November is National Marrow Awareness Month
Advances in Stem Cell Transplantation and Factors Affecting
Outcomes
Bone marrow transplants from unrelated donors (called allogeneic
transplants) have become a more accepted treatment used early in the disease
course. Tens of thousands of patients have received bone marrow transplants-and
cord blood and peripheral blood stem cell transplants-to treat many different
diseases.
Advances in Preparative Regimens
The standard for preparing for a bone marrow transplant (called a
preparative regimen) is chemotherapy and/or radiation. The purpose is to:
- Get rid of remaining disease
- Prevent the transplanted graft (donor cells) from being
rejected
This regimen is aggressive and uses a lot of toxic agents that are
hard on the patient's body.
Recent advances
Now transplant doctors are developing
less harsh preparative regimens. These regimens may be better for a wider range
of patients. The most important change in this area is the non-myeloablative
transplant (also called a reduced-intensity regimen transplant).
A non-myeloblative transplant does not completely destroy the
patient's diseased marrow. Patients receive lowered doses of chemotherapy
drugs, but enough to achieve engraftment. Engraftment is the stage when the
stem cells given during the transplant start to grow and make blood cells. This
allows for blood and marrow cells from both the donor and recipient to coexist
within the recipient's body (called a mixed chimerism). Eventually, the goal is
for most, if not all, of the recipient's blood and marrow cells to be of donor
origin.
Although the non-myeloablative approach is fairly new, transplant
doctors are finding it useful in treating:
- Older patients
- Patients with less optimal organ function who cannot get a
standard, myeloablative stem cell transplant
- Patients with diseases that are slow to develop such as:
chronic myelogenous leukemia, myelodysplastic syndromes, chronic lymphocytic
leukemia, low-grade lymphoma, genetic disorders and autoimmune diseases
Advances in Stem Cell Sources
Although bone marrow has traditionally been the source of the stem
cells used in transplantation, there are now two other sources of these
cells.
- Peripheral blood stem cells (PBSC): Donors are first
given a growth factor (such as filgrastim) that helps move blood stem cells
from the donor's marrow into the circulating blood. Then through a process
called apheresis, these PBSCs can be collected.
Potential
advantages: Studies have shown that PBSCs engraft sooner than bone marrow
stem cells. Also, there is no need for anesthesia.
Potential
disadvantages: PBSC recipients often have a greater chance of chronic
(ongoing) graft-versus-host disease (GVHD). GVHD is a condition where the
transplanted donor's T-cells attack the recipi-ent's body. It can be mild or
serious and is sometimes life threatening.
- Umbilical cord blood: Cord blood is obtained at birth
and stored until needed for transplantation.
Potential advantages:
There is a faster time to obtain a matching graft. Donation poses no risk
to mother or baby. There is also a lower risk of GVHD. Another advantage is
less strict matching requirements between the donor and recipient. This is
because the T-cells found in the cord blood are less mature. These immature
T-cells are much less likely to attack the recipient's body.
Potential disadvantages: Compared to bone marrow and PBSCs,
there is a smaller amount of stem cells in each cord blood unit. Cord blood
transplants may only be suitable for children and small adults. And, unlike in
peripheral blood stem cell transplants and marrow transplants, if there is
graft failure, the original donor cannot give more cord blood stem cells. There
is also a chance of passing on an unknown genetic disease. However, mothers are
screened for many genetic diseases before a cord blood unit is donated.
Advances in Supportive Care
There have also been major advances in the control of infection
after transplant. Drugs and antibiotics are being used that:
- Decrease the cases of fatal bacterial infection
- Improve treatment of cyto-megalovirus (CMV) infections. CMV is
a virus that can cause pneumonia in blood stem cell transplant recipients
- Hold promise both for treatment and prevention of fungal
infection
Advances in Dealing with Graft-Versus-Host Disease
Graft-versus-host disease (GVHD) remains one of the most serious
complications from a allogeneic stem cell transplant. GVHD is caused by the
donor's cells attacking the recipient's cells. A variety of new medications and
approaches are being used to prevent and treat GVHD.
Factors Affecting Outcomes
In addition to good patient-donor tissue matching matching,
National Marrow Donor Program® (NMDP) research has found several factors
that lead to better transplant outcomes:
- Younger donors (less than 45 years)
- Younger recipients
- Good transplant timing
NMDP research shows that when
transplants are performed early in the disease process, there is a lower risk
of transplant-related deaths. There is also a lower chance of the disease
coming back. This is why it is important to be referred to an NMDP transplant
center early in the disease course.
November is the National Marrow Donor Program's Awareness
Month. To learn more about blood stem cell transplantation, visit the National
Marrow Donor Program's web site, www.marrow.org.
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