Bringing Gene-Therapy Product Quality Into Focus

Tim Kelly

September 28, 2022

3 Min Read

Regulatory agencies are scrutinizing gene-therapy product quality more closely than ever, yet such therapies still are produced in small batches and at high costs. Thus, drug companies are struggling to make safe and efficacious gene therapies available to patients. In an April 2022 presentation, Tim Kelly (chief executive officer of Oxford Biomedica Solutions, OXB Solutions) emphasized the importance of addressing both process output and product quality when manufacturing adenoassociated virus (AAV)-based gene therapies. Such an approach requires deep expertise and comprehensive capabilities.

Kelly’s Presentation
Product quality has become a priority for the gene-therapy industry amid clinical-trial holds relating to problems with chemistry, manufacturing, and controls (CMC). Meanwhile, regulatory requirements are increasing for AAV-based products. Authorities expect companies to know product critical quality attributes (CQAs) at increasingly early clinical stages. Agencies also are requesting data from a growing breadth of analytical methods and are requiring that quality control (QC) methods be qualified and even validated early in clinical development. Such concerns are compounding perennial limitations, including small batch sizes, low titers from upstream processes, and trade-offs between AAV titer and product quality during scale-up.

To address such obstacles, gene-therapy manufacturers must leverage deep expertise, abundant experience, and end-to-end capabilities. Kelly noted that having an excellent transfection step is important but insufficient; technical challenges arise during AAV production, purification, formulation, and fill–finish. Manufacturers need comprehensive capabilities and talented staff who have worked with several AAV constructs. He added that program success hinges on a team’s ability to learn about product CQAs. Regulatory agencies are emphasizing methods for quantifying ratios of full to empty/partially full AAV capsids in gene-therapy products. Accurate methods for potency testing also have become important tools. However, manufacturers must be well versed in a complete panel of analytical methods to establish AAV-product quality.

OXB Solutions has established a platform process at its 91,000-ft2 multiproduct facility in Bedford, MA. The process covers all activities from construct design through pivotal-trial manufacturing and has been proven for good manufacturing practice (GMP) compliance at scales up to 500 L. Transfection and cell-culture steps are performed in single-use suspension bioreactors using serum-free media. Downstream purification includes two chromatography steps. The platform has produced more than 45 GMP batches since 2019, enabling five successful investigational new drug (IND) applications. The process has been scaled to 2,000 L, with results from different constructs showing comparable output and quality.

The platform includes access to a comprehensive set of in-house analytical methods, including assays for stability testing and product release. Special methods have been developed for deep genetic sequencing and potency testing.

The platform is designed to optimize vector output and quality. Originally, OXB Solutions used a triple-plasmid transfection system. That process yielded ~100 mL of drug substance, with ~1013 vg/mL. Improvements to the process and to manufacturing execution have increased overall yields and full:empty capsid ratios significantly. OXB Solutions also has developed an optimized dual-plasmid system, with which harvests from a 500-L bioreactor can deliver 1.5 × 1015 vg/L. Purified drug substance can contain 2 × 1017 vectors per batch, up to 90% of which are fully intact. Titers approaching 1015 vg/L have been recorded at the 2,000-L scale.

OXB Solutions offers a full panel of qualified methods to support production of material for phase 1 clinical studies. Orthogonal potency testing also is available at that stage. Drug products can be prepared for cold storage (2–8 °C) using a proprietary formulation.

Questions and Answers
What advice do you have for scaling AAV production up to 2,000 L? It is critical to optimize the transfection step, as OXB Solutions has done using its dual-plasmid system. Careful characterization also helps to ensure that a process can be scaled linearly.

How do purity levels compare between your triple- and dual-transfection systems? OXB Solutions has compared the systems using seven AAV constructs based on three serotypes. Purity levels have tracked closely across all those studies.

What analytical methods are used to evaluate AAV products? The OXB Solutions platform process uses mass spectrometry (MS) and high-performance liquid chromatography (HPLC) extensively during characterization, including assessment of product stability. Analytical ultracentrifugation (AUC) is used to quantify full:empty capsid ratios.

Find the full webinar online at

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