Researchers at the University of California San Diego School of Medicine and their colleagues have developed the first comprehensive map of the dramatic changes that take place in the blood system over the course of the human lifetime.

The team quantified the gene expression of more than 58,000 individual hematopoietic (blood) stem cells at seven stages, from early fetal development to old age. They documented consistent changes in the types of blood cells that are produced in response to the functional demands of each life stage:

The researchers also found that changes in blood cell types across the lifetime can have important implications for blood cancers. They classified acute myeloid leukaemia cells by their resemblance to gene expression of stem cells at different life stages, discovering that the normal stem cell age most reflective of leukaemia cells in patients with acute myeloid leukaemia can vary widely, regardless of a patient's age.

What's more, patients whose leukaemia cells more closely reflected young blood cell production had a much worse prognosis than those whose leukaemia cells more closely reflected old blood cell production. The researchers believe the cancer cells may reprogram themselves to have fetal attributes that make them more aggressive. Further investigation identified seven transcription factor genes that strongly influence whether leukaemia cells look like old or young blood cells.

Future studies are planned to test whether the disease takes advantage of the highly proliferative capacity of young blood cells to make patients' leukaemia more deadly than older, less vigorous blood cells. They are also hopeful that leukaemia cells could eventually be reprogrammed.

"If we can develop drugs that target key factors that drive young blood cell production, maybe the leukaemia will just reflect old blood cell production and be easier to treat," said Hojun Li, M.D., PhD, an assistant professor of paediatrics at UC San Diego School of Medicine, UC San Diego Moores Cancer Center member and an attending physician at Rady Children's Hospital-San Diego, who led the study along with R. Grant Rowe, M.D., Ph.D., an assistant professor of paediatrics at Boston Children's Hospital, Harvard Medical School.