Genome editing technology is arousing tremendous enthusiasm among researchers studying the life sciences, according to our partner The Conversation.
Among its applications, let us discover the treatments of cancer and hereditary hemoglobinopathies, the fight against diseases transmitted by certain insects and the concept of "plant breeding".
The analysis of this phenomenon was carried out by Hervé Chneiweiss, research director of the Neurosciences laboratory and chairman of the Inserm ethics committee, and François Hirsch, member of the Inserm ethics committee.
In 2012, the year of the publication of Jennifer Doudna and Emmanuelle Charpentier who would earn them the Nobel Prize in chemistry eight years later, the Pubmed bibliographic database listed 145 scientific publications containing the term “CRISPR”.
In April 2021, there are 23,838.
This explosion of research illustrates the extraordinary enthusiasm that this genome editing technology has aroused among researchers studying the life sciences.
To understand the hopes it gives rise to, we invite you to discover four concrete applications.
General diagram of the genome editing process © Epigeneticist / Wikimedia, CC BY-SA 4.0
1. As a cancer treatment
Most cancers are recognized and attacked by the immune system, in particular by certain white blood cells, the infiltrated T lymphocytes. The tumor nevertheless manages to progress because of its ability to inhibit the action of the immune system (it induces "immunosuppression") and because the cells which constitute it have immune evasion mechanisms which allow them to escape the defenses. of the body.
However, it is possible to increase the patient's natural anti-tumor immune response, thanks to adoptive T cell therapy (or "adoptive cell therapy", ACT in English).
This personalized approach consists of removing T lymphocytes from the sick person, multiplying them in vitro, then re-administering them by infusion, often after having modified them to improve their capacities to fight tumor cells.
Spectacular results have been obtained using this technique, demonstrating that adoptive transfer of genetically modified T cells can induce complete and lasting remissions in patients with various blood cancers (hematological cancers).
CAR-T are therefore T lymphocytes equipped with a CAR molecule adapted to the cancer to be treated © Inserm
The CAR (for Chimeric Antigene Receptor) approach is one such adoptive T cell therapy. It consists of introducing genes encoding receptors for synthetic antigens into the T cells taken from the patient. In immunology, the term antigen designates any element foreign to the organism capable of triggering an immune response. In this case, the antigens concerned are molecules present only on the surface of tumor cells. Once reintroduced into the patient's body, the modified T cells will be able to recognize and bind to the cells carrying the antigen. Activated by this binding, they then destroy these tumor cells.
Clinical data collected since 2010 indicates that CAR T cells have the potential to cure patients with advanced leukemia, in adults and children with relapsed / refractory acute lymphoblastic leukemia (ALL) and diffuse large B-cell lymphoma ( DLBCL).
Several treatments implementing them have been authorized since 2018 (Yescarta by Gilead and Kymriah by Novartis).
CAR T cells are also beginning to demonstrate robust anti-tumor activity in patients with multiple myeloma.
One of the major problems with this approach is its cost, in the order of € 400,000 per treatment.
In addition, a limitation of the effectiveness of adoptive T cell therapy is the depletion of transferred T cells, which is the source of relapse.
In addition, while CAR T cells are revolutionizing the treatment of blood cancers, they have not been shown to be clinically effective for solid tumors.
Cancer cell (white) attacked by two T cells (red) © Nih Image Gallery / Flickr, CC BY-NC
Precision genome editing using CRISPR / Cas9 could overcome these obstacles.
This technology is in fact easily "multiplexable", in other words it can be used to simultaneously modify numerous regions of the DNA of a cell.
Recent work has given encouraging results in two patients with myeloma and one patient with metastatic sarcoma, these three cancers having been shown to be refractory to treatment. CRISPR / Cas9 allowed the simultaneous elimination of two different molecules in the T cells of these patients: the natural surface molecule allowing the activation of T cells (TCR) and the immune control molecule PD1. These T cells have also been modified to produce a synthetic TCR specific to cancer cells, to allow them to recognize tumor cells.
