Without treatment, affected children have to live in sterile conditions
Children seriously ill because their immune systems have genetic flaws could have their lives saved by a safer form of bone marrow transplant, doctors say.
The London team says the treatment for so-called "bubble" children - who have to live in sterile conditions - almost eliminates the need for chemotherapy.
The Great Ormond Street doctors used antibodies to clear patient bone marrow and make room for donor stem cells.
They report in The Lancet the method cuts both rejection and side-effects.
Chemotherapy has both short- and long-term consequences, ranging from hair loss to damage to organs such as the liver and lungs.
But it has been used as standard to kill the patient's own bone marrow and make room for stem cells.
This treatment has saved the lives of many children with serious genetic defects in their immune systems - primary immunodeficiencies or PID - that render even the most minor infections life-threatening.
Fifty such transplants are carried out each year.
But some children are deemed too sick to withstand the high doses of drugs needed to wipe out the bone marrow.
Gentler chemotherapy has been developed, but is still too much for certain groups of patients, such as babies.
The new technique, developed by doctors from Great Ormond Street Hospital (GOSH) and the UCL Institute of Child Health, uses an antibody that targets a molecule specific to blood and bone cells - meaning other tissues are left undamaged.
The team, led by Dr Persis Amrolia, reported that 13 of the 16 patients treated in the study had survived and been cured of their underlying disease.
They recovered twice as quickly as those given standard treatment, although there were still some complications.
"Because this approach was experimental, we only used it on the sickest children, who we felt could not tolerate standard transplant chemotherapy.
"Given how sick these children were before transplant, the results are remarkable," said Dr Amrolia.
"What's really encouraging is that pretty much all the children who survived now have a really good quality of life.
"There's still a lot to do and the challenge now is to develop similar targeted approaches for children with other genetic diseases and leukaemia."
Chris Hughan, chief executive of The Primary Immunodeficiency Association, said: "We welcome this important study as it heralds a potential breakthrough in the treatment of paediatric PID patients who need a bone marrow transplant (BMT) but have significant chronic infection or organ damage at the time.
The new treatment "provides a viable alternative conditioning treatment for children unable to tolerate intensive transplant chemotherapy".
"We look forward to supporting this new BMT programme at GOSH and making our members aware of this exciting new treatment development."