Non-clinical safety assessment crucial for CRISPR-based gene therapies

The rapid evolution of CRISPR/Cas genome editing has redefined the possibilities of cellular and gene therapy, enabling precise correction, disruption, and regulation of disease-associated genes. Yet, as genome editing technologies transition from laboratory innovation to clinical application, ensuring robust non-clinical safety assessment has become a critical priority.

This new review, published in Genes & Diseases, by authors from Cell and Gene Therapy Catapult, Guy's Hospital, United Kingdom, provides a comprehensive evaluation of non-clinical safety considerations required for the responsible development of CRISPR/Cas-modified cellular and gene therapy products.

The review systematically examines safety risks across ex vivo and in vivo genome editing platforms, emphasizing that non-clinical programs must extend beyond proof-of-concept to include toxicology, biodistribution, immunogenicity, tumorigenicity, and long-term persistence analyses. Adopting a regulatory-aligned, risk-based approach consistent with FDA and EMA guidance, the authors underscore that study design must be tailored to the specific gene therapy product, delivery route, target tissue, and intended patient population.

Central to the discussion are genotoxic risks associated with CRISPR-induced double-strand DNA breaks. Error-prone repair through non-homologous end joining may generate unintended insertions, deletions, chromosomal rearrangements, and p53-mediated DNA damage responses, potentially enriching oncogenic clones. The review highlights how advances such as high-fidelity Cas variants, base editing, and prime editing technologies may mitigate these risks by reducing off-target activity and minimizing double-strand break formation.

Delivery strategy is presented as a major determinant of safety. Viral vectors-including adeno-associated virus, adenovirus, and lentivirus-offer efficient gene transfer but raise concerns regarding immunogenicity, insertional mutagenesis, and dose-related toxicity. Non-viral approaches, particularly lipid nanoparticle-mediated delivery of Cas9 mRNA or ribonucleoprotein complexes, are discussed as emerging platforms that allow transient nuclease expression and potentially improved safety profiles.

The authors also address immunological challenges stemming from the bacterial origin of Cas proteins. Evidence of pre-existing anti-Cas9 antibodies and reactive T cells in human populations underscores the need for immune screening, epitope engineering, and careful monitoring during clinical development. Integration of in silico guide RNA design tools, next-generation sequencing-based off-target analysis, and long-term tumorigenicity assessment is recommended to strengthen translational confidence.

Collectively, this review positions non-clinical safety evaluation as a multidisciplinary foundation for CRISPR/Cas therapeutic advancement. By outlining structured risk mitigation strategies, it provides a practical roadmap for accelerating genome-edited therapies toward clinical application while maintaining rigorous patient safety standards.