mRna avoids chemo in gene therapy transplants, Italian study

In a study published in ‘Cell’, a group of scientists from the San Raffaele-Telethon Institute for Gene Therapy (Sr-Tiget) in Milan, led by Luigi Naldini, showed how to break down one of the most important barriers that limit recourse to stem cell transplantation for gene therapy, i.e. the need to administer chemotherapy drugs before reinfusing the correct version of their cells into patients. In the work, funded by the Telethon Foundation, the Sr-Tiget researchers combined molecular approaches and innovative techniques based on messenger RNA, obtaining “a new therapeutic protocol, currently experimental, safer and less debilitating”, which promises 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 – says Naldini, director of Sr-Tiget and full professor of Histology and Gene and Cell Therapy at the Vita-Salute San Raffaele University in Milan. – and pave the way towards therapeutic regimens that no longer include the use of chemo or radiotherapy, minimizing the short and long-term side effects caused by the high toxicity of these treatments “. Gene therapy – remember from the SR-Tiget – consists in correcting the function of a defective gene in the ‘sick’ 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; their reinfusion (transplant). 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 called mobilization and is generally very well tolerated. Once the blood is reached, 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. Before being able to re-transplant the correct cells, however, it is necessary to create a space in the patient’s bone marrow where all blood cell lines can take root and repopulate with their progeny. In other words, 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, it is necessary to resort to so-called conditioning protocols, based on chemo or radiotherapy, which like all treatments of this type are associated with both acute toxicity (damage to the mucous membranes, high risk of infections, sometimes even lethal) and long-term (organ damage, second tumors, infertility) and are therefore applied only in patients in condition to receive them and for the treatment of serious diseases. It is this last step that represents the main barrier to a wider and safer use of stem cells in therapy. And its eventual overcoming has represented for many years the “mirage” of many experimental researches. “In our work – explains Attya Omer Javed, first author of the study – we have shown how the drugs used for mobilization, if used maximizing their effectiveness, on their own they can create in the bone marrow, in a narrow time window, the sufficient space necessary for the engraftment of the correct stem cells. So without the use of chemo or radiotherapy regimens “. At the basis of the discovery – a note details – is the idea of ​​putting 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. The first step was to take full advantage of 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 the 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 occupying the niche, compared to those just exposed to the treatment. To further enhance their advantage, the scientists decided to use mRna technology (the same used for the development of vaccines against Covid-19) and favor an expression of proteins – still higher than the physiological one, but still temporary. . “We started testing the use of messenger Rna to promote the temporary expression of a gene even before the development of modern mRna vaccines – highlights Naldini – Now, thanks to the extraordinary results in terms of efficacy and safety in vaccines, we can hope in a faster transition to the clinic. ” Using cells from healthy donors, patients and animal models, the research team demonstrated the therapeutic efficacy of the new mobilization-coupled transplant protocol in an animal model of primary immunodeficiency. The result was 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, scientists demonstrated the versatility of application of this strategy 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 obtained after transient enhancement of genetically corrected cells in the experiments described above were replicated in humans – concludes Naldini – 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 “.