Stem cell transplants

Stem cell transplantation replaces the damaged stem cells in the patient’s bone marrow with healthy new stem cells to enable the bone marrow to resume its vital functions.

What is a stem cell transplant?

When a child’s bone marrow has been badly damaged - either by the leukaemia or by the treatment used to eradicate the leukaemia – the bone marrow may need to be ‘kick-started’ into producing new blood cells. This is achieved via stem cell transplantation.

Stem cell transplantation is the term now used in place of bone marrow transplantation. In a bone marrow transplant the stem cells are harvested directly from a donor’s bone marrow.

Today the stem cells are mostly harvested from the donor’s circulating blood, a far less invasive procedure. A special type of stem cell transplant is a cord blood stem cell transplant. This uses stem cells harvested from the umbilical cord at the time of birth.

A stem cell transplant involves the use of very high-dose chemotherapy (and possibly whole body radiotherapy) to destroy the child’s bone marrow and immune system. This is called myeloablation. The destroyed marrow must then be replaced with stem cells from a donor or sometimes with stem cells harvested from the patient before treatment.

When is stem cell transplant used?

Stem cell transplantation is not generally used in the treatment of children with good-risk acute lymphoblastic leukaemia (ALL) or acute myeloid leukaemia (AML).

A small proportion of children with high-risk disease may be considered for a possible stem cell transplant whilst in first remission but, other than this, stem cell transplantation is restricted to the treatment of children who have experienced a relapse early in their treatment or who have suffered more than one relapse.

In contrast stem cell transplantation offers the only possibility of a cure for children with chronic myeloid leukaemia (CML).

What are the risks?

Stem cell transplant is an inherently risky procedure. The child’s own bone marrow must first be completely destroyed and this is achieved via high dose chemo- and/or radiotherapy. This effectively destroys the child’s immune system and at this stage even the slightest infection could be devastating.

The transplant itself can cause all sorts of complications including the risk of graft rejection and graft versus host disease in which the grafted stem cells start attacking the patient’s other cells.

Where do the stem cells come from?

A stem cell transplant may be either allogeneic (from a donor) or autologous (the child’s own stem cells).

Allogeneic transplants contain functioning cells from the donor’s immune system. These may recognise the recipient’s cells as foreign and attack them. This is called graft versus host disease (GvHD).

To minimise the risk of GvHD and the risk of rejection of the graft by the patient’s own immune system, doctors must find a matched donor. The preferred donor, where available, is a sibling with a closely matched tissue type. If not available, an unrelated donor from the national register may be considered.

The risks of rejection and of GvHD are both greater with an unrelated donor. For many children with acute leukaemia it will not be possible to find a matched unrelated donor in time. This is a particular problem for children from ethnic minorities as tissue types differ between ethnic populations; most volunteer donors are Caucasian.

Autologous transplants are safer in terms of avoiding graft failure or GvHD but allogeneic transplants carry a higher chance of eliminating the leukaemia because of a reaction called graft versus leukaemia (GvL) in which the donor’s stem cells attack any remaining leukaemia cells.

For more information, visit the National Bone Marrow Register (new window will open).