The idea behind these manipulations was to improve the anti-tumor capacities of T cells and increase their persistence in the body of patients.
The results are encouraging: the T cells thus modified were still alive and active 9 months after the treatments, in the 3 participants in the clinical trial.
No clinical toxicity was observed, and a marked regression of the myeloma was observed.
2. As a treatment for hereditary hemoglobinopathies
Hereditary diseases of hemoglobin - the protein that fixes oxygen in our red blood cells - are serious blood diseases that shorten the life expectancy of millions of people around the world.
These hemoglobinopathies include sickle cell anemia and β-thalassemia in particular.
Patients with sickle cell disease have a unique mutation in the gene that codes for the protein β-globin, the main component of adult hemoglobin. This mutation results in the production of hemoglobin which polymerizes when deoxygenated. Red blood cells take on a crescent, or sickle, shape. They form microthromboses (occlusion of small blood vessels), which causes severe pain, damages many organs, and leads to anemia by destruction of red blood cells, hence the other name for this disease, "sickle cell anemia".
Patients with β-thalassemia, for their part, also have mutations in the β-globin gene or in its regulatory regions. These changes lead to a deficient production of β-globin which causes anemia requiring blood transfusions. One solution to severe forms of both diseases is the transplantation of blood-producing stem cells from the bone marrow, but few patients have compatible donors.
For more than twenty years, different gene therapy strategies have targeted blood-producing stem cells.
Without success, because the exercise is particularly difficult: it is necessary to modify a large number of cells, by targeting only the precursors of red blood cells, by obtaining a high level of expression of β-globin, all without risking that these manipulations do not trigger long-term tumor development.
VIDEO:
What is sickle cell disease?
(Inserm / Youtube, 2018)
The new generation of gene therapy has taken advantage of an observation: the hereditary persistence of fetal hemoglobin. During gestation, the hemoglobin produced by the fetus differs from that which will be used after the child is born. The production of this fetal hemoglobin usually decreases soon after birth, and "adult" hemoglobin becomes the majority. However, in some people, this switch does not happen and the genes used to produce fetal hemoglobin remain active. The persistence of these genes has been found to decrease the clinical manifestations of β-thalassemia and sickle cell anemia.
We know the “switch” involved in turning off genes in fetal hemoglobin and turning on β-globin genes: it is a protein called BCL11A. Researchers therefore naturally wondered whether it was possible, by suppressing BCL11A, to restore the production of fetal hemoglobin. A recent clinical trial explored this lead in a patient with sickle cell anemia and another with ß-thalassemia. Researchers sought to inactivate BCL11A using CRISPR-Cas9 in blood-producing stem cells.
The article reports an effectiveness of 69 to 85% at the target site. The result was a significant production of fetal hemoglobin, which freed patients from the need for blood transfusions, solved their anemia problems and made vaso-occlusive crises disappear. These patients are part of a larger trial, with encouraging results in a total of nine patients.
Before the start of the clinical trial, researchers also made a major effort to identify off-target genomic effects of CRISPR.
Indeed, it happens that this technique, however precise it may be, does not cut only the targeted DNA sequence.
They used several break prediction methods, performed precise sequencing of these sites and did not observe off-target editing.
However, it remains to verify in the long term the stability of the beneficial results and the absence of harmful effects.
3. To fight against diseases transmitted by certain insects
Another area in which the potential applications of CRISPR technology raise therapeutic hopes is the eradication of animal species harmful to humans by the so-called "gene
drive
" approach.
It is estimated that each year vector-borne diseases are responsible for the death of 700,000 people around the world and especially in countries with the most fragile economies.
The diseases concerned are mainly dengue, chikungunya, yellow fever, Zika virus diseases, malaria, itself responsible for the death of nearly 400,000 people, the vast majority of which concern children under 5 years old.
