Base Editing Technique

Why in news?

• In the UK, a teenage girl’s incurable T-cell acute lymphoblastic leukaemia (T-ALL) has been cleared from her body through the first use of a revolutionary type of method called Base Editing.

About T-cell acute lymphoblastic leukaemia (T-ALL):

• It is a kind of blood cancer.
• T-ALL affects the stem cells in the bone marrow that produce a particular kind of white blood cells (WBC) called T-lymphocytes (T cells).
  • These cells provide person immunity by killing cells carrying infections, activating other immune cells, and regulating the immune response.
  • While found in both children and adults, T-ALL’s incidence decreases with age.

T-ALL treatment:

• Typical treatment for T-ALL is similar to that of any leukaemia– chemotherapy and stem cell/bone marrow transplant.
• Doctors will first administer multiple rounds of chemotherapy. This either kills the cancerous cells or stops them from further dividing. The exact schedule is guided by an individual’s age and general health. If this fails, and the individual is suitable, doctors will conduct a bone marrow transplant.
• Overall treatment for T-ALL is pretty effective– children have a survival rate of over 85% after five years of receiving this treatment. Unfortunately, the teenage girl lay in the unlucky 15% of children where the treatment just did not work.
• The doctors then used a technology called base editing, which was invented only six years ago.

About Bases in DNA:

• Bases are the part of DNA that stores information and gives DNA the ability to encode phenotype, a person’s visible traits. Bases are the language of life.
• The four types of base – adenine (A), cytosine (C), guanine (G) and thymine (T) – are the building blocks of the human genetic code.
• Just as letters in the alphabet spell out words that carry meaning, the billions of bases in human DNA spell out the instruction manual for every human body.
• Adenine always binds to thymine, while cytosine and guanine always bind to one another. This relationship is called complementary base paring.
• These complementary bases are bonded together via hydrogen bonds, which can be easily broken apart when the DNA needs to unzip and duplicate itself.

What is Base Editing Technique?

• Base editing is a CRISPR-Cas9-based genome editing technology that allows the introduction of point mutations in the DNA without generating potentially harmful double strand breaks (DSBs)
• Base editing allows scientists to zoom into a precise part of the genetic code and then alter the molecular structure of just one base, converting it into another and changing the genetic instructions.
• Base editing is a promising therapeutic strategy for genetic diseases caused by point mutations, such as many blood disorders.
• The doctors in the UK used this tool to engineer a new type of T-cell that was capable of hunting down and killing cancerous T-cells.

PRACTICE QUESTION:

In the context of cell biology, consider the following statements:

1. Bases are the part of DNA that stores information

2. Bases give DNA the ability to encode phenotype, a person’s visible traits

3 Base genome editing technology allows the introduction of point mutations in the DNA without generating potentially harmful double strand breaks (DSBs)

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3 only

(c) 1 and 2 only

(d) 1,2 and 3

Answer