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Grant Cameron, Director at Clydeworth Consulting, examines the benefits of process intensification and highlights the steps which will improve process productivity, reduce environmental impact and decrease the cost of therapy manufacture while maintaining product quality.
The move to continuous bioprocessing has been a major topic for a number of years however, challenges remain despite technological and regulatory progress. Biological drug and therapy developers and manufacturers are under scrutiny regarding pricing and this pressure is passed down to their suppliers to respond positively to these challenges. This article draws attention to the benefits of process intensification which includes –but is not exclusively continuous – and to highlight that a series of steps can be taken to improve process productivity, reduce environmental impact and decrease the cost of therapy manufacture while critically maintaining or even improving product quality. The move to an intensified process can be a managed, stepwise transition rather than a giant leap into the unknown which is often how it appears from marketing campaigns and media articles.
Is it all about continuous?
We have witnessed in the last 18 months the importance that rapid production of quality biological therapies and vaccines can play globally. The ability of the bioprocessing industry to dramatically shift priorities and scale up production of new entities demonstrates the ingenuity, resourcefulness and ability of the sector. However, outside of Covid-related emergencies, a critical factor for the industry is that developers and manufacturers are under pressure to reduce the price of their drugs and therapies and in particular, biologics and cell therapies. The final price of a therapy is a multi-faceted question, particularly in the first world. However, a critical factor underpinning any negotiations is what it costs to make the therapy in the first place; the Cost Of Goods (COG). To enable worldwide distribution of high quality, efficacious biologics – in particular to poorer countries – a low manufacturing cost per dose should help in more equal distribution notwithstanding the political barriers that will inevitably delay efforts.
Singe use products
The industry, including the suppliers of the technologies and equipment used to make biologics, are aware of this pressure and have been investing in processes and technologies to reduce cost, increase flexibility while maintaining or improving product quality. The market for therapies is moving away from the blockbuster drug to address conditions which affect smaller populations. This means that a production facility must be able to manage multiple products and this has been made possible by the implementation of Single Use Products (SUP). The range of SUP now covers the majority of the bioprocess range from bioreactors, storage and mixing bags, filter cartridges, chromatography modules and crossflow cassettes. These enable a facility to carry out a rapid change in the product being manufactured as there is limited cleaning and validation required – nowhere is this seen more clearly than in the embracing of SUP by Contract Development and Manufacturing Organizations (CDMOs). These play a critical role in supporting small innovative companies to produce GMP material for clinical trials, for early commercialisation, ongoing commercial production and for capacity issues throughout the product lifetime for small and large biopharma companies alike.
Waiving IP as a solution
Historically, process developers and manufacturers have made much of creating a platform, for instance, for the production of a monoclonal antibody therapy (mAb). Irrespective of the target of the mAb most companies follow a similar process as one mAb is very similar, in a physicochemical sense, to any other. While each process is ‘tweaked’ to maximise production yields and quality, the platform process is well known and understood. The value in a mAb therapy is not so much about how you make it but the efficacy of the product and the potential market size. Therefore, in the mAb market there is openness in discussing and sharing process developments, even if not in specific technical detail. This is in contrast for instance to the classical blood and plasma market where everyone has the same starting material and is purifying the same target molecules. Therefore, the critical know-how is in how to extract the targets efficiently and cost-effectively. The value to the company is the process which is guarded tightly even if only by minor modification from the standard Cohn Process.
During the Covid crisis there was government and media attention around countries waiving the IP rights for Covid-19 vaccines to speed up supply in particular to poorer countries. While it is understood that any patent protection is to prevent un-licensed production of the therapy, patent documents in themselves do not give the level of technical and process detail required to proceed with manufacturing the product to the same quality and cost as the original manufacturer. Any changes to the process require fresh regulatory approval which to a major extent would negate any time benefit derived from the waiving of patent protection. Working closely with the product and patent owner, offering additional capacity and capable staff to increase production may yield better results, under licence, and not cause damage to the existing legal framework surrounding IP protection of critical biologics.
Future industry goals
Industry Advocacy Groups such as the BioPhorum Operations Group have published Technology Roadmap documents3 which detail future industry goals. These include a ten-fold decrease in the COG for a monoclonal antibody therapy from greater than $100/gram to ~$10/gram while also reducing the capital investment, space requirement and resource utilisation. These documents have been drawn up by a team of end-users and suppliers and to a degree could be considered as the JFK ‘moon-shot’ vision setting exercise for the bioprocess industry. Reaching these goals will require substantial innovation, investment and commitment from industry players, healthcare systems and governments.
In addition to the reduction in COG the BPOG roadmap considers an increase in production capacity from a facility with lower capital investment, improving the robustness of operation with lower product wastage and also reducing environmental impact due to reductions in water and energy usage. Many of these goals can be reached by process intensification practises.
