Nonclinical toxicity study duration in AAV gene therapy development: Evidence from industry survey supports adequacy of short-term assessments

Abstract

Adeno-associated virus (AAV)-based gene therapies are emerging as transformative treatments for serious diseases; however, determining the optimal duration of nonclinical toxicity studies remains a key regulatory and scientific question. To address this, the EFPIA Gene Therapy Working Group surveyed 24 AAV gene therapy programs across 13 companies to assess current practices and the value of long-term (≥6 months) toxicity studies. Results showed that ≤3-month studies were sufficient to characterize the toxicology profile in 87.5% of programs that completed a toxicity assessment in a ≥6-month long-term chronic studies, with only one program identifying new toxicities in longer chronic studies with impact on clinical development. Common AAV-related toxicities, such as liver and dorsal root ganglia effects, were observed within the first 6 weeks post-administration. Longer studies were often driven by sponsor's perception based on internal experience or need to assess durability, rather than regulatory requirements. These findings aligned with regulatory reviews of approved AAV products (e.g., Zolgensma, Luxturna, Roctavian) that consistently demonstrated the adequacy of ≤3-month studies for approved and marketed products. The outcome of this survey supports a risk-based, science-driven approach to in vivo study duration, emphasizing that shorter-term studies are generally sufficient for identifying relevant toxicities associated with AAV-based gene therapies. Embracing this approach can reduce animal use, accelerate development timelines, and support harmonized regulatory expectations for AAV gene therapy products.

Keywords: AAV gene therapy; chronic toxicity; nonclinical toxicology; platform-related toxicity; regulatory; risk assessment; study duration.

Graphical abstract

Figure 1

Summary of company demographics of survey respondents Most survey respondents are from large biopharmaceutical companies with a gene therapy portfolio larger than 2 programs, and predominantly more than 5 programs, including 25% of respondents from companies exclusively focused on gene therapy product development.

Figure 2

Program features frequently captured in the survey Most survey responses reflected programs in early clinical development with gene replacement mode of action predominantly by systemic or intra-cerebrospinal fluid routes of administration.

Figure 3

Species selection for IND/CTA-enabling toxicology Species selected for IND/CTA-enabling toxicology (A) and pharmacology studies (B). Mouse was predominantly used in pharmacology studies, while NHPs and mouse were the species of choice for toxicology studies.

Figure 4

Survey responses on the study duration for the toxicology assessment of AAV-based gene therapy candidates Longest toxicity assessment included any toxicology assessment performed as a component of pharmacology studies, while IND/CTA-enabling toxicology assessment were studies primarily designed for toxicology assessment.

Figure 5

Factors influencing the decision to perform ≥6 months toxicity assessment

Figure 6

Assessing the ability for the detection of common AAV platform-related toxicities such as dorsal root ganglia toxicity and hepatotoxicity in ≤3-month toxicity studies