Freezing mammalian cells for production of biopharmaceuticals

Harnessing genetic engineering to drive economic bioproduct production in algae

Our reliance on agriculture for sustenance, healthcare, and resources has been essential since the dawn of civilization. However, traditional agricultural practices are no longer adequate to meet the demands of a burgeoning population amidst climate-driven agricultural challenges. Microalgae emerge as a beacon of hope, offering a sustainable and renewable source of food, animal feed, and energy. Their rapid growth rates, adaptability to non-arable land and non-potable water, and diverse bioproduct range, encompassing biofuels and nutraceuticals, position them as a cornerstone of future resource management. Furthermore, microalgae's ability to capture carbon aligns with environmental conservation goals. While microalgae offers significant benefits, obstacles in cost-effective biomass production persist, which curtails broader application. This review examines microalgae compared to other host platforms, highlighting current innovative approaches aimed at overcoming existing barriers. These approaches include a range of techniques, from gene editing, synthetic promoters, and mutagenesis to selective breeding and metabolic engineering through transcription factors.

Employing active learning in the optimization of culture medium for mammalian cells

Medium optimization is a crucial step during cell culture for biopharmaceutics and regenerative medicine; however, this step remains challenging, as both media and cells are highly complex systems. Here, we addressed this issue by employing active learning. Specifically, we introduced machine learning to cell culture experiments to optimize culture medium. The cell line HeLa-S3 and the gradient-boosting decision tree algorithm were used to find optimized media as pilot studies. To acquire the training data, cell culture was performed in a large variety of medium combinations. The cellular NAD(P)H abundance, represented as A450, was used to indicate the goodness of culture media. In active learning, regular and time-saving modes were developed using culture data at 168 h and 96 h, respectively. Both modes successfully fine-tuned 29 components to generate a medium for improved cell culture. Intriguingly, the two modes provided different predictions for the concentrations of vitamins and amino acids, and a significant decrease was commonly predicted for fetal bovine serum (FBS) compared to the commercial medium. In addition, active learning-assisted medium optimization significantly increased the cellular concentration of NAD(P)H, an active chemical with a constant abundance in living cells. Our study demonstrated the efficiency and practicality of active learning for medium optimization and provided valuable information for employing machine learning technology in cell biology experiments.

A biocompatible cell cryoprotectant based on sulfoxide-containing amino acids: mechanism and application

The preservation of cells at cryogenic temperatures requires the presence of cryoprotectants (CPAs). Dimethyl sulfoxide (DMSO), as a state-of-the-art CPA, is widely used for the storage of many types of cells. However, its intrinsic toxicity is still an obstacle for its applications in clinical practice. Herein, we report a DMSO analogue, L-methionine sulfoxide (Met(O)-OH), as a CPA for cell cryopreservation. The molecular-level cryopreservation roles of Met(O)-OH were investigated by experiments and molecular dynamics simulations. The results also found that Met(O)-OH showed high ice recrystallization inhibition (IRI) activity and the ice crystals in Met(O)-OH solution tend to be relatively round and smooth; moreover, the ice size was significantly reduced to 30.26 μm compared with pure water (135.87 μm) or DMSO solution (45.08 μm). At the molecular level, Met(O)-OH could stably bind the surface of the ice crystals and form more stable hydrogen bonds with ice compared with L-methionine. Moreover, Met(O)-OH could significantly reduce the damage to cells caused by osmotic shock and did not change the cell viability even at high concentration (4%). Based on these results, nucleated L929 cells and anuclear sheep red blood cells (SRBCs) were used as cell models to investigate the cryopreservation activity of Met(O)-OH. The results suggested that, under the optimum protocol, Met(O)-OH showed an effective post-thaw survival efficiency with ultrarapid freezing, and the post-thaw survival efficiency of L929 cells reached 84.0%. This work opens up the possibility for an alternative to traditional toxic CPA DMSO, and provides insights for the development of DMSO analogues with non-toxic/low toxicity for cell cryoprotection applications.

