It's what's on the inside that counts: Capsid content as a critical quality attribute for AAV characterization

Recombinant adeno-associated virus (rAAV) vectors exhibit complex heterogeneity in capsid content. Although a growing array of analytical platforms can interrogate different capsid attributes, no single method provides a comprehensive or unequivocal assessment. Critically, current approaches often fail to evaluate genome integrity, an emerging important quality attribute. Incomplete genomes can contribute to viral genome titers without conferring therapeutic benefit, while simultaneously increasing immunogenic burden and risk of adverse events. Discordant results from orthogonal assays further complicate interpretation and cross-laboratory comparisons. Here, we highlight the limitations of existing characterization strategies and advocate for robust analytical frameworks that directly assess genome completeness. We propose best-practice guidelines, including improved genome integrity assays and harmonized reporting, to better link capsid content analytics with potency and patient safety in gene therapy development.