Gene Therapy Utilizing Adeno-Associated Viral (AAV) Vectors: Historical Data Review To Characterize Common Challenges And Identify Opportunities For Refinement

By Kelsey Brooks, Stefanie Orr, Ashwini Ravichandran, Kevin Hsu, Shu Yun Cheng, Narine Lalayeva, and Norbert Makori

Recent advancements in gene therapy using both viral and non-viral vectors have driven progress in preclinical and clinical drug development. In preclinical research, the safety assessment of adeno-associated viral (AAV) vector-based therapeutics relies primarily on nonhuman primates (NHPs). However, the prevalence of naturally occurring neutralizing antibodies (nAb) in these animals necessitates extensive screening to identify a sufficient cohort with negative titers. Additionally, corticosteroid pretreatment is often required before AAV vector administration to mitigate potential adverse reactions.

To address these challenges, we analyzed data from 22 toxicology studies conducted over recent years, aiming to determine the typical number of animals required for nAb screening, establish appropriate corticosteroid dosing prior to AAV vector administration, and characterize the most common in-life observations. Our findings indicate that approximately 38% (430/1119) of screened animals met the criteria for study inclusion, exhibiting negative or low viral titers (≤5 nAb50 in HEK293 cells). Pretreatment with 2 mg/kg of dexamethasone administered 1–2 hours before AAV dosing effectively mitigated immune-related responses. Notably, AAV administration had no discernible effect on body weight, and most post-dose clinical signs were minor and not directly linked to the vector.

This historical dataset provides a valuable reference for optimizing study designs in AAV vector-based therapeutics, supporting more efficient screening strategies and contributing to the refinement and reduction of animal use in safety testing.