An antibody is a molecule produced by the organism to detect and neutralise specific pathogens. Antibodies are the defence proteins that our immune system produces when it is exposed to an infectious microorganism or a vaccine.
Antibodies bind themselves to the pathogene and broadcast a signal which activate a defence mechanism and specifics cells that will destroy it. They can also prevent the microorganism from reproducing.
Antibodies can also recognize foreign cells (for example, after a transplant) or mistakenly attack cells in the body (in so-called “autoimmune” diseases such as lupus erythematosus or multiple sclerosis).
An antigen is a molecule recognized by the immune system, they can come from outside the body like viruses or bacteria or be created within the organism by cells, it is the case when the individual develops cancer or autoimmune diseases. The presence of an antigen in a cell causes an immunitary response against it.
A specific antibody is created by lymphocytes to neutralise a specific antigen. When an antibody encounters its specific antigen, the antibody binds to this antigen to form a molecular assembly which is called antigen-antibody complex. The antigen is neutralised and the complex is then destroyed.
In an antigen-antibody reaction, the antibody is created by the organism and is specific to an antigen, specific antibodies stay in the organism, detect and neutralize every specific antigen that it encounters.
So-called “monoclonal” antibodies are antibodies made specifically to treat a disease. For example, if immune cells are exposed to a protein necessary for the proliferation of cancer cells, the antibody obtained will bind to this protein, prevent it from fulfilling its role (for example by masking it) and disrupt tumour growth. With monoclonal antibodies, it is thus possible to neutralise a protein very specifically without affecting the others. Monoclonal antibodies created by the organism can also be produced by other types of cell in vitro.
They are produced by cells (this can be a mammalian cell, bacteria or yeast) that have been selected and cultured for their ability to produce a particular antibody. This was first obtained by exposing strictly identical immune cells (a cell clone) to a so-called “antigen” against which this clone produced an antibody, as in an immune reaction.
All monoclonal antibodies have a name ending in mab (which comes from the abbreviation Monoclonal AntiBodies): adalimumab, denosumab, infliximab, ustekinumab, etc.
Production
As mentioned above, monoclonal antibodies can be created in the laboratory through different processes. One of these process is the development of the hybridoma technique by César Milstein and Georges Köhler in 1975 made it possible to obtain a large quantity of antibodies at low cost and thus allow them to be used in many applications
This technique involves injecting the antigen of interest into a mouse and then removing the spleen cells after a few weeks. Among these cells are plasma cells secreting antibodies directed specifically against the chosen antigen.
These plasma cells are fused with tumour cells called myeloma cells (immortal cells) through the addition of polyethylene glycol (PEG) which induces membrane fusion and thus makes it possible to obtain hybridomas which have the capacity to multiply more rapidly and to last longer (the hybridoma which secretes a monoclonal antibody is immortal) than the normal cells of the body producing antibodies and to develop specific antibodies indefinitely.
The cells are then distributed in multiwell plates so that there is only one cell per well. In order to eliminate plasma cells and unfused myeloma cells, a selective culture medium (HAT culture medium) will be used.
Unfused plasma cells die rapidly and used myeloma cells having a non-functional gene for an enzyme involved in nucleotide synthesis-hypoxanthine-guanine-phosphoribosyl-transferase (HGRPT) are unable to survive in HAT (hypoxanthine aminopterin thymidine) medium, the medium where mammalian cells are cultivated.
Only hybrid cells multiply. After about ten days, each well is checked for the presence of antibodies directed against the antigen used to immunise the mouse. To detect the presence of antibodies, the specific antigen is added to the well and if an antigen-antibody reaction occurs, it means that there are antibodies in the well. The antibodies are collected and stored to be later validated and used as treatment
Inconvenience
Since most monoclonal antibodies are produced in rodent cells, an immune reaction can be observed when they are injected into a patient. This immunity gradually inactivates the beneficial action of the monoclonal antibody. To remedy this problem, “chimeric” or “humanised” antibodies are produced.
“Chimeric” antibodies are obtained by grafting the constant parts of human immunoglobulin onto the variable parts of a mouse antibody.
“Humanised” antibodies are produced by microbial fermentation or by transgenic mice containing only part of the human genes at the origin of the Antibodies. They are potentially better tolerated in the human body.
