Gentler bone marrow transplants treat adults with sickle cell

Adults with the inherited blood disorder 'sickle cell anaemia' may be treated using blood stem cells transplanted from a healthy tissue-matched donor, scientists based at the US National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, have shown. The treatment successfully boosted levels of normal red blood cells in nine out of 10 of the adults who have so far been given the experimental therapy, according to a study published in the New England Journal of Medicine last week.

Normally red blood cells are doughnut-shaped, but in people with sickle cell anaemia they become banana or 'sickle' shaped when they shed their oxygen load, making them prone to getting stuck in the small blood vessels. This triggers bouts of extreme pain and can potentially cause strokes and permanent damage to many different organs.

Red blood cells originate from blood stem cells found in the bone marrow, which is why transplanting bone marrow from a matched donor can potentially provide a cure for patients with sickle cell anaemia. Standard bone marrow transplants involve first destroying all of the patient's own bone marrow using a dose of chemotherapy, radiation, or a combination of the two. This aspect of the treatment is dangerous for adults, but the procedure has been successfully used to cure some 200 children with sickle cell disease.

In an attempt to develop a treatment which would be safe for adults, the researchers used a less aggressive form of radiation to treat ten patients aged 16-45 with sickle cell anaemia, before giving them a bone marrow from a tissue-matched donor. Because the treatment only partially killed off their own blood stem cells, the patients produced a mixture of both normal and defective red blood cells, but the normal red blood cells were able to compensate for the defective ones because they live longer, said the researchers. 'Because sickle red blood cells only live about six or seven days and normal red blood cells live 120 days, if you can get a little bit of the donor cells in there, the donor cells take over,' John Tisdale, one of the lead authors of the study, told Reuters.

'The simplicity, low toxicity, and high efficacy of this approach make it feasible for use at most transplantation centers,' Matthew Hsieh, the lead author, and colleagues concluded. However, the need for a period of intensive care in a highly sterile environment subsequent to the treatment will make it unsuitable for developing countries, where the condition tends to be most prevalent, noted New Scientist. It is thought that the increased prevalence seen in warmer climates may be because carrying the condition confers resistance to malaria.

Following the treatment, patients face a lifetime of taking powerful drugs in order to prevent their own immune system from attacking the donor blood stem cells. It is not yet clear whether it may be possible to wean the patients off of these drugs, which weaken the immune system making them prone to illness and infection.