Using continuous processing instead of batch-based processing provides therapeutic manufacturers with a number of advantages. For example, the continuous approach can accelerate production, cut energy needs, reduce waste, and minimize the risk of human error.

GEN recently interviewed several continuous bioprocessing specialists to learn more about this emerging technology. Here is our panel:

Ping Y. Huang, PhD
Director, BioProcess Development, AGC Biologics

Sanchayita Ghose, PhD
Director, Biologics Development, Bristol-Myers Squibb

Dr. Andrew Bulpin, PhD
Head of Process Solutions, MilliporeSigma

Peter R Levison, PhD
Executive Director of Business Development, Pall Life Science

Gerben Zijlstra, PhD
Platform Marketing Manager, Continuous BioManufacturing, Integrated Solutions, Sartorius-Stedim Biotech


GEN: In integrated continuous bioprocessing, various “next generation” technologies are under consideration, including high density cell seeding. Could you comment on this and other innovative approaches and how they fit into your company’s development plans?

Ping Y. Huang, PhD

Huang: Innovations such as integrated bioprocess and other technologies are key to increase productivity and shorten development timelines and to bring more candidates into clinical development. We all know that patients are waiting for more treatment options and this is one of the motivations for many of our scientists coming to work every day.

Ghose: The “one size fits all” concept is rarely applicable in real life situation. This is also true for the concept of integrated continuous bioprocessing, which has seen the advent of multiple discrete technologies that can be used on their own, in groups or integrated into one cohesive process flow. The specific applications and approach that a company adopts will differ based upon the requirements of the end user.

BMS has adopted the use of single-use equipment in some of its manufacturing facilities that primarily allows a faster speed of changeover to accommodate the needs of a strong pipeline. However, we have been well aware historically of the limitations of scale beyond 2,000 L for single-use facilities. Hence, our strategy and focus have been on developing high productivity, cost effective processes that enable larger batch output and filing/launch even at the 2,000 L scale. The multiple continuous processing technologies (upstream and downstream) that BMS has adopted have been mainly geared towards throughput improvement, cost reduction, and getting the most from our existing manufacturing foot-print.

Bulpin: Current and future market needs are driving these innovative approaches. We recently launched our BioContiuum™ Platform, which is a toolbox of process intensification, process analytics, software, automation, and single-use technologies. We believe that it will advance the industry by improving process economics without sacrificing titer or product quality. These features have the potential to revolutionize drug manufacturing, driving improvements in process efficiency and simplifying plant operations and consistency in manufacturing.

Millipore Sigma has been developing and acquiring technologies for the last several years as part of our next generation processing focus, including Clarisolve® polymers and depth filters for those customers who are looking to intensify the upstream portion of their process.

Expanding this vision to the downstream area, our MilliporeSigma’s Pellicon® Single-Pass Tangential Flow Filtration (SPTFF) is a more flexible alternative to the conventional TFF processes. The lack of a recirculation loop, leading to a smaller footprint, makes this operation convenient to accommodate anywhere in a biomanufacturing process where volume reduction is needed, including before or after a column chromatography step.

Levison: Integrated continuous bioprocessing can be viewed as either a continuous downstream process following a fed-batch cell culture or as a continuous downstream process integrated with a continuous upstream process based on perfusion cell culture. In the former case, the cell culture tends to be rate-limiting as the downstream process can be completed typically within 1-2 days. To reduce overall process time high density cell seeding through N-1 perfusion is becoming more widespread. Regardless of whether the cell culture is fed-batch- or perfusion- based once the harvested cell culture fluid (HCCF) is available, the downstream processing sequence is consistent in each application.

However, the process requirements are quite distinct. To address this challenge, Pall Biotech offers a portfolio of scalable single-use technologies for continuous bioprocessing. Our platform is based on acoustic wave separation that can be used either for clarification of fed-batch cell culture or cell retention in perfusion cell culture.

The Cadence® Acoustic Separator Systems generate HCCF from high cell density cultures at high product yield suitable for subsequent purification and UF/DF steps. In addition, we have Cadence BioSMB Process Systems designed for both fed- batch and perfusion applications, Cadence Virus Inactivation system and novel Single Pass TFF platforms for both continuous concentration and diafiltration.

Zijlstra: Sartorius-Stedim Biotech is heavily focusing on providing solutions for next generation processes and in particular for Process Intensification. Specifically, for high cell density seeding, Sartorius-Stedim Biotech has recently launched the FlexSafe RM 200 perfusion bioreactor.

