Restoring the Vision of Gene Therapy
Gene therapy—fix a genetic disease by giving the patient a working copy of the relevant gene—is in the news. Researchers in Oxford, UK and in Philadelphia, Pennsylvania, recently announced that they had successfully improved the vision of human patients with rare genetic diseases, and Italian scientists have successfully ameliorated two other genetic diseases. These results, and the citation tallies tracked by the Web of Science, represent therapy of a kind for gene therapy itself, which got off to a very shaky start.
In 1980, UCLA researcher Martin J. Cline incurred the wrath of the US research establishment for breaching ethical guidelines in one of the first attempts to use gene therapy, on the disease thalassemia. Cline had permission to use two separate genes in the therapy, but administered the two genes linked in a plasmid vehicle. That made his experiment the first to use recombinant DNA in a human being. The therapy didn’t actually work, although in the furor that followed it was hard to determine why. In the early 1990s there were a couple of (fully approved) attempts to treat severe combined immunodeficiency in children, including one by the Italian research group mentioned above. Then, in 1999, a patient in a trial died as a result of adverse reactions. The subsequent enquiry uncovered widespread problems in other trials, and again scientists and institutions were censured and fined.
Undeterred, researchers kept at it, and their recent successes make plain how long the development of successful breakthrough therapies can take, and how dependent they are on animal models. The latest resurgence of optimism, for example, probably dates to work by a team led by Albert Maguire and Jean Bennett of the University of Pennsylvania, published in The Lancet in 2009 (this and other pertinent papers are included in the accompanying table, listed by citations; see paper #3). The team treated 12 patients, ranging from 8 to 44 years old, who suffered from Leber’s congenital amaurosis, in which a defect in a gene called RPE65 causes retinal degeneration and blindness. Maguire and Bennett injected the eye with an adeno-associated virus contained a good copy of the gene. All patients improved, the 8-year old improving most, almost to the level of normal-sighted.
Selected Papers on Gene Therapy, 1989-2014
Listed by citations
|1||L. Naldini, et al., “In vivo delivery and stable transduction of nondividing cells by a lentiviral vector,” Science, 272(5259): 263-7, 1996. [Salk Inst., La Jolla, CA; Whitehead Inst., Cambridge, MA]||2,744|
|2||A.M. Maguire, et al., “Safety and efficacy of gene transfer for Leber’s congenital amaurosis,” New Engl. J. Med., 358(21): 2240-8, 2008. [12 US and Italian institutions]||674|
|3||A.M. Maguire, et al., “Age-dependent effects of RPE65 gene therapy for Leber’s congenital amaurosis,” Lancet, 374(9701): 1597-1605, 2009. [9 US and Italian institutions]||220|
|4||A. Veske, et al., “Retinal dystrophy of Swedish briard Briard-beagle dogs is due to 4-bp deletion in RPE65,” Genomics, 57(1): 57-61, 1999 [U. Klinikum Hamburg Eppendorf, Germany; Linkoping U., Sweden; Swedish U. Agr. Sci. Fac. Vet. Med., Uppsala]||101|
|5||G. Le Meur, et al., “Restoration of vision in RPE65-deficient Briard dogs using an AAV serotype 4 vector using an AAV that specifically targets the retinal pigmented epithelium,” Gene Therapy, 14(4): 292-303, 2007. [CHU Nantes, France; Ecole Natl. Vet., Nantes, France; UCL, London, UK; Hop. St. Eloi, Montpelier, France] Web of Science||78|
|6||K. Narfstrom, et al., “The Briard dog: A new animal model of congenital stationary night blindness,” British J. Ophthalmology, 73(9): 750-6, 1989. [Swedish U. Agr. Sci. Fac. Vet., Uppsala; Linkoping U., Sweden]||55|
|7||A. Aiuti, et al., “Lentiviral hematopoietic stem cell gene therapy in patients with Wiskott-Aldrich Syndrome,” Science, 341(6148): 865, 2013. [15 institutions worldwide]||14|
|8||A. Biffi, et al., “Lentiviral hematopoietic stem cell gene therapy benefits metachromatic leukodystrophy,” Science, 341(6148): 864, 2013. [Ist. Sci. San Raffaele, Milan, Italy]||11|
|9||R.E. MacLaren, et al., “Retinal gene therapy in patients with choroideremia: Initial findings from a phase ½ trial,” Lancet, 383(9923): 1129-37, 29 March 2014. [12 institutions worldwide]||3|
|SOURCE: Thomson Reuters Web of Science|
How did the team reach that point? Briard dogs suffer from a similar condition that affects their sensitivity to light, as shown by Swedish researchers in 1989 (paper #6). A decade later, the same team established the details of a mutation in RPE65, which by then was known to be defective in human patients (paper #4). In 2007, following a successful demonstration that gene therapy could halt the disease in animals, a French team tested a modified viral gene-delivery system specifically designed to evaluate RPE65 replacements tailored for use in humans. Injection of the modified virus into the eye markedly improved vision in Briards, provided they were treated early in life (paper #5). Maguire and Bennett showed that a similar approach was safe and effective against Leber’s congenital amaurosis in human patients (#2), and the following year confirmed that treatment early in life gave the best results.
Maguire and Bennett and Robert MacLaren’s Oxford team, which announced similar success against another inherited retinal disease, choroideremia, in January (paper #9), used a virus that carries no known risks to ferry the good genes into their patients. The Italian team, which is based at the San Raffaele Telethon Institute for Gene Therapy (TIGET) in Milan, used a modified version of the human immunodeficiency virus HIV. The Italian researchers focussed on retroviruses like HIV because they insert their payload into the DNA of the cells they infect, suggesting that they might be ideal vectors for inserting working copies of defective genes.
In 1996 Luigi Naldini’s group reported that the modified HIV succesfully introduced working genes in human and animal cell lines, in a highly-cited paper (#1 in the table). By August 2013, the system had been used safely and effectively to treat patients with metachromatic leukodystrophy (MLD; paper #8) and Wiskott-Aldrich Syndrome (WAS; #7). Both are rare genetic diseases. MLD is caused by a lack of aryl sulfatase A, which results in degeneration of the fatty myelin sheath that insulates nerve fibers. Death often follows swiftly after the onset of symptoms. WAS affects the immune system and blood-clotting and is also generally fatal.
For both these diseases, the Italian team used autologous stem cell transplants. That is, they extracted blood stem cells from the patient’s bone marrow. These cells are incubated with a lentivirus that contains a good working copy of the gene in question and are then injected back into the patient. They multiply, differentiate, and move out of the bone marrow to colonize the rest of the body, and in both MLD and WAS relieve the symptoms. The recently published results are still preliminary, for the first three patients in each trial. MLD “did not manifest or progress in the three patients 7 to 21 months beyond the predicted age of symptom onset.” For WAS, “all three patients showed … improvements in platelet counts, immune functions, and clinical scores.” In both sets of patients, gene therapy did not create any changes in known cancer genes, one worry when using vectors that integrate into the DNA.
It looks as if gene therapy is now poised to come in from the cold and be more widely tested and adopted. These latest findings focus on rare inherited genetic diseases, which will certainly be of interest to patients who suffer such diseases. Of wider interest, gene therapy is also under development to fix the genes that go awry in cancer. The history of these kinds of treatment for cancer is almost as long, and almost as convoluted, and when those methods come to fruition many more people will be able to benefit.
Dr. Jeremy Cherfas is a science writer based in Rome, Italy.
The data and citation records included in this report are from Thomson Reuters Web of ScienceTM. Web of ScienceTM is a registered trademark of Thomson Reuters. All rights reserved.