The Importance of Mammalian Cell Culture for Medical ResearchAbstractA vanguard of medical research, mammalian cell culture (MCC) is vital to a researcher’s arsenal.  The ability to model healthy and disease conditions in a controlled environment is of great importance. MCC is incredibly versatile, covering a vast scope of research, from cancer to the production of vaccines. Without MCC, medical research would be severely hampered.IntroductionEnabling researchers to better understand cellular processes and interactions in vitro is invaluable. MCC can either be carried out in 2D or 3D, dependent upon the need of the experiment. Mammalian cell use is significant in that the knowledge learnt from these studies may then have a medical application to help patients through novel therapies/treatments. Applications of MCC highlight its value in medical research.Wound HealingTo investigate the repair of epithelium, researchers use monocultures. This models regions such as the skin, intestine, or kidney; possibly describing cell kinetics or haemostasis. A scratch assay (Fig.1A) uses a monolayer to study epithelial cell migration and proliferation in wound healing. When a wound is healing, the cells communicate and interact, so co-culture cell models (Fig.1B) are used, for example, fibroblast and keratinocyte interaction.(1)  Figure 1 (A) Monoculture scratch assay for epithelium. (B) Co-culture scratch assay. (1)HIV-MTB InteractionCo-infection culture is complicated, studying both the individual and joint pathogenic effect(s) of disease(s). Co-infection with HIV and Mycobacterium Tuberculosis (MTB/TB) has a synergistic effect, whereby TB turns from latent to active and immune collapse contributes to HIV pathogenesis. 3D culture enables the assessment of host-pathogen interactions; the presence of bacterial cells in granulomas in MTB are used to understand its mechanism and find drugs to combat it. Tolerating HIV/MTB attachment, entry, and replication while eliciting a cell based specific immune response makes human macrophages good models for this study.(2)CancerPrimary cancer cell culture (Fig. 2) allows preservation of heterogeneous malignant tumour cells providing the means for proliferation and migration, also creating a favourable tumour-microenvironment for progression and propagation. Cell line homogeneity gives an unrealistic view of the disease, therefore lessening our understanding of cancer development.(3)During phase 3 clinical trials, many drugs fail, with partial attribution to the unrealistic 2D monolayer microenvironment (Fig.3A). 3D morphology/physiology is more representative, mimicking tumour cellular heterogeneity. In 3D culture (Fig.3B,3C), the proliferation of ovarian cancer cells was reduced after treatment with paclitaxel by 40-60%, while in 2D 80% reduced cell viability was obtained. This shows the greater resistance to anticancer drugs of 3D cultures, therefore giving more accurate perceptions.(4) Figure 2 Excision of fresh tissue from surgery giving an ex vivo cell population. (3)Figure 3 (A) 2D monolayer cell culture (B+C) 3D cell culture with cells grown on and in matrix, more representative of tumour heterogeneity. (4)High voltage intensity leads to total permeabilization of the cell membrane, while a low intensity voltage leads to transient permeabilization. Via electroporation, cisplatin’s cytotoxic effect becomes significantly larger, with the increased effect only lasting 24-48hrs after the procedure.  Primary cell culture taken from pancreatic cancer was used for the experiment.(5)Cancer cell apoptosis, with low toxicity to normal cells can be induced by treating the tissue with non-equilibrium atmospheric pressure plasma (N-APP) producing both reactive oxygen/nitrogen species. A co-culture of normal/cancerous liver cells was used to study the effect plasma activated medium (PAM: N-APP), to find which dose is most effective. It was found that H2O2 and NO concentrations increased upon treatment. Ten minutes is the optimum treatment time with PAM, resulting in the most cancer cell apoptosis, but the least normal cell damage. (6)An experiment investigated quorum sensing engineered salmonella, which can secrete anticancer proteins, eliciting in tumours a specific protein expression. In concentrated areas of tumour tissue, the drug will only be capable of being expressed via a quorum sensing switch. Through a 3D-tumour-on-a-chip device, this method has been shown to be an effective therapeutic strategy.(7)Lung-On-A-Chip Organs on-a-chip create the mechanical and circulatory environment present in vivo through the combination of 3D cell culture and microfluidic technology. Lung organoid platforms allow disease modelling and drug development.