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Casgevy Therapy – A Gene Therapy for Sickle Cell Disease

Context:

  • Recently, The UK drug regulator approved a gene therapy (Casgevy therapy) to cure sickle cell disease and thalassemia, a landmark breakthrough.

What is Casgevy Therapy?

  • This is the first licensed therapy in the world based on gene editing technology CRISPR-Cas9.
  • It  is a one-time therapy that edits the faulty gene that leads to these blood disorders, potentially curing the person for life.

Casgevy therapy

Gene Therapy:

  • Technique to replace defective genes with healthy genes to treat genetic disorders.
  • Artificial method that introduces DNA into the cells of the human body.
  • First developed in 1972, but has limited success.
  • Two Major types of gene therapy: Somatic gene therapy and germline gene therapy.

Gene Editing:

  • Gene editing is a technique of making specific changes to the DNA at a specific sequence.
  • For this DNA is inserted, deleted, modified or replaced in the genome.
  • For this CRISPR CAS9 (Genetic Scissor) is used.
  • It involves cutting specific DNA sequences with ‘engineered nucleases’ enzymes.

About CRISPR-Cas9:

  • CRISPR stands for ‘Clustered Regularly Interspaced Short Palindromic Repeats’.
  • Cas9 stands for CRISPR-associated protein 9, & is the nuclease part that cuts the DNA.
  • CRISPR is the DNA-targeting part of the system which consists of an RNA molecule, or ‘guide’, designed to bind to specific DNA bases through complementary base-pairing.
  • The CRISPR-Cas9 system was originally discovered in bacteria that use this system to destroy invasions.
  • It is the most common, cheap & efficient system used for genome editing.

How does the therapy work?

  • Errors in the hemoglobin gene cause both sickle cell disease and thalassemia.
  • The therapy uses the patient’s own blood stem cells, which are precisely edited using Crispr-Cas9. 
  • The therapy targets a gene called BCL11A, which is crucial for switching from fetal to adult hemoglobin.
  • The therapy uses the body’s mechanisms to produce more foetal hemoglobin, alleviating the symptoms of the two conditions.

How is the therapy prepared and given?

  • Apheresis:  The first step is extracting blood stem cells from the bone marrow and filtering the blood for different components. 
  • Harvesting and Editing: The cells are then sent to the manufacturing site, which takes about six months to be edited and tested.
  • Conditioning: Before a transplant with the edited cells, the doctor gives a conditioning medicine for a few days to clear the bone marrow of other cells that will be replaced by the modified cells.
  • Transplantation: The patient has to stay in the hospital for at least a month so that the edited cells reside in the bone marrow and start making red blood cells with normal haemoglobin.
  • Side effects: similar to those associated with autologous stem cell transplants, including nausea, fatigue, fever, and increased risk of infection.
  • Haemoglobin: a protein in the red blood cells that carries oxygen to organs and tissues.
  • Foetal Haemoglobin, naturally present in everyone at birth, does not carry the same abnormalities as adult haemoglobin. 

What are the challenges of this treatment?

  • High Cost of Treatment:  a high proportion of people with these conditions live in poorer countries and are unlikely to be able to afford the therapy 
    • Estimates suggest it could be as much as $2 million per patient, which aligns with other gene therapies. 
  • Absence of Local Manufacturing Facilities: The harvested blood stem cells must be sent across countries.
  • Earlier Treatment: Permanent treatment has been a bone marrow transplant.
    • Donor rejection is the major challenge.

About sickle cell disease:

  • Genetic Disorder: The genetic error in sickle cell disease leads to red blood cells assuming a crescent shape. (See image) 
  • Unlike the disc-shaped normal cells, the sickle-like cells cannot move around easily in the vessels, resulting in blocked blood flow. 
  • Effects: severe pain, life-threatening infections, anemia, or a stroke.
  • Prelevance in India: An estimated 30,000-40,000 children in India are born with the disorder every year.
  • Symptoms: The symptoms manifest in people who inherit a pair of damaged genes from both parents. Those who carry only one copy of the gene from one parent can lead a normal life.

Casgevy therapy

About Thalassaemia: 

  • Thalassemia is an inherited (i.e., passed from parents to children through genes) blood disorder caused when the body doesn’t make enough of a protein called haemoglobin.
  • Thalassaemia leads to low levels of haemoglobin and shows symptoms like fatigue, nausea, shortness of breath, and irregular heartbeats. 
  • People with the condition need blood transfusions throughout their life. The transfusions also lead to excess iron accumulation in the body, which needs chelation.
  • India also has the largest number of children with thalassaemia major in the world about 1-1.5 lakh.

Source: Indian Express

 

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Quick Revise Now !
UDAAN PRELIMS WALLAH
Comprehensive coverage with a concise format
Integration of PYQ within the booklet
Designed as per recent trends of Prelims questions
हिंदी में भी उपलब्ध

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