The tools used to fortify the body against infection are also one of the causes of the most common form of childhood leukaemia, say researchers.
The machinery used to produce millions of antibodies in the immune system can misfire, making cells more likely to become cancerous.
The UK research group hopes to understand why some children do not respond to treatment.
The findings were published in the journal Nature Genetics.
Patients with leukaemia produce abnormal blood cells, and acute lymphoblastic leukaemia is the