Gene therapy is a medical technique that involves altering a person’s genes to treat or prevent disease. It aims to correct defective genes responsible for disease development or to introduce new genes into the body to help fight a condition.
There are three main approaches to gene therapy:
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Replacing a mutated gene with a healthy copy of the gene.
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Inactivating (or "knocking out") a faulty gene that is functioning improperly.
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Introducing a new or modified gene into the body to help treat a disease.
Gene therapy is typically delivered using vectors, often viruses that have been modified to carry human DNA without causing illness.
It has been used or is being researched for a range of conditions, including:
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Genetic disorders like cystic fibrosis or sickle cell anemia,
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Certain types of cancer,
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Some viral infections like HIV.
Let's look at gene therapy for sickle cell disease as an example.
Background on the disease:
Sickle cell disease is a genetic disorder caused by a mutation in the HBB gene, which provides instructions for making hemoglobin—the protein in red blood cells that carries oxygen. The mutation causes red blood cells to become stiff and shaped like a sickle (crescent), leading to blockages in blood flow, pain, anemia, and organ damage.
How gene therapy works in this case:
One promising approach uses CRISPR-Cas9 gene editing to reactivate a normally silent gene that produces fetal hemoglobin (a form of hemoglobin that babies naturally produce before birth). Fetal hemoglobin doesn’t sickle and can replace the faulty adult version.
Step-by-step process:
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Stem cells are collected from the patient’s bone marrow or blood.
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In the lab, CRISPR is used to edit a specific gene (often BCL11A) in these cells to “turn on” the fetal hemoglobin production.
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The patient receives chemotherapy to destroy their existing bone marrow.
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The edited stem cells are returned to the patient via infusion.
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These new cells produce red blood cells with healthy fetal hemoglobin, reducing or eliminating symptoms.
This method has shown remarkable success in clinical trials, with some patients becoming symptom-free.
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