Approaches To Gene Therapy Flashcards
What is gene therapy?
To repair a genetic defect
- replacement of an inoperative (defective) gene
- removal of a mutated gene
What is the here and now approach?
Somatic cell target
What is the next generation approach?
Germ cell targets
When did the first human gene therapy trial begin?
In 1990 - treated two patients with severe combined immune disorder (SCID)
What is the primary limitation in gene therapy?
Efficient gene delivery to body
What are genetic diseases that could be targeted by gene therapy?
SCID
X-linked immunodeficiencies
Innate immune system defects
What is an example of a disease where phagocytes lose their function?
Chronic granulomatous disease
What comes under receptor genes trasnferred in gene therapy clinical trials?
Chimeric antigen receptors
SCID common gamma chain receptor
Why is it important to think about where the defect needs to be repaired?
Accessibility e.g. skin or haematopoietic stem cells are easy to access but solid organs are not
Might not have to repaid every cell in the body to achieve a good result
What are the types of gene therapy vectors that can be used?
Retroviruses
Adenoviruses
Adeno-assocaited viruses
Herpes simplex viruses
Non-viral delivery
What are retroviruses like when used for gene therapy?
Don’t know where retroviruses will insert , can lead to problems in cancerous development
These are popular vectors though
What are adenoviruses like for vectors?
Can infect a wide variety of cells so these are good
What are adeno-associated viruses like for vectors?
If you have a small gene sequence to deliver then these are good
Integral into a particular site on chromosome 19
What are herpes viruses like as vectors?
Can have lots within them but they often have particular cell types in which they are prone to e.g. neurons
What is a non-viral delivery method?
Can use a gene gun, based on compressed gas gun
Coat gold particles with DNA, put them onto a surface, fire something at that surface , with compressed air, hits the surface, flexes surface, fires gold off and whizzes thorugh cells and trail DNA behind in the cells
What does lipid coated vectors mean?
They interact with cell membrane
What are viral modifications that need to happen for a viral vector?
To ensure virus carrier is not capable of replication
- ‘skeletonising’ virus genome to remove other genes
- removing immunostimulatory short sequences
‘ adding immunosuppressive short sequences
- pseudotyping for targeting
What is pseudotyping?
Descirbes a viral vector that might have a tropism for a certain cell type, change spike protein to change it for something completely different
What factors can reduce effectiveness of gene therapy?
Short-lived expression and retention
Immune responses to the agent or delivery system
Unforeseen effects
Multi-gene disorders
What to do about defects giving altered function?
Dominant mutations (i.e. not lack of function)
Need to remove mutant protein/gene - RNAi
Gene editing - replace defective copy
What were early issues with gene therapy?
1999, gene therapy suffered a major setback with he death of 18-year old
Died from multiple organ failures, 4 days after starting
What happened with gene therapy in 2003?
FDA place a temporary halt on all gene therapy trials using retro viral vectors in blood stem cells
What happened in 2009 with gene therapy?
Correction of Wiskott-Aldrich syndrome
Worked but 7 out of 10 children developed acute lymphocytic or lymphoid leukaemia within 1-3 years
What is SCID X-1?
Common gamma chain defects
What did gene therapy do for SCID x-1?
Corrects gamma defect in T and NK cell development but not B cells
What does common gamma chain associate with?
IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21
What is IL-7 in particular important for in SCID-X1?
Important for T and NK cell development
What is adenosine deaminse deficiency?
Adenosine is a poison that can build up in the body
What was first gene therapy approved for adenosine deaminse deficiency?
Trimvelis
What is the main FDA approved gene therapy?
KYMRIAH
What is problem with CRISPR/Cas9?
Not specific enough, have to worry about off target effects
