Gene therapy

Question 1

What is gene therapy?

Answer 1

• The act of replacing a defective gene with a normal healthy gene
• The more complicated definition: “Treatment of genetic disorder in adults + children by genetic modification of human body cells

Question 2

Targeted diseases for gene therapy

Answer 2

• Most diseases have a genetic/hereditary component
• Relatively few diseases linked to a single gene
• Cancer is the most common disease target for gene therapy

Question 3

Routes of delivery/administration

Answer 3

• Some organs are just more difficult to reach, where, so we use ex vivo where we just take them out, modify them then put them back
• Some methods:
  + Intravenous injection
  + Direct injection ie Organ surface instillation
  + Intra-arterial injection
  + Intraportal injection
  + Retrograde intravenous injection
  + Intratracheal administration ie inhalation
• We can also use viral vectors as a method of delivery

Question 4

Considerations when choosing delivery method

Answer 4

• Efficiency of gene delivery
• Therapeutic gene size
• Safety
• Duration of expression required

Question 5

Viral vectors

Answer 5

• Viruses are very good at forcing uptake of genetic material where cells normally refuse + commonly used as the vector of choice
• Virus is edited to have less “viral” genes, often to be replication-deficient
• Viruses eventually will be countered by immune response, lowering its efficiency

Question 6

Non-viral vectors

Answer 6

• Includes:
  + Naked DNA
  + Liposomes
• But we have yet to figure out methods to allow the uptake + entry of these vectors/methods and we continue to rely on viruses since they have evolved to force entry into cells

Question 7

Common viral families used as vectors

Answer 7

• Adenoviridae
• Parvoviridae
• Togaviridae
• Herpesviridae
• Retroviridae
• Poxviridae

Question 8

Gene-directed Enzyme Pro-Drug Therapy

Answer 8

• Used in cancer
• Examples of the enzymes used:
  + Thymidine kinase
  + Cytosine deaminase
  + Nitroimidazole reductase
• Enzymes in the cancer cell will synthesise a cytotoxic drug that will kill the cancer cell, keeping it localised + only affects the target cell
• Through the Bystander effect, neighbouring tumour cells are killed by the cytotoxic component without viral entry
• Hasn’t been successful yet

Question 9

CAR (Chimeric Antigen Receptor)-T cell therapy

Answer 9

• The far more successful method to deal with cancer for the time being, used to treat blood-borne cancers ie leukaemia + completely cure
• We draw blood and filter out for T cells
• We then modify them to recognise cancer cells by making the T cells to produce CAR, which are attracted to malignant proteins on the surface of cancer cells
• They are then grown in the lab for ~10 days
• We still use chemo to eliminate the patient’s old WBCs to help the body accept the new T-cells

Question 10

Gene editing vs gene therapy

Answer 10

• Gene editing is the insertion, replacement/deletion of DNA using artificially engineered nucleases
• Gene therapy replaces an entire gene