Gene therapy could cure cancer

(MainsGS3:Science and Technology- developments and their applications and effects in everyday life.)

Context:

• Scientists in the United Kingdom testing a new form of cancer therapy, reported success in a teenage girl, Alyssia, with a form of cancer called T-cell acute lymphoblastic leukaemia.

Form of blood cancer:

• T-cell acute lymphoblastic leukemia is the form of blood cancer in which the T-cells, which are a class of white blood cells, equipped to hunt and neutralize threats to the body, turn against the body and end up destroying healthy cells that normally help with immunity. 
• The disease is rapid and progressive and is usually treated by chemotherapy and radiation therapy.

Base editing:

• A person’s genetic code is several permutations of four bases: Adenine (A), Guanin (G), cytosine (C) and thymine (T). Sequences of these bases, akin to letters in the alphabet, spell out genes that are instructions to produce the wide array of proteins necessary for the body’s functions. 
• In Alyssia’s case, her T-cells — perhaps because of a mis-arrangement in the sequence of bases — had become cancerous and a way to correct this mis-arrangement could mean a healthier immune system. 
• In the last two decades, the world of biomedical engineering has been enthused by a technique that allows genes to be altered and errors ‘fixed.’ The most popular among these approaches has been the CRISPR-cas9 system.
• While still a nascent technology, base editing is reportedly more effective at treating blood disorders which are caused by so-called single point mutations, or when a change in a single base pair can cause terminal disease.

CRISPR-Cas 9 system:

• Inspired by how certain bacteria defend themselves against viruses, by snipping out and storing pieces of their genes, the CRISPR-Cas 9 system consists of an enzyme that acts like molecular scissors. 
• It can be made to cut a piece of DNA at a precise location and a guide RNA can be used to insert a changed genetic code at the sites of the incision. 
• While there are a few ways to effect such changes, the CRISPR-cas9 system is believed to be the fastest, most versatile system to effect such gene editing.
• Working of base-editing:

• The objective of gene therapy in the case of T-cell leukamia was to fix her immune system in a way that it stops making cancerous T-cells. 
• First, healthy T-cells were extracted from a donor and put through a series of edits. 
• The first base edit blocked the T-cells targeting mechanism so it would cease attacking Alyssa’s body, the second removed a chemical marking, called CD7, which is on all T-cells and the third prevented the cells from being killed by a chemotherapy drug. 
• Finally, the T-cells were programmed to destroy all cells — cancerous or protective — with CD7 marked on it. 
• After spending a month in remission, she was given a second donor transplant to regrow her immune system that would contain healthy T-cells.

Conclusion:

• The clustered, regularly interspaced, short palindromic repeats, or CRISPR/CRISPR-associated protein 9 (Cas9) (CRISPR-Cas9) system has revolutionized genetic manipulations and made gene editing simpler, faster and easily accessible to most laboratories.