Fed-batch to continuous processes
The current embedded bioprocess is termed as fed-batch processing. A fed-batch process is where the cells are grown to a suitable cell density and viability in a small starting volume and transferred serially into larger and larger volume bioreactors until reaching the desired production bioreactor scale, perhaps 2,000L. The series of cultures prior to the production bioreactor is termed the seed train and is a key focus for intensification to decrease the timeline and technical risks while increasing output. This cell culture is grown with the product, in this case a mAb, being manufactured by the cells and secreted into the medium for 10–14 days prior to separation of the cells from the medium containing the product of interest. The entire process takes a number of weeks to get to the production bioreactor so late-stage failures of equipment or consumables can carry substantial cost and frustration so steps which diminish the risks and timelines are welcome.
One of the key solutions that has been marketed widely is a move from the current paradigm of fed-batch bioprocess to a continuous process akin to those employed with great success in other industries. The promise of lower COG, high production capacity within a smaller, more environmentally friendly footprint with even improved product quality is compelling and attractive. However, many challenges remain for the industry to move to continuous bioprocess and it remains to be seen how many existing and new processes become truly continuous. Continuous bioprocessing brings with it multiple technical, regulatory and equipment challenges however, particularly in the upstream area, has been implemented to great effect. The Center for Drug Evaluation and Research (CDER) as part of the US FDA is actively engaging in producing guidance documents and opinion pieces to support the move4 .
The marketing story
The marketing campaigns from the larger players on the supplier side have, for many years, been focused on educating and informing end-users in the biopharma companies what this change will mean and how companies claim or intend to support the move. While market education is invaluable and a great deal of material has been written or discussed in webinars and conferences, the step from fed-batch to continuous can be substantial. This is particularly true if it looks like it needs to be carried out in one ‘giant leap’.
Not always one giant leap
For those not embedded in bioprocess lore it could be seen that this is an inevitable step and it must or should be done in one move. However, it should be made clear that there are many ‘baby steps’ that can be taken which deliver great value with smaller technical and commercial risk. This article will explain some of the smaller steps. These should be kept in mind instead of seeing this change as a high risk, potentially high reward gamble. It is likely, at least in the medium term, that the process approaches that are employed will be far more heterogeneous than in the past and only a certain, possibly small, percentage of processes will ever reach the fully continuous paradigm due to commercial or technical imperatives. Papers such as Xu et al (2020)1 demonstrate that, within companies such as Bristol-Myers Squibb, process intensification is receiving close attention however the developments are being taken in multiple smaller steps over time as they learn about what works and the results presented show the gains that can be achieved in this manner. As they progress their in-house platform is improved for the next molecule that comes down the pipeline.
COG may not be the main pressure
For any company or product, the question of what you are trying to achieve and how far are you willing to go, remains.
Take, for example, a small biotech company with a promising candidate molecule. It has raised funds it believes, to get to the next product value inflexion point – for instance to move from pre-clinical to a post Phase I first-in-human trial. Assuming all goes well they can raise more funds, partner or trade sell to move the candidate therapy on to later trials. The issue is that the funds need to be spent in a way to get them to the inflexion point as quickly as possible. From the bioprocess perspective that means producing a small quantity of material under cGMP conditions to support the planned initial trials. The product value derives from the trial results primarily and not from how efficiently or cheaply you make the product, always assuming quality is maintained. At this point, how much effort is the small biotech going to make to develop a highly efficient, technically challenging process? The conclusion may be not very much which moves the need for advanced process development down the timeline. To be clear, the small biotech still needs to select an appropriate clone, develop media and a feeding strategy that meets the quality, production and regulatory requirements, however would / should continuous bioprocessing be high up their agenda? At some point in the development of the therapy a keen focus will be brought to optimise the production process for robust operation and minimise cost however it remains to be seen across different companies with varying pressures and philosophies when that focus will be directed to process optimisation. Even when that decision point is reached there are a number of options that can be considered that range from sticking to the well-understood path of fed-batch production to the less well understood, more technically challenging and more open to regulatory scrutiny of continuous processing.
The key bioprocess remains the classical monoclonal antibody (mAb) produced in Chinese Hamster Ovary (CHO) cells in a stirred tank bioreactor. The 100th mAb was approved by the FDA in the first half of 2021 and remains by far the powerhouse of biological therapies and the price pressure therefore will fall heavily on this area. However, much is known about the critical quality attributes (CQAs) of mAbs so they are in a strong position to support process intensification development. The recent success of mRNA vaccines from BioNTech/Pfizer and Moderna could herald a shift in this priority however it will not overtake the market power of mAbs for quite some time despite the excitement and investment.
