Bone marrow
Blood cells are made in the bone
marrow by stem cells. Bone marrow is the soft 'spongy' material in the
centre of bones. Large flat bones such as the breast-bone (sternum) and
pelvis contain the most bone marrow. To constantly make blood cells you
need a healthy bone marrow. You also need nutrients from your diet
including iron and some vitamins.
Stem cells
Stem cells are primitive
(immature) cells. There are two main types in the bone marrow - myeloid
and lymphoid stem cells. These derive from even more primitive common
'pluripotent' stem cells. Stem cells constantly divide and produce new
cells. Some new cells remain as stem cells and others go through a
series of maturing stages ('precursor' or 'blast' cells) before forming
into mature blood cells.
Blood cells
Mature (fully formed) blood cells are released from the bone marrow into the bloodstream. Mature blood cells are:
- Red cells (erythrocytes). These make blood a red colour.
One drop of blood contains about five million red cells. Red cells
contain a chemical called haemoglobin. This binds to oxygen, and takes
oxygen from the lungs to all parts of the body.
- White cells (leucocytes). The different types of white cells are
called neutrophils (polymorphs), lymphocytes, eosinophils, monocytes,
and basophils. They are part of the immune system. Their main role is
to defend the body against infection.
- Platelets. These are tiny and help the blood to clot if we cut ourselves.
Stem cells rapidly multiply to make millions of blood cells
each day. Because of this they are more easily killed by chemotherapy
than most other cells in the body. This is because chemotherapy drugs
work by killing rapidly dividing cells (such as cancer cells).
When is a stem cell transplant used for treatment?
A stem cell transplant is an option which is considered for various
cancer conditions. For example, for types of leukaemia, lymphoma and
myeloma. Your specialist will advise when it may be an appropriate
option. As a rule, it is not often a 'first line' treatment.
Conventional chemotherapy or other treatments tend to be used first.
However, the treatment of cancer and leukaemia is a changing and
developing area of medicine. Techniques such as stem cell transplant
continue to be refined and improved and may be considered in various
different circumstances.
The higher doses of chemotherapy and
radiotherapy that can be used in conjunction with a stem cell
transplant can improve the chance of a cure for some conditions in
certain circumstances.
A stem cell transplant is also used for some rare non-cancerous blood disorders.
Where are stem cells obtained from?
An autologous transplant
This means that
the stem cells used for the transplant come from your own body. They
are usually collected when you are free of any sign of disease (when
you are 'in remission') following conventional chemotherapy or other
treatments. The stem cells can be used soon after being collected. They
can also be frozen, stored and used in the future if needed.
An
autologous stem cell transplant is also called 'stem cell support' as
the stem cells come from your own body. So, strictly speaking, it is
not a transplant from a donor.
An allogenic transplant
This means the stem
cells used for the transplant come from someone else - a donor. This is
often a close relative such as a brother or sister where there is a
good chance of a close 'match'. Unrelated donors are sometimes matched
to people needing a transplant.
Stem cells can be collected:
- From the bone marrow. This involves a small operation to collect some marrow from the pelvic bone.
- From the blood. Some stem cells occur in the blood (most are in the
bone marrow). The stem cells in the blood can be collected
('harvested') by a machine called a cell separator. The bloodflow is
diverted from a vein in the arm to pass through the machine which
separates out the stem cells. The procedure takes about 4-6 hours.
Drugs are given for a few days before this procedure to stimulate the
body to make more stem cells in the bone marrow which 'spill out' into
the blood.
How is a stem cell transplant given?
It is very similar to a blood transfusion. Following the intense course
of chemotherapy (and sometimes radiotherapy), the solution containing
stem cells is given into one of your veins via a drip. The stem cells
travel through your bloodstream and end up your bone marrow. Here they
start to make blood cells.
It can take several weeks for your
bone marrow to recover, to take up the transplanted stem cells, and to
make enough new blood cells. During this time you will need to be in
hospital and be closely monitored. You may need several blood
transfusions during this time until you are making enough blood cells.
Antibiotics are given to minimise the risk of infection. Also, drugs
are given to help stimulate the stem cells to multiply as quickly as
possible.
What are the main risks of having a stem cell transplant?
There is a risk of serious problems with a stem cell transplant. For example:
- Infection is the main risk. Following the intense
chemotherapy, and before the time your bone marrow is working again,
you have very low immunity. During this time you are at risk of serious
and life-threatening infections. This is why antibiotics are given and
you will be nursed away from other people until your bone marrow
recovers. This can take several weeks.
- Bleeding problems from the low level of platelets after the chemotherapy.
- It you have a transplant from a donor, there is some risk that the
'match' will not be perfect, and the donor cells may react with your
body's cells. This is called 'graft versus host disease'. This is not
always serious but sometimes it can be.
- Rarely, the transplanted stem cells fail to work.
- There is a risk of short-term and long-term side-effects from intense chemotherapy (and/or radiotherapy).
Your specialist will discuss the risks and possible side-effects involved with a stem cell transplant.
Further help and information
Cancerbackup
3 Bath Place, Rivington Street, London, EC2A 3JR
Tel: 0808 800 1234 Web: www.cancerbackup.org.uk
Provides information and support to anyone affected by cancer.
National Blood Service
To learn more about being a bone marrow and stem cell donor see
www.blood.co.uk/pages/marrow_info.html
© EMIS and PiP 2008 Updated: 18 Jan 2008
