Health Update

Umbilical Cord Blood Stem Cells

Blood obtained from the umbilical cord at birth is rich in stem cells that can generate red blood cells and cells of the immune system. By storing these cord blood stem cells at birth, problems associated with immune rejection of foreign cells, if required later in life, will not occur. These stored cord blood cells can also be used to treat a range of blood disorders and immune system conditions such as leukaemia, anaemia and autoimmune diseases in the donor, compatible siblings or other tissue matched individuals. After transplantation, the haematopoietic stem cells can repopulate the bone marrow of the patient, providing a source of blood cells. It currently constitutes an increasingly used alternative to bone marrow transplantation.

In order to have cord blood cells available for transplantation a number of banks were created worldwide. These banks are run by either hospitals or non-profit organizations that collect the samples from donors and provide them when the cells are needed for transplantation. Recently, private firms have been offering to future parents the conservation of blood from the umbilical cord of newborn children for one’s own use or for the use of close relatives. Different types of cord blood banks can be distinguished : private or public, for-profit or non-profit.

Characteristics of cord blood

Umbilical cord blood was found to be rich not only in normal blood cells but also in haematopoietic stem cells. These stem cells are found only in insignificant numbers in normal adult peripheral blood. After transplantation, the haematopoietic stem cells can repopulate the bone marrow of the patient, providing a source of blood cells.

An important characteristic of cord blood cells is their immunological immaturity. Therefore, haematopoietic stem cells from cord blood are less likely to induce immunological reactions when transplanted than haematopoietic stem cells from bone marrow. Furthermore, in laboratory experiments it has been shown that cord blood stem cells can differentiate into a number of different cell types, which could give rise to future potential new therapeutic uses.

Advantages of cord blood cells compared to bone marrow

The collection of cord blood units is easy and non-invasive for the donor and therefore the number of potential donors is higher than for bone marrow.

Cord blood units are stored in advance and are therefore rapidly available when needed while bone marrow has to be collected from the donor just before transplantation and there is always a risk of last minute consent refusal.

The HLA type does not need to be a perfect match in case of allogeneic cord blood cell transplantation because these cells are less likely to induce immunological reactions than bone marrow cells.

Current uses of cord blood

• Cord blood can be an alternative to bone marrow transplantation in the treatment of patients with blood and immune disorders requiring a source of haematopoietic stem cells
• Cord blood is currently being used for the treatment of leukaemia, lymphomas, aplastic anaemia and hereditary disorders of the blood.
• It is also used as a source of stem cells for current research.

Allogeneic transplantation

In all the current uses of cord blood indicated above, the transplantations are allogeneic and the cells used are obtained from donation. The use of autologous graft would be inappropriate in case of a genetic disease as the cells of the patient would carry the same genetic defect, or in case of leukaemia, as the cells of the patient could also become malignant. In the case of an allogeneic transplantation there is always a risk that the body rejects the transplanted tissue. Therefore, HLA-typing is essential to have the best possible HLA matching between donor and recipient in order to minimize rejection effects and optimize the chances of therapeutic success.

The residual HLA differences between donor and recipient may induce a limited immunological reaction. In the treatment of leukaemia, this “graft against host reaction” is beneficial and contributes to destruction of the leukaemia cells.

Limitations of the use of cord blood cells

In order to be useful for transplantation samples have to contain a sufficient number of cells according to the patient’s weight and therefore mainly young patients of small weight can benefit from this kind of transplantation. Nevertheless, recent experience shows that it is possible to combine several samples in order also to treat adults9. Further, research on methods of cell expansion is actively being pursued in order to overcome the problem of the limited number of cells contained in cord blood samples, which would allow a more systematic treatment of adults. Until now between 2 500 and 3 000 transplantations from cord cells have been carried out worldwide10. Studies show higher survival rates for children than for adults.

Source: http://ec.europa.eu/european_group_ethics/docs/avis19_de.pdf