Immunogenicity of Adeno-Associated Viral Vectors
AAV is one of the most actively studied gene therapy vectors and it has been successfully developed as a commercial vector for gene therapies1–3
AAV vectors are less immunogenic when compared with other viral vectors; nevertheless, they can still trigger an immune response4
Example: Onasemnogene abeparvovec-xioi: an AAV9-delivered SMN gene therapy3
- In clinical trials, evidence of prior exposure to AAV9 (i.e. anti-AAV9 antibodies) was uncommon3
- Following treatment, anti-AAV9 antibody titers increased in all patients, with most exceeding 1:819,2003
- Data on re-treatment in the presence of high anti-AAV9 antibody titers are not available3
An innate immune response can be triggered by:
that are included in the AAV vector cassette, which can theoretically be recognized as foreign by the host cell5,6
AAV inverted terminal repeat (ITR) sequences.
Toll-like receptors (TLRs) are one of the most extensively studied and prominent components of the cellular innate immune response1. AAV ITRs are CpG-rich double-stranded DNA structures, which can act as antigens for TLR-95
Pre-existing binding or neutralizing antibodies* to naturally occurring AAV serotypes are common in the population, but are generally low in children7-9
- Anti-AAV9 capsid antibodies are typically low in children8
- In one study†, the presence of IgG binding anti-AAV9 antibodies in children aged 2 to 7 years was 6% (figure)8
- In another study, the average prevalence of
anti-AAV2 and anti-AAV8 neutralizing antibodies in infants (<1 year) was 15%‡9
Binding IgG Seropositivity Prevalence in Healthy Subjects4
Assays have been developed to detect the presence of pre-existing anti-AAV antibodies10,11, and anti-AAV antibody screening is commonly employed in clinical trials of AAV-based gene therapies12,13
Figure created from data in Table 2 in Fu H, et al. Hum Gene Ther Clin Dev 2017;28(4):187–196. *Binding antibodies are defined as all isotypes capable of binding to the therapy, whereas neutralizing antibodies are a subpopulation of total binding antibodies that bind to epitopes crucial for facilitating successful transduction of the target cells14,15; †Carried out using serum samples taken from patients enrolled in a natural history study or an MPS III inflammation study at Nationwide Children’s Hospital, with control samples obtained from healthy subjects via BioServe or the MPS III inflammation study8; ‡Based on plasma samples from 175 anonymous infants from Children’s National Medical Center (Washington, DC) using a threshold titer of ≥1:205.
AAV, adeno-associated virus; IgG, immunoglobulin G; MPS, mucopolysaccharidosis.
Seropositivity for neutralizing factors* against AAV is prevalent in the general population; however, titers against certain serotypes may be low7
- Among those who were seropositive, neutralizing factor* titers were lower for AAV5, AAV8, and AAV9 compared with other serotypes in the majority of patients7
Prevalence of Neutralizing Factors* in the Serum in Healthy Subjects
Based on an analysis of serum samples collected from 226 healthy volunteers
Distribution of Neutralizing Factor* Titers in Healthy Subjects†
Figures reproduced from Figure 3 in Boutin S, et al. Hum Gene Ther 2010;21(6):704–712. *Neutralizing factors are defined as neutralizing antibodies and unidentified factors present in the serum that may contribute to neutralization7; †The percentage of total neutralizing factor titers is shown for all the seropositive samples displayed in the graph on the right7. AAV, adeno-associated virus.
AAV vectors can induce cell-mediated immunity via the presentation of capsid proteins to cytotoxic T cells16
- CD8+ T cells can destroy cells that have been transduced by AAV vectors, hence leading to the loss of transgene expression16
Figure reproduced from Figure 2 in Colella P, et al. Mol Ther Methods Clin Dev 2018;8:87–104. AAV, adeno-associated virus; CD, cluster of differentiation; ER, endoplasmic reticulum; MHC, major histocompatibility complex; sc, self-complementary; ss, single strand; TLR, toll-like receptor.
- Naso MF, et al. BioDrugs 2017;31(4):317–334;
- LuxturnaTM [package insert]. Philadelphia, PA; Spark Therapeutics, Inc.; 2017. Available at: http://sparktx.com/LUXTURNA_US_Prescribing_Information.pdf. Accessed July 24, 2019;
- ZolgensmaTM [package insert]. Bannockburn, IL: AveXis Inc.; 2019. Available at: https://www.avexis.com/content/pdf/prescribing_information.pdf. Accessed July 24, 2019;
- Sack BK, Herzog RW. Curr Opin Mol Ther 2009;11(5):493–503.
- Brown N, et al. Hum Gene Ther 2017;28(6):450–463;
- Megias J, et al. Stem Cells 2012;30(7):1486–1495.
- Boutin S, et al. Hum Gene Ther 2010;21(6):704–712;
- Fu H, et al. Hum Gene Ther Clin Dev 2017;28(4):187–196;
- Calcedo R, et al. Clin Vaccine Immunol. 2011;18(9):1586–1588;
- Vandamme C, et al. Hum Gene Ther 2017;28(11):1061–1074;
- Falese L, et al. Gene Ther 2017;24:768–778;
- Ferreira V, et al. Front Immunol 2014;5:82;
- FDA. FDA Briefing Document. Advisory Committee Meeting, October 12, 2017. Available at: https://www.fda.gov/media/108375/download. Accessed June 22, 2019;
- FDA. The immunogenicity of therapeutic proteins- what you don’t know can hurt you and the patient. Available at: https://www.fda.gov/media/89071/download. Accessed June 25, 2019;
- Fitzpatrick Z, et al. Mol Ther Meth Clin Dev 2018;9:119–129.
- Wang D, et al. Nat Rev Drug Discov 2019;18(5):358–378.
- Nayak S, Herzog RW. Gene Ther 2010;17(3):295–304.
- Bessis N, et al. Gene Ther 2004;11:S10–S17.