Breaking down one of the most important barriers limiting the application of stem cell transplantation in gene therapy, namely the need to administer chemotherapy drugs before infusing the corrected cells into patients. An objective achieved by a group of researchers from the San Raffaele-Telethon Institute for gene therapy (SR-Tiget), led by Luigi Naldini, who have just published a research on Cell.
In the study, carried out with the funding of the Telethon Foundation, the SR-Tiget researchers combined molecular approaches and techniques based on messenger RNA, obtaining a new therapeutic protocol – for now still experimental – safer and less debilitating, which promises to to increase the number of patients and diseases for which gene therapy could be a concrete option.
“The results obtained represent an important milestone for the applications of gene therapy based on blood stem cells and pave the way towards therapeutic regimens that no longer involve the use of chemo or radiation therapy, minimizing short and long-term side effects. caused by the high toxicity of these treatments “he comments Luigi Naldinidirector of SR-Tiget and full professor of Histology and Gene and Cellular Therapy at the Vita-Salute San Raffaele University of Milan.
Chemotherapy in gene therapy protocols
Gene therapy aims to correct the function of a defective gene in “diseased” cells by transferring a correct and functional version of the same gene. In the context of haematological diseases, a typical gene therapy protocol involves three phases, spaced by several days: the collection of blood stem cells from the patient, their genetic correction in the laboratory and, finally, their re-infusion (or transplant ) in the patient. In the first phase, the patient is subjected to a drug regimen that pushes a part of the stem cells to leave the niche in which they reside within the bone marrow to reach the bloodstream. This treatment is also known as mobilization and is generally very well tolerated. Once in the blood, the stem cells can be collected, purified and transferred to the laboratory, where they are genetically corrected with lentiviral vectors for gene transfer or with CRISPR editing procedures.
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The bone marrow
Before being able to re-transplant the corrected cells, however, it is necessary to “make room for them” in the patient’s bone marrow, where they can take root and repopulate all the blood cell lines with their corrected progeny. It is necessary to eliminate the stem cells carrying the pathological mutation that have remained in the patient and in the meantime have reoccupied the entire niche. To do this, one must resort to protocols, called “conditioning”, based on chemotherapy or radiotherapy, which, like all treatments of this type, are associated with both high and acute toxicity (damage to the mucous membranes, high risk of infections sometimes even lethal) and long-term (damage to organs, second tumors, infertility) and are therefore applied only in patients in conditions of receiving them and for the treatment of serious diseases. This last step therefore represents the main barrier to a wider and safer use of stem cells in therapy: its eventual overcoming has therefore been the mirage of many experimental researches for many years.
The new protocol
“In our work we have shown how the drugs used for mobilization – if used to maximize their effectiveness – can by themselves create, in a narrow time window, the sufficient space in the bone marrow necessary for the engraftment of the correct stem cells without the use. of chemo or radiotherapy regimens, “he explains Attya Omer Javed, first author of the study. The idea behind the discovery is to put the correct cells in competition with each other with those residing and still carrying the mutation, making it more difficult for the latter – and easier for the former – to repopulate the stem cell niche within the marrow.
The first step was to exploit the mobilization treatment: in order to work, this treatment damages the surface proteins that blood stem cells use to anchor themselves within the marrow, but the researchers observed that these “anchor proteins” are effectively reconstituted in corrected cells during the culture phase in the laboratory. If reinfused at the peak of a mobilization treatment, the corrected cells therefore have an advantage in filling the niche over those just exposed to the treatment. To further enhance their advantage, the researchers decided to use messenger RNA technology – the same used for the development of vaccines against Covid-19 – and favor a higher than physiological, but still temporary, expression of proteins. still.
“We began testing the use of messenger RNA to promote the temporary expression of a gene even before the development of modern mRNA vaccines. Now, with the extraordinary results in terms of efficacy and safety in vaccines, we can hope for a transition. faster in the clinic “explains Naldini.
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Cells from healthy donors
Using cells from healthy donors, patients and animal models, the research team demonstrated the therapeutic efficacy of the new mobilization-coupled transplantation protocol in an animal model of primary immunodeficiency. The result is the reconstitution of a functional immune response without any need for conditioning. Subsequently, by applying the protocol in an experimental model with human stem cells, they demonstrated its versatility of application in the context of gene transfer procedures with lentiviral vectors or gene editing with CRISPR, paving the way for a future clinical development.
“If the exchange efficiency – concludes Naldini – obtained after transient enhancement of genetically correct cells in the experiments described above were replicated in humans, it could be effective for the treatment of numerous genetic diseases, from primary immunodeficiencies to hereditary anemia and storage diseases. , and not only, opening new horizons of application for modern gene and cell therapy techniques “.