* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download No Slide Title
History of genetic engineering wikipedia , lookup
Point mutation wikipedia , lookup
Saethre–Chotzen syndrome wikipedia , lookup
Adeno-associated virus wikipedia , lookup
Genetic engineering wikipedia , lookup
Gene desert wikipedia , lookup
Gene expression profiling wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Public health genomics wikipedia , lookup
Epigenetics of diabetes Type 2 wikipedia , lookup
Genome (book) wikipedia , lookup
Gene expression programming wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Gene nomenclature wikipedia , lookup
Microevolution wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Neuronal ceroid lipofuscinosis wikipedia , lookup
Gene therapy wikipedia , lookup
Gene therapy Goal: Treat a genetic disease (a defect in some gene) by replacing the defective gene. Why is gene therapy appealing? Consider hemophilia, a bleeding disease caused by a defect in a blood protein, a clotting factor, required to activate clotting. There are two forms of hemophilia, one due to a mutation in clotting factor VIII, hemophilia A, one due to defect in clotting factor IX, hemophilia B. Both are sex-linked diseases (genes on the X chromosome). The disease affects ~ 30,000 American males. The disease is characterized by frequent spontaneous bleeding episodes, usually into soft tissues and joints. Bleeding into closed spaces can be fatal. Current treatment: Infusion of clotting factor concentrates in response to bleeds. Clotting factor isolated from human blood became available in the 70s. Many patients getting this isolated factor became infected with blood-born pathogens such as hepatitis and HIV. Now a cloned clotting factor is available—it doesn’t come from human blood—so young patients are not infected with these viruses. Nevertheless the current treatment has many disadvantages -ongoing tissue damage occurs because bleeds are treated rather than prevented. -inconvenience. The clotting factor protein has to be injected. It can not be taken orally as the digestive enzymes in our intestine would destroy it. -protein has short half life. Clotting is only enhanced for a brief time after treatment. -expense. World wide only 20 - 30% of hemophiliacs are treated. Kathy High Dr. Kathy High at CHOP has been studying the possibility of gene therapy for this disease. Why is this a good disease to try gene therapy? Precise regulation of gene expression is not required. Raising blood levels of clotting factor even a few percent is a big help; if as high as 100%, it is still ok. Animal models exist (mice and dogs with hemophilia) so gene therapy can be tested on them first. Determination of efficacy is straight forward—measure clotting time. Tissue specific expression of gene is not required –only need secretion of the protein into blood. How does one get the cloned gene into cells? In this case, the investigators chose to use a virus, adeno-associated virus (AAV-2). This is a non-pathogenic, replication-deficient virus—(most of us have it). The coding sequence of the virus was replaced with gene of interest. Using this virus, sustained expression of a target gene has seen in skeletal muscle, liver and CNS. Advantages of gene-based therapy Continuous maintenance of clotting factor in the plasma. Bleeds would be prevented rather than treated after they occurred. Risks of blood products avoided Cheaper? Long term? •More convenient Who is being treated by current attempts at gene therapy? An individual? Or the progeny of an individual? What determines whether the progeny or just the individual will be affected by the therapy? If the added gene is incorporated into somatic cells—liver, muscle, (any cell except germs cells)-- only the treated individual will be affected. If the gene is incorporated into germ cells, i.e. eggs and sperm, then the progeny will also be affected. Gene therapy is only being used to treat an individual. The government requires controls (separate studies) to demonstrate that germ cells are not being affected. Results: Test on animals, both small animals (mice) and large animals (dogs) were successful. Virus did not appear in the semen. Initial tests on humans with hemophilia were approved by the FDA. The initial tests were positive: The gene was expressed in the liver, Clotting times were increased. No virus was detected in semen Leg muscle was injected with adeno-associated virus carrying a corrective gene for hemophilia Cells expressing clotting factor are green. Trials of gene therapy of hemophilia were recently stopped because the virus was found in the semen of one of the individuals in the trial. Currently the trial is on hold.