THE concepts of gene therapy arose initially during the 1960s and early 1970s whilst the development of genetically marked cells lines and the clarification of mechanisms of cell transformation by the papovaviruses polyoma and SV40 was in progress. With the arrival of recombinant DNA techniques, cloned genes became available and were used to demonstrate that foreign genes could indeed correct genetic defects and disease phenotypes in mammalian cells in vitro. Efficient retroviral vectors and other gene transfer methods have permitted convincing demonstrations of efficient phenotype correction in vitro and in vivo, now making gene therapy a broadly accepted approach to therapy and justifying clinically applied studies with human patients.[10]
Gene therapy in the clinic- the highs and the lows:
• 1970:
Before the advent of recombinant DNA tools, Stanfield Rogers and colleagues at Oak Ridge National Laboratory, Oak Ridge, Tennessee, undertake a rudimentary and unsuccessful attempt at gene therapy. They administered wild-type Shope papillomavirus to two severely handicapped young girls with the nitrogen metabolism disorder hyperargininemia. However, the procedure was based on a mistaken assumption—that the virus expressed an arginase enzyme, which would correct the girls’ genetic deficiency.
• 1980:
Martin Cline of the University of California, Los Angeles (UCLA), conducts the first gene therapy trial involving recombinant DNA. Bone marrow cells from two patients, in Italy and Israel, who had the inherited blood disorder β-thalassemia, which causes insufficient hemoglobin levels, were isolated and transformed with the human β-globin gene. A viral thymidine kinase gene, intended to boost the transformed cells’ ability to replicate, was also included in the vector. It subsequently emerged that the five review committees that assessed the trial had not been informed that the protocol involved the delivery of recombinant DNA13. Cline was later found to be in breach of federal regulations on human experimentation and National Institutes of Health (NIH) guidelines on recombinant DNA research. He was sanctioned by the NIH.
• 1990: Michael Blaese, French Anderson and colleagues at the NIH perform the first approved gene therapy trial in patients. It involved retroviral-mediated transfer of the gene encoding ADA into the T cells of two children with severe combined immunodeficiency (SCID)14. One patient, Ashanti DeSilva, exhibited a temporary response, although she continued on enzyme replacement therapy. The response was far more limited in the second patient. |  |
• 1992: Claudio Bordignon, Fulvio Mavillo and colleagues at HSR-TIGET begin the first human gene therapy trial involving genetically modified stem cells, in two infants with SCID. The protocol involved the coadministration of autologous peripheral blood lymphocytes and hematopoietic stem cells, each of which had undergone retroviral-mediated transfer of the ADA gene. It led to both short-term and long-term reconstitution of the subjects’ immune system and correction of growth failure, although they required ongoing enzyme replacement therapy as well. |  |
• 1999: Jesse Gelsinger, an 18 year old with a relatively mild form of the nitrogen metabolism disorder ornithine transcarbamylase (OT) deficiency, is the first person to die on a gene therapy trial because of vector associated toxicity. He experienced a severe inflammatory response after undergoing an infusion to the liver of an adenoviral vector carrying the gene encoding OT. He then suffered lung failure followed by multiple organ failure. The subsequent investigation into the dose-escalating phase 1 study at the Institute for Human Gene Therapy (IHGT), at the University of Pennsylvania, Philadelphia, uncovered protocol violations and failures to report previous adverse events. Gelsinger’s liver status immediately before receiving the vector, according to some critics, ought to have ruled him out of the study. James Wilson, IHGT director and lead investigator on the trial, was suspended from clinical research for five years, whereas two colleagues received lesser sanctions. The University of Pennsylvania and the Children’s National Medical Center, in Washington, DC, which was a partner in the trial, subsequently paid fines of over $500,000 each. The case uncovered widespread underreporting of adverse events in other gene therapy trials. |
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• 2000: Alain Fisher and Marina Cavazzana-Calvo at the Necker Hospital for Sick Children reported a dramatic clinical improvement in two children with X-linked SCID (SCID-X1), a genetic disorder characterized by the failure of T-cells and natural killer cells to differentiate. The patients’ bone marrow cells were modified by transfer of the gene encoding the interleukin-2 receptor gamma chain, encoded by amurine retroviral vector17. It was hailed as the first clear-cut success in the field. Twenty children in all received this treatment, but five subsequently developed leukemia, one of whom died, after the activation of proto-oncogenes promoting T-cell proliferation by an enhancer sequence encoded by the vector. |  |
• 2003:
Shenzhen SiBiono GenTech (Shenzhen, China) gains approval in China for treating head and neck cancer with Gendicine, a modified adenovirus vector encoding the p53 tumor suppressor gene. Sunway Biotech (Shanghai) gained approval two years later for H101, which is based on Onyx-15, a recombinant oncolytic adenovirus originally developed by Onyx Pharmaceuticals (Emeryville, CA, USA), which targets p53-deficient tumor cells. Western critics have questioned the two approvals, due to a lack of available information on the two therapies18.
