Explain what qualifies the gene therapy method to cure sickle cell disease as an ex vivo approach.

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1. Understand the term 'ex vivo gene therapy': Ex vivo gene therapy involves modifying the patient's cells outside of their body. In this method, cells are extracted from the patient, treated or genetically altered in a controlled laboratory environment, and then reintroduced into the patient's body.
2. Identify the cells targeted in sickle cell disease: For sickle cell disease, the target cells for gene therapy are the hematopoietic stem cells (HSCs), which are responsible for producing all types of blood cells, including red blood cells that are affected in sickle cell disease.
3. Recognize the process of cell extraction: In the treatment of sickle cell disease using ex vivo gene therapy, HSCs are extracted from the patient's bone marrow or blood.
4. Acknowledge the genetic modification step: Once the HSCs are extracted, they are genetically modified in the lab to correct the mutation in the HBB gene that causes the production of abnormal hemoglobin, leading to sickle cell disease.
5. Explain the reintroduction of modified cells: After the genetic modification, the corrected HSCs are infused back into the patient's body, where they can engraft in the bone marrow and start producing healthy red blood cells, thus treating the disease.