An allogeneic haemopoietic stem cell (HPC) transplant involves matching a patient’s tissue type, specifically their human leukocyte antigen (HLA) tissue type, with that of a related or unrelated donor. HLA proteins are found on all cells of our body and are the main way the immune system tells the difference between our own cells and foreign cells.

The closer the HLA match between a donor and recipient, the greater the chance a transplant will be successful.

If the HLA match is not close enough, the donor’s immune system, which accompanies the donated stem cells, recognises the HLA mismatch, and will attack the recipient’s tissues. This process is known as graft versus host disease (GVHD).

Approximately 70% of people with a haematological malignancy or bone marrow failure syndrome who need an allogeneic transplant have a HLA-identical sibling or unrelated donor available.

For patients who need a stem cell transplant but do not have a HLA-matched related or unrelated donor, recent medical advances have made possible the use of a partially matched or haploidentical related donor. A haploidentical related donor is usually a 50% match to the recipient and may be the recipient’s parent, sibling or child.

The advantage of having a haploidentical transplant is that it increases the chance of finding a donor as almost everyone has at least one haploidentical relative. Relatives can usually be asked to donate stem cells much more quickly than unrelated volunteer donors, particularly when the volunteer donors live in other countries, thereby allowing transplants to be done in a more timely way.

With improvements in medical treatment, complications of a haploidentical transplant, such as GVHD, rejection of the graft and slow recovery of the immune system appear not to be increased compared to transplants using HLA matched related or unrelated donors.

Since this is a relatively new approach to stem cell transplantation, a haploidentical transplant is a treatment option that is not offered in all treatment centres.