It is a multi-step process.
First, blood stem cells from a patient’s bone marrow (where all blood cells originate) are removed from the body.
In the laboratory, a gene-editing tool called Crispr is used.
This allows a specific gene to be pinpointed and very precise editing to take place.
However, instead of directly editing a faulty gene, Casgevy instead takes advantage of a process that happens when babies are in the womb, where they make red blood cells with foetal haemoglobin (a key protein that carries oxygen). This switches to the adult form once they are born.
Crucially foetal haemoglobin is not affected by sickle cell disease, so Crispr acts by dampening down the “switch” that makes the body produce the adult form.
Patients have to undergo “conditioning” chemotherapy to make sure their bodies are ready to accept the edited stem cells.
Modified stem cells are then transfused back into the body, where they multiply and increase the production of stable, well-functioning red cells.
The full treatment must be considered carefully – it can involve lengthy stays in hospital and may have side effects, including headaches and bleeding problems.
