Differential Prevalence of Antibodies Against Adeno-Associated Virus in Healthy Children and Patients with Mucopolysaccharidosis III: Perspective for AAV-Mediated Gene Therapy

Abstract

Recombinant adeno-associated virus (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 mucopolysaccharidosis (MPS) III patients, the seroprevalence profiles of AAV1-9 and rh74 were investigated in MPS IIIA/IIIB patients and in healthy children. Using enzyme-linked immunosorbent assay for αAAV-IgG, significantly higher seroprevalence was observed for AAV1 and AAVrh74 in 2- to 7-year-old MPS III patients than in healthy controls. Seroprevalence for the majority of tested AAV serotypes appears to peak before 8 years of age in MPS III subjects, with the exception of increases in αAAV8 and αAAV9 Abs in 8- to 19-year-old MPS IIIA patients. In contrast, significant increases in seroprevalence were observed for virtually all tested AAV serotypes in 8- to 15-year-old healthy children compared to 2- to 7-year-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 who 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 one to five of the tested AAV serotypes, mostly with low levels of αAAV-Abs (1:50-100), while a minority (22%) were seropositive for six or more 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.

Keywords: AAV; MPS III; pre-existing Abs; seroprevalance.

Conflict of interest statement

H.F. and D.M.M. are co-inventors of ABO-101 and ABO-102 of Abeona Therapeutics, Inc., and hold stock of the company. None of the other coauthors have any conflicts of interest.

Figures

Figure 1.

Prevalence of antibodies (Abs) against different adeno-associated virus (AAV) serotypes in mucopolysaccharidosis (MPS) III patients and healthy children. Serum samples from patients with MPS IIIA (aged 2–18 years; n = 24) or MPS IIIB (aged 2–20 years; n = 14) and healthy individuals (aged 2–15 years; n = 35) were assayed by binding enzyme-linked immunosorbent assay (ELISA) for total immunoglobulin G (IgG) against AAV1–9 and rh74. Serum total αAAV-IgG levels are expressed as ELISA titer, and ELISA titer ≥1:50 was considered as seropositive. (a) all subjects; (b) aged 2–7 years; (c) aged >8 years. *p < 0.05 vs. HC; +p = 0.06–0.07 vs. HC; !p = 0.09 vs. HC; ^p < 0.05 vs. MPS IIIA. HC, healthy controls.

Figure 2.

Age impacts on prevalence of Abs against different AAV serotypes in MPS III patients and healthy children. Serum samples from patients with MPS IIIA (aged 2–18 years; n = 24) or MPS IIIB (aged 2–20 years; n = 14) and healthy individuals (aged 2–15 years; n = 35) were assayed by binding ELISA for total IgG against AAV1–9 and rh74. Serum total αAAV-IgG levels are expressed as ELISA titer, ELISA titer ≥1:50 was considered as seropositive. (a) healthy controls; (b) MPS IIIA; (c) MPS IIIB. #p < 0.05 vs. 2–7 years of age; @p = 0.07 vs. 2–7 years of age.

Figure 3.

Levels of IgG against different AAV serotypes in MPS III patients and healthy children. Analyses were performed to determine the variation of αAAV-Ab levels in seropositive MPS III patients and healthy children (A, B). Serum total αAAV-IgG is expressed as ELISA titer, and ELISA titer ≥1:50 is considered as seropositive. *p < 0.05 vs. HC; +p = 0.06–0.07 vs. HC; !p = 0.09 vs. HC; ^p < 0.05 vs. MPS III; 1, n = 1; 0, n = 0.