Approaches To Gene Therapy

Question 1

What is gene therapy?

Answer 1

To repair a genetic defect
- replacement of an inoperative (defective) gene
- removal of a mutated gene

Question 2

What is the here and now approach?

Answer 2

Somatic cell target

Question 3

What is the next generation approach?

Answer 3

Germ cell targets

Question 4

When did the first human gene therapy trial begin?

Answer 4

In 1990 - treated two patients with severe combined immune disorder (SCID)

Question 5

What is the primary limitation in gene therapy?

Answer 5

Efficient gene delivery to body

Question 6

What are genetic diseases that could be targeted by gene therapy?

Answer 6

SCID
X-linked immunodeficiencies
Innate immune system defects

Question 7

What is an example of a disease where phagocytes lose their function?

Answer 7

Chronic granulomatous disease

Question 8

What comes under receptor genes trasnferred in gene therapy clinical trials?

Answer 8

Chimeric antigen receptors
SCID common gamma chain receptor

Question 9

Why is it important to think about where the defect needs to be repaired?

Answer 9

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

Question 10

What are the types of gene therapy vectors that can be used?

Answer 10

Retroviruses
Adenoviruses
Adeno-assocaited viruses
Herpes simplex viruses
Non-viral delivery

Question 11

What are retroviruses like when used for gene therapy?

Answer 11

Don’t know where retroviruses will insert , can lead to problems in cancerous development
These are popular vectors though

Question 12

What are adenoviruses like for vectors?

Answer 12

Can infect a wide variety of cells so these are good

Question 13

What are adeno-associated viruses like for vectors?

Answer 13

If you have a small gene sequence to deliver then these are good
Integral into a particular site on chromosome 19

Question 14

What are herpes viruses like as vectors?

Answer 14

Can have lots within them but they often have particular cell types in which they are prone to e.g. neurons

Question 15

What is a non-viral delivery method?

Answer 15

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

Question 16

What does lipid coated vectors mean?

Answer 16

They interact with cell membrane

Question 17

What are viral modifications that need to happen for a viral vector?

Answer 17

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

Question 18

What is pseudotyping?

Answer 18

Descirbes a viral vector that might have a tropism for a certain cell type, change spike protein to change it for something completely different

Question 19

What factors can reduce effectiveness of gene therapy?

Answer 19

Short-lived expression and retention
Immune responses to the agent or delivery system
Unforeseen effects
Multi-gene disorders

Question 20

What to do about defects giving altered function?

Answer 20

Dominant mutations (i.e. not lack of function)
Need to remove mutant protein/gene - RNAi
Gene editing - replace defective copy

Question 21

What were early issues with gene therapy?

Answer 21

1999, gene therapy suffered a major setback with he death of 18-year old
Died from multiple organ failures, 4 days after starting

Question 22

What happened with gene therapy in 2003?

Answer 22

FDA place a temporary halt on all gene therapy trials using retro viral vectors in blood stem cells

Question 23

What happened in 2009 with gene therapy?

Answer 23

Correction of Wiskott-Aldrich syndrome
Worked but 7 out of 10 children developed acute lymphocytic or lymphoid leukaemia within 1-3 years

Question 24

What is SCID X-1?

Answer 24

Common gamma chain defects

Question 25

What did gene therapy do for SCID x-1?

Answer 25

Corrects gamma defect in T and NK cell development but not B cells

Question 26

What does common gamma chain associate with?

Answer 26

IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21

Question 27

What is IL-7 in particular important for in SCID-X1?

Answer 27

Important for T and NK cell development

Question 28

What is adenosine deaminse deficiency?

Answer 28

Adenosine is a poison that can build up in the body

Question 29

What was first gene therapy approved for adenosine deaminse deficiency?

Answer 29

Trimvelis

Question 30

What is the main FDA approved gene therapy?

Answer 30

KYMRIAH

Question 31

What is problem with CRISPR/Cas9?

Answer 31

Not specific enough, have to worry about off target effects