Stem cell transplants are normally only recommended if:

• the recipient of the transplant is in relatively good health, despite their associated condition (which is why stem cell transplants are often done when cancer is in remission)
• stem cells are available from a brother or sister with the same tissue type, which reduces the chances of the transplant being rejected or graft versus host disease
• the associated condition is not responding to other forms of treatment or it is felt that there is a high risk of the condition returning without a transplant
• it is felt that the benefits of a transplant outweigh the risks

The importance of tissue type

All human tissue carries a special genetic 'marker' or code, known as a human leukocyte antigen (HLA). Ideally, you should receive your transplant from somebody with an identical or very similar HLA tissue type.

This is because if the transplanted tissue has a different HLA type, your immune system might regard it as a foreign object and reject the transplant.

Alternatively, the cells from the transplanted tissue may regard the rest of your body as a foreign object and begin attacking it, leading to graft versus host disease.

Your HLA is inherited from your parents. If you have a brother or a sister who is willing to be a donor, they will need to be tested to see if their HLA type is the same. There is a one-in-four chance that each sibling will be an exact match.

British Bone Marrow Registry

If none of your siblings are suitable donors or if you are an only child, a search of the British Bone Marrow Registry will be conducted. The British Bone Marrow Registry contains a list of all the people willing to donate stem cells, along with their HLA type.

You may have to wait several years before a suitable donor can be found. However, in some rare cases, waiting without treatment may be considered too dangerous, so a partially matched donor may be used instead. This will increase the risks of complications, but your treatment team may recommend it if they feel that the benefits outweigh the risks.