As a 2D rocking motion bioreactor bag with an integrated viable cell density sensor the system is simple to operate in perfusion mode. And with integrated filter welded into the bottom, no external filter and associated controller (e.g., ATF) are required, making the RM 200 perfusion a highly cost-efficient alternative for high cell density seeding. Furthermore, with a working volume of 100 L and proven cell densities well in excess of 50 mln cells/mL, 1000 L bioreactors can be inoculated with well over 5 mln cells/mL and 2000 L bioreactors well over 3 mln cells/mL, thereby reducing the main culture duration and allowing more batches to be produced.

For seed train perfusion approaches at higher volumes (e.g., 200 – 500 L) and for intensified batch or continuous perfusion in the main bioreactor, Sartorius-Stedim Biotech has recently announced a collaboration with Repligen on the integration of the ATF controller functionality in the Sartorius bioreactors, thereby reducing complexity and footprint, as well as enabling improved perfusion process control in stirred tank bioreactors.


GEN: GE Product Manager Jenny Dunker asks “could a hybrid of batch and continuous unit operations be the best solution for your process train?” She suggests that continuous processing is considered more complex than batch processing, and presents a feedback/feedforward control strategy. Please offer your opinion based on your experiences.

Huang: She is exactly right. That is why almost all FIH (first in humans) processes start with batch processes. We are developing an Integrated Recovery & Purification (IRP) train that can be operated as batch mode in FIH, then operated continuously in late and commercial stages to reduce cost without scaleup or scaleout.

Sanchayita Ghose, PhD

Ghose: BMS does use a ‘hybrid’ approach combining batch and continuous unit operations to make it optimum for our multiple processes (both old and new). For the upstream process, we have maintained a fed-batch production bioreactor philosophy, but employ high inoculation cell densities through use of perfusion culture at the seed bioreactor stage generating the inoculum. This results in shorter upstream process durations and opportunities for increased titer.

For the downstream process, numerous continuous manufacturing technologies such as multicolumn continuous chromatography for capture, integrated pool-less polishing steps and automated viral inactivation are being employed. This results in significant cost reduction at the clinical stage and prevents downstream from being the bottleneck in handling higher titers.

All these technologies have been implemented in our largest single-use facility in BMS’s biologics manufacturing network at our flagship campus in Devens, Massachusetts. This facility can flexibly accommodate both traditional as well as this hybrid model for continuous manufacturing interchangeably.

Bulpin: The BioContinuum™ Platform features next generation processes enabling technologies to obtain incremental process benefits now, with a mind to the continuous process of the future. It was designed as a series of products and services from upstream through to final concentration so that customers can pick and choose what they want to employ in order to solve their biggest challenges. With these features in mind, it offers the flexibility that Dunker has in mind in her comments.

Levison: The basic approach to downstream processing in continuous mode is the same as in batch. One uses the same chromatography media, the same filtration media and the same buffers; you simply operate them in a different way. Complexity is a relative term and with the introduction of commercial scalable continuous technologies the perceived complexity should be significantly reduced. Whether an end-user moved directly from batch to fully continuous or adopts a hybrid approach is dependent on many factors ranging from facility fit, process economics, appetite for risk, and regulatory concerns. Typically, each process step in the DSP train will have different performance and cost structure and so selection of the most critical steps for conversion from batch to continuous is thought to the most prudent approach.

In a mAb process the Protein A capture step is often viewed as cost sensitive and a continuous capture step has been shown to offer significant performance and economic benefits. In a perfusion process there can be significant product losses in the cell retention step especially where a filtration system is used. A continuous approach using the Cadence Acoustic Separator Technology minimizes this effect as it does not rely on filtration-based cell retention.

Zijlstra: Indeed several “short” hybrid perfusion approaches have already been mainstream for a while and others are currently emerging. For example, N-1 perfusion, followed by high inoculation seeding has been used for commercial production for many years and is currently being adopted by several manufacturers as a platform technology by BMS and other firms. Concentrated Fed Batch (where the main bioreactor is perfused, but the product remains in the bioreactor) has been used for commercial production by Amgen. More recently short perfusions, with direct product capture of the product from the retention system on connected chromatography skids are being reported by BL Pharma Ltd., in Hyderabad India and by WUXI who reported record (cumulative) yields corresponding to 51 g/L.

