Commonly used continuous cell lines: A comprehensive guide

Cell lines

Cell culture is the technique of growing eukaryotic or prokaryotic cells in physiological conditions, used widely in different branches of live sciences. Two types of cells used for cell cultures are primary cells and cell lines. 

Continuous cell lines are important biological tools widely used in basic biological research, toxicology studies, and in the production of biologicals like vaccines, antibodies, and proteins.  These consist of cells that have been continually passed over a long period. It can be finite or continuous. Some of the commonly used continuous cell lines are discussed below.

CHO cells

• CHO (Chinese Hamster Ovary) cells are commonly used cell lines in biological and medical research. Dr. Theodore Puck obtained the original CHO cell line (CHO-K1) from the ovary of an adult, female Chinese hamster in 1956. Since then, various variants have been developed. Some of the variants are CHO-DG44 and CHO-DXB11.
• Around 70% of recombinant proteins are produced in CHO cell lines. Some of the blockbuster, top-selling drugs in today’s market made by using CHO cell lines are:
  • Humira (Anti-TNF-a mAb)
  • Enbrel (TNF alpha receptor fusion)
  • Eylea (anti-VEGF)
  • Herceptin (anti-HER2 mAb)
• The advantages of the CHO cell line are:
  • Good growth phenotypes in both suspension and adherent culture. 
  • Easy to grow in large-scale culture.
  • High viability, high productivity, and highly transfectable.
  • Easy adaptation to various chemically defined media.
  • Tolerant of harsh bioprocess conditions 
  • Less susceptible to human virus infection.
  • Can perform human-compatible glycosylation which enables it to produce various human recombinant proteins. Prokaryotic bacterial cells like E. Coli aren’t fully equipped for mammalian glycosylation.

HeLa cells

• HeLa cells are the first immortalized human cell line. They were isolated from rare cervix adenocarcinoma of patient Henrietta Lacks (so the name HeLa) admitted to John Hopkins Hospital, Baltimore, Maryland in 1951. 
• HeLa cells have a diameter of around 10-20 uM and have a complex karyotype characterized by aneuploidy (abnormal number of chromosomes in the haploid set) and hyper triploid chromosomal number (3n+).
• Since the development of HeLa cells, it has been extensively used in many scientific studies worldwide. Experiments performed on these cells have played a significant role in the development of the polio vaccine, and treatments for cancer, HIV, and COVID-19 vaccine.
• Some of the outstanding uses of HeLa cells in the health field are:
• Jonas Salk, who developed the polio vaccine, used HeLa cells to test the polio vaccine.
  • These cells were used in experiments that helped to find out that HPV (Human Papilloma Virus) causes cervical cancer. This made the basis for the development of the HPV vaccine and Harald zur Hausen was awarded with Nobel Prize for his discovery.
  • Development of various cancer treatments like camptothecin, hydroxyurea. 
  • First human-animal hybrid was created by fusing mouse embryo cells with HeLa cells. 

A549 cells

• A549 cells are human lung adenocarcinoma cell lines established by D.J. Giard et al. in 1972. They are squamous alveolar basal epithelial cells. 
• These cells are commonly used as models of lung cancer as well as other lung-related infections like asthma, allergies, and other respiratory diseases for research.
• A549 CDX mouse model, a mouse model created by using A549 cell-derived xenograft is an extensively used xenograft lung cancer model. This mouse model plays an important role in the development of some of the anti-cancer therapeutics like paclitaxel, lapatinib, erlotinib, and gefitinib. 

HEK293 cells

• HEK cells are typically adherent, less circular than other cell types, and have dendrites-like processes.
• Since its development, various derivatives have been introduced like HEK-293T, HEK293FT, HEK293F, HEK293A etc. HEK293F are HEK293 cells modified for adaptation in suspension culture in serum-free media. HEK293T is established by expressing SV-40 T-antigen mutant in HEK293 which enables them to produce recombinant protein within plasmid vectors containing SV40 promoter. 
• Some major advantages of using HEK293 cells are 
  • Ease of transfection
  • High protein production
  • Reproducibility of results, and
  • Capability to adapt to suspension-free culture. It is suitable for small-scale production of production of proteins in academic labs as well as large-scale biotherapeutics production. 
• Some of the FDA approved biological produced in HEK 293 cells include:
  • NUWIQ (recombinant anti-hemophilic factor)
  • Onasemnogene (AAV-based Spinal Muscular Atrophy gene therapy
  • Lisocabtagene  maraleucel (CD-19 directed CAR T therapy)
  • Idecabtagene vicleucel (BCMA-directed CAR T therapy)
• Some limitations of this cell line are the risk of viral and bacterial contamination and degradation of the health of cells when cultured for an extended period. 

K562 cell line

• These are the first human-immortalized myelogenous leukemia cell lines to be established. These are lymphoblast cells derived from a 53-year-old female patient with chronic myelogenous leukemia. K562 cell lines are suspension cell lines.
• K562 cells are multipotential, hematopoietic, and undifferentiated malignant cells that can be differentiated into early-stage erythrocytes, monocytes, and granulocytes.
• These cells are used in natural killer (NK) assays and tumorigenicity studies. K562 cells express ligands for activatory NK receptors, which make them susceptible to NK cell-mediated cytotoxicity. They are used as target cells in NK assays. 

References

1. https://www.intechopen.com/chapters/53566#
2. https://www.sciencedirect.com/science/article/pii/S1740674921000068
3. https://biomanufacturing.org/uploads/files/547998065159985597-cho-history.pdf
4. https://www.sciencedirect.com/science/article/abs/pii/B9780080885049000805
5. https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/jat.3470
6. https://embryo.asu.edu/pages/hela-cell-line
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3763245/
8. https://cls.shop/blog/hela-cells#:~:text=Hela%20cells%20have%20a%20complex,aneuploidy%20in%201385%20cells%20examined.
9. https://www.frontiersin.org/articles/10.3389/fbioe.2021.796991/full
10. https://www.synthego.com/hek293
11. https://www.enzo.com/note/what-are-the-advantages-of-using-chinese-hamster-ovary-cho-cells/#
12. https://pmc.ncbi.nlm.nih.gov/articles/PMC5614136/
13. https://altogenlabs.com/xenograft-models/lung-cancer-xenograft/a549-xenograft-model/