News & Events

Clean Mails – February 2024

A complete testing approach to rAAV vectors

Recombinant adeno-associated virus (rAAV) vectors have emerged as powerful, diverse and precise gene therapy tools, offering promising solutions to previously untreatable genetic disorders. As modified versions of naturally occurring AAVs, they can be harnessed for their ability to target specific tissues and cells by engineering their tropism. AAV vector testing thus needs a comprehensive approach to best meet key technical parameters of different serotypes. AAV vector quality control testing should include various tests to assess for purity, identity, biosafety and potency of rAAVs while taking into account process development (production context, choice of construct, etc.).

With a growing number of GMP and non-GMP assays and methods for AAV vector testing, Clean Cells continues to show flexibility in development and routine application, having partnered with several organizations worldwide to develop serotype-specific assays (AAV2, AAV5, AAV6, AAV8, AAV9). Our ability to generate chimeric AAV with a trusted partner and two detection platforms (HEK293 and HeLa) most notably allow us to quickly develop crucial assays such as replication competent AAV (rcAAV) testing for novel serotypes.

Methods for various production contexts

Comprehensive quality control approaches are key to AAV vector testing and characterization from different production backgrounds: assays should thus consider if the vectors have been produced with plasmids (typically on HEK293 cells) or through other methods (Sf/baculovirus system, novel stable cell line…). With a 200+ portfolio of qPCR assays developed and validated according to ICHQ2 guidelines, Clean Cells is at the forefront of detection and quantification of DNA sequences relating to AAV vector testing, in particular for residual DNA testing (host cell, plasmid, transgene, Adv5, etc.). Comprehensive and compendial testing packages in support of AAV testing have also been developed and validated to characterize substrates (cells, viruses) according to the worldwide regulatory requirements (EP, USP, JP, ICHQ5A). Our production platform provides essential support to sponsors in generating fully characterized cell banks (Sf, HEK293) and virus seeds (baculovirus) in a GMP setting.

Identity, potency and safety of AAV vectors

Safety and potency of products should be established through robust and bespoke AAV vector testing methods, best tailored for each serotype. In particular, assays should show that the process yields qualitative vectors, able to properly infect targeted cells while not generating replication competent AAVs. Through qualified ELISA, qPCR, dPCR and infectivity assay modalities, we can perform non-GMP and cGMP assays for AAV vector testing at different R&D and clinical stages with adequate validation levels, including:

Test nameDescription
Physical particles titrationELISA assay targeting capsid proteins on rAAV particles
Vector genomes titrationAAV vector testing of ITR2 sequence by qPCR/dPCR on rAAV particles
Infectious particles titrationTCID50 determination by Spearman-Kärber-based titration assay on HeLaRC32-complementing cells coupled to ITR qPCR techniques to detect proliferative conditions
Replication-Competent AAV particles (rcAAV) detection3-roung infectivity-based assay on HeLa cells with readout by quantification of rcAAV-specific sequences (rep sequences) by RTqPCR techniques

Bespoke AAV vector testing approaches for evaluation of transduction efficacy, expression efficacy (mRNA by qPCR, protein expression by ELISA), biological activity of expressed proteins, should be taken into consideration when developing novel rAAVs. Clean Cells, with a rich background in development of tools for biologics and AAV characterization, can there be a trusted partner for potency evaluation.

New methods for increased adaptation

Novel tools have recently emerged allowing for increased flexibility in testing, which can be used to derisk processes and/or as complementary AAV vector testing methods intended for regulatory dossiers.

Next-Generation Sequencing is such a modality improving AAV vector QC and turnaround, allowing for quick determination of identity while having the potential to assist in biosafety by detecting contamination events. In addition to NGS, our testing platform welcomes rAAVs testing projects at every stage of development or clinical phase and systematically explores new techniques for continuous improvement of AAV vector testing and characterization.