Gene Therapy

Gene Therapy

• Gene therapy is a medical method that treats or prevents disease by correcting the underlying genetic problem.
• Doctors use techniques to alter a person’s genetic makeup instead of using drugs or surgery.

T-cell Acute Lymphoblastic Leukemia

• It is a type of blood cancer in which the T-cells turn against the body and destroy healthy cells that normally help with immunity.
• It is a rapid and progressive disease and is usually treated by chemotherapy and radiation therapy.
• T-cells are a class of white blood cells that are equipped to hunt and neutralize threats to the body.

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• The patient had tried several of the standard treatments including chemotherapy and radiation with limited success.
• The patient then enrolled in a new experimental trial and became the first to receive experimental gene therapy that relied on a new technique called ‘base editing.’

What is Base Editing?

• A person’s genetic code is made up of combination of four bases— Adenine (A), Guanine (G), cytosine (C) and thymine (T).
  • Sequences of these bases give instructions to genes to produce the wide array of proteins necessary for the body’s functions.
• Sometimes because of a mis-arrangement in the sequence of bases, wrong instructions are passed, making cells malfunction. Cells can also turn cancerous.
• Base editing technique allows genes to be altered and errors fixed by making changes at the bases. CRISPR-cas 9 system is the most popular method of gene editing.
• In this case, researchers improvised the technique to be able to directly change certain bases: thus, a C can be changed into a G and T into an A.
• Applications: Base editing is more effective at treating blood disorders which are caused by so-called single point mutations. These mutations can cause terminal disease.

Using Base Editing to Treat T-cell Leukemia

• The main objective behind gene therapy in the case of T-cell leukemia was to fix immune system in a way that it stops making cancerous T-cells.
• In the first step, healthy T-cells were extracted from a donor and put through a series of edits.
  • The first edit changed T-cells targeting mechanism so it would stop attacking patient’s body.
  • The second edit removed a chemical marking, called CD7, which is present on all T-cells.
  • The third edit prevented the cells being killed by a chemotherapy drug.
  • The T-cells were programmed to kill all cells — cancerous or protective — with CD7 marker.
• After a few days, the patient was given a second donor transplant to regrow immune system containing healthy T-cells.
• Effectiveness:
  • After three months of the treatment, investigation does not suggest any signs of the disease resurfacing.
  • However, it still cannot be established if treatment has reliably and entirely fixed the immune system.

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