Gene therapy and gene editing

In a nutshell

Gene therapy is a technique that changes a person's genes to treat or cure diseases such as cancer. Gene therapy only modifies body cells and is not passed on to the children of those being treated.

Gene therapies

Most gene therapies involve inserting a normal version of an allele into cells that carry a defective version of that allele. A deactivated virus is normally used as a vector to transfer the gene into the cell. A major difficulty with gene therapy lies in how to deliver the replacement gene effectively.

Example

Inserting copies of a normal allele into the chromosomes of a person who carries the faulty cystic fibrosis allele.

Biology; Global challenges; KS4 Year 10; Gene therapy and gene editing

1.	Cells that carry the defective gene are removed from the affected patient.
2.	A healthy version of the human gene is inserted into the virus vector.
3.	The edited virus enters the cells that were removed from the patient.
4.	The modified cells are injected back into the patient.
5.	The modified cells can now carry out their normal function inside the patient's body.

Gene therapy trials assess the safety of gene therapy techniques. Currently, there are thousands of ongoing gene therapy trials that show potential for improving human health.

Failures in gene therapy

In the early days of gene therapy, there were many failures.

Example

In the late $1990s$ , gene therapy was developed to treat 'bubble-boy' syndrome. Some children showed dramatic improvement, but $3-6\ years$ later others developed leukaemia and died.

Genome editing

This involves replacing or removing sections of the DNA in the genome using 'molecular scissors'. This is an old technique, however, recent technological advances have meant the precision and efficiency of gene editing have improved.

Example

In $2015$ , a five-month-old girl with incurable leukaemia (cancer) was treated with new gene technology. Scientists edited the genome of some donated human immune cells. The edited genomes contained new instructions that made these immune cells seek out and destroy the cancer cells. Her cancer went into remission.

Germline gene therapy

Gene therapy does not stop the affected person from passing on the inherited condition to their children. This is because only their body cells are modified, not their germ cells (gametes). Germline gene therapy is currently illegal and would be both technically and ethically difficult.