Inspired by existing natural versions of gene drive, genome editing is here used to propagate lasting genetic changes.
These will lead either to infertility of the species to be eradicated, or to the production of proteins by the animal itself, rendering it incapable of harboring the pathogenic virus.
Several research laboratories are developing this approach, which would make it possible to obtain results that are faster, more efficient and less expensive than the more traditional ones already used in Brazil, the United States or Burkina Faso.
VIDEO:
Burkina Faso: controversy over GMO mosquitoes against malaria (TV5Monde / Youtube, 2019)
>
Currently, several laboratory studies have demonstrated the potential of gene drive, but many limits to the application in real situation remain.
These include the fear of the loss of control over genetically modified animals and the unmeasured ecological impacts of the disappearance of species often playing an essential role in fragile ecosystems.
Many international organizations and representatives of civil society quickly took a stand for the regulation of these techniques.
Likewise, the International Association for Research and Innovation Responsible for Genome Editing (Arrige) notably recalled that the deployment of these techniques must be done in full transparency and in consultation with the communities living in the most vulnerable areas. exhibited.
These particularly vulnerable communities could indeed suffer from the misuse or poor implementation of this new technology, even if it is in their own interest.
4. For plant breeding
Since the Neolithic, human communities have not stopped selecting plants or crossing different species to obtain those that would be best suited to their needs.
This plant breeding has successfully improved the crops that are the basis of global food production.
The use of genome editing for plant breeding has been one of the fastest growing.
It does not in fact raise the same type of ethical questioning as its use in animals, and especially in human beings.
In addition, this approach quickly demonstrated its strong potential to improve, facilitate and accelerate plant breeding. The stakes here are considerable: this technique is called upon in particular to improve yields and provide plants with better resistance to diseases, pests and "abiotic stress" (sub-optimal growth conditions caused, for example, by drought, excess water, temperature extremes, salt stress, mineral deficiencies and growth retardation or damage following spraying of products), reducing the use of toxic inputs for the environment.
Very quickly large industrial groups, such as Bayer-Monsanto, Pioneer, as well as the French biotech Cellectis, negotiated patents to produce modified plants that can now be found on the unregulated North American market.
This ranges from mushrooms that no longer turn brown with age, to soybean oil modified for better stability and the absence of unsaturated fatty acids, to corn plants with better yields.
VIDEO :
A genetic modification to improve the resistance of plants to heat (Salk Institute / Youtube, 2019)
The United States has in fact recognized that, unlike genetically modified organisms (GMOs), plants obtained after genome editing do not contain a foreign gene inserted randomly, but reproduce a trait already observed in the gene of certain varieties of genome. the plant.
They are followed by many other countries, Australia, Japan, Canada, India ...
By contrast, following a referral from a French association collective, the Court of Justice of the European Union ruled in July 2018 that products derived from targeted mutagenesis methods, including genome editing, must be regulated by the complete provisions of the European directive governing the deliberate release of GMOs.
Our "DNA" file
Many scientists consider this decision inappropriate and urge a review of the legal framework that takes into account the real benefits and risks of this technology.
Thus, the European Federation of Academies of Sciences and Humanities (Allea) - which represents more than 50 academies from more than 40 countries of the European Union and of third countries - considers that the maintenance of the restrictions could hamper the selection of more cultures. productive, more diversified, more resistant to climate change and with a reduced environmental footprint.
Only a decision of the Council of the European Union specifying the place of genome editing in plant modification, will or will not allow Europe to maintain its autonomy in terms of the development of seeds improved by genome engineering.
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This analysis was written by Hervé Chneiweiss, research director of the Neurosciences laboratory and chairman of the Inserm ethics committee, and François Hirsch, member of the Inserm ethics committee.
The original article was published on The Conversation website.
Declaration of interests
The authors do not work, do not advise, do not own shares, do not receive funds from an organization that could benefit from this article, and have not declared any affiliation other than their research organization.
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