Differential prevalence of antibodies against adeno-associated virus in healthy children and patients with mucopolysaccharidosis III: perspective for AAV-mediated gene therapy.

Recombinant AAV vectors are promising gene therapy tools. However, pre-existing antibodies (Abs) to many useful AAV serotypes pose a critical challenge for the translation of gene therapies. As part of AAV gene therapy program for treating MPS III patients, we investigated the seroprevalence profiles of AAV1-9 and rh74 in MPS IIIA/IIIB patients and in healthy children. Using ELISA for αAAV-IgG, we observed significantly higher sero-prevalence for AAV1 and AAVrh74 in 2-7y-old MPS III patients than in healthy controls. Seroprevalence for the majority of tested AAV serotypes appear to peak before age 8y in MPS III subjects, with the exception of increases in αAAV8 and αAAV9 Abs in 8-19y-old MPS IIIA patients. In contrast, we observed significant increases in seroprevalence for virtually all tested AAV serotypes in 8-15y-old healthy children compared to 2-7y-olds. Co-prevalence and Ab level correlation results followed the previously established divergence-based clade positions of AAV1-9. Interestingly, the individuals positive for αAAVrh74-Abs showed the lowest co-prevalence with Abs for AAV1-9 (22-40%), however, all or nearly all (77-100%) of subjects that were seropositive for any of serotypes 1-9, were also positive for αAAVrh74-IgG. Notably, the majority (78%) of αAAV seropositive individuals were also Ab-positive for 1-5 of the tested AAV serotypes, mostly with low levels of αAAV-Abs (1:50-100), while a minority (22%) were seropositive for ≥6 AAV serotypes, mostly with high levels of αAAV-IgG for multiple serotypes. In general, the highest IgG levels were reactive to AAV2, AAV3, and AAVrh74. The data illustrate the complex seroprevalence profiles of AAV1-9 and rh74 in MPS patients and healthy children, indicating the potential association of AAV seroprevalence with age and disease conditions. The broad co-prevalence of Abs for different AAV serotypes reinforces the challenge of pre-existing αAAV-Abs for translating AAV gene therapy to clinical applications, regardless of the vector serotype.