Genetics is the science that deals with the study of genes, as well as DNA and RNA molecules. This field has made significant advances in recent years, developing tools that allow the modification of organisms’ DNA sequences. One of the most innovative is the CRISPR technique, which is very easy to use and has multiple applications.
All living organisms have DNA and RNA molecules, which contain information that determines their characteristics. The information in these microscopic molecules has been the subject of study for many years.
Gene editing is one of the most important achievements of science. In fact, studies claim that there are several clinical trials on human genes to treat diseases. The application of gene editing can bring about change in a number of areas, especially in health.
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What is CRISPR-Cas9?
CRISPR-Cas9 is one of the 3 gene editing tools currently available. It is based on the CRISPR regions of bacteria. The word CRISPR is an acronym. It stands for “clustered regularly spaced short palindromic repeats”.
These palindromic repeats are characterised by a sequence of nucleotides and spacers. Nucleotides are the basic units that make up a DNA molecule. Spacers are fragments of DNA that are sandwiched between the nucleotides.
Spacers function as a source of additional information, thereby altering the organism’s genetics. A published study states that bacteria add viral DNA sequences as spacers for their defence against a particular virus. These allow the creation of specific enzymes that will cut a segment of DNA without altering the organism’s genetic information.
The CRISPR technique for genetic modification was officially created in 2012. It was the brainchild of scientists Jennifer Doudna and Emmanuelle Charpentier. The idea was to create a simple, fast and inexpensive tool that would allow a DNA sequence to be modified and changes to be made with extreme precision.
How does CRISPR work?
This method is also known as genetic scissors or genetic copy-paste and its mechanism of action is very simple. It can use multiple enzymes, although Cas9 is the most commonly used. First, an RNA molecule encoding the Cas9 enzyme and a guide RNA must be introduced into the cell.
The guide RNA will tell the enzyme which specific segment of DNA to cut. The cutting is carried out with great precision, just as it happens inside bacteria. Specialists must also insert the DNA sequence to be inserted into the cell.
After the DNA has been cut, the cell will start the process of gene repair and insert the desired sequence into the main strand. The inserted sequences are created in specialised laboratories, however, they retain the name CRISPR in honour of the bacterial mechanism.
What can CRISPR-Cas9 be used for?
The possibilities offered by gene editing are unimaginable. They range from correcting defective genes and eradicating diseases to producing more resistant crops. CRISPR has no specific application at present, so it is only used for research purposes.
Many laboratories have used this tool to study different phenomena and learn all its mysteries. CRISPR-Cas9 has been used to create transgenic plants and to study the reprogramming of stem cells. It has also been used to study certain diseases in depth, such as schizophrenia.
One of the fields where this technique can be exploited is biomedicine. It can be a useful tool to treat and prevent diseases that alter a single specific gene. These genetic scissors could also help in cancer therapies.
Among the possible uses the researchers suggest are the following:
- Creating crops that emit less pollution.
- Making transplantable organs, tissues and cells from animals.
- Making new enzymes resistant to temperature changes.
- Growing grass for cows that is easier to digest.
- Treating virus-borne diseases such as HIV.
- Preventing the transmission of heritable diseases.
- Creating antibacterial products with a broader spectrum of action.
What are the potential drawbacks?
One of the main limitations of applying CRISPR is the cutting of DNA outside the target gene. Studies claim that off-target effects are likely to occur in up to 50% of cases. These unwanted cuts can have serious consequences, even turning healthy cells into cancerous ones.
In some cases, guide RNAs and DNA modifications can induce apoptosis, i.e. cell death. It is also possible to develop an immune response to the Cas9 enzyme.
Introducing CRISPR into the human body is a major challenge. Some of the viruses used in the technique may have an affinity for different cells, so they can affect unwanted tissue and cause cellular changes.
Moral issues have also delayed the clinical application of gene editing in general. Some researchers have expressed concerns about misuse. It is argued that they may be used to create people with specific characteristics rather than to cure diseases.
Human clinical trials
So far, human clinical trials with the CRISPR technique are very limited and conducted in small populations. One of the first experiments generated a lot of controversy worldwide. It occurred in 2018, when Chinese scientist He Jiankui announced the birth of two human immunodeficiency virus (HIV)-resistant twins modified with CRISPR-Cas9.
The study was published in a specialised journal in China, however, controversy arose due to possible long-term adverse effects. In addition, He Jiankui ignored all the concerns of the international community regarding the alteration of the germ cell line.
Another human clinical trial in China used CRISPR to treat lung cancer in 12 patients. The experiment involved altering patients’ T lymphocytes for subsequent inoculation. None of the patients treated developed adverse effects, although the study is still in phase 1.
Around the world, there are dozens of human clinical trials with CRISPR. In addition, multiple in vitro studies have shown promising results in the treatment of diseases. However, the technique still needs to be perfected.
CRISPR is one of the most revolutionary scientific discoveries of recent years. It makes it possible to cut specific segments of the DNA chain and modify the characteristics of a cell. The numerous applications could lead to major breakthroughs in various fields, especially in medicine.
Unfortunately, it has many limitations that have hindered its large-scale use. Researchers must carry out further studies and refine the technique before it can be used in humans and exploit its full potential.