Human cell lines

Cells that have been immortalized and grown in vitro from primary explants of human tissue or bodily fluid are referred to as a "human cell line.

Since the beginning of the 20th century, scientists have used cell lines to obtain insight into cell biology and metabolism. Cell lines or immortal cell lines have become a popular model in the cell culture literature, serving as a well-characterized and optimized entity for pharmacological investigations, biochemical tests, bioactive synthesis, etc. Cost-effective, user-friendly, and able to undergo more passes than primary cells, cell lines are preferred by scientists. Cell lines are simple to manipulate and propagate, making them preferred for numerous screenings due to the benefit of a limitless supply of materials.

CLS Cell Lines Service GmbH supplies one of the biggest collections of human cell lines from almost every kind of human tissue, in order to meet this vast demand.

Immortality of human cell lines

Cells that have been immortalized can be cultivated forever when their growth has been artificially stimulated. Different types of cancers and other cells with chromosomal defects or mutations that allow them to proliferate indefinitely provide the basis for immortalized cell lines. 

As a result of their rapid proliferation, the dish or flask containing immortalized cells will become overcrowded. That is why scientists create more space for proliferating cells by passaging (or dividing) onto fresh plates.

Differences to cancer cell lines

It is important to note, that there is a fundamental distinction between tumor cells and immortalized cells: tumor cells exhibit many classic characteristics, such as loss of contact inhibition, poor adhesion, and apoptosis inhibition, whereas immortalized cells maintain their normal genotype and phenotype.

Methods for generating immortal cells

Spontaneous mutation

During the process of cell division and multiplication, certain initial cells may be altered and exceed their lifetime. These cells will be harvested for expanded cell culture and will undergo spontaneous mutation to become immortalization cells. In most instances, however, the cells will change into tumor cells, rendering this technique ineffective. Therefore, tumor cells are the finest example of spontaneously immortalized cells, which may have acquired genetic modifications to survive senescence and become immortal.

Inducing cell immortality by virus genes

Numerous viral genes have the ability to influence the cell cycle, allowing them to achieve immortality by eliminating the biological brakes on proliferative regulation. To promote immortalization, the simian virus 40 (SV40) T-antigen is one way. It has been shown that SV40 T-antigen is the simplest and most dependable agent for the immortalization of several cell types, and its mechanism in cell immortalization is well known. An example is the cell type HEK293T (also known as 293T).

Telomerase Reverse Transcriptase (TERT) Protein Expression

Telomerase is a ribonucleoprotein that may prolong the DNA sequence of telomeres, therefore preventing cellular senescence and allowing cells to divide indefinitely. This protein is inactive in the majority of somatic cells, but when TERT is produced exogenously, the cells are able to maintain enough telomere lengths to prevent replicative senescence. Currently, human telomerase reverse transcriptase (hTERT) is the most used method for cell immortalization.

HeLa: The first immortalized human cell line

In 1951, Dr. Jones of Johns Hopkins Hospital in Baltimore diagnosed Henrietta Lacks with malignant adenocarcinoma of the cervix. Dr. George Gay (1917-1994), head of the Tissue cell culture laboratory, received the materials after the cervical biopsy.

Mary Kubicek, one of his assistants, was the first to discover that the cells could survive in a nutritional solution made from chicken plasma. She then cultivated the Lacks specimen in roller tubes with the use of cell culture media. Cells in well-established cultures expanded rapidly, survived for many passages, and divided every 20 hours.

The patient's name, Henrietta Lacks, inspired the name of the cell line; nevertheless, for a long time, researchers assumed that HeLa cells really came from either Harriet Lane or Helen Larsen. There was a period of secrecy around the identity of Henrietta Lack, the woman whose cells were used to develop the first HeLa cells, until 1971, when the journal Obstetrics and Gynecology revealed her to be the original source.

Advantages and Disadvantages of using human cell lines

There are several benefits for using immortalized cell lines. Because most laboratories employ standard cell lines, immortalized cells are generally well-defined. They are homogenous and genetically identical populations, which facilitates the production of reliable and repeatable outcomes. Immortalized cells are often simpler to cultivate than primary cells since they grow more robustly and do not need to be extracted from tissues.

Due to their rapid and continuous growth, it is also feasible to extract huge quantities of proteins for biochemical testing. Additionally, it is feasible to generate cell lines that continually produce a gene of interest, such as a fluorescently tagged or mutant protein.