All these approaches have relatively short bioreactor runs (10 – 21 days) in common and a single batch of product per bioreactor. These approaches seem to fit well with current operational and regulatory practice and therefore seem to be adopted more easily.

Fully continuous processes with 30 – 90 perfusion runs and/or fully connected continuous DSP are being piloted in big pharma advanced developments labs. However, they do not (yet) seem to improve cost-of-goods, while operational and regulatory risks definitively increase. Therefore, they currently seem to be only implemented if the product requires it, for example in the case of unstable proteins.


GEN: While a number of biotech drugs have been manufactured via continuous cell culture techniques, downstream processing remains a batch operation? Is this your experience and please comment on your plans for adoption of continuous downstream processing technologies?

Huang: Yes, it is my experience that downstream processing has remained batch operation. I am promoting a drastic integration in IRP similar to Integrated Circuitry so that the connections can be unified, and harvest and purification operations can be automated without human operators. More importantly, development of this technology allows the manufacturing footprint and the construction costs to be drastically reduced.

Ghose: The aspects of continuous manufacturing for both upstream and downstream biologics manufacturing being incorporated at BMS have mainly been to address our current growing pipeline needs. Our applications have primarily been for stable, easily expressed monoclonal antibody processes that require moderate volumes and throughputs, such as for most oncology or immuno-oncology therapies.

As mentioned before, we have used perfusion only at the seed bioreactor stage while keeping the production bioreactor in fed-batch mode. Furthermore, for the downstream process, we have made the capture step continuous for better utilization of the expensive Protein A resin and have automated/connected some of the subsequent polishing unit operations. This strategy still maintains the concept of a single batch of drug substance, while delivering on the throughput advantages of a continuous process.

Andrew BulpinBulpin: While it is true that the primary application of process intensification has historically been on perfusion, we can see significant benefits to process economics by expanding this intensification approach to downstream purification.

For instance, our Flow Through Polishing Toolbox provides a demonstrated robust purification across eight molecules including those with yields greater than 90%. For the overall process, 10% COGS reduction and 47% buffer reduction and an opportunity for more batches/year due to significantly decreased process time. We noted a 72% decrease in polishing process time and a 24% decrease in overall DSP process time. In addition, a 40% reduction in facility footprint can be created by eliminating intermediate hold tanks, single-skid operation and up to 50% reduction in resins and filtration, as well as an estimated 87% less buffer requirements for polishing operations.

Levison: We have developed products for continuous clarification, continuous chromatography, continuous virus inactivation, continuous concentration, and continuous diafiltration. These products enable a relatively simple and speedy transition from an established batch process to a more streamlined continuous process while maintaining product quality and yield.

Zilstra: The primary focus of Sartorius-Stedim Biotech will be on intensification of DSP in general. Continuous processing is not a target in itself, but when adding value may be applied, especially where process steps are connected in a flow through mode or when intermediate storage can be minimized.

Recently Sartorius Stedim Biotech has announced a collaboration with NovaSep to develop membrane adsorber chromatography system especially for this purpose.


GEN: It has been argued at meetings and in the literature that “adoption of a fully continuous process will be an evolutionary process driven by regulators, continuing technological developments, and increased industry experience.” This is a rather all-inclusive list. In your company’s experience, which of these three aforementioned factors was most critical, and were there other contributors to the development of this process?

Huang: Industry needs to develop technologies, then submit them to regulators with side-by-side comparison of the products produced by convention and new approaches. New technologies will be adapted gradually if they can be demonstrated to be safer, better, and faster.

Ghose: We agree that a strong foundation of science, relevant academic collaboration, industry benchmarking and key regulatory interactions are all crucial to the successful implementation and adoption of continuous bioprocesses. At BMS, during our initial conceptual phase, we kept a strong focus on technological advancements through key internal investments and strategic collaborations to help develop the best state-of-the-art process flow. As the projects get closer to implementation and filing, we are focusing on developing the right validation and regulatory strategy to enable a successful filing.

Bulpin: There is not one factor that plays a more important role than the other. They should be viewed as three legs of a stool. Without one of the three pillars you mention in your question, the ability to evolve to a fully continuous process will fail. An element that is missing in this list is education and training. Employee adoption and understanding of how these new process intensification methodologies and technologies work is critical. Employees need to be given the opportunity to evaluate the value of these techniques and troubleshoot and test process development technologies.

