Choice of Upstream Bioreactor Technologies for Industrial Scale Viral Manufacturing (White Paper USD3244)

Gene therapy, including oncolytic viruses, where new genetic material is introduced into the body, holds promise to cure or alleviate symptoms of many different diseases. In the last few years, the field has seen rapid growth with at least 11 drugs approved globally. A search on the term ‘gene therapy’ returns 734 industry sponsored clinical trials worldwide with 464 in the US. The promise of the field has led to large amounts of investment and it is expected that the value of the gene therapy market will exceed $10B in 2025(1).
Viruses are a popular choice for gene delivery due to their target cell specificity, relatively high target cell infectivity and low toxicity upon infection. Table 1 shows typically used viruses and their suitability for various applications. Adeno-associated virus (AAV) vectors are the most widely used system in current clinical development.
Gene therapy can be broadly broken down into two categories depending on whether the genetic modification takes place in– or ex-vivo. This, along with the length of genetic material being introduced, the cell type being targeted, and whether the therapies’ efficacy requires integration of the genetic material into the patient’s genome determines which vector is best suited.

Clinical Success
Current clinical interest in gene therapy is recent. The field had been under a cloud since the death in 1999 of a young patient brought most clinical trials to a halt(2). Two events are often cited as catalysts for the revitalization of the field. The first was the publication of clinical trial results of a successful gene therapy trial in hemophilia B in which, of the six patients treated, 4 were able to discontinue clotting medications while the other two were able to reduce their doses, with no significant adverse events being reported(3). The second was the approval by the European Medicines Agency of UniQure’s Glybera♦ to treat lipoprotein lipase deficiency in 2012(4). More recently the approval of Kymriah♦ in August 2017 and Yescarta♦ in October 2017, the world’s first two marketed chimeric antigen receptor (CAR)-T cell therapies (5) for the treatment of various leukemias and lymphomas, is a significant milestone in this very promising new class of therapies that could be adapted to a wide variety of diseases. The approval of Luxturnau in the USA shows the continued momentum in the field. Table 2 shows the gene therapies with marketing approval.

Much of the initial development of these therapies takes place at academic centers but as the therapies progress into clinical development, there is a requirement to increase quantity and quality of the virus produced. This requires investment and therapies generally get licensed out to established companies or spun-off into separate companies in order to raise the capital required. As the industry matures, companies will require higher quality products at an earlier stage in development and manufacturing systems that can scale to meet projected commercial demand.

Culture Systems for Viral Vector Manufacturing
A major decision in viral vector product development for gene therapy is the choice of expression system. This can be either adherent or suspension-adapted cells. Adherent cells are cells which must be attached to a surface in order to grow and produce the intended virus. Suspension cells can be grown in traditional suspension bioreactors. Typically, most suspension cells were originally adherent and have been adapted to work in suspension culture.
In addition to the type of cell culture another consideration is the means by which the material to assemble the virus is introduced into the production cell. Transient transfection, infection and creation of producer cells lines are all utilized. Transient transfection uses plasmid DNA, usually two or three plasmids, each with part of the genetic material required to assemble the virus within the cell. An infection process uses recombinant viruses containing vector genetic information to infect the target cell and cause it to create the viral vector. Producer cells are cells into which the genetic material to create the viral vector is stably integrated into the cell.
Early on in therapeutic development, viral vectors are manufactured using transient transfection in adherent cells on 2-dimensional systems such as cell factories or roller bottles. These processes are sufficient for Phase I/II trials which are typically only a few patients. Scale-up to Phase III/commercial-scale, requires a change in manufacturing to achieve the amount of virus required to treat even a small patient population. As gene therapy evolves, it will move towards indications requiring high amounts of virus either because of the tissue targeted (e.g. muscular dystrophy) or the large patient populations (e.g. hemophilia, cystic fibrosis).
Scale is also a consideration as therapies move into Phase III and beyond. Batch size can vary widely depending on the number of patients and the dose required per patient. For some rare diseases, one batch may only produce enough virus for one patient. However, for some of the more prevalent indications, batches must be able to produce enough virus for hundreds of patients. As a result, batch sizes could vary from 1012 viral genomes (vg)/batch up to 1018 vg/batch or even higher. Cell factory and roller bottle processes quickly run into scaling issues where the number of vessels required leads to very long manufacturing times, high labor costs and high risk due to the number of manipulations required.
The alternatives are to scale-up an adherent cell process in a fixed-bed bioreactor or move to suspension culture using stirred tanks. Suspension culture requires either adapting the adherent cells to suspension, or moving to a different system such as producer cell lines or insect cells. These changes are not trivial and can have an effect on product quality, yield, cost and acceptance by regulatory agencies all of which can have a serious impact on project timelines and ultimately time to market.
Hemophilia A is an example of the manufacturing challenge of a high dose therapy for a large patient population. Hemophilia A affects an estimated 16,000 males in the U.S. and 320,000 worldwide. During clinical trials, patients have been given 6 x 1013 vg per kilogram of patient body weight(3). If this becomes the approved dose and assuming the average patient weighs 35 kg (the target patient population is generally under 12 years of age), then a typical dose is 2.1 x 1015 vg/patients. Using a suspension culture, baculovirus-based process to produce AAV and assuming a 25% final yield after downstream processing including empty capsid removal means that the upstream process has to produce 1.68 x 1016 vg/patient. Treating 1000 patients/year would require 1.68 x 1019 vg coming from the upstream process. Assuming 2 x 1014 vg/liter, 42,000 liters of culture material would need to be produced annually.

