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.

The Impact of Pre-existing Immunity on the Non-clinical Pharmacodynamics of AAV5-Based Gene Therapy

“…Antibodies specific for AAVs may neutralize transduction of AAV gene therapy vectors or may simply be binding antibodies with no neutralizing activity but are readily detectable by ELISA-based methods regardless. For some common serotypes, the prevalence of antibodies in humans may reach 60% but is reported to be lower for AAV5, with a range of 3.2% to 40% and varying by geographic location 4, 5, 13, 14, 15…”

Immunogenicity of adenovirus-vector vaccine targeting hepatitis B virus: non-clinical safety assessment in non-human primates

“…An unsolved challenge in the development of gene therapy drugs is that the vectors and their encoding proteins ultimately become immunogenic in some patients, thereby provoking an immune response resulting in immunotoxicity [11]. In contrast to therapeutic proteins whose immunogenicity is mainly evaluated by measuring the levels of anti-drug antibodies produced, there is currently no well-established and widely accepted method for the immunogenicity assessment of gene therapy drugs [12,13]. Therefore, in the present study, we focused on evaluating the immunogenicity of the subcutaneous injection of Ads-HBV vaccines in a non-human primate at different doses to obtain reference data through a non-clinical safety assessment in preparation for a clinical trial.…”

Evading the AAV Immune Response in Mucopolysaccharidoses

“…In the MPS population, Fu et al reported in a seroprevalence study comparing MPS types IIIA, IIB, and healthy children for seropositivity (≥1:50 titer) that no significant difference was apparent between the groups. Additionally, children younger than eight years old were observed to have significantly lower neutralizing AAV titers (serotypes 1-3, 5-9) compared to children older than eight years [47]. Therefore, the characteristics that primarily influence the seroprevalence of neutralizing AAV antibodies can be summarized as age and geographic location ( Table 2).…”

“…Table 2. Seroprevalence studies among the human population in varying ages, geographic regions, diseases, and serotypes [47][48][49][50][51]. All studies are comprised of male and female subjects.…”