In the summer of 2012, the announcement of the editing methodology which earned two Nobel Prizes. Its application is being tested for various pathologies
August 17, if you consider the issue of Science on paper, Crispr genetic scissors will be 10 years old. The work that announced the invention, in fact, was published in the scientific journal in the summer of 2012. Meanwhile the technique entered dozens of clinical trialsgot the first hits and gave away the Nobel to Emmanuelle Charpentier and Jennifer Doudna. Furthermore, in this decade, Crispr has evolved. No longer a single genetic modification technique, but an umbrella abbreviation, which includes many. Each with its strengths and some flaws.
Original model
Luigi Naldini, A pioneer of old and new gene therapy, he shares the widespread enthusiasm for the rapid results obtained for some rare diseases. But the geneticist of the San Raffaele Telethon Institute in Milan is little inclined to celebrations and prefers to dwell on the doubts to dispel in order to continue the journey safely. Crispr’s original model uses the Cas9 protein to cut the DNA double helix. the most tried-and-tested version but also the riskiest, tell us. In fact, severing both filaments can give rise to unwanted rearrangements, extensive and difficult to highlight. It is possible that cells carrying macro-mutations are disadvantaged and tend to disappear on their own, but long-term studies will be needed to ascertain this.
Encouraging data
At the moment, however, the data are encouraging. The most advanced international experimentation concerns diseases with defects in the protein that colors the red blood cells, and also in progress in Italy. The first patients reached excellent hemoglobin levels and were able to stop transfusions, he assures Franco Locatelli, director of the Department of Oncohematology and Cell and Gene Therapy of Bambin Ges in Rome. I am a thalassemia brother and sister, to whom other volunteers have joined in the meantime: We are 14 subjects for thalassemia and 7 for sickle cell anemia. And pediatric trials are also starting, for children between 2 and 11 years old. In this case Cas9 is used to restart fetal hemoglobin productionwhich usually fades as it grows, but can be useful in compensating for defects in the adult form.
Correctors
Other groups around the world are starting to test the latest generation approaches. There are base correctors (in English, basic editing), which scratch the DNA double helix instead of cutting it, reducing but not eliminating the risk of unwanted mutations. The latest arrivals are the trigger correctors (prime editing) which have the merit of changing the sequence without cutting, but have yet to debut in the clinic. Furthermore, depending on how it is used Crispr can be used to silence a gene, replace a target sequence or make a targeted correction.
Limits
Unfortunately, at least for now, the treatments proposed for hemoglobinopathies all share the same limitation: the stem cells corrected out of the body and then reinfused can find a place in the patient’s marrow only after invasive chemotherapy treatment. What is the best platform? There is room for different options. The arrival of the latest innovation does not imply that we must abandon the most tried and tested approaches, explains Naldini. After working to fine-tune the viral vectors used in classical gene therapy, his group now uses Crispr to change long stretches of DNA by providing a template. The first experimental treatment for our classic targets, primary immunodeficiencies, is expected to be ready for the clinic by early 2024.
Epigenetic editing
But Naldini looks already further, to the so-called epigenetic editing, in which the target sequence is not modified but it is made more or less active thanks to external chemical changes. Together with Angelo Lombardo the creator of the hit and run approach, which is now being developed by a company founded together with American researchers. One of the most important bets for the next 10 years will be to expand the range of treatable diseases. To date, the international clinical trial database counts about twenty experiments in which some variant of Crispr is used. In most cases they are in their infancy and have not yet produced scientific publications, but the list is getting longer.
Different applications
The first results in the counteract the build-up of a defective protein in the liver
(transthyretin). Progress towards a common form of hereditary blindness (Leber amaurosis) bodes well. But work is also beginning on inflammation, infections and even on the elimination of HIV sequences inserted in the human genome. Crispr is also used to produce immunocompatible pancreatic cells for those suffering from diabetes, but also to enhance immunotherapy against some forms of cancer. At Bambin Ges we are interested in the latter trend for acute lymphoblastic leukemia T. Editing can increase the persistence and efficiency of CAR-T, which are immune cells modified to recognize and attack tumors, Locatelli tells us. In itself the Crispr technique is cheap, but a complete personalized treatment ends up costing over a million euros.
The problem of sustainability
The great challenge of the future, therefore, will be the sustainability of these therapies and their large-scale applicability. Ensuring equal access, even in low-income countries, is Jennifer Doudna’s major ethical concern. But also in Europe we must organize: the scientific community is still shocked by the abandonment of the European market by a leading company in gene therapy, which has deprived many patients of a valid treatment option even if conceived in the pre-Crispr era. The fact that the pathologies potentially treatable with Crispr are numerous, in short, does not guarantee that they can be cured in this way in practice.
August 5, 2022 (change August 5, 2022 | 10:00)
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