|
Cord blood represents a rich source of Haemopoetic Stem Cells (HSC) of the adult type. To date, the
benefits of umbilical cord blood transplantation has been demonstrated conclusively using homologous (allogenic)
umbilical cord blood transplantations from unrelated donors in childhood leukaemias. Autologous transplantations
may be used in some patients if there was no other source of compatible stem cells available, although this would
not be the therapy of choice for genetic based diseases .
Since the first stem cell transplant from umbilical cord blood in 1988, cord blood transplantation has been successfully
used to treat cases of childhood leukaemia and other immune disorders. Recently researchers have suggested that the use of
stem cells can be extended to include many other disorders (myelo and lymphoproliferative disorders, liposomal storage diseases),
however this projected use remains speculative.
For several years, commercial cord blood banks in the USA have been offering mothers the opportunity to store their own baby's
cord stem cells indefinitely, in case that particular baby or her siblings ever develop an illness such as leukaemia, which could
be treated by cord blood stem-cell transplantation. Commercial cord blood banking has recently attracted considerable media
attention and these companies are now targeting women in UK. In May 2000, the Federal Minister for Health announced that the
Commonwealth Government would assist in the establishment of an Australian National Cord Blood Collection Network (NCBCN).
The Australian Bone Marrow Donor Registry (ABMDR) was contracted to manage the (four-year) "Development Phase" of the National C
ord Blood Collection Network. The network was officially launched under the name "AusCord" in September 2002.
Almost every country has different types of structures for cold blood banking. These banks may approach obstetricians
directly but, together with midwives, they are increasingly being confronted with this issue when parents request that
their baby's cord blood be collected and shipped for storage.
Types of cord blood donation
The use of allogeneic haemopoietic stem cells (HSC) is limited by the need to find an HLA-compatible
donor. The main indication for cord blood transplantation is relapsed acute lymphoblastic leukaemia in
children. For those with no suitable family member, cord blood banks have been set up along similar lines to registries
of bone marrow donors to facilitate matching. Over 65 000 units have been stored worldwide and, as for bone marrow, there
is an international search facility. Because of higher stem cell numbers, HSC from bone marrow or cytokine-stimulated HSC
release into peripheral blood collected by apheresis have been preferred in the UK for HSC transplantation. If a compatible
donor cannot be found, either in the family or from one of the six million unrelated bone marrow donors worldwide, and then
compatible cord blood may prove a feasible option as a source of HSC .
Thirty percent (30 percent) of Australian patients in need of an allogeneic bone marrow transplant have a suitable family
donor, that is, 5 or 6 out of 6 Human Leukocyte Antigen (HLA) matched close relative. Of the remaining 70 percent of patients,
only 20 – 25 percent are able to find an unrelated bone marrow donor on the existing registries. Therefore, over 50 percent of
patients in need often-allogeneic transplant do not have a histocompatible related or unrelated donor .
This same group may be eligible for a cord blood transplant as it is known that the degree of compatibility between the
patient and the cord unit does not need to be as stringent as in bone marrow transplantation, with matching acceptable
to a level of 4 out of 6 match. This is because graft-versus-host disease is lower in cord blood transplants at a given
level of match, thereby increasing an individual’s chances of finding a suitable cord blood donation at an acceptable level of match.
The main indication for cord blood transplantation is relapsed acute lymphoblastic leukaemia in children. Following
the experience at the New York Cord Blood Bank and the National Marrow Donor Program in the United States in identifying
suitably matched donors (5 out of 6 and 6 out of 6 HLA matches) for patients, the NCBCN expect that a collection of 20,000
cord blood units will enable 80 - 90% of Australian requests to be met
Directed Donations In At Risk Families
The collection of cord blood units for use by siblings born into a family where there is a known genetic disease
amenable to HSC transplant remains a recommendation. There is a 1 in 4 chance that the cord blood will be an acceptable
match for the affected sibling.
Some transplant centers currently recommend cord blood collection and storage for siblings born into a family where
there is a known genetic disease amenable to HSC transplantation. If the cells are HLA-compatible, they may be used
for the affected child. If not, they may be useable for a future HLA-compatible sibling. If the newborn child itself
develops the disease, its own cord HSC may in future be useable as a vehicle for somatic gene therapy, when these
techniques have been fully developed.
Cord blood can also be stored from siblings of a child with an acquired disease who may require HSC transplantation.
Its utility is less clear now that improvements in chemotherapy mean that transplantation in childhood leukaemia is
used less frequently and that beneficial graft versus leukaemia effects are achieved by use of haploidentical
peripheral blood T cell-depleted stem cells. The clinician caring normally initiates such donations for the sick
potential recipient making appropriate arrangements with the National Blood Service cord blood bank.
Directed Donations In Low-Risk Families
Obviously as the name suggests families do this type of donation who are under less risk. In the absence of any
demonstration project, it is difficult to estimate the likelihood that an individual directed donation would be
used. This applies especially given that many of the projected usages of stem cells remain speculative and subject
to research yet to be done. One commercial storage provider estimates that likelihood of a child developing a disease
that could be treated by stem cells by the age of 18 years as around one in 300-400.
Although other family members might also use stored cells, this figure seems a gross overestimate of the probability
that a stored cord sample will ever be used. One bank in the USA has to date issued only two units out of 10 000 stored,
although this figure may rise with time. At present, it is not possible to conclude that storing cord blood for one's
child will not be of value, although the likelihood that it would ever be used is very low.
It is estimated that of approximately 200,000 placental blood units stored for the exclusive use of the baby from whose
birth the placental blood was obtained, at most, 74 units (and this is very likely a gross overestimate) might "possibly"
be used and 199,926 would be taken out of circulation for use by patients who require an allogeneic transplant.
|
|