a strong correlation (r: 0.97, p: < 0.0001) was observed between anti-AAV9 and anti-AAVrh74 IgG levels in plasma. Conclusions The levels of anti-AAV9 and anti-AAVrh74 antibodies in human milk are remarkably lower than those in plasma. Consequently, breastfeeding should not be restricted for term infants who are potential candidates for AAV-related gene therapy products.