One-year-old baby Daryl was diagnosed as having a rare and aggressive form of leukaemia and needed a bone marrow transplant to survive. Four possible donors were located on international registers, but each was found to be unsuitable because they carried an infectious virus.
Doctors at the National Children's Bone Marrow Transplant Centre at Our Lady's Hospital for Sick Children, Crumlin, decided to use a new, alternative treatment, based on the use of blood taken from the umbilical cord of newborns. The transplant, carried out earlier this year, was a success and Daryl has tested clear of his illness for some months.
He will need intensive supervision for the next year, says Dr Aengus O Marcaigh, who performed the transplant. The case shows the potential, however, of a technique so new that only 400 such transplants have been carried out so far worldwide. The first was in 1989 and that patient is still doing well.
Leukaemia is a cancer which causes a dangerous proliferation of white blood cells. These originate in the bone marrow where white and red blood cells and platelets which help blood clotting are produced. Leukaemia therefore causes a general and life-threatening disturbance to the body's entire blood-making system.
Treatment for some types of leukaemia call for the use of radiation or chemotherapy to wipe out all marrow, replace existing blood and then transplant marrow from a donor. When injected, these donor marrow cells migrate through the bloodstream to lodge in bone tissue, where they are capable of regenerating a completely new blood supply system.
There are risks however. When you wipe out the patient's blood production system you wipe out their immune system with it, making any infection a real danger. There is a period of some weeks - just over six in Daryl's case - before the transplant "takes" and new blood cells are produced. "It is a long and dangerous period because during this time the patient has no immune system."
Cross-infection from the donor is also possible. Up to half of the population carries the Cytomegalo virus, which could transfer with the marrow, Dr O Marcaigh says.
Very close tissue-matching is also necessary to help prevent rejection of the transplanted tissues, or conversely, the graft's rejection of the donor. "One of the main reasons we match so closely is because of graft versus host disease," says Dr O Marcaigh.
Marrow is a mix of these blood cell types but also the source of those which are known as stem cells. These cells are the most primitive blood precursor cells, O Marcaigh explained. They self-perpetuate in that as a stem cell divides to mature into a red or white cell it leaves behind a complete stem cell and so the process continues and fresh cells are always available.
The umbilical cord is also a rich source of stem cells, however, which led doctors to consider the cord as an alternative source of stem cells for transplantation. "It is an unlimited source of stem cells because cords are being thrown away every day."
The use of cord blood seems to hold other advantages, however. "It is believed there is a reduced incidence of graft versus host rejection," Dr O Marcaigh says. It also seems to be easier to achieve a match when comparing with cord blood donors. The blood can also be frozen and held in a cord bank until needed if a match is achieved, or a portion from a single cord can be retained in case the patient relapses and needs a new transplant.
Tissue typing here is done by the Blood Transfusion Service Board at Pelican House. Ireland hasn't got a cord bank but Dr O Marcaigh believes we should have one. The Transplant Unit at Crumlin is, however, a member of a European network of such centres and can search for marrow and cord blood matches over this system. There are five cord banks on the Continent and banks in Britain and the US.
Cord cells are coming into use "if a suitable bone marrow donor isn't available", Dr O Marcaigh says. Doctors have been slow to use this source of stem cells if marrow is available. Dr O Marcaigh puts this down to "fear of the unknown".
Doctors working in the area are more familiar with marrow transplantation. There are also other problems, for example, the amount of stem cells from a single cord might not be sufficient to treat an adult case and cells from two cords can not be mixed.
The Children's Research Centre in Crumlin is involved in studies of the cellular characteristics of cord stem cells and published a paper in the US medical journal, Blood. The existence of the centre means that both basic research and clinical studies can proceed on stem cell transplantation, O Marcaigh said.
There are ethical issues that need discussion, Dr O Marcaigh says. Marrow is always taken with the full consent of the donor. While parents might agree to donate a cord for leukaemia treatment, the baby which "owns" the blood can't grant this permission. There is also the possible transfer of either diseases or even future blood-related genetic disorders.
Even so, the treatment holds much promise. The success rate is at least equivalent to marrow transplantation, even though it has so far tended to be used as a last resort in very difficult cases.