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Gene therapies represent a very different paradigm than conventional therapeutics. Not only are most single-dose, curative treatments, many candidates in the clinic that are nearing commercialization target rare diseases with limited patient populations and no existing treatment options. Downstream separation issues, lack of appropriate analytical tools, and capacity and sourcing issues are all challenges manufacturers are facing. There is no one-size-fits all manufacturing solution for these complex products. Purity requirements, vector quantity, and other needs vary depending on the indication, size of the patient population, route of administration, and dosage required.
Solutions for the Immediate Term—Scalable Transfection
For the immediate term, it is important to focus on existing production processes that are more appropriate for GMP manufacturing, scale up, and commercial launch. Transient transfection is the fastest and most widely used and regulatory-validated approach, and the scalability limitations can be successfully overcome with scaling out and pooling strategies.
Fixed-bed bioreactor options for scalable adherent transient transfection are also available. The iCELLis Bioreactor platform from Pall Biotech has been used for the commercial production of approved products, and the introduction of the scale-X fixed-bed bioreactor portfolio from Univercells Technologies supports the viability of this approach, which in theory has the potential to offer greater scalability than the iCELLis Bioreactor with a comparable growth substrate for the cells.
Co-infection methods using the insect-based baculovirus expression vector system (BEVS) and human-derived herpes simplex virus (HSV) type 1 systems are ultimately more scalable than transient transfection. Active infection methods, in fact, have proven to be efficient even at the 2,000L scale. Additionally, these methods often result in higher yields by at least 10-fold and higher percentages of full capsids out of the bioreactor, increasing the feasibility of ion-exchange methods to achieve an acceptable purity profile.
Solutions for the Longer Term—Cell Lines and Potency Assays
The most robust and scalable solutions for AAV vector manufacturing leverage packaging and producer cell lines. Packaging cell lines contain the rep and cap components, and only the gene of interest (GOI) must be transfected into the cell. Producer cell lines have both the rep and cap components and the GOI integrated into the host cell genome.
It cannot be stressed enough that putting off development of potency assays until after Phase I studies can leave drug developers scrambling to put good methods into place when their products are successful and ready to move to late-stage development. The need to demonstrate correct expression and activity is a very complex challenge that can be compounded if left until late in the development cycle. The lack of a good potency assay also makes the burden of demonstrating comparability even higher, and practically ensures that no process changes will be made regardless of the need for optimization.
About the Center for Breakthrough Medicines
With in-house capabilities for plasmid manufacturing, quality by design (QbD) process development, high throughput vector manufacturing and integrated analytical and testing capabilities at a single source, CBM’s vector solutions drastically simplifies the value chain and accelerates timelines at every stage of development and commercialization. Since inception CBM has actively aligned with partners across academia and industry to bring in novel technologies and platforms to ensure quality while accelerating manufacturing of vector based therapies.