(8)Influenza VaccineProduced in Madin-Darby canine kidney cells, a novel influenza vaccine was found to have the same tolerability profile as a control (embryonated chicken egg derived) vaccine in clinical trials (2 studies – phase I+II and III). With the cell-culture derived vaccine being well tolerated and immunogenic, this method of production will reduce reliance on eggs, offer better flexibility (e.g. during seasonal high demand/pandemics), reduce contamination risk comparatively and eliminate egg allergen problems.(9,10)Biotherapeutic Efficiency Inhibiting the onset of cell death is essential for optimizing mammalian cell culture technology for biotherapeutics, by enhancing cell survival for greater productivity.  Altering the media supplied (nutrients/anti-apoptotic compounds) to cells may prolong their viability. Inhibiting apoptosis in culture by genetic strategies have been successful. Inhibition of pro-apoptotic molecules by the expression of the genes Bcl-2 and Bcl-xL has been found.(11)Chemical Weapons – TreatmentA vesicant agent (Fig.4), Sulphur Mustard (SM) causes necrosis, apoptosis and inflammation. No causal antidote exists; however, it has been found that compounds may counteract the effects. A monoculture of keratinocytes and a co-culture of keratinocytes and immunocompetent cells were used to evaluate the efficacy of 3 anti-inflammatory compounds after treatment with SM. Dexamethasone has a generic protective effect providing a small reduction of apoptosis and interleukin production. Ibuprofen in both cultures greatly amplified apoptosis and necrosis.  The effects of SM on cells were significantly reduced with Diclofenac, showing that it may modify the immune response.(12) Figure 4 A WW1 soldier suffering the effects of SM gas with visible blistering around neck, armpits and wrists. Click image for reference.Neurodegenerative Disease – iPSCsLoss of functionality by neuronal degeneration characterises Neurodegenerative Diseases e.g. Alzheimer’s Disease (AD). In vitro disease models are now possible through the production of patient-specific induced pluripotent stem cells (iPSC). Creating therapeutic strategies may now be completed by using AD patient’s neural cells to make an in vitro AD model through iPSC technology. Identifying targets for drugs and deciphering disease mechanism(s) is made possible via the combination of cell culture along with CRISPR-Cas9 gene editing, which may introduce genetic variations of disease or rectify patient-specific mutations.(13)ContaminationCommonly antibiotic resistant, and visually undetectable to the eye, mycoplasma contaminates cell lines and adversely affects research. An estimation of mycoplasma contamination of cell lines is approximately 5-30%. False results and endangerment of cell physiology occurs.  Rigorous aseptic technique and control of aerosol sources prevent this. Most effective solution is to dispose of contaminated cells.(14)While Chlamydia and mycoplasma infections can be antibiotic resistant, amphipathic peptides can effectively combat them. A potential prophylaxis/therapy of these infectious diseases has been suggested; induced melittin gene expression in a plasmid vector, which has been transfected into HeLa cell lines. This gives a means of production of melittin for inhibiting mycoplasma/chlamydia infection.(15)It is estimated that approximately 15-20% of research papers are flawed due to cell cultures which have been cross-contaminated/misidentified. The first established human cancer cell line, HeLa (Fig.5), was widely distributed between labs. Researchers were oblivious as to cross contamination and the robustness of HeLa cells in culture.(16) Figure 5 HeLa Cells immunohistochemically stained: First established human cancer cell line. Click image for reference.ConclusionDespite mammalian cell culture being a revolutionary method of research, there are a few concerns. Ethically, the use of Foetal Bovine Serum is a concern for animal welfare(17), and the use of HeLa cells(18), with no consent being given for the tissue used for research. However, without MCC, medical research would be severely restricted. Continued research in the field of MCC is critical, spearheading the fight against disease.References(1)  Vidmar J, Chingwaru C, Chingwaru W. Mammalian cell models to advance our understanding of wound healing: a review. J Surg Res 2017:269.(2)  Chingwaru W, Glashoff RH, Vidmar J, Kapewangolo P, Sampson SL. 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