Base Editing

In news: Described by scientists as “the most sophisticated cell engineering to date,” an experimental treatment would provide the teenager Alyssa, diagnosed with blood cancer, a new lease of life.

About T-Cell blood cancer:

• T-cell acute lymphoblastic leukaemia (T-ALL).
• 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 a person immunity by killing cells carrying infections, activating other immune cells, and regulating the immune response.
• At least 20% of these WBC are atypical– as they accumulate in the bone marrow, they crowd out “good” WBCs and hence weaken the immune system.
• These unhealthy cells can also accumulate in other parts of the body like the liver, spleen and lymph nodes.
• While found in both children and adults, T-ALL’s incidence decreases with age.

Its treatment:

• Similar to any leukaemia– chemotherapy and stem cell/bone marrow transplant.
• Chemotherapy – either kills the cancerous cells or stops them from further dividing.
• It may also wreck immunity system along with it.
• If chemotherapy fails, bone marrow transplant is done.
• Patients receive an infusion of healthy bone marrow cells that will hopefully multiply and restore immunity.
• Overall treatment for T-ALL is pretty effective– children have a survival rate of over 85 per cent after five years of receiving this treatment.

Treatment received by Alyssa:

• Alyssa received a dose of healthy T-cells from a donor that would hopefully attack her cancerous cells without destroying each other.
• Known as CAR-T therapy, this principle has been around for a while, but Alyssa’s case was different.
• Traditionally, CAR-T therapy involves following steps:
• First, an individual’s own T-cells are removed, which are then modified and reintroduced to the individual.
• Adding a gene to T-cells that causes them to seek out and destroy cancerous cells.
• The modified cells are known as CAR-T cells.
• Problem with CAR-T therapy: Very often, when an individual is really sick, it is simply impossible to obtain enough healthy T-cells to create CAR-T cells.
• While donors can provide healthy T-cells to an individual, these T-cells from a foreign body attack every single cell in that patient’s body, making the treatment counterproductive.
• Thus, scientists have resorted to what is known as base editing– through this technique of genetic editing, they make it possible for one donor to supply T-cells to multiple recipients, without the traditional risks associated with it.
• Thus, Alyssa received genetically modified cells that were programmed to specifically attack her cancer while leaving the rest of her body alone.

What is base editing?

• Bases are the language of life.
• Just as letters in the alphabet spell out words that carry meaning, the billions of bases in our DNA spell out the instruction manual for our body.
• Scientists can zoom into a precise part of the genetic code to alter the molecular structure of just one base, effectively changing its genetic instructions.
• A team at the Great Ormond Street Hospital managed to use base-editing to create a new type of T-cell from a healthy donor that would not attack other cells in Alyssa’s body, not kill each other, survive chemotherapy and finally, hunt down all other T-cells in Alyssa’s body (healthy and cancerous).

Source: Indian express

Previous Year Question

Q.1) What is Cas9 protein that is often mentioned in news? (2017)

1. A molecular scissors used in targeted gene editing
2. A biosensor used in the accurate detection of pathogens in patients
3. A gene that makes plants pest-resistant
4. An herbicidal substance synthesized in genetically modified crops