In recent decades, cell and gene therapy has developed from a hypothesis to a life-saving reality. But what do we mean when we talk about gene and cell therapy?
This page contains a simple explanation of genes, proteins, cells and stem cells as context for how gene and cell therapy work. We are currently developing a more detailed factsheet on these concepts.
Our bodies are composed of cells, which are the basic functional unit of all forms of life. The word ‘tissue’ is used to describe groups of similar cells working together to carry out a specific job. There are around 200 cell types in our bodies, all of which perform different jobs and make up different organs. For example, a brain cell looks and works very differently from a lung, liver or blood cell.
DNA is a chemical structure that stores information within our cells, acting like blueprints for building the cells. Genes are small sections of DNA that carry the code for making specific proteins. Proteins are the components or building blocks of our cells.
Every human cell contains the full set of that individual’s DNA. However, different genes are activated in different cells, and at different times, depending on that cell’s role in the body. This means that specific proteins are produced in specific cell types, controlling their function and behaviour. As a cell becomes more specialised, the number of genes it can activate decreases.
In turn, the action of many specialised cells together controls the development and function of larger structures in the body like organs.
Stem cells are unspecialised cells. Because they have not yet committed to a specific role, they have the potential to activate a wide range of genes and develop into other cell types. Stem cells are important in the growth and development of the body, as well as in repair after injury.
Some traits are determined by our genes alone (such as blood type), while others are influenced by our genes and our environment (such as height, which affected by genetics and nutrition). Humans typically have two copies of each gene, one inherited from each parent. Some genes have multiple functional forms (called alleles), which produce different physical traits, such as eye colour, hair texture, or blood type.
A protein’s biological function is controlled by its shape. A change in a gene which results in a different protein shape is called a mutation. Many mutations are harmless; they produce a slightly different protein which can still perform its biological function, giving rise to the natural diversity within humans.
However, some mutations have harmful outcomes, where a necessary protein is not produced, or is produced incorrectly. This might mean it cannot carry out its job in the cell, or even actively causes damage within the cell. Either outcome can result in illness.
Gene therapy is a technique that uses or manipulates genetic material like DNA to treat, prevent or cure a disease or disorder.
Many genetic disorders require lifelong management. For some of these conditions, gene therapy may treat the root cause by:
Example: In X-Linked Severe Combined Immunodeficiency Disorder, a mutation in a specific gene means that those affected cannot produce working immune cells to fight off infections. An approved gene therapy provides them with a correct copy of the gene, allowing the production of healthy immune cells.
This type of gene therapy is a complex process. It requires scientists to identify the specific disease-causing gene, and to know exactly how to target it. Just as there is no one type of surgery, there is no single 'gene therapy' which can be used to treat genetic conditions. Some conditions can result from multiple genetic mutations, meaning that some sub-types of the condition can be treated with gene therapy while others cannot. For some conditions, gene therapies can be a one-off, permanent cure, but this is not always the case.
There are also other uses for gene therapy which do not directly address the root genetic cause of a disease.
Example: In people with cancer, the immune system is usually working normally, but it cannot detect cancer cells to destroy them as they are too similar to the rest of the cells in the body. A type of gene therapy called CAR-T therapy is currently used to treat specific kinds of cancer. It equips a patient’s immune cells with the gene for a special receptor that allows them to recognise and kill cancer cells.
Gene therapy is still a relatively new field, and its applications are evolving as research progresses, and new technologies are discovered.
Cell therapy (or cellular therapy, or cytotherapy) is the use of cells to treat diseases, intervening at a cellular rather than genetic level. It involved injecting, grafting or implanting living cells into a patient. Stem cells are often used in cell therapy, as they can produce a range of different cell types to repair the affected tissue.
Cell therapy may be performed with cells from a healthy donor (allogenic) or with the patient’s own cells (autologous).
Example: A haematopoietic stem cell transplant (bone marrow transplant) is used to replace damaged blood cells with healthy ones. It can be used to treat conditions affecting the blood cells, such as leukaemia and lymphoma.
A tissue-engineered product is a medicine containing bioengineered cells or tissues, which is intended to repair, restore or improve how well a tissue or organ works. Again, tissue engineering may use stem cells to produce different cell types.
Example: Spherox is a treatment made from a patient’s own cartilage tissue to repair damage to the knee. Healthy cartilage cells are taken from the patient, grown in the laboratory under strict conditions to help them form specialised structures, and then injected back into the knee where they bind to the damaged cartilage and help to repair it.
Classifying a therapy can be very complicated, as it may depend on many different factors.
We have provided a simplified explanation of these therapies to help you understand their basic principles. However, there is often overlap in the methods and techniques used across different types of treatments. For example, tissue engineering typically involves the use of cells or stem cells, which may be genetically edited, while gene therapy may involve extracting a patient’s cells, genetically editing them, and reintroducing them into the body.
Factors that affect therapy classification can include how the treatment is manufactured, or how it works in the body. Legal definitions and classifications also vary between countries and regulatory systems. The same therapy may be described differently depending on the context, and multiple descriptions can still be accurate.
Example: Within the EU, CAR-T therapy is typically legally classified as a gene therapy, but it is also sometimes described as cell-based gene therapy or an immunotherapy, since it modifies the immune system to target disease.
If you are interested in learning more about classification, our Research Pathways directory contains resources to help different researchers and other stakeholders understand the legal and regulatory aspects for cell and gene therapy development in Europe.
Advanced therapy medicinal products (ATMPs) are medicines for human use based on cells, genes or tissues. The term 'ATMP' is a specific legal classification for medicines. To be considered an ATMP, a medicine must be based on at least one of the following:
ATMPs are a subset of gene and cell therapies; not all gene and cell therapies are medicines or correspond to the legal definition of ATMPs.
Example: a bone marrow (haematopoietic stem cell) transplant is not considered an ATMP because the cells have not been substantially altered or manipulated outside the body, and are being used for the same purpose in the cell donor and the patient. If the cells from the donor are processed in ways that are deemed to change their behaviour, they are then classified as an ATMP. Likewise, if those cells were used for a different purpose in the patient than the donor, they would be considered an ATMP.