Use
CHRONIC INFLAMMATORY DISEASES
So-called “chronic” inflammatory diseases are essentially autoimmune diseases (or in which autoimmunity plays a role). In these diseases, the immune system reacts abnormally by attacking cells in the body to which it should not be sensitive.
He can attack:
– cells of joints, ligaments or tendons as in rheumatoid arthritis or spondyloarthritis;
– skin cells as in psoriasis or lupus;
– nerve fibres as in multiple sclerosis;
– the cells of the intestine as in Crohn’s disease and ulcerative colitis, etc.
The monoclonal antibodies developed to treat these diseases target proteins that are involved in this abnormal immune reaction (like AGR2, HER2, CD20 or CRP). By neutralising these proteins, it is possible to reduce or even block the autoimmune aspect of the disease.
For example, several biotherapies based on monoclonal antibodies aim to neutralise the action of an immunity mediator called Tumour Necrosis Factor Alpha (TNF alpha).
These antibodies can either neutralise TNF alpha or bind to the cell membrane protein to which TNF alpha must bind to act (the “membrane receptor”).
Other antibodies target interleukin 6 (another immune mediator) or certain immune cells (eg B-CD20 lymphocytes). In all cases, monoclonal antibodies act like a grain of sand in the gears of the immune reaction.
CANCER
Monoclonal antibodies used in the treatment of cancers have various modes of action. Some aim to neutralise substances necessary for the growth of tumours (growth factors, for example human epidermal growth factor (EGFR)).
Others bind to membrane receptors and block the proliferation of these cancer cells by disrupting communication between cells. Finally, others prevent the formation of new blood vessels that the tumour needs to grow. For example, trastuzumab is a monoclonal antibody used to act against HER2 protein which is expressed at the surface of the cells in some cases of breast cancer, it blocks the action of the membrane receptor and so halt the tumour growth.
It is also possible to attach a chemotherapy molecule to an antibody that recognizes cancer cells. Thus, chemotherapy is brought closer to its target. These are called “conjugated antibodies”.
Depending on their indication, monoclonal antibodies against cancer can be used alone or in combination with “conventional” chemotherapy drugs. In some cases, monoclonal antibodies greatly increase the effectiveness of chemotherapy.
Today, around ten monoclonal antibodies against cancer are prescribed in daily practice and more than 150 are in development.
COVID 19
Monoclonal antibodies are used in some treatments against COVID 19, it is the case for ronaprève (Roche-Regeneron), evusheld (AstaZeneca) xevudy (GlaxoSmithKline) and paxlovid.
Monoclonal antibodies directed against the SARS-Cov2 virus constitute a treatment against Covid-19, the aim of which is to prevent the most vulnerable people from developing serious forms of the disease.
These monoclonal antibody treatments for Covid-19 provide an immune shield against the disease to patients most likely to develop acute and severe forms.
It is not a question of inducing the production of antibodies by patients (principle of vaccination) but of administering directly active antibodies to them. Especially for patients most likely to develop severe forms of the disease.
The monoclonal antibodies developed against Covid-19 are designed to attack a specific part of the virus: this is the Spike protein located on the surface of the virus, which helps it to attach and enter human cells.
By preventing it from attaching itself, the virus thus has less hold on patients, and becomes much less offensive. It is therefore an aid provided to the immune system at the start of the infection even before the patient’s immune defences develop.
Latest news
January 23, 2022, (CNN) Federal regulators are considering limiting the authorization of certain monoclonal antibody treatments that have not proved effective against the Omicron variant of the coronavirus, a source familiar with the decision-making.
The US Food and Drug Administration could decide in the coming days to take steps to curb the use of antibody treatments produced by Eli Lilly and Regeneron, the source said, pointing to the growing body of evidence that shows their monoclonal therapies don’t effectively neutralise the virus’ Omicron variant.
The National Institutes of Health had recently updated its guidelines to advise clinics against using these treatments on patients with mild to moderate Covid-19 due to their diminished effectiveness against the Omicron variant.
The continuous appearance of new forms and variations of sars cov-2 could let one think that new treatments and clinical trials, likely to combine different monoclonal antibodies, will emerge in the next months or days. Nevertheless mab have been used for years to treat many other diseases and are proved to be efficient and their use doesn’t seem to be a subject of discord in most cases.
SOURCES
https://www.inserm.fr
https://www.pasteur.fr
https://solidarites-sante.gouv.fr
https://www.medecinesciences.org
