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, BBC reported.
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.