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Gene therapies: The transformative potential of precision medicine

How Do Viruses Make Us Sick?

Cell and gene therapies have undergone significant advancements, thanks to groundbreaking research and the emergence of new cutting-edge technology. This momentum has shifted the spotlight back onto the potential these therapies may hold. With the UK asserting itself as one of the leading countries in the research and development of these novel types of medicines, and the number of UK clinical trials for advanced therapy medicinal products (ATMPs), which include gene therapies, is increasing every year.1

Your DNA, genes and chromosomes work together to tell your body how to form and function.

What are gene therapies?

Gene therapies are novel treatments which target diseases of genetic origin through the replacement, addition or deactivation of a specific gene.2 Unlike traditional medicines, they have the potential to eliminate the need for ongoing treatment by addressing the fundamental cause; allowing for an improved quality of life, and/or significant relief from the associated symptoms.3

Genes as molecular blueprints

Imagine a gene as a recipe in a cookbook. Like a recipe allows for the creation of a specific dish, a gene allows for the production of protein essential for maintaining the correct structure and function of the body. Our DNA contains thousands of functional genes, each comprised of a sequence of pairs of tiny biomolecules called nucleotide bases; resembling rods pairing the backbones of our DNA together. It is the order and quantity of those base-pairs which make each gene unique.4 Ranging from hundreds to thousands of pairs, it is these varying sequences that define a particular physical or biochemical trait of an organism. 

Genetic disorders

When the mutation of a gene occurs, the specific steps of our biomolecular recipe are rearranged with varying consequences. Usually these alterations do not carry any ill effects, with many being addressed by specialised DNA-reparing enzymes found within most cells, but at times the impact of a mutation can have serious consequences. If our cells are unable to repair the error, the resulting genetic material can lead to the production of proteins which no longer function as they’re supposed to or can prevent their construction altogether.5 From the reduction in our blood’s ability to clot6, to a weakened ability to fight off infections7; the resulting genetic disorder can have a detrimental impact on an individual’s health.

Our genes contain four types of nucleotide bases: : adenine (A), cytosine (C), guanine (G), and thymine (T).

These changes in the sequence of our DNA are often inherited from the parents and are present in an individual at birth, but they can also be acquired over one’s lifetime. Some people may be more susceptible to genetic mutations due to environmental factors such as air or water pollution, exposure to other mutagens or dietary choices, while for others these changes may occur at random as an error during the natural process of cell division.5

Genetic mutations are responsible for approximately 80% of known rare diseases.8

How do gene therapies work? 

Gene therapies target the root cause of a given genetic disorder in three distinct ways;

  • by replacing the malfunctional gene with its therapeutic counterpart,
  • by 'turning off' the faulty gene, or
  • by providing genetic instructions, which can eliminate diseased cells within the body

To do this, scientists first have to deliver genetic material into the nulceus of a cell. There are currently two ways to potentially achieve this, either through 'viral vectors' or 'non-viral vectors'.10

A viral vector approach involves using a genetically-engineered virus stripped of its ability to infect and replicate. Because viruses are particularly good at entering cells, they make excellent delivery vehicles for 'packages' such as genetic materials and instructions.

Viral containers protect the therapeutic gene during transport and allow for its release once it enters the cell.

Using a non-viral vector approach involves delivering genetic material into a cell using either a physical method, such as a needle entering a cell, or a chemical technique, where natural or synthetic materials such as fat molecules, polymers or nanoparticles are used.10

Regardless of the delivery mechanism, once the therapeutic gene successfully enters the cell’s nucleus, its sequence is copied and reassembled into a set of protein-building instructions using the cell’s internal machinery. With this new blueprint in place, our cells can use it to build proteins which have been damaged or are missing. This supply of protein potentially brings therapeutic change to how our organs, tissues and a number of internal processes work, offering the potential to restore healthy function to the body.  

In-vivo and ex-vivo delivery systems 

There are two ways of delivering new genetic material to the body: in-vivo and ex-vivo.11

In-vivo involves the modification of cells inside the patient’s body through direct delivery of the gene via injection into the bloodstream or into specific tissues and organs. In contrast, ex-vivo therapy involves the removal and isolation of target cells and the subsequent introduction of the therapeutic gene outside of the patient’s body.11

Whether an in-vivo or ex-vivo approach is used is typically determined by the underlying condition being addressed. The ex-vivo method of delivery is frequently used to treat hereditary haemoglobinopathies, immunodeficiencies, and cancers, and benefits from the reduced risk of an immune response against the gene carrier; in-vivo delivery tends to be better suited when targeting specific damaged or malfunctioning organs and can prove to be a faster and more cost-efficient method by avoiding the complex process of isolating target cells from the patient's body.11

The future of gene therapies 

Several gene therapies have already received regulatory approval and become available in the UK, however they are still largely only administered as part of strictly regulated clinical trials, meaning that approval bodies should anticipate an increase in appraising these therapies in the future. Once approved by regulatory bodies such as the Medicines and Healthcare Products Regulatory Agency (MHRA), medicines then need to be assessed for how effective and safe the treatment is and if it's considered cost effective for the NHS - this decision is made by The National Institute for Health and Care Excellence (NICE) in England, the Scottish Medicines Consortium (SMC) in Scotland, the All Wales Medicines Strategy Group (AWMSG) in Wales, and the Department of Health, Social Services and Public Safety (DHSSPS) in Northern Ireland. Whilst a gene therapy may provide a one-time treatment offsetting longer-term costs, they are costly to develop and require a high level of skill, knowledge and specialised equipment often resulting in high up-front costs. This is why, at Pfizer, we believe the way in which these ground-breaking therapies are assessed needs to evolve, to make sure it better captures the value offered to patients, the NHS and wider society, something we highlighted in our 'From Promise to Reality' report. The report calls for the formation of a Gene Therapy Taskforce, building on the mission-led approach we saw with the Vaccine Taskforce, created as a result of the COVID-19 pandemic and applying the same sense of urgency and collaboration to another area of great unmet need for patients. Stakeholders from across the rare disease community could work together towards a shared goal of ensuring gene therapies can reach the patients who need them.

Gene therapies have the potential to transform the lives of people with devastating diseases, but the reality is that at present these therapies may struggle to reach patients unless our current assessment systems evolve. We must work together and act now to change this.


  1. Cell and Gene Therapy Catapult. UK ATMP Clinical Trials Report 2022. Accessed Nov 2023.
  2. MedlinePlus. What is gene therapy? Accessed Nov 2023.
  3. PubMed Central. Addressing the Value of Gene Therapy and Enhancing Patient Access to Transformative Treatments. Accessed Nov 2023.
  4. NCBI. Overview: Gene Structure - Holland-Frei Cancer Medicine. Accessed Nov 2023.
  5. NCBI. Mutation, Repair and Recombination - Genomes. Accessed Nov 2023.
  6. National Human Genome Research Institute. About Hemophilia. Accessed Nov 2023.
  7. National Human Genome Research Institute. About Severe Combined Immunodeficiency. Accessed Nov 2023.
  8. European Commission. Rare diseases. Accessed Nov 2023.
  9. Your Genome. What is gene therapy? Accessed Nov 2023.
  10. Genehome. Vectors: Tools for gene therapy. Accessed Nov 2023.
  11. Science Direct. Gene therapy. Accessed Nov 2023.
PP-UNP-GBR-4905 / November 2023
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