Single-Use, Fixed-Bed Bioreactors
Fixed-bed bioreactors have emerged as an ideal technology to support the large-scale (1016 – 1017 vg per batch) production of viral vectors. Primary advantages of employing a fixed-bed bioreactor technology include direct transfer of the 2D reference process which minimizes risk and saves time; larger surface areas to which adherent cells can attach, expand and then be infected or transfected for viral vector production; the ability to achieve higher densities of cells/mL; real-time control of parameters such as pH, dissolved oxygen (DO), temperature, perfusion, and agitation; and low shear-stress on shear-sensitive cells(6).

The iCELLis® bioreactor is a fully-integrated, high-cell density bioreactor designed to simplify processes by combining the advantages of single-use technologies with the benefits of a fixed-bed system. The compact system – designed for quick implementation and ease-of-use – represents a new generation of single-use bioreactors.

Looking to learn more about moving up from lab scale to industrial scale? Download the full white paper, “Choice of Upstream Bioreactor Technologies for Industrial Scale Viral Manufacturing” to discover:

• What are the best upstream technology choices for viral vector manufacturing?
• How are scale, cost and process development time affected?
• How does upstream technology influence the entire manufacturing workflow?

To download the full white paper click here


© 2018, Pall Corporation. Pall, Allegro, and iCELLis are trademarks of Pall Corporation. ® indicates a trademark registered in the USA and TM indicates a common law trademark. Filtration.Separation.Solution. is a service mark of Pall Corporation. uGlybera is a trademark of Uniqure, Imlygic is a trademark of Amgen, Kymriah is a trademark of Novartis, Luxturna is a trademark of Spark Therapeutics, Strimvelis is a trademark of GSK, Yescarta is a trademark of Kite Pharma/Gilead, and Zalmoxis is a trademark of Molmed.

1. Roots Analysis (2015). Gene Therapy Market 2015-2025.
2. Raper et al. (2003). Molecular Genetics and Metabolism 80(1-2):148-58.
3. Nathwani et al. (2011). New England Journal of Medicine, 365 (25):2357-65.
4. European Medicines Agency Website
5. FDA Website,
6. Oh et al. (2012, March). Meeting Lot-Size Challenges of Manufacturing Adherent Cells for Therapy. Bioprocess International.
7. Powers et al. (2016). Human Gene Therapy Methods 27(3):112-2
8. Lesch et al. (2015). Human Gene Therapy 26(8):560-71
9. Wang et al. (2015). Journal of Immunotherapy. 38(3):127-35

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