Gene Therapy Flashcards
Gene Therapy
Replacing defective genes with genes cloned from healthy individuals
Cause of Cystic Fibrosis
Mutant recessive allele in which 3 DNA bases, AAA, are missing. -> Deletion mutation. CFTR gene normally produces a protein with 1480 amino acids, Deletion results in loss of 1 amino acid but this loss makes protein unable to perform its role of transporting chloride ions across epithelial membranes,
CFTR
Chloride-ion channel protein that transports Cl- out of epithelial cells, water follows by osmosis to keep epithelial membranes moist.
What happens when CTFR isn’t made or doesn’t function properly?
Epithelial membranes are dry and mucus they produce remains viscous and sticky.
Symptoms of Cystic Fibrosis
- Mucus congestion in lungs, leading to a higher risk of infection -> mucus traps disease-causing organisms can’t be removed
- Breathing difficulties and less efficient gaseous exchange
- Accumulation of thick mucus in pancreatic ducts, prevents pancreatic enzymes from reaching duodenum leading to formation of fibrous cysts
- Accumulation of thick mucus in sperm ducts in males -> infertility
How can cystic fibrosis be treated with gene therapy?
- Gene replacement
- Gene supplementation -> 1 or more copies of healthy dominant genes are added alongside defective genes -> effects are masked
Germ-line gene therapy
Replacing or supplementing defective gene in fertilised egg. Ensures that all cells of organism will develop normally + cells of offspring. -> More perm. solution but ethical issues.
Somatic-cell gene therapy
Targets just affected tissues e.g. lungs. Additional gene is not present in gametes not passed on. Cells of lungs are continually dying and being replaced, treatment needs to be repeated periodically. Limited success. LT aim -> target undifferentiated stem cells that give rise to mature tissues.
What is the aim of somatic-cell gene therapy?
Introduce cloned normal genes into the epithelial cells of the lungs.
Outline the use of a harmless virus
- Adenoviruses are made harmless by interfering with a gene involved in their replication
- Adenoviruses are then grown in epithelial cells in lab along plasmids that have normal CFTR gene inserted
- CFTR gene becomes incorporated into dnA of adenoviruses
- These adenoviruses are isolated from epithelial cells and purified
- Adenoviruses with CFTR gene are introduced intranasally
- Adenoviruses inject DNA which includes normal CFTR gene into epithelial cells of lungs
Wrapping the gene in lipid molecules
- CFTR genes are isolated from healthy human tissue and inserted into bacterial plasmid vectors
- Plasmid vectors are reintroduced into their bacterial host cells and gene markers are used to detect which bacteria have successfully taken up plasmids with gene
- Bacteria are cloned to produce multiple copies of the plasmids with gene
- Plasmids are extracted from the bacteria and wrapped in lipid molecules to form a liposome
- Liposomes containing CFTR gene are sprayed into nostrils of patient as an aerosol + drawn down into lungs during inhalation
Why are the deliveries in gene therapy for cystic fibrosis not always effective?
- Adenoviruses may cause infections
- Patients may develop immunity to adenoviruses
- Liposome aerosol may not be fine enough to pass through tiny bronchioles in lungs
- Even where CFTR gene is successfully delivered to the epithelial cells, very few are actually expressed
Severe Combined immunodeficiency
SCID is a rare inherited disorder.
-> no cell-mediated immune response or ability to produce antibodies
Cause of SCID
Individuals inherit a defect in the gene that codes for enzyme ADA. This enzyme destroys toxins that would otherwise kill WBC’s.
What are the current treatments for SCID?
Patients being raised in strictly sterile environment, giving them bone marrow transplants or ADA injections.
