The next week
Nia is 13
In the laboratory, doctors change some genes in the blood-making stem cells they collected from Nia. They correct the globin gene, so Nia's body can make normal hemoglobin.
Your doctors will change genes in the blood-making stem cells they collect from you.
Here is what happens:
- It happens in a laboratory after the cells are collected from your body.
- It only takes a few days to change the genes, but your cells stay in the laboratory for a few months for safety testing.
- The genetically-changed stem cells are tested to make sure the gene changes are correct.
The doctors only change the genes in the cells they collected.
- They do not change other cells in your body.
- You can’t pass on these gene changes to your children.
Gene therapy changes the genes that cause sickle cell disease.
- Genes are instructions for your cells.
- In sickle cell disease, you have a gene with the wrong instructions (a mutation). This is why your body makes the sickle cells, not healthy red blood cells.
- In gene therapy, your blood-making stem cells are genetically changed to have instructions to make healthy red blood cells.
Blood-making stem cells
A stem cell is a type of cell that can become (or make) other types of cells. In gene therapy for sickle cell disease, your blood-making stem cells are used. You might also hear the term bone marrow stem cells. These cells make:
- Red blood cells. These carry oxygen to all the other cells in your body.
- White blood cells. These fight germs and are also called immune system cells.
- Platelets. These help your blood clot (stop bleeding) when you have a cut.
There are different ways that doctors can change genes.
Add a new gene
- Doctors can add a new gene to your blood-making stem cells with correct instructions.
- Your stem cells will follow the correct instructions and make healthy red blood cells.
- Your stem cells will also keep making some sickle cells, but not enough to cause problems. It happens because the wrong instructions (a mutation) also stay in your cells.
‘Turn on’ a gene
- Doctors can ‘turn on’ a gene in your blood-making stem cells to make fetal hemoglobin. It is the type of hemoglobin that you made before you were born (inside the mother’s womb).
- This gene for fetal hemoglobin got turned off after you were born, and you stopped making fetal hemoglobin. If the gene is turned on again, you will start making fetal hemoglobin again.
- Your stem cells will also keep making some sickle cells, but not enough to cause problems. This is because the gene with wrong instructions also stays in your cells and not all cells have been modified.
Fix the gene mutation
- Doctors can fix the gene with wrong instructions (mutation).
- They edit the instructions to be correct.
- Your blood-making stem cells will follow the correct instructions, and you can make healthy red blood cells.
Technology your doctor might use:
CRISPR
CRISPR (also called CRISPR-Cas9) is like a tiny molecular scissor that can cut out parts of a gene.
- Doctors can use this to turn genes on or off.
- They can also use it to fix instructions on a gene.
Lentivirus
A lentivirus is like an envelope carrying new genes into a cell.
- Doctors can use it to add new genes to cells.
- The lentivirus is a modified HIV virus, but it does not cause HIV/AIDS. All the HIV-causing genes have been removed from the virus. The virus becomes an empty envelope with nothing bad inside. Your doctors put new genes into the empty envelope, and it carries the new genes into your cells.
- If your doctors use a lentivirus to add new genes, you might get a false positive on some tests for HIV. This is not because you have HIV. It is because the test is looking for pieces of the empty envelope (lentivirus). Your doctor can explain which HIV tests will give a false positive and which HIV test will show (correctly) that you do not have HIV.