Gene Therapy was initially meant to introduce genes straight into human cells, focusing on diseases caused by single-gene defects, such as cystic fibrosis, hemophilia, muscular dystrophy (see video 2) and sickle cell anemia (see also Wiley database on indications addressed by gene therapy clinical trials). Three types of diseases for gene therapy can be distinguished:
|Monogenic disorders, single locus (gene) is defective and responsible for the disease, 100% heritable. Examples: Sickle cell anemia, Severe Combined Immunodeficiency (ADA-SCID / X-SCID), Cystic fibrosis, Hemophilia, Duchenne muscular dystrophy, Huntington’s disease, Parkinson’s, Hypercholesterolemia, Alpha-1 antitrypsin, Chronic granulomatous disease, Fanconi Anemia and Gaucher Disease.|
|Polygenic disorders, multiple genes involved, disease may be dependent on environmental factors and lifestyle. Examples: Heart disease, Cancer, Diabetes, Schizophrenia and Alzheimer’s disease.|
|Infectious diseases, such as HIV.|
Remarkable strides have been achieved through gene therapy in the field of medical treatment, leading to extraordinary advancements in combating a wide spectrum of genetic disorders and diseases. See also Major developments in gene therapy, Gene Therapy: Medicine of the 21st Century and Individualized Drugs & Gene Therapy (video 6). A comprehensive 20 minutes video on gene therapy: 'Gene Therapy a new tool to cure human diseases'. Some of the most notable breakthroughs encompass:
Severe Combined Immune Deficiency (ADA-SCID)
Commonly referred to as "bubble boy disease," ADA-SCID is a condition where children are born with compromised immune systems, rendering them highly susceptible to infections. Pioneering research in Italy marked a significant milestone by achieving a form of "cure" or long-term correction for patients with this genetic disorder. This innovative approach involved introducing a therapeutic gene known as ADA into bone marrow cells within a controlled laboratory setting. Subsequently, these genetically modified cells were reintroduced into the patients, effectively restoring their immune systems. This groundbreaking procedure has enabled treated patients to lead normal lives without requiring further interventions. (see also Description of ADA deficiency, ADA: The First Gene Therapy Trial, from the National Institutes of Health and SCID.net)
Chronic Granulomatus Disorder (CGD)
CGD is a genetic disorder impairing the immune system's ability to combat bacterial and fungal infections, often leading to life-threatening consequences. Building upon techniques akin to the ADA-SCID trial, researchers in Germany successfully treated CGD patients. The genetically corrected immune systems of these individuals have provided robust defense against microbial infections for a minimum of two years.
Hemophilia, characterized by impaired blood clotting, poses the risk of severe internal and external bleeding. A clinical trial conducted in the United States aimed to address this issue by introducing therapeutic genes into patients' livers. This approach granted patients the ability to achieve normal blood clotting times. Nonetheless, the therapeutic effects were transient due to the immune system recognizing the genetically modified liver cells as foreign entities. Strategies involving immune suppression or alternative gene delivery methods are currently being explored to attain more sustainable results.
Blindness (Leber's Congenital Amaurosis)
Leber's congenital amaurosis, an uncommon inherited eye disease resulting in profound vision loss or blindness from birth or infancy, has spurred pioneering gene therapy clinical trials. Research conducted at institutions like Moorfields Eye Hospital and University College London has yielded promising outcomes in restoring vision or slowing the disease's progression through gene therapy techniques. The first patient was operated upon in early 2007. Researchers at Children's Hospital of Philadelphia and the University of Pennsylvania have treated six young people via gene therapy. Eye Surgeon Dr. Al Maguire and gene therapy expert Dr. Jean Bennett developed the technique used by the Children's Hospital (see also video 5).
Gene therapy has introduced groundbreaking approaches for cancer treatment, encompassing strategies such as ssuicide gene therapy, oncolytic virotherapy, anti-angiogenesis, and therapeutic gene vaccines. Cancer research constitutes a substantial portion of gene therapy trials, accounting for approximately two-thirds. Advanced-phase trials, including Phase III trials of Ad.p53 for head and neck cancer, Phase III gene vaccine trials for prostate and pancreatic cancer, and Phase I/II trials for various cancers affecting the brain, skin, liver, colon, breast, and kidney, are presently underway and conducted in academic medical centers and biotechnology companies.
Recent gene therapy advancements offer hope for addressing neurodegenerative disorders such as Parkinson's Disease and Huntington's Disease. Positive results in animal models have spurred the initiation of Phase I clinical trials for these conditions, providing critical insights into gene therapy's potential in treating neurodegenerative disorders.
Gene therapy research has opened avenues for effective treatments in mesothelioma patients. While specific gene therapy approaches are tailored to different cancers, preliminary studies have shown promise in treating mesothelioma. Clinical trials involving suicide genes have exhibited encouraging early results. Nevertheless, further research is needed to refine and develop effective gene therapy treatments for this condition.
Cystic fibrosis, a hereditary disorder affecting the respiratory and digestive systems, leads to the production of thick and sticky mucus that obstructs airways and ducts. Gene therapy aims to deliver functional copies of the faulty CFTR gene into affected cells, enabling them to produce normal mucus and improving lung function.
Beta-thalassemia, a blood disorder characterized by reduced or absent hemoglobin production, causing anemia and complications, seeks to introduce functional beta-globin genes into bone marrow cells via gene therapy. This enables the production of healthy red blood cells.
Sickle Cell Disease
Sickle cell disease, resulting from a mutation affecting hemoglobin, causes misshapen red blood cells prone to clumping, leading to pain and organ damage. Gene therapy aims to modify hematopoietic stem cells to produce corrected hemoglobin, preventing the formation of sickled cells.
These groundbreaking advancements underscore the immense potential of gene therapy as a transformative tool in addressing a broad array of genetic disorders and diseases. As ongoing research continues to push the boundaries of scientific understanding, the future of gene therapy holds unparalleled promise in revolutionizing approaches to medical treatment.
Video 5: Gene Therapy for blindness (YouTube, 0:58)
Video 6: Individualized Drugs & Gene Therapy (YouTube, 8:58)
- Alliance for Cancer Gene Therapy
- American Cancer Society
- Bioscience Explained
- Gene Therapy and Children, KidsHealth
- Genetic Science Learning Center
- Human Genome Project Information
- ICTVdB, The Universal Virus Database
- Molecular Medicine in Action
- National Cancer Institute
- Understanding the Human Genome Project - Online education kit
- Viral Vectors and Gene Therapy, All the Virology on the www
- Images of gene therapy
- PowerPoint presentations on gene therapy
- YouTube videos about gene therapy