The production process of a biological therapy is usually split into two areas; upstream and downstream. This article focuses mainly on upstream topics with little focus on downstream. However, the interplay between the functions cannot be understated and downstream colleagues should be involved when considering intensification of the upstream as changes there can have dramatic consequences. The maturity in intensification of the mAb process remains heavily weighted towards upstream currently and there are a number of downstream challenges still to be resolved adequately.
The upstream portion is from starting a CHO cell culture, often from a frozen aliquot from a Working Cell Bank, through a multi-step volume scale up (the seed train) to the production bioreactor (up to 2,000L which is the largest SUP bioreactor system widely available). Upstream often includes primary recovery which is the separation of the cells from the liquid. The liquid is the spent medium which, for a CHO culture, contains the mAb product of interest as it is secreted by the cells into the liquid. The concentration of the mAb in the liquid is the titre and plays a key role in determining the COG and the downstream requirements. For a mAb in a fed-batch process a typical titre could be considered as 3–6 g/L so yield from a 2,000L bioreactor could be 6–12kg of product, before losses in downstream purification.
To increase cell density and maintain high cell viability in longer term cultures the key technology is perfusion. This is a technique where the cells can be kept in the bioreactor and continue to divide and grow while fresh medium is added and the volume maintained by filtration of the medium which also removes waste materials and sometimes the product. Removal of the waste materials supports longer term cultures as they would be deleterious to the cells as they increase in concentration. Perfusion is possible with the inclusion of a Cell Retention Device (CRD) into the bioreactor setup. There are CRD options depending on goals and they all work in conjunction with the removal of ‘spent’ media and replenishment with fresh to maintain consistent bioreactor volume:
- A molecular weight selective membrane incorporated into a rocking motion bioreactor bag which retains cells and product in the bag while exchanging media
- A microfiltration membrane in an external device with molecular weight cut off which retains the cells in the bioreactor however allows the product to be exchanged with the spent media
- An ultrafiltration membrane with small molecular weight cut off in an external device which keeps cells and product inside the bioreactor while permitting media exchange
The CRD technology is a critical component of a number of process intensification processes and is applied in a number of ways and often in a number of places within the culture process with varying benefits and risks. In the case where the cells continue to produce product and it is removed continually the process can truly be called a continuous upstream process. Cultures can be maintained for weeks or even months however the majority of current continuous cultures are kept for three to four weeks only. Reasons for this can be that the required productivity is achieved within this timescale, that longer periods increase technical risk and that some SUP components used in the process are not validated currently for longer time periods.
Downstream is essentially the purification of the target molecule from the cell-depleted spent medium liquid to a form which is suitable for injection into a human. Core technologies employed downstream are listed briefly below however this list is far from exhaustive
- Depth filtration
- Sterile filtration (nominal 0.2µm pore size)
- Virus filtration (nominal 20nm pore size)
- Affinity (Protein A for mAb purification)
- Ion Exchange
- Hydrophobic Interaction
- Tangential Flow Filtration (TFF)
- Dialysis/diafiltration (buffer exchange)
- Ultrafiltration (Concentration)
These technologies are used in the purification processes for most modalities, sometimes multiple times, however the order in which the technologies are applied and their particular usage details give each process their distinctive features, benefits and contribution to the overall COG. An exception to this would be a cell therapy, where the cell itself is the product and the liquid is waste. Separation, concentration, washing and preservation/maintenance of the cells requires different approaches and the downstream portion for those therapies can be short.
There are a number of options that can be considered which can deliver improvements in speed, titre and volumetric productivity which are technically less challenging, quicker and less costly to implement. It should also be noted that there is no single big thing that can be done to revolutionise a process. The following is a high-level list as a guide for further research and consideration.
High density cell banks
GMP bioproduction starts with the selection and characterisation of a single clone. This clone is grown and then aliquots are frozen to create a Master Cell Bank. A great deal of analysis is carried out to characterise this bank and from that a Working Cell Bank is created. Typically, a small volume (less than or equal to 5mL) of frozen cells are the starting point of the seed train. Every seed train starts with a fresh ‘identical’ aliquot from the Working Cell Bank so the manufacturer is confident that the clone will behave as characterised and will produce the desired product to the required quality.
The innovation is to increase the cell density from 1-10 million cells/mL up to 50–100million cells/mL within the frozen aliquot and/or the volume frozen from sub-5mL to tens or even hundreds of mL frozen and stored in specialised bags. Starting your seed train with a higher cell density and larger volume can reduce the number of cultures that you need to grow before getting to the production bioreactor thus saving time and reducing risk. Over the course of a seed to production run it should be possible to save three–five days from a total timeline of 30–40 days with reduced technical and operational risks.
