Single-use systems (SUS) are now used in the majority of biopharmaceutical processes involving animal cell cultures. Single-use filters, plastic storage bags, single-use mixers and single-use bioreactors for upstream processing (USP) in pre-clinical and clinical sample production are the items most commonly used. However the biopharmaceutical industry is also making greater use of SUS for downstream processing (DSP), formulation and filling. Stirred-tank single-use bioreactors for microorganisms are one of the current development priorities. There is also a need for single-use equipment to process stem cells and T-cells.
Single-use (disposable) systems are only intended to be used once. All parts that come into contact with the product are made of Food and Drug Administration (FDA) approved plastics such as polyethylene or polycarbonate. The systems are normally beta or gamma sterilized by the manufacturer so that they are ready to use. Acceptance of SUS in biopharmaceutical production has greatly increased over the past 15 years. This is particularly the case for all processes which involve animal cell cultures where there is a need for rapid development and efficient production of low to medium volume products such as therapeutic antibodies, hormones, enzymes and vaccines. It is probably safe to assume that SUS is used in 2/3 of new process designs for these applications.
The trend can be explained by increased product titers (and the resulting decrease in the size of production bioreactors down to 1 m3 or 2 m3) as well as by the advantages of SUS compared to re-useable equipment made of glass or steel. Besides faster production throughput (elimination of the sterilization and cleaning procedures), increased flexibility (faster product changeover) and improved safety (minimum risk of product cross-contamination) are also cited as reasons. In addition, SUS reduces the upfront investment cost of a production system by around 40%, and it takes less time to install the system and get it up and running.
Single-use equipment is ubiquitous in production of pre-clinical and clinical samples, but it is used to a lesser extent in commercial biopharmaceutical production. Limitations affecting the single-use systems which are currently available on the market is cited as the reason why this is the case.
Leachables and Extractables (L&E) are the main weakness of SUS
Leachables and Extractables (L&E) are chemical substances which migrate from plastic under process conditions or in worst case scenarios and which degrade the product. The lack of procedures for standardized tests to detect L&E along with the absence of appropriate analysis protocols is the biggest weakness of SUS. The identification of bis(2,4-di-tert-butylphenyl)phosphate (bDtBPP) as a cytotoxic leachable for various Chinese Hamster Ovary (CHO) cell lines has not changed that. The results of investigations conducted by a team of Amgen specialists under the direction of Matthew Hammond did, however, accelerate development of more robust, optimized films (e.g. Aegis5-14 films from ThermoFisher Scientific or Flexsafe S80 from Sartorius Stedim Biotech) for storage, mixer and bioreactor bags. Recent studies based on a DECHEMA recommendation showed that the risk of cell growth inhibition can be excluded for Flexsafe S80 if the concentration of the antioxidant Irgafors 168 is minimized, and that applies not only to CHO cells.
In addition to DECHEMA which is developing recommendations and guidelines for standardization of SUS in the German-speaking region based on the efforts of its Single-Use Technology in Biopharmaceutical Production Working Group, the organizations listed in Fig. 1 are also active. Besides the L&E problem, issues relating to integrity, supplier qualification, material and component exchangeability and process characterization of single-use bioreactors are also being addressed.
Single-use process platforms, complete single-use USP lines and initial single-use production plants
Nevertheless, the advantages of SUS outweigh the disadvantages listed above if the right equipment is selected and it is used properly. Single-use systems now exist for all USP and DSP process steps. Suitable single-use equipment (mixers, transfer systems, dosing systems, filling needles, etc.) is even available for formulation and filling. Complete single-use production plants such as WuXi PharmaTech in Shanghai are, however, still the exception (approx. 10%). Hybrid production plants (approx. 75%) are the dominant form. Single-use filters, plastic storage bags, single-use mixers and single-use bioreactors are used together with equipment made of stainless steel. Process platforms (e.g. for media production, fermentation, biomass separation, virus separation and inactivation, formulation and filling) designed by the SUS market leaders (GE Healthcare, Pall Life Sciences, Merck MilliPore, Sartorius Stedim Biotech and ThermoScientific) are widely used at these plants.
The fact that this application space remains a bottleneck for volumes > 500 L (single-use centrifugation limitations, single-use protein A chromatography, lack of sensor systems) despite the progress that has been made in single-use DSP explains the trend towards production facilities with USP which is completely SUS based. A prime example of this approach is Shire’s manufacturing facility with a 2000 L bioreactor in Lexington, Massachusetts. Velaglucerase Alfa, which has been approved by the European Medicines Agency (EMA) and the FDA to treat Gaucher disease, is the first commercial biopharmaceutical to be produced at a production facility which has a complete single-use USP line. However without scalable single-use biotechnology and the associated peripheral equipment, this type of manufacturing facility would not exist.
Coming up: Overview of the new generation of bioreactors and new DSP process designs – stay tuned for part 2 of this trend report
Want to learn more? Check the exhibitor and product catalogue of ACHEMA 2015 at www.achema.de