Millipore Sigma is heavily involved and interested in collaborations with the BioPhorum Operations Group (BPOG), the National Institute for Innovation in Manufacturing Biopharmaceuticals (NIIBML), and the EU research program, Horizon2020.

Market drivers are creating a paradigm shift and the need for innovation in a very conservative industry. The significant impact of next-generation processing is clear. However, the requirements to change any approved commercial process are onerous. This manufacturing evolution requires a three-way collaboration between suppliers, biomanufacturers and regulators, and sometimes even beyond by including both academic and industrial associations.

Peter R Levison, PhD

Levison: Each of these factors does in reality influence adoption of continuous processing. It is not difficult technically to transition from batch to continuous but until its adoption is widespread and routine in the manufacture of licensed biopharmaceuticals then these factors will often be raised as concerns. The regulators are visible at continuous processing conferences and give supportive presentations on the benefits of adopting continuous bioprocessing. Draft guidelines exist now on continuous processing so the regulatory concerns are perhaps less critical as they were a few years ago. The process equipment required to carry out continuous bioprocessing is commercially available and is becoming established in the market so this is becoming a less critical factor.

With the widespread availability of process equipment, the industry is becoming more experienced with it, so this factor should also become less critical. I do believe that adoption of continuous bioprocessing will be an evolution but many of the perceived barriers and concerns relating to adoption are now being overcome so it is a question of when continuous bioprocessing will be routinely adopted rather than if!

Zilstra: I fully agree with the statement above that indicates that adoption will be an evolutionary process. Although from a regulatory perspective, continuous processing is already supported and even endorsed, there are still many unknowns. It is therefore still up to the Biomanufacturers to convince the regulators they are in full control.

The first hurdle will be based on the technical experience of the industry. Although the feasibility of continuous upstream and in some cases downstream processes have been demonstrated, it may still require a substantial development effort to achieve a situation where these processes can be operated without technical issues. Only then can sufficient data be generated to model the product quality’s dependence on all raw material and process parameters, all its process excursions and myriad of permutations.


GEN: Single-use equipment options are more and more widely adopted, yet they may not fit well for continuous manufacturing, as they were not designed for constant use. Is there a solution to this conundrum?

Huang: I believe the IRP train I presented is a solution to this conundrum. We cannot use the approach of industrial refineries, as we need an alternative so that the disposable components in our process can be replaced quickly. More specifically, we need a technology whereby virus filters can be replaced and their integrity evaluated.

Ghose: As part of our process intensification strategy, we have been able to make use of the best of both worlds, i.e., single-use systems and continuous bioprocessing. Our process development philosophy was geared with that end goal in mind. As such, the specific technologies that we have adopted at our Devens facility are all amenable for single-use processing.

Bulpin: As other technologies are evolving to meet the needs of the industry, we believe that single-use technologies will also evolve. Stronger and more robust films are being developed. The need for closed devices to maintain process sterility and the ability to sanitize products will help to make single-use technologies more suitable for continuous manufacturing. Additionally, it will be important to understand over what duration these processes will run. This could also be a factor in driving the evolution in single-use. That being said, we can see that single-use technologies are certainly capable of being utilized today in process intensification, as noted in the use of single-use in the Horizon2020 collaboration.

Levison: Pall Biotech has a portfolio of single-use equipment specifically designed for continuous bioprocessing. From the outset we made a decision to focus on single-use technologies for continuous manufacturing. Products were designed for continuous operation for the duration of a run, be it fed-batch or perfusion. The single-use flow paths have been shown to support operation for the duration of the run and with the use of novel connector technology in a closed system. Furthermore, we designed ease of installation of the single-use flowpaths across the entire continuous portfolio to ensure minimal downtime during equipment setup and changeover while ensuring that the process was operator friendly in the process environment.

Gerben Zijlstra, PhD
Gerben Zijlstra, PhD

Zilstra: Probably there can be found pragmatic solutions to this issue. In most cases longer use of tubing and (intermediate) bags can easily be validated. Components that wear and tear can be exchanged on a regular basis based on relatively straight forward physical characteristics. Fouling and contaminant build-up are more difficult challenges and establishing the proper exchange interval may require substantial experimental examination and verification.


John Morrow, Jr., PhD ([email protected]), is president of Newport Biotechnology Consultants. He is also the co-editor of “Biosimilars of Monoclonal Antibodies: A Practical Guide to Manufacturing, Preclinical, and Clinical Development, published by John Wiley and Sons.

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