ADA gene therapy: why the lymphocytes must be topped up.

ADA enzyme level after gene therapy: engineered lymphocytes die off so ADA decays and must be topped up, while an embryonic-cell insertion stays permanent.

Keep ADA above the threshold for 24 months with the fewest infusions, then show that the embryo route needs none.

Calling ADA gene therapy with lymphocytes a permanent cure.

• Gene therapy is a set of methods for correcting a gene defect diagnosed in a child or an embryo. It treats disease by putting genes into the person's cells and tissues.
• A normal gene is delivered into the person or embryo to take over the function of the non-functional gene and compensate for it.
• The first clinical gene therapy was in 1990: the patient, a girl aged 4, had adenosine deaminase (ADA) deficiency.
• ADA is an enzyme crucial for the immune system to work. The disorder arises from deletion of the gene for ADA.
• Some children with ADA deficiency can be cured by bone marrow transplantation; others receive enzyme replacement therapy, injections of working ADA. Neither approach is completely curative.
• In gene therapy, lymphocytes from the patient's blood are grown in culture outside the body, a functional ADA cDNA is introduced into them using a retroviral vector, and the cells are returned to the patient.
• These lymphocytes are not immortal, so the patient needs periodic infusions of the engineered cells.
• Putting the ADA gene, isolated from marrow cells, into cells of an early embryo could cure the disorder permanently.

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