Two unrelated cord blood units can be used to treat adults with leukaemia.
 A 19-year-old girl has successfully battled leukaemia following a stem cell transplant using umbilical cord blood from two unrelated individuals. Polytechnic student Candy Yeow underwent a novel procedure known as double cord blood transplant after a match could not be found for a bone marrow transplant.
Dr Mickey Koh, Singapore General Hospital’s consultant haematologist and Deputy Director for the Centre for Transfusion Medicine at Health Sciences Authority, said a double cord blood transplant is an option for Singaporean adult patients suffering from leukaemia. Since families are small, many patients may have only one sibling or none at all. Therefore a patient may not be able to get a suitable match.
Dr Koh explained, “Bone marrow transplants work better if the donor is a sibling. There’s a 25 per cent chance that their cells make a perfect match with the patient and this minimises side effects. If the sibling is unsuitable, we can search bone marrow registries worldwide for unrelated donors. But the Asian registry is under-represented and finding a match is relatively more difficult. Moreover, this process may also take considerable time."
Novel double cord blood transfusion
The alternative to a bone marrow transplant is cord blood transplant. Pioneered in France in 1998, the procedure was then confined to a single cord blood unit and initially used on children aged 12 and below. Cord blood is collected at childbirth and donated to public cord banks or stored by parents with private cord blood companies. Donated cord blood can be obtained from an international network of healthcare facilities including the Singapore Cord Blood Bank at KK Women’s and Children’s Hospital.
As a single unit of cord blood may not contain sufficient stem cells needed for an adult, a novel procedure would be to combine two cord blood units to increase the stem cell dose. However, this initially raised the issue on whether the two separate units would react with one another or against the patient.
Dr Koh said, “A double cord blood unit transplant is an innovative concept which enables us to use cord blood in adults. The best thing about cord blood transplants is that differences in blood group between the recipient and donors do not matter as much. The two units of cord blood can also be of different blood groups.”
Recipient rid of diseased cells
Before a cord blood transplant is carried out, a recipient undergoes chemotherapy and radiotherapy to clear his bone marrow of leukaemic cells. The donated two units of cord blood are then transfused into the recipient.
“The stem cells from the donors’ blood interestingly then migrate to the recipient’s ‘empty’ bone marrow. In time, the cord blood units ‘engraft’ or grow in the recipient’s bone marrow and produce new platelets, white and red blood cells. It is very much like waiting for a seed to germinate.”
Blood disease specialists like Dr Koh are currently doing research into the post-transplantation process.
“Biologically speaking, there were three ‘people’ flowing in one body after the transfusion – Candy’s cells and the two different cord blood units. But invariably, we always see one of the two cord units taking over, sometimes as soon as six weeks so that eventually, one cord predominates while the other fades away. Candy’s blood type has also changed from her original to that of the new cord unit. Research is still undergoing to understand more of this process and to predict which of the two units will eventually engraft”.
Possible new treatment option
SGH’s Department of Haematology runs the largest adult stem cell programme in Singapore. Since last year, doctors have performed three cases of double cord transplants. Candy Yeow is the longest survivor with the best results as she is in remission and does not require any medication.
While double cord blood transplant is still a relatively new procedure, Dr Koh and the rest of the transplant team are also embarking on a parent-child bone marrow transplant programme in a bid to increase treatment options. “This does present with additional new problems and risks as the match in such instances is usually only about 50 per cent. The risks are therefore much higher. However, the parent-child bone marrow transplant is a possibility as the genetic match may reach 50 per cent.”
Ref: Y07
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