Gene Therapy: Introduction, Types, Methods, Mechanism, Risks, Application


  • It is a novel medical treatment approach which is primarily an experimental technology.
  • A normal gene is inserted to replace or alteration of an abnormal gene that utilizes short oligonucleotide sequences to treat hereditary or acquired genetic defects instead of conventional drug compounds.
  • This technique is widely used to treat defective genes which eventually contribute to the development and progression of disease.
  • Several viruses are used in gene therapy. Among which adeno-associated virus [AAV]) that have been majorly used which modify or replace the disease-causing genetic material with a therapeutic gene; however, non-viral vectors are also available.


Ex Vivo-

The term “ex vivo” means “outside of the living body”.  This technique is a medical procedure that involves removing of cells from the patient followed by genetically modified in a laboratory, using specialized approaches like adding a new gene to the cell or fixing a gene in a cell that is causing a disease. And, then reintroduced the modified or engineered cell into the patient body.

Mechanism of gene therapy

Fig: Gene Therapy


The term “in vivo” means “inside the living body”. The corrected, new gene or engineered genetic material is delivered directly to the target cells or tissues within the patient’s body through an intravenous line (IV) or through local delivery.  The new gene is also introduced inside to the patient’s cells, tissues, and organs via a viral vector.

 Somatic Gene Therapy-

In somatic gene therapy, the somatic (non-reproductive) cell of a patient is targeted for foreign gene transfer. Somatic cell cells that do not produce the eggs and sperm. In this case the modification caused by the insertion of foreign genes is restricted to the individual patient only, and not inherited by the patient’s offspring or later generations.

Germ Line Gene Therapy-

The functional or modified or corrected genes are inserted in the germ cells, i.e., sperm or eggs.  Therefore, targeting of germ cells makes the genetic heritable so that it can be passed from one generation to others.


  • Gene therapy processes try to rectify genetic abnormalities by delivering therapeutic genes to specific cells. Gene delivery can take several forms, including viral vectors and nonviral techniques like lipid nanoparticles altering the genetic code to recover the functions of critical proteins.
  • Nanoparticles, a newer technology to deliver the genetic material or gene-editing components into cells. It is extremely small structures that have been produced for numerous applications. For gene therapy, these tiny particles are engineered with special properties that allow them to target specific cell types. Nanoparticles are less likely to elicit immunological responses than viral vectors and are easier to build and modify for specific applications.
  • Eventually, once within the target cells, the additional genes can integrate into the genome or remain distinct, depending on the desired outcome. However, gene therapy confronts several hurdles, including immunological reactions to vectors, poor gene transfer efficiency, and off-target consequences. Overcoming the difficulties is critical to realizing gene therapy’s full potential as a transformative medical intervention.
  • The introduction of CRISPR gene editing has opened up new avenues for its application and use in gene therapy, as it allows for the correction of a specific genetic problem rather than just replacing a gene.
  • When selecting a gene integration approach, one should evaluate the target cell type, the intended stability and duration of gene expression, integration efficiency, and any potential off-target consequences.
  • Induced Pluripotent Stem Cells (iPSCs), Mesenchymal Stem Cells (MSCs), Mature Differentiated Immune Cells, Hematopoietic Stem Cells (HSCs) are the several types of common immune cells used in cell therapy. However, the choice of cell type depends on factors such as the specific therapeutic application, the desired differentiation potential, immunogenicity, scalability and safety considerations for clinical use.

What is gene therapy used for?

The majority of gene treatments are currently in clinical trials. Clinical trials are critical in identifying safe and effective medicines. Gene therapy is being tested in clinical trials to treat cancer, macular degeneration, and other eye illnesses, as well as some hereditary problems including HIV/AIDS.

The U.S. Food and Drug Administration (FDA) has approved several gene therapies drugs. These include:

Some of them are:

  • ADSTILADRIN, a gene-based therapy for non-muscle invasive bladder cancer (NMIBC) with carcinoma in situ (CIS)
  • CARVYKTI, a cell-based therapy for multiple myeloma
  • Elevidys, a gene therapy for Duchenne muscular dystrophy
  • Roctavian, a gene therapy for Hemophilia A
  • KYMRIAH, a CAR T-cell therapy for leukemia and lymphoma
  • Casgevy and Lyfgenia, gene therapies for sickle cell disease
  • Luxturna®: Approved in December 2017, Luxturna is a one-time treatment used to improve vision in people with genetic vision loss due to certain inherited retinal (eye) diseases.
  • Zolgensma®: The FDA approved Zolgensma in May 2019 to treat spinal muscular atrophy in children younger than 2 years old.

Potential Risks and Challenges:

  • Allergic reactions
  • Possible Tumor
  • Damage to organs or tissues if an injection is involved
  • Infection Caused by Viral VectorUnintended Genetic Changes

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