• 2003: Carl June, of the University of Pennsylvania, Boro Dropulic, then of Virxsys (Gaithersburg, MD, USA), and colleagues start the first human trial involving a lentiviral vector19. The phase 1 study, in HIV patients who had failed antiviral therapy, assessed the safety of a conditionally replicating HIV 1–derived vector expressing an antisense sequence against the HIV-1 envelope gene. |  |
• 2008: Introgen Therapeutics (Austin, TX, USA) files the first biologics license application for a gene therapy with the FDA, for Advexin (contusugene ladenovec), a modified adenovirus vector carrying the p53 tumor suppressor gene. Although the FDA originally granted Advexin a fast-track designation in head and neck cancer, the agency refused to accept the application for review, citing incompleteness. The company filed for bankruptcy protection shortly afterward. |  |
• 2008: Ark Therapeutics files for European approval of Cerepro (sitimagene ceradenovec) in malignant glioma, but a year later the Committee for Human Medicinal Products handed down a negative opinion, citing a negative risk-benefit profile, due to insufficient efficacy and risks of hemiparesis (slight paralysis on one side) and seizures. Cerepro consisted of the HSV thymidine kinase (tk) gene, encoded by a replication-deficient adenoviral vector lacking the E1 and E3 regions. It was injected into the brain immediately after surgical removal of the tumor. Subsequent administration of the prodrug ganciclovir resulted in the production of a toxic metabolite that prevents DNA replication in dividing cells. |
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• 2009: Jean Bennett, of the University of Pennsylvania, in Philadelphia, and colleagues report that an eight-year-old boy with Leber’s congenital amaurosis attained normal eyesight after AAV-mediated transfer of a gene encoding the retinal pigment epithelium-specific 65 kDa protein (RPE65). The degenerative disorder causes severe vision loss at birth or in early childhood and normally leads to total blindness during adulthood. All participants in the 12-patient study, whose ages ranged from 8 to 44 years, gained some improvement in eyesight, although the youngest obtained the greatest benefit. |  |
• 2010: Amsterdam Molecular Therapeutics files a marketing authorization application in Europe for Glybera (alipogene tiparvovec) in lipoprotein lipase deficiency, a genetic condition characterized by high levels of blood triglycerides. It can lead to regular debilitating and even fatal attacks of pancreatitis. The LPL gene, encoded by an AAV vector, is administered by means of multiple subcutaneous injections to the upper thighs during a single outpatient procedure. |  |
• 2010: Philippe Leboulch, of the University Paris Descartes, and colleagues report that a young adult patient with a severe form of β-thalassemia no longer required monthly blood transfusions after ex vivo modification of his bone marrow cells with a self-inactivating lentiviral vector expressing the β-globin gene. Analysis of the transformed population of red blood cells indicatedthat most of the initial benefit arose from a partially dominant clone, in which the vector insertion activated HMGA2, a gene associated with the formation of malignant and benign tumors. However, its dominance appeared to decline over time.[12] |  |
