Each year, over 10,000 people in the United States suffering from
blood cancers such as leukemia and lymphoma are told they need a bone marrow transplant
to survive. The doctors first search the patient’s family for a possible match.
Unfortunately around 70% of these patients will not find a match within their
family. In these cases, the doctors turn to public databases of volunteer bone
marrow donors such as Be The Match registry.
The registry connects patients with volunteer donors.
When a volunteer joins the database, they have a swab taken of their
cheek cells (I joined long before this method was widely used and gave a blood
sample). These cells are tissue typed to determine that persons HLA profile
(Human Leukocyte Antigen). An HLA profile is simply a snapshot of the genetic
markers that make up your immune system.
The donor and patient HLA profiles are compared. To be considered for
transplant they must match at a minimum of 5 of 6 points on 3 major markers (HLA A, HLA B, and HLA C) in order to be considered for transplant.
Each of us inherits 1 set of genes from
our mother and 1 set of genes from our father for each of these major markers.
This is why there are 6 points for the 3 major markers.
A perfect match is considered a 10 of
10 (they look at minor markers HLA DRB1 and HLA DQ). The better the HLA match,
the higher the chance of a successful transplant. Blood types do not matter at
all. In fact, if the blood types of the donor and recipient are different, the
recipient’s blood type will switch to their donor’s after the transplant (see
the cool facts below).
The name “Bone Marrow Transplant” is a
bit of a misnomer. In reality, the donor is giving some of the blood stem cells
that live in their bone marrow (called hematopoietic stem cells). These stem
cells are the young cells that can become red blood cells, platelets, and white
blood cells (the basis of our immune system). There are many different types of
stem cells, check out this NIH page for more information about stem cells.
There are two methods of collecting
stem cells; bone marrow harvest (used 25% of the time) and Peripheral Blood Stem Cell collection (used 75% of the time).
Bone marrow harvesting is by far the
most well known collection method. This method is done as an outpatient procedure
with the donor under general anesthesia. A small bit of bone marrow is
extracted from the back of the donor’s pelvic bone. The bone marrow replaces
itself naturally within 4 to 6 weeks. Contrary to popular belief, this
procedure is not painful but donors will likely feel a bit sore at the
collection site. Click here for a 46 second video of the bone marrow collection
procedure:
Peripheral Blood Stem Cell, or PBSC,
collection is by far the most common method used today. This method is also
done as an outpatient procedure. For five days leading up to donation you are
given an injection of Filgrastim, a drug that stimulates your body to increase
production of stem cells and causes them to migrate from your bone marrow to
your blood stream. Your blood is then removed through an IV in one arm and
passed through an apheresis machine that separates out the stem cells. The
remaining blood is then returned to you in an IV in your other arm. Your stem
cells replace themselves naturally within 4 to 6 weeks. Click here for a 45
second video of the PBSC collection procedure:
The stem cells, once collected, will be
sent via a specially trained courier to the patient's transplant center (the
donor and recipient are not at the same facility). The transplant is a very
anti-climactic IV drip into the patient and usually occurs within 12 – 24 hours
of the collection. The infusion can take anywhere from 1 to 3 hours. Once in
the patient's body, the stem cells know to migrate to the bone marrow where
they will “engraft” and begin producing white blood cells and other blood
products. Engraftment usually occurs in 10 to 20 days after the transplant and
is signaled by a sudden and sustained jump in the patient’s white blood cell
count.
In order to prepare the patient for transplant, they are given high doses of chemotherapy and possibly total body radiation
therapy. The type and length of treatment varies between patients and is based
on age, disease, and severity of the disease. The treatment hopefully destroys
all cancer cells in the patient’s body along with the blood-forming cells in
the bone marrow. This serves to “clean out” the old bone marrow and create room
for the newly infused stem cells. The treatment also destroys the patient’s
immune system to prevent it from attacking the new stem cells.
The new stem cells are responsible for
not only creating new blood cells but also fighting any remaining cancer cells.
They are literally on a “seek and destroy” mission. It’s very similar to a
computer being restored to "factory settings" where the transplant
team uses the donor’s stem cells to re-boot the patient’s immune system. If the
transplant works perfectly the patient will become cancer free.
Sometimes (less than 10% of the time)
an additional blood donation is asked of the donor for the recipient. The
request could be for: T-cells (a type of white blood cell), PBSC, Marrow, Whole
Blood, or Platelets.
For more information on what the
transplant process is like for the recipient go to this page. This page also includes the benchmarks of
the recovery process for the recipient.
Recovery time for the donor post-donation varies
based on the collection procedure. PBSC donors usually report full recovery in
2-7 days and Marrow donors usually report full recovery in a few weeks. Both
types of donors can usually resume normal activities within 24 to 48 hours of
their procedure.
Really cool facts about Bone Marrow
Transplants:
-Post-transplant, the recipient will
switch to their donor’s blood type (if they’re not already). This is because
the donor’s stem cells (which carry the donor’s DNA) are producing the new
blood cells.
-The recipient will carry their donor’s
DNA in their blood. This is called chimerism and the degree to which this can
happen is explained here. (Look under “Steps of a
reduced-intensity transplant”, #3.)
-The odds of a patient finding an
unrelated donor with their HLA profile: 1 in 20,000.
-1 in 40 members of the Be The Match
Registry will be asked to undergo further blood testing as a preliminary match.
-1 in 540 members of the Be The Match
Registry will actually go on to donate.
-It is impossible to determine the odds
of any one person on the registry being called to donate since the match is
determined by tissue type. Due to the variation, you might have a common tissue
type and be one of many possible matches for a patient. On the flip side, you
might be the only person out of the 10.5 million registry members who can save
a person’s life.
-The odds of a Caucasian finding a
match in the database is >90%. Non-Caucasians are not well represented in
the database so the odds decrease dramatically for non-Caucasians.
-Over 25,000 bone marrow transplants
are performed worldwide each year. The Be The Match registry facilitates approximately
5,200 of these transplants. If you are called to donate it is possible
your recipient lives outside of the United States.
-The Be The Match Registry receives
around 3,000 queries each day for
patients looking for donors.
-Identities of donors and recipients are
required by law to be kept confidential. The donor will know the age, sex, and medical condition of their
recipient. The recipient will know the age and sex of their donor. Depending on
the specific regulations of the transplant center, contact may be made after a
period of one year if the donor and recipient sign consent forms releasing
their information to each other.
Still have questions? Information
regarding all things Bone Marrow Transplant can be found on the Be The Match
registry’s website: http://marrow.org. The information is written for
non-medical professionals and is very understandable. For information focused
on donors and the process they go through, go to this page: http://marrow.org/Registry_Members/Donation/Donation.aspx.
A timeline of what happens after you
join the registry, are selected as a possible match, and are selected to donate
can be found here: http://marrow.org/Registry_Members/Now_That_You_ve_Joined.aspx
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