Section 4 Lesson 6 – Gene Therapy

What is Gene Therapy? Gene therapy involves using copies of a cloned gene to replace a defective gene. If it works it can allow a genetic problem to be solved rather than just managed. What is Gene Therapy (The General Explains) - YouTube

How does it work?

Virus Vectors Viruses are successful because they are able to take over a cell for production of their own proteins. This feature makes them ideal vectors for gene therapy. The viruses to be used need to be modified to they will not replicate and they need to have the desired gene added to their genome.

Limitations – 1. The Nature of the Gene Defect The Human Genome Project has opened the door for more conditions to be treated through gene therapy. This is because the very first problem is that the gene responsible for the condition must be identified. Once identified, its function must be comprehensively studied and the gene must be cloned. So far the most successful uses of gene therapy have been to treat: Leber’s congenital amaurosis (retinal disease) X-linked SCID (severe combined immunideficiency) ADA-SCID Adrenoleukodystrophy (results in deterioration of brain function) Chronic myelogenous leukemia (cancer of the white blood cells) Parkinson’s Disease (degenerative disorder of the nervous system)

Limitations – 2. The Target cells in the patient The vector needs to be able to get into contact with the cells that need modification. This can be done in 2 ways: In vivo – the virus is introduced directly into the patients body. This is how Cystic Fibrosis is treated through use of a nebuliser containing viral vectors directly into the lungs. Ex vivo – this involves removing stem cells from the patient, infecting them with the vector virus containing the gene then injecting the cells to the correct site.

Limitations – 3. The Method of Delivery of the Normal Gene There are a number of other methods of delivering the normal gene to the cells that do not require the use of viruses. Liposomes A liposome is an artificial lipid sphere with an aqueous core. The DNA is in the aqueous core and the lipid outer layer is able to fuse with the cell membrane to deliver the DNA into the cell.

Limitations – 3. The Method of Delivery of the Normal Gene 2. Human Artificial Chromosomes (HAC) Work is being carried out to create a small stripped down human chromosome that would be delivered to cells as an additional artificial chromosome containing only the genes desired. The chromosome used sop far has been based on Chromosome 21 and has been found to be mitotically stable for up to 6 months. Issues with use include delivery of the chromosome to the target cells.

Limitations – 4. The Expression and Stability of the Normal Gene in the Target Cells Once the gene has made it into the target cells it needs to be transcribed by the cell. This often doesn’t happen and trials are costly and time consuming.

Ethics of Gene Therapy What are some of the ethical considerations for using gene therapy? What is normal and what is a disability or disorder, and who decides? Are disabilities diseases? Do they need to be cured or prevented? Is somatic gene therapy (which is done in the adult cells of persons known to have the disease) more or less ethical than germline gene therapy (which is done in egg and sperm cells and prevents the trait from being passed on to further generations)? In cases of somatic gene therapy, the procedure may have to be repeated in future generations. Note: Germline gene therapy is not currently being carried out.

Your Task This week I would like you to focus on completing any Scholar Activities you still have to do. Please put aside time to do this and get up to date. 2. Update your glossary with the terms in red.