Growth and interferon-gamma production in batch culture of CHO cells

Online flow cytometry for monitoring apoptosis in mammalian cell cultures as an application for process analytical technology

Apoptosis is the main driver of cell death in bioreactor suspension cell cultures during the production of biopharmaceuticals from animal cell lines. It is known that apoptosis also has an effect on the quality and quantity of the expressed recombinant protein. This has raised the importance of studying apoptosis for implementing culture optimization strategies. The work here describes a novel approach to obtain near real time data on proportion of viable, early apoptotic, late apoptotic and necrotic cell populations in a suspension CHO culture using automated sample preparation in conjunction with flow cytometry. The resultant online flow cytometry data can track the progression of apoptotic events in culture, aligning with analogous manual methodologies and giving similar results. The obtained near-real time apoptosis data are a significant improvement in monitoring capabilities and can lead to improved control strategies and research data on complex biological systems in bioreactor cultures in both academic and industrial settings focused on process analytical technology applications.

A characterization of four B16 murine melanoma cell sublines molecular fingerprint and proliferation behavior

Background

One of the most popular and versatile model of murine melanoma is by inoculating B16 cells in the syngeneic C57BL6J mouse strain. A characterization of different B16 modified cell sub-lines will be of real practical interest. For this aim, modern analytical tools like surface enhanced Raman spectroscopy/scattering (SERS) and MTT were employed to characterize both chemical composition and proliferation behavior of the selected cells.

Methods

High quality SERS signal was recorded from each of the four types of B16 cell sub-lines: B164A5, B16GMCSF, B16FLT3, B16F10, in order to observe the differences between a parent cell line (B164A5) and other derived B16 cell sub-lines. Cells were incubated with silver nanoparticles of 50–100 nm diameter and the nanoparticles uptake inside the cells cytoplasm was proved by transmission electron microscopy (TEM) investigations. In order to characterize proliferation, growth curves of the four B16 cell lines, using different cell numbers and FCS concentration were obtained employing the MTT proliferation assay. For correlations doubling time were calculated.

Results

SERS bands allowed the identification inside the cells of the main bio-molecular components such as: proteins, nucleic acids, and lipids. An "on and off" SERS effect was constantly present, which may be explained in terms of the employed laser power, as well as the possible different orientations of the adsorbed species in the cells in respect to the Ag nanoparticles. MTT results showed that among the four tested cell sub-lines B16 F10 is the most proliferative and B164A5 has the lower growth capacity. Regarding B16FLT3 cells and B16GMCSF cells, they present proliferation ability in between with slight slower potency for B16GMCSF cells.

Conclusion

Molecular fingerprint and proliferation behavior of four B16 melanoma cell sub-lines were elucidated by associating SERS investigations with MTT proliferation assay.

Engineering Chinese hamster ovary (CHO) cells to achieve an inverse growth - associated production of a foreign protein, beta-galactosidase

Protein synthesis in mammalian cells can be observed in two strikingly different patterns: 1) production of monoclonal antibodies in hybridoma cultures is typically inverse growth associated and 2) production of most therapeutic glycoproteins in recombinant mammalian cell cultures is found to be growth associated. Production of monoclonal antibodies has been easily maximized by culturing hybridoma cells at very low growth rates in high cell density fed- batch or perfusion bioreactors. Applying the same bioreactor techniques to recombinant mammalian cell cultures results in drastically reduced production rates due to their growth associated production kinetics. Optimization of such growth associated production requires high cell growth conditions, such as in repeated batch cultures or chemostat cultures with attendant excess biomass synthesis. Our recent research has demonstrated that this growth associated production in recombinant Chinese hamster ovary (CHO) cells is related to the S (DNA synthesis)-phase specific production due to the SV40 early promoter commonly used for driving the foreign gene expression. Using the stably transfected CHO cell lines synthesizing an intracellular reporter protein under the control of SV40 early promoter, we have recently demonstrated in batch and continuous cultures that the product synthesis is growth associated. We have now replaced this S-phase specific promoter in new expression vectors with the adenovirus major late promoter which was found to be active primarily in the G1-phase and is expected to yield the desirable inverse growth associated production behavior. Our results in repeated batch cultures show that the protein synthesis kinetics in this resulting CHO cell line is indeed inverse growth associated. Results from continuous and high cell density perfusion culture experiments also indicate a strong inverse growth associated protein synthesis. The bioreactor optimization with this desirable inverse growth associated production behavior would be much simpler than bioreactor operation for cells with growth associated production.

Higher expression of fab antibody fragments in a CHO cell line at reduced temperature

A chimeric Fab was expressed in Chinese hamster ovary cells under the control of the CMV promoter in a two-stage production process. Cells were first grown to 90% confluence at 37 degrees C in a proliferation phase, followed by a production phase at either 37 degrees C or 28 degrees C. Medium supplemented with serum and medium free from serum was tested in the production phase at both temperatures. Comparison of Fab expression revealed that reducing the temperature to 28 degrees C resulted in a 14-fold increase in product yield when cells were cultivated in serum-containing medium, and in a 38-fold increase in product yield when serum-free medium was applied.

Regulation of cell cycle and productivity in NS0 cells by the over-expression of p21CIP1

We have constructed NS0 myeloma cell lines that inducibly express the p21CIP1 cyclin dependent kinase inhibitor, using the Lacswitch system. Ectopic p21(CIP1) protein expression was rapidly induced within 12 h of addition of IPTG, causing G1-phase arrest and almost complete inhibition of cell proliferation. The production of a chimeric IgG4 antibody, expressed constitutively from an independent promoter, was found to be significantly increased by more than 4-fold in p21CIP1-arrested cells. This study demonstrates for the first time the successful construction of anchorage-independent and proliferation-controlled NS0 cell lines with enhanced secreted chimeric antibody production independent of the inducible promoter activity used to achieve cytostasis.

Overview of protein expression by mammalian cells

This unit reviews the stages involved in protein production in mammalian cells using a stable-expression approach. Choice of cell type is discussed, as is transfection of the host cells, methods for selection and amplification of transformants, and growth of cells at appropriate scale for protein production. Since post-transcriptional modification and intracellular protein transportation are important features of recombinant-protein production in mammalian cells, some description of these mechanisms is included.