What is mRNA
The mRNA is a molecule that carries the genetic information contained in the DNA of the cell nucleus outside it so that structures called ribosomes read that information and convert it into the sequence of amino acids that make up proteins. In cells, mRNA cannot be copied back to DNA or “reinserted” into it.
Cells produce tens of thousands of mRNA molecules every day. These molecules mature in the nucleus, come out of it and produce proteins until they break down and disappear. The mRNA does not usually last long within cells and is continually replenished as needed.
Viruses also need mRNA to make the proteins that are part of their structure. But their mRNA can only be inserted into the DNA of the cells they infect if it is a retrovirus. Because only these viruses contain a special enzyme called reverse transcriptase that converts RNA to DNA. And also another enzyme that allows that viral DNA to insert itself into human DNA.
Without these enzymes it is impossible for RNA to be transformed into DNA and even less to insert itself into the DNA of our cells. Therefore, when some insist that mRNA vaccines can “make us transgenic” or “cause disease,” they do so without any scientific basis.
What are mRNA Vaccines
The mRNA vaccines are very simple, they contain the mRNA of a part of the virus genome that will produce the protein against which the immune response is to be achieved. This mRNA is introduced into a structure similar to that of the cell membrane and liposomes used in cosmetics, but small in size. And nothing more.
Once inoculated, the mRNA contained in these structures is introduced into the muscle cells and these begin to produce the virus protein. Our cells behave as if they were infected by the virus and produce the same protein that the virus would produce inside. And it provokes the reaction of the immune system.
In the case of the SARS-CoV-2 vaccine, the cells express the Spike (S) protein of the virus. This protein is what the virus uses to latch onto cells and infect them. Lymphocytes B recognize this protein as foreign to our body and end up producing different antibodies against different areas of this protein.
All cells in our body have proteins known as major histocompatibility complexes (MHC). The MHCs are responsible for teaching cytotoxic T lymphocytes (Tc) a sample of pieces of the proteins that cells are producing. In the case of a viral infection, or a vaccine such as the one described, this sample includes the proteins of the virus.
In addition, other cells that we know as antigen presenting cells can take these proteins, digest them in internal compartments and show fragments to the T helper (Th) lymphocytes that are responsible for controlling the immune response.
Therefore, with mRNA vaccines, in a very simple way, it is possible to activate the entire immune system but without suffering virus infection. Possibly that has made its effectiveness very high without showing any side effects. In fact, they have been studied and improved for thirty years. And they have given very promising results against the flu, Zika or rabies.
MRNA vaccines, great promise for the future
The first great advantage of these vaccines is their ease of manufacture. It is enough to know the sequence of the organism’s genome to be able to produce the mRNA of the structure against which the immune system is to be activated. If, as is happening with SARS-CoV-2, the organism mutates, the mRNA can be easily changed.
Other vaccines, such as those based on adenovirus, require the insertion of part of the virus genome into the genome of another and the cultivation of these viruses in bioreactors, a much more complex process. And those based on proteins do not activate Tc lymphocytes as occurs naturally.
The thing does not end here. The second great advantage of mRNA vaccines comes from their great effect on older people. Age-related defects in the immune system make older people do not respond well to most vaccines. Without going any further, the effectiveness of the flu vaccine in the elderly population is around 65%.
However, mRNA vaccines have achieved greater than 85% effectiveness in this same population.
In short, the great response of the immune system of the elderly to these vaccines opens the possibility of improving immunization against viruses as dangerous as influenza or other respiratory viruses. In addition to the fact that the security they are showing and the ease of modification makes them a great promise for the future in the prevention of infectious diseases.