Solving gene therapy manufacturing challenges with continuous processing
Tania Pereira Chilima, CTO at Univercells Technologies examines the challenges gene therapies face during production and how integrated and continuous processing can help.
Over the last decade, the industry has advanced monoclonal antibody (mAb) processes, working toward continuous processing to reduce manufacturing footprint and increase the overall productivity. Initially this work started with increasing upstream productivity before moving into overcoming midstream and downstream processing challenges. These unit operations would eventually be combined via significant technology innovations.
With so much progress made in mAb production, the industry is now seeking answers for newer modalities like gene therapies (GTs). Though demand for gene therapies is skyrocketing, these products are dependent on the availability of viral vectors for commercialisation. Present technologies used for mAbs deliver low titers and limited performance, constraining developers to scaling-out their process rather than scaling-up. The need to run parallel operations increase the overall volume and footprint needed to achieve commercial production scales.
A rapidly growing sector
The gene therapy (GT) market is expected to be worth USD 12 bn by 2025. These products target several indications with no current treatment, resulting in significant improvements in patients’ quality of life and in some cases a chance at life altogether. In contrast with mAbs, where the annual demand (in the US) can be estimated to be between hundreds of grams (e.g. Remicade®) to the hundreds of kg (e.g. Rituxan®), GT products can have differences in demand above 7logs. For example, an AAV-based treatment for Leber’s congenital amaurosis may have a dose size of 1x1011 viral genomes (vgs) whilst a treatment for Spinal muscular atrophy (SMA) would likely have doses in the range of 1x1014 vgs. Moreover, a treatment for Duchenne muscular dystrophy (DMD) is forecasted to result in an annual demand 1x1020 vgs due to a combination of high dose per patient and annual demand.
As GT developers often endeavour to target different indications, the significant differences in annual demand has caused GT manufacturers to adopt different technologies for different types of applications, rather than adopting a single technology and adapting the scale according to the indication requirements as it is done in the mAbs industry.
A different set of challenges
Laboratory-based viral vector manufacture relies on a scale-out approach to reach the target scale. Technologies used in this approach include cell factories and hyperflasks. Scaling-out to achieve large quantities of viral vectors, as for any other class of biologics, offers several drawbacks such as capacity constraints, high number of manual operations, etc. leading to footprint, CAPEX/OPEX and reproducibility issues.
Packed-bed bioreactors, historically used for vaccine applications, have been adapted to the gene therapy field to provide a scalable solution for viral vector production using adherent cells. However, it became apparent that these bioreactors could not provide sufficient capacity for GT products with high annual demands. These capacity constraints have incentivised gene therapy developers to look to suspension cell culture in stirred tank bioreactors (STRs).
STRs seem to be the most flexible and scalable technology across the traditional technologies used for GT manufacture. However, at very large annual demands (e.g., Hemophilia A or Duchenne Muscular Dystrophy), even 2,000L STRs would not suffice. For such scenarios, the capacity gap can only be addressed by scaling out production with multiple systems in parallel. When using STRs with 1,000’s of liters of harvest volume, significant volumes of product containing media must be processed at the interface between upstream and midstream processing which has an impact on the facility design and footprint as well as ease of operations. This effect is magnified for indications requiring multiple STRs operating in parallel such as Duchene Muscular Dystrophy. Moreover, developing and scaling-up viral vector processes in stirred tank bioreactors can be costly and time-consuming and require significant knowhow and many times yield lower specific cell productivities that adherent-based processes.
mAb developers have applied integrated continuous processing with STRs operating in perfusion chained to multi-column systems to increase productivity while reducing footprint. Direct transfer of these process designs to GT manufacture using STRs poses challenges given the shear sensitive nature of HEK293 cells (generally used for viral vector production), making it difficult to incorporate cell retaining systems such as ATFs and TFFs.
Continuous improvement
Recent technology innovation offers a paradigm shift in integrated continuous manufacture of viral vectors with next generation equipment purposefully designed to overcome challenges. These technologies apply the principles of process intensification and chaining to enable integrated continuous processing and redefine scalability in GT manufacture. Intensification refers to achieving high capacity in small operating footprint and chaining refers to connecting different unit operations together synchronising and automating them.
Looking ahead
Increasing demand for flexible expression systems for adherent and suspension processes will continue to drive the acceleration of new approaches for efficient, cost-effective GT processes. Technology innovation and adoption can help the industry to overcome the barriers to commercial gene therapy production in high performance, integrated, continuous solutions.