A mutation in hereditary enzyme galattocerebrosidasi changes the metabolism of myelin, leading to serious problems for the central nervous system. Now lentiviral microRNA and come to the rescue.
Devised a new strategy of gene therapy for Krabbe’s disease, a severe genetic disorder that affects the nervous system: thanks to gene therapy with hematopoietic stem cells an international team of researchers led by Luigi Naldini at the San Raffaele Telethon Institute for Gene Therapy (HSR-TIGET) in Milan has succeeded for the first time to treat the disease in the animal model. The important result is reported in the pages of Science Translational Medicine, the new magazine published by the prestigious international scientific journal dedicated to translational research, that is strongly marked by the transfer “from the laboratory bench to the bedside.”
As explained by Alessandra Biffi, Luigi Naldini co-director of the study, “Krabbe disease, also called globoid cell leukodystrophy is a lysosomal storage disease that strikes in childhood and has a course of rapidly progressive and always fatal. The disease is hereditary and is due to defects in the gene for galattocerebrosidasi (GALC) enzyme responsible for disposal of certain components of myelin, the insulating covering of nerves essential for the conduction of impulses in the central and peripheral nervous system. When the enzyme is defective, is minus the natural turnover of these substances, which accumulate in lysosomes as well (the structures normally delegated to the waste disposal cell) and become toxic to myelin. The result is a progressive arrest of psychomotor development of affected children, that they lose motor skills and cognitive skills already acquired.”
Unfortunately, to date there is no treatment to prevent or stop the progression of disability, nor seek to restore lost functions. In some cases, can slow the progression of the disease by carrying out a transplant of hematopoietic stem cells (stem cells of all elements of the blood) from a healthy donor before the onset of symptoms (ie within the first 4 months of life). Not always, however, there is a compatible donor, also this type of transplant has the risk of rejection by the body to the stem cell donor.
Biffi continues: “Our experience in other similar diseases has shown that it can make treatment more effective and less risky genetically correcting the patient’s own hematopoietic stem cells. This is done by exploiting the particular viral vectors (lentiviral those) that will produce in cells of the patient with a higher than normal production of therapeutic gene (GALC in this case), in the absence of risks to the incompatibility between donor and recipient of the transplant.”
This approach, based on the possibility of using mature cells of the blood – derived hematopoietic stem cell transplantation – as a vehicle to transport the enzyme functioning in the nervous system affection, has already been successfully applied by researchers in HSR models pre-TIGET Preclinical other lysosomal storage diseases and is currently the subject of an ongoing clinical trial in patients with metachromatic leukodystrophy. So far, however, was not possible to apply it to Krabbe disease because, as explained Naldini “we came across an unexpected toxicity of the enzyme GALC for blood stem cells, which however did not occur in their differentiated progeny. We then devised a new strategy to regulate the expression of therapeutic gene, which must be inserted into stem cells to ensure its long-term maintenance and transmission to all their offspring, but there has to deliver its product. So we served microRNAs, small regulatory elements of the expression of other genes. Each micro-RNA can “turn off” the expression of a battery of other genes by recognizing a “bar code” stamped on their message.”
Thanks to a new method developed from them to see the activity of microRNAs in single living cells, researchers have tried HSR-TIGET which were selectively expressed in the rare stem cells from bone marrow and not in their offspring being differentiation. They thus identified the first microRNA specific for hematopoietic stem cells and inserted the bar code recognized by one of these microRNAs in a lentiviral vector for gene therapy to Krabbe disease, which in this way is sensitive to silencing by microRNA. “Even if the carrier is inserted into stem cells, the therapeutic gene can be expressed only in their mature progeny, after the microRNA has died” explains Naldini (see figure below).
“The transplantation of genetically corrected cells in animal model of Krabbe’s disease, which presents a very human-like,” has significantly improved living conditions and survival of treated animals. In particular, this approach to gene therapy was more beneficial than the traditional transplanting healthy donor. In addition, our strategy is promising not only for the treatment of Krabbe’s disease, for which we intend to move to a clinical trial on patients as soon as we concluded the other preclinical studies necessary – that is expected in 2 years – but also because it allows you to make more effective and safe gene therapy based on hematopoietic stem cells in many other genetic diseases.”
Sign their work as first author Bernhard Gentner, a German medical researcher and Ilaria Visigalli, both in training at the HSR-TIGET and University San Raffaele, and other employees of the University of Toronto. The study was carried out with funds from Telethon, European Community, Fondazione Cariplo (project Nobel), National Tay Sachs and Allied Diseases Association, European Association leukodystrophy (ELA).
