Scientists have identified and tracked rare immune system cells that could some day be programmed to keep cancer at bay for life.

A new study raises the prospect of vaccine-like treatments that protect against cancer for life.

Scientists have identified and tracked rare immune system cells that could be programmed to keep cancer at bay over a period of many years.

The "stem memory" T-cells would keep patrolling the body looking out for enemy tumour cells. When any are encountered, they would be recognised and attacked.

Lead researcher Professor Chiara Bonini, from the University of Milan in Italy, said: "T-cells are a living drug, and in particular they have the potential to persist in our body for our whole lives.

"Some of these memory T-cells will persist through the entire life of the organism ... Imagine translating this to cancer immunotherapy, to have memory T-cells that remember the cancer and are ready for it when it comes back."

For such an approach to work, the memory T-cells would have to be primed by genetic modification to attack the target cancer.

But the first step is to single out those cells with the ability to persist for a long time.

Bonini's team studied 10 cancer patients who underwent bone marrow transplants and were infused with T-cells that were tagged so they could be tracked.

Small numbers of the cells were still found to be circulating in the patients' blood streams after 14 years.

The research was described at the annual meeting of the American Association for the Advancement of Science taking place in Washington DC.

Commenting on the study, British immunologist Professor Daniel Davis, from the University of Manchester, said: "These T-cells, the stem memory T-cells first identified in 2011, have stem cell-like properties and are thought to be important for long-lived immune responses.

"The implication is that infusing genetically modified versions of these particular T-cells ... could provide a long-lasting immune response against a person's cancer.

"Immunotherapy has great potential to revolutionise cancer treatment and this study shows which type of T-cells might be especially useful to manipulate for long-lasting protection.