Advances in formulation and manufacturing strategies for the delivery of therapeutic proteins and peptides in orally disintegrating dosage forms

Therapeutic proteins and peptides (TPPs) are increasingly favoured above small drug molecules due to their high specificity to the site of action and reduced adverse effects resulting in increased use of these agents for medical treatments and therapies. Consequently, there is a need to formulate TPPs in dosage forms that are accessible and suitable for a wide range of patient groups as the use of TPPs becomes increasingly prevalent in healthcare settings worldwide. Orally disintegrating dosage forms (ODDF) are formulations that can ensure easy-to-administer medication to a wider patient population including paediatrics, geriatrics and people in low-resource countries. There are many challenges involved in developing suitable pharmaceutical strategies to protect TPPs during formulation and manufacturing, as well as storage, and maintenance of a cold-chain during transportation. This review will discuss advances being made in the research and development of pharmaceutical and manufacturing strategies used to incorporate various TPPs into ODDF systems.

Proline pre-conditioning of cell monolayers increases post-thaw recovery and viability by distinct mechanisms to other osmolytes

Cell cryopreservation is an essential tool for drug toxicity/function screening and transporting cell-based therapies, and is essential in most areas of biotechnology. There is a challenge, however, associated with the cryopreservation of cells in monolayer format (attached to tissue culture substrates) which gives far lower cell yields (<20% typically) compared to suspension freezing. Here we investigate the mechanisms by which the protective osmolyte l-proline enhances cell-monolayer cryopreservation. Pre-incubating A549 cells with proline, prior to cryopreservation in monolayers, increased post-thaw cell yields two-fold, and the recovered cells grow faster compared to cells cryopreserved using DMSO alone. Further increases in yield were achieved by adding polymeric ice recrystallization inhibitors, which gave limited benefit in the absence of proline. Mechanistic studies demonstrated a biochemical, rather than biophysical (i.e. not affecting ice growth) mode of action. It was observed that incubating cells with proline (before freezing) transiently reduced the growth rate of the cells, which was not seen with other osmolytes (betaine and alanine). Removal of proline led to rapid growth recovery, suggesting that proline pre-conditions the cells for cold stress, but with no impact on downstream cell function. Whole cell proteomics did not reveal a single pathway or protein target but rather cells appeared to be primed for a stress response in multiple directions, which together prepare the cells for freezing. These results support the use of proline alongside standard conditions to improve post-thaw recovery of cell monolayers, which is currently considered impractical. It also demonstrates that a chemical biology approach to discovering small molecule biochemical modulators of cryopreservation may be possible, to be used alongside traditional (solvent) based cryoprotectants.

Cell cryopreservation is an essential tool for transporting cell-based therapies, and is essential in most areas of biotechnology. Here proline pre-incubation prior to cell monolayer cryopreservation is explored, increasing post-thaw yields.

Synthetically Scalable Poly(ampholyte) Which Dramatically Enhances Cellular Cryopreservation

The storage and transport of frozen cells underpin the emerging/existing cell-based therapies and are used in every biomedical research lab globally. The current gold-standard cryoprotectant dimethyl sulfoxide (DMSO) does not give quantitative cell recovery in suspension or in two-dimensional (2D) or three-dimensional (3D) cell models, and the solvent and cell debris must be removed prior to application/transfusion. There is a real need to improve this 50-year-old method to underpin emerging regenerative and cell-based therapies. Here, we introduce a potent and synthetically scalable polymeric cryopreservation enhancer which is easily obtained in a single step from a low cost and biocompatible precursor, poly(methyl vinyl ether-alt-maleic anhydride). This poly(ampholyte) enables post-thaw recoveries of up to 88% for a 2D cell monolayer model compared to just 24% using conventional DMSO cryopreservation. The poly(ampholyte) also enables reduction of [DMSO] from 10 wt % to just 2.5 wt % in suspension cryopreservation, which can reduce the negative side effects and speed up post-thaw processing. After thawing, the cells have reduced membrane damage and faster growth rates compared to those without the polymer. The polymer appears to function by a unique extracellular mechanism by stabilization of the cell membrane, rather than by modulation of ice formation and growth. This new macromolecular cryoprotectant will find applications across basic and translational biomedical science and may improve the cold chain for cell-based therapies.