Rocking motion perfusion cultures
Rocking Motion (RM) bioreactors have become a mainstay in bioprocessing over the last 20 years and in more recent years can include the capability of carrying out perfusion cultures within the bag. There is an upper volume limit of around 100L working volume in a 200L bag therefore they are not large enough to replace a stirred tank bioreactor as a production bioreactor for mAb processes, however, they are used in regenerative medicine cell therapy campaigns. When focussing on seed train intensification however at the smaller volumes with the perfusion capabilities they can be cultured to very high cell densities (~100 million cells/mL) at high cell viability (>95%) so can reduce the number of steps before inoculating the production bioreactor. When used in conjunction with high cell density cell bank starter cultures, days can be taken out of the entire bioproduction run and saving on resources and again reducing risk.
The concept of continuous bioprocessing in marketing literature has commonly placed perfusion of the production bioreactor at its heart. An alternative is to intensify the N-1 bioreactor, whether STR or rocking motion bag, which in turn increases the number of cells added from the N-1 to the production (N) bioreactor. This has two impacts; the first is to reduce the time of the production run and the other is to increase the volumetric productivity. The precise benefits of these approaches are subject to the specific clone and approaches however as a guideline it may be possible to save 10% in the total process time with a volumetric productivity gain from 20–50% over a fed-batch process. Again, this approach can be used in conjunction with high cell density cell bank starting material and rocking motion perfusion cultures in a serial manner building up the benefits generated by these approaches however the process is still not continuous.
The final step
We have seen that modifications made to the seed train can have positive impacts on time, resources and productivity without making substantial capital investments or taking technical, commercial or regulatory risks. However, even with the final production bioreactor there are options to improve the process in particular if the seed train has been intensified in steps beforehand.
Concentrated Fed Batch (CFB) – the CRD attached to the production bioreactor is in ultrafiltration mode so media is exchanged with the cells and the product accumulating in the bioreactor. The product and cells are concentrated in the production bioreactor and the challenge is the clarification of the bioreactor at high cell density.
Dynamic Perfusion – similar in set up to CFB however the CRD is in microfiltration mode so the cells are retained in the bioreactor while the product is removed with the spent media and can be fed into the downstream process. As the majority of the product is removed over time then this can be collected or processed in small batches or continually and the final bioreactor contents may or may not be processed depending on whether it is economically and technically viable
Continuous Perfusion – Continuous perfusion is what the majority would understand by ‘continuous upstream processing’ and in addition to the microfiltration CRD also has scheduled cell bleeds where a larger portion of the media, including cells and product is removed and fresh medium replaced. Product is removed continually and processed as per dynamic perfusion.
As stated, it may be necessary to clarify high cell density bioreactors from a number of these scenarios. The classical route of depth filtration begins to be challenged above cell densities of 20 – 30 million cells/mL and in perfusion cultures cell densities of in excess of 50 million to even 100 million cells/mL are reported (Saballus et al, (2021)2). This requires approaches such as centrifugation and while the predominant technology may still be the disc-stack option there are now single-use centrifugation systems available (kSep from Sartorius, CultureOne from Alfa Laval) which are relatively agnostic of cell density.
With the high-level terms of continuous bioprocessing or process intensification there are options that should be considered depending on the goals and needs of the process, the product and the company involved. The key takeaway is not to be consumed with continuous being the only option.
There are companies making excellent material to educate on this topic and hopefully this article outlines some of the variety that can be considered away from company marketing campaigns. Talk to a number of companies who are active in the space; Cytiva, Merck Millipore, Pall, Repligen, Sartorius and ThermoFisher for instance. Their experts and application specialists will know the risks and rewards well. Do not be afraid to ask for support and talk to more than one as each company has strengths and weaknesses! Also remember these approaches require advanced training of staff to support highly technical processes with regulatory oversight. This can be a positive topic to support the maintenance or building of a highly technically proficient and motivated workforce. Process intensification is very much worthwhile however it can be approached one step at a time with clear, measurable benefits.
Volume 22, Issue 4 – Fall 2021
About the author
Grant Cameron, PhD, is Director at Clydeworth Consulting. He formed Clydeworth Consulting after holding the position of Head of Product Management for downstream products at Sartorius Stedim Biotech. He has over 25 years’ experience in the supply of equipment, consumables and services to the biopharma market.
- Jianlin Xu*, Matthew S. Rehmann, Mengmeng Xu, Shun Zheng, Charles Hill, Qin He, Michael C. Borys and Zheng Jian Li (2020) Bioresour. Bioprocess 7:17. https://doi.org/10.1186/s40643-020-00304-y
- Martin Saballus, Lucy Nisser, Markus Kampmann and Gerhard Greller (2021) Biochemical Engineering Journal 167: 107887. https://doi.org/10.1016/j.bej.2020.107887