The most significant drawback of employing immortalized cells is that they cannot be called "normal" since they proliferate continuously and may express unique gene patterns not present in any in vivo cell type. Consequently, they may lack the required characteristics and functions of reasonably normal cells.

In addition, the features of a cell might alter and become even more distinct from those of a "typical" cell during periods of continuous development. Therefore, it is essential to regularly evaluate the features of cultivated cells and to avoid using cells that have been passaged an excessive number of times.

Even though cell lines are simple to deal with, the physiological significance of these investigations may be low. They have little similarity to human metabolism and physiology, let alone human anatomy.

Numerous changes in the genotype and phenotype of these cells are caused by immortalization and repeated passage. Due to the absence of morphological or functional characteristics, cell lines may be incapable of inducing pertinent biomarkers.

Consequently, it is usually preferable to confirm cell lines before to use to ensure that they are neither misdiagnosed nor contaminated.

Human cell lines in biopharmaceutical applications

Cell lines are not only used for modeling biological systems and diseases, but also for practical biotechnological purposes in the production of proteins, viruses, and more. Discover the cells used in these applications:

The technology of hybridoma cells

The manufacture of monoclonal antibodies specific to an antigen of interest is a component of hybridoma technology. The somatic fusion of B lymphocytes of the spleen with immortal myeloma cells produces a hybridoma cell line that can be perpetually propagated to produce clonally identical antibodies, as these hybridoma cells inherit the indefinite growth characteristics of myeloma cells and the antibody secretion capabilities of B-lymphocytes. Antibodies generated from a single hybridoma cell line are homogenous and recognize a single epitope on an antigen.

Using hybridoma technology, monoclonal antibodies are used in the following applications:

Biochemical analysis: Monoclonal antibodies changed laboratory diagnostics. Biochemical analysis (RIA, ELISA), immunohistopathology, and diagnostic imaging regularly use antibodies (immunoscintigraphy).

Immunotherapy: Human, humanized, and chimeric monoclonal antibodies are used in immunotherapy for the treatment of cancer, autoimmune illnesses, infectious diseases, cardiovascular and other non-oncological conditions, as an adjuvant to organ donation, and for targeted drug delivery.

Protein purification: Monoclonal antibodies are used to purify proteins and are particularly beneficial for the purification of recombinant proteins (immunoaffinity chromatography).

Generating recombinant proteins in mammalian and insect cells

Due to their capacity for protein synthesis, eukaryotic cell lines have become indispensable to produce recombinant proteins. Their capacity to facilitate protein folding and molecular assembly exceeds that of other systems. Expression vector engineering and transfection into the host system are the first steps in the creation of recombinant proteins, followed by cell selection, cloning, screening, and assessment. To achieve quality and scalability criteria, recombinant protein producers need efficient and cost-effective expression hosts.

Cultivation of viruses

The introduction of cell culture methods has drastically altered viral isolation and proliferation in the laboratory. For isolating, detecting, and identifying viruses, cell-based production methods provide a practical and cost-effective method for isolating, detecting, and identifying viruses. Greater process control results in a more dependable and well-characterized product with quicker and shorter production cycles than animal-based or egg-based systems.

Important are cell-based manufacturing techniques for viral culture and vaccine manufacture for:

• Virus detection/identification
• Host-pathogen interaction research
• Viral structure and replication
• Vaccine production

Future and perspectives

Since the establishment of the HeLa cell line, immoral cancer cells have been extensively studied as biological models to examine cancer's biology (including cancer initiation, progression, metastasis, the tumor microenvironment, and cancer stem cells) and to develop new anticancer drugs or alternative forms of therapy, such as hyperthermal therapy and the use of nanoparticles.

Due to cancer heterogeneity and drug-resistant tumors in patients, however, numerous data gained from the investigation of immortal cancer cell lines imply that cancer cell lines are not representative enough.

Research using cancer cell lines provides the chance to get a better understanding of the biology of tumors and enables high-throughput screening for drug development.

Although several significant experiments employing cancer cell lines were carried out, the findings provide only a limited amount of information and have a poor clinical correlation.

This is one of the reasons why this kind of study does not fully represent the clinical situation. Therefore, primary tumor cell cultures (for example, a three-dimensional tumor cell culture obtained from solid tumor specimens) are able to provide more precise information on particular cancer cases and enable the development of therapeutic settings.