Innovation in Cell Banking, Expansion, and Production Culture

Cell culture-based production processes enable the development and commercial supply of recombinant protein products. Such processes consist of the following elements: thaw and initiation of culture, seed expansion, and production culture. A robust cell source storage system in the form of a cell bank is developed and cells are thawed to initiate the cell culture process. Seed culture expansion generates sufficient cell mass to initiate the production culture. The production culture provides an environment where the cells can synthesize the product and is optimized to deliver the highest possible product concentration with acceptable product quality. This chapter describes the significant innovations made in these process elements and the resulting improvements in the overall efficiency, robustness, and safety of the processes and products.

Serum- and albumin-free cryopreservation of endothelial monolayers with a new solution

Cryopreservation is the only long-term storage option for the storage of vessels and vascular constructs. However, endothelial barrier function is almost completely lost after cryopreservation in most established cryopreservation solutions. We here aimed to improve endothelial function after cryopreservation using the 2D-model of porcine aortic endothelial cell monolayers. The monolayers were cryopreserved in cell culture medium or cold storage solutions based on the 4°C vascular preservation solution TiProtec^®, all supplemented with 10% DMSO, using different temperature gradients. After short-term storage at −80°C, monolayers were rapidly thawed and re-cultured in cell culture medium. Thawing after cryopreservation in cell culture medium caused both immediate and delayed cell death, resulting in 11 ± 5% living cells after 24 h of re-culture. After cryopreservation in TiProtec and chloride-poor modifications thereof, the proportion of adherent viable cells was markedly increased compared to cryopreservation in cell culture medium (TiProtec: 38 ± 11%, modified TiProtec solutions ≥ 50%). Using these solutions, cells cryopreserved in a sub-confluent state were able to proliferate during re-culture. Mitochondrial fragmentation was observed in all solutions, but was partially reversible after cryopreservation in TiProtec and almost completely reversible in modified solutions within 3 h of re-culture. The superior protection of TiProtec and its modifications was apparent at all temperature gradients; however, best results were achieved with a cooling rate of −1°C/min. In conclusion, the use of TiProtec or modifications thereof as base solution for cryopreservation greatly improved cryopreservation results for endothelial monolayers in terms of survival and of monolayer and mitochondrial integrity.

Polyproline as a Minimal Antifreeze Protein Mimic That Enhances the Cryopreservation of Cell Monolayers

Tissue engineering, gene therapy, drug screening, and emerging regenerative medicine therapies are fundamentally reliant on high-quality adherent cell culture, but current methods to cryopreserve cells in this format can give low cell yields and require large volumes of solvent "antifreezes". Herein, we report polyproline as a minimum (bio)synthetic mimic of antifreeze proteins that is accessible by solution, solid-phase, and recombinant methods. We demonstrate that polyproline has ice recrystallisation inhibition activity linked to its amphipathic helix and that it enhances the DMSO cryopreservation of adherent cell lines. Polyproline may be a versatile additive in the emerging field of macromolecular cryoprotectants.

