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Bone Marrow is the spongy tissue found
in the cavities of the body's bones, where all the body's blood cells
are produced.
Every type of blood cell in the marrow begins its life as a stem cell.
The stem cells then divide and form different cells that make up your
blood and immune system. These include white cells that fight infection
(leukocytes), red cells that carry oxygen (erythrocytes), and platelets
which are clotting agents. Without bone marrow, and the disease fighting
blood cells it produces, your immune system will be severly impared and
you will have little defense against even the most common infection.
The goal of a bone marrow transplant is to cure many different types of
cancer and disease. The type of transplant depends on who donates the
marrow.
Allogeneic transplant--The person giving the bone marrow or stem cells
is a genetically matched family member (usually a brother or sister).
Unrelated allogeneic transplant (MUD) --The person donating marrow is
unrelated to the patient. Chances of finding an unrelated compatible donor
from the general population depends on the uniqueness of tissue type.
Genetic and ethnic background can also affect the likeihood of finding
a donor.
Syngeneic transplant--The person donating the bone marrow or stem cell
is an identical twin.
Autologous transplant--The patient donates his/her own bone marrow or
stem cells prior to treatment for re-infusion later.
Peripheral blood stem cell transplant--The patient or a donor donates
stem cells collected from the circulating blood system instead of from
bone marrow. The only difference with this kind of BMT is the source of
the stem cells and how they are collected.
Allogeneic, unrelated and syngeneic are most commonly used in persons
with diseases affecting the bone marrow, like leukaemia, aplastic anemia,
and some lymphomas. The basic idea here is to replace the unhealthy marrow
with healthy marrow.
Sometimes a disease like leukemia interferes with stem cell growth, causing
cells to stop developing or to become defective, or, in some cases, both.
Eventually these immature blood cells enter the bloodstream causing the
affected person to become seriously ill. A bone marrow transplant offers
the gift of like to patients whose marrow is diseased. The transplant
is the transfer of healty marrow from a donor to the patient. The key
factor is that the healthy marrow contains healthy stem cells.
Sometimes a patient can give his own marrow back to himself. This is called
an autologous BMT. It is often hard to understand how a sick person could
be their own donor and be healthy again. The autologous transplant (or
rescue as it is often known) isn't necessarily performed because there's
something wrong with the bone marrow or the stem cell production. It is
preformed because the dosage of chemotherapy and radiation needed to kill
the cancer is so high it will destroy the patients existing bone marrow.
Without this marrow there is no immune system and the patient willl eventually
die. Instead, the patients own marrow, collected (harvested) prior to
chemo and radiation, is reinjected and the immune system is reestablished.
Meanwhile, the hope is that the cancer tumours and cells have been destroyed.
Bone marrow transplantation is a lot different from other types of organ
transplants. For one thing, there is no surgery on the day of the proceedure.
The new marrow doesn't have to be placed inside an incision or stitched
into place. It is fed into the body intravenously, like a blood transfusion.
Many patients and their familes find the actual day of the transplant
a bit of an anticlimax. The patient receives the harvested stem cells
through and IV and they find their way to the marrow space in the bones.
If the transplant goes well, stem cells from the new marrow will begin
producing life-sustaining blood cells. In the case of a bone marrow transplant,
this takes two to four weeks. In a peripheral stem cell transplant, the
stem cells will begin reproducing generally within two weeks.
Adapted from nbmtlink's bmt resource guide.
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