We often hear about stem cells in the media, from their potential to treat human disease to the ethical issues surrounding the production and use of embryonic stem cells.
But what part do stem cells play in cancer research?
What are stem cells?
A stem cell is a kind of ‘starter cell’ that has the potential to develop into many different cell types in the body. When a stem cell multiplies, the resulting cells either remain as stem cells or, under the right conditions, can become a type of cell with a more specialised function, such as a muscle cell, red blood cell or brain cell.
Stem cells occur naturally in the body in various places and stages during our lifetime. They can broadly be divided into two categories: embryonic stem cells and adult stem cells.
Embryonic stem cells
Embryonic stem cells are found in early stage embryos that are a few days old. These remarkable cells give rise to all the different tissues and organs of the body. The generation and use of human embryonic stem cells is controversial and tightly regulated. In the UK, the Human Fertilisation and Embryology Authority (HFEA) governs the use of human embryos and stem cells for research.
Many researchers working in this field use either mouse embryos as a source of stem cells, or work on existing human embryonic stem cell lines that were generated in the past. Some scientists are also exploring the potential of stem cells taken from the blood in the umbilical cord.
Adult stem cells
Adults also have some stem cells, but these have a more limited repertoire, with each type of stem cell only able to develop into a specific subset of cells. For example, adult stem cells in the bone marrow, known as haematopoietic stem cells, can usually only give rise to different types of blood cell – though some scientists have recently found ways to convert them into kidney or liver cells as well.
Because adult stem cells can be produced without the need to use embryos, their use in research has fewer ethical complications. But because they can only develop into a limited number of cell types, some researchers argue that this makes them less useful.
Dr Lilian Clark, Cancer Research UK’s executive director of science, said: “Although most cancer scientists’ stem cell research currently involves adult stem cells, future patients with serious illnesses including cancer could benefit from research involving embryonic stem cells. “We therefore believe that the necessary research should be permitted within a well-regulated environment.”
We would like to stress that Cancer Research UK does not fund any research that uses human embryos or foetal tissue. However, we are funding a very small number of research projects that use human embryonic stem cell lines grown in the lab. These cell lines were originally produced from human embryos by other (non-Cancer Research UK) scientists.
A few researchers funded by the charity are studying embryonic stem cells made from mouse embryos. But mainly our scientists are investigating the role of adult stem cells in cancer.
Why do scientists study stem cells?
There are a number of reasons why stem cells have the potential to be very useful in scientific and medical research. Firstly, because stem cells can effectively grow forever, they can be grown in the lab without the need to constantly go back and isolate fresh new stem cells. This enables scientists to have a constant supply of cells for their experiments.
Also, as stem cells can grow into other cell types, scientists can potentially treat them in a certain way to turn them into the types of cells that they want to use. Cells generated in this way have several potential medical applications, as well as use in research. For example, in the future scientists may be able to use stem cells to generate more brain cells for people with conditions such as Parkinson’s disease.
One day it may even be possible to grow new organs in the laboratory for people who require transplants. If scientists were able to use the patient’s own stem cells to make the new organ, they would potentially overcome some of the problems of transplant rejection.
And it is also possible that researchers will one day be able to overcome the effects of faulty genes in cancer and other diseases by encouraging stem cells with a correct version of the gene to develop into the type of cell to be replaced.
How could stem cell research help to beat cancer?
As well as the examples above, stem cells have considerable potential for cancer research and for improving the treatment of the disease. Cancer cells share many characteristics with stem cells – including, and perhaps most importantly, the fact that they are ‘immortal’. So understanding more about stem cells can help us to learn more about cancer.
Scientists also now believe that stem cells may play a direct role in the development of cancer, as some tumours are thought to develop when normal stem cells become faulty. This has led to the idea of ‘cancer stem cells’, which have now been identified in a range of cancer types, including bowel, breast and prostate cancer. We recently blogged about Cancer Resaerch UK scientist Owen Sansom’s discovery that faulty stem cells could fuel bowel cancer.
Researchers think that some cancers may be made up of a population of cancer stem cells, as well as ‘bulk’ tumour cells. It is possible that many cancer treatments only kill the bulk cells, and fail to tackle the cancer stem cells. This could explain why some cancers can start growing again after treatment.
The challenge for scientists is to understand where cancer stem cells come from, and to devise ways to target them with effective treatments. To do this, they need to study the molecular makeup and behaviour of stem cells in great detail.
Stem cell research funded by Cancer Research UK
The charity has a long history of supporting work in this area. For example, we funded Professor Mike Dexter at the Paterson Institute for Cancer Research who developed a method for long-term culture of bone marrow cells.
This led to many important discoveries about bone marrow stem cells, including how they replenish our blood cells throughout life. And his work greatly aided our understanding of cancers of the blood, such as leukaemia and multiple myeloma.
We’ve also previously blogged about Dr Owen Sansom’s research into bowel cancer stem cells.
There are some examples of our research into stem cells and cancer below, and there are more examples in this section of our Research Highlights pages.
Stem cells and cancer spread
In 2003, Cancer Research UK-funded scientists in Manchester published the results of their work on mouse embryonic stem cells. They used these stem cells to make some important discoveries about how cancer spreads. They found key similarities in the way cancer cells spread from a tumour and move around the body with the movement of stem cells as they form new tissues during an embryo’s development.
The researchers saw that a molecule called 5T4 played a key role in the ability of stem cells to move around. This was an important finding as 5T4 is also present in many different types of cancer. This work raised the possibility that treatments targeted against 5T4 could help to combat cancer spread.
Bone marrow transplants
In 2002, Cancer Research UK-funded scientists at the Paterson Institute discovered a new technique for bone marrow stem cell transplants. These are sometimes used to treat people with leukaemia or lymphoma whose cancers have not responded to standard treatments.But the high-dose chemotherapy that often follows transplantation can kill the stem cells.
The Manchester researchers managed to genetically engineer the stem cells so that they would be resistant to chemotherapy after transplantation.
Leukaemia stem cells
A Cancer Research UK team in London is currently studying the haematopoietic stem cells in our bone marrow. These give rise to all the different types of cells in our blood, including red blood cells that carry oxygen, and white blood cells that fight infection. Our researchers have found evidence that leukaemia starts when haematopoietic stem cells multiply out of control.
The scientists are investigating this phenomenon, and working to identify the characteristics of leukaemia stem cells that will help to determine their origin. These studies will aid our understanding of leukaemia, and could lead to new ways to diagnose and treat the disease in the future.
Furthermore, the team is exploring the potential of another type of bone marrow stem cells (called mesenchymal stem cells) to be converted into other cell types within the body. So far, the researchers have managed to turn these stem cells into a wide range of other cell types including fat, bone, cartilage, muscle and nerve cells.
Some of the team’s recent experiments have also shown that mesenchymal stem cells can actually become part of the liver, lung, muscle or kidney. In the future, these cells could potentially be transplanted into patients to replace tissues damaged by diseases such as cancer. However, much more work needs to be done before this can become a reality.
It’s clear that stem cells are a hot topic in cancer research, and we anticipate many more interesting and important discoveries in this area in the future.
This article was first published in the Behind the Headlines section of our website. We have now moved this content to the blog.
- Tracking down bowel cancer stem cells
- August 2008 podcast featuring scientists talking about cancer stem cells
- Cancer stem cells on Wikipedia
- Cancer stem cells – the root of all evil? (The Economist)
- Cancer Research UK Research highlights – stem cells
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