Protective effects of osmolytes in cryopreserving adherent neuroblastoma (Neuro-2a) cells

A simple method to cryopreserve adherent monolayers of neuronal cells is currently not available, but the development of this technique could facilitate numerous applications in the field of biomedical engineering, cell line development, and drug screening. However, complex tissues of some exceptional animals survive freezing in nature. These animals are known to accumulate several small molecular weight solutes prior to freezing. Following a similar strategy, we investigated the effects of osmolytes such as trehalose, proline, and sucrose as additives to the traditional cryoprotectant dimethyl sulfoxide (Me2SO) in modulating the cryopreservation outcome of mouse neuroblastoma (Neuro-2a) cells. Neuro-2a cells adhered to cell culture plates were incubated for 24 h at varying concentrations of trehalose, proline, sucrose and combinations of these compounds. Cells were cryopreserved for 24 h and cell viability post-freezing and thawing was quantified by trypan blue exclusion assay. On average, only 13.5% of adherent cells survived freezing in the presence of 10% Me2SO alone (control). Pre-incubation of cells with medium containing both trehalose and proline severely decreased cell proliferation, but increased cell recovery to about 53% of control. Furthermore, characterization using Raman microspectroscopy revealed that the addition of both trehalose and proline to 10% Me2SO substantially increased the size, and altered the nature, of ice crystals formed during freezing. Our results suggest that pre-incubation of Neuro-2a cells with trehalose and proline in combination provides cell protection along with alterations of ice structure in order to increase cell survival post-freezing.

Approach toward an efficient inoculum preparation stage for suspension BHK-21 cell culture

Mammalian cells are the most frequently used hosts for biopharmaceutical proteins manufacturing. Inoculum quality is a key element for establishing an efficient bioconversion process. The main objective in inoculation expansion process is to generate large volume of viable cells in the shortest time. The aim of this paper was to optimize the inoculum preparation stage of baby hamster kidney (BHK)-21 cells for suspension cultures in benchtop bioreactors, by means of a combination of static and agitated culture systems. Critical parameters for static (liquid column height: 5, 10, 15 mm) and agitated (working volume: 35, 50, 65 mL, inoculum volume percentage: 10, 30 % and agitation speed: 25, 60 rpm) cultures were study in T-flask and spinner flask, respectively. The optimal liquid column height was 5 mm for static culture. The maximum viable cell concentration in spinner flask cultures was reached with 50 mL working volume and the inoculum volume percentage was not significant in the range under study (10-30 %) at 25 rpm agitation. Agitation speed at 60 rpm did not change the main kinetic parameters with respect to those observed for 25 rpm. These results allowed for a schedule to produce more than 4 × 10(9) BHK-21 cells from 4 × 10(6) cells in 13 day with 1,051 mL culture medium.

Rakkyo fructan as a cryoprotectant for serum-free cryopreservation of mammalian cells

Cryopreservation refers to the long-term storage of mammalian cells. Mammalian serum is generally used as a cryoprotectant, but is associated with problems including the risk of contamination by pathogens and quality control issues. Therefore, a serum-free cryopreservation method needs to be established. In this study, we focused on rakkyo fructan, a fructose polymer, derived from the Japanese shallot as an alternative factor to serum. Fructan contributes to tolerance to frost and dehydration in plants by stabilizing the plant membrane. However, whether fructan protects mammalian cells against freezing stress remains unknown. The ability of rakkyo fructan to be an alternative cryoprotectant to fetal bovine serum (FBS) was examined in the present study. 2E3-O, a mouse hybridoma, was preserved in rakkyo fructan, was highly viable after being defrosted, and then proliferated rapidly. When rakkyo fructan was combined with dimethylsulfoxide (DMSO), its ability to protect the hybridoma against freezing stress was improved. The rakkyo fructan and DMSO mixture was used in the cryopreservation of the mammalian cell lines CHO-DP12, a producer of recombinant antibodies, and HepG2, human hepatoma cells frequently tested in bio-artificial livers. Following the freezing and thawing processes, CHO-DP12 cells retained their ability to produce recombinant antibodies and as did HepG2 cells for albumin and mRNA expression of cytochrome P450 enzymes. These results indicate that rakkyo fructan is a promising cryoprotectant that prevents mammalian cells from freezing stress similar to FBS.