Immune memory attributed to stem cells

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A new study provides the first evidence that certain cells responsible for the immune system's memory are essentially adult stem cells. The scientists behind the discovery are excited about its promising implications for the future of immune-based therapies for infections and cancers.

Illustration of white blood cells

“In principle, one individual T cell can be enough to transfer effective and long-lasting protective immunity for a defined pathogen or tumour antigen to a patient,” says leading scientist Dirk Busch from the Technische Universität München in a press release. “Isn’t that astonishing?”

The immune system’s job is to recognise and combat disease threats, for instance viruses, and to remember the culprits and ‘stop them at the door’ if they ever return. That’s why – when the body is exposed to a virus through infection or vaccination – the immune system can prevent the disease from recurring. But exactly how this immune memory works has been somewhat of a mystery to scientists.

Over the past decade, a growing body of research has supported the hypothesis that the immune memory arises from a pool of immune cells with stem-cell-like characteristics. But until recently, conclusive evidence has been lacking, largely because experiments could only be done on populations of cells.

By combining their technological and clinical expertise, researchers in Germany and the USA were finally able to map the fates of individual T cells – a type of white blood cell – and their descendants over several cell generations. The latest results provide the first real evidence for the stem cell hypothesis of immune memory, as reported in the journal Immunity.

“Evidence that defies conventional wisdom”

Separating and tracking cells from different populations through a series of experiments using laboratory mice, the researchers demonstrated that long-term immune memory depends on the ‘stemness’ of a defined subpopulation of T cells.

The crucial feature or ‘stemness’ of these so-called central memory T cells involves their ‘multipotency’. That is, their ability to spawn a variety of daughter cells tailored to fight – and remember – particular foreign invaders or pathogens. The ‘stemness’ also refers to the cells’ ability to renew themselves indefinitely.

What’s unique about the central memory T cells is that they can renew themselves into specialised, secondary memory T cells – which lie in wait to counter a second attack by a particular pathogen – while at the same time they remain multipotent.

“Once again science throws up evidence that defies the conventional wisdom,” says Wayne Murrell, a stem cell expert from Oslo University Hospital, who was not involved in the study.

Implications for future immune-based therapies

An implication of this new evidence is that central memory T cells might give an edge to future immune-based therapies for infections, cancers and other conditions in patients with a compromised immune system. A small number of individual T cells could be harvested from the blood of a patient, engineered or ‘trained’ in the laboratory to become highly specialised ‘fighter’ cells, and then transferred back into the patient.

“These results are extremely exciting and come at a time when immunotherapy is moving into the mainstream as a treatment for cancer and other diseases,” says Stanley Riddell from the Fred Hutchinson Cancer Research Center and the University of Washington, who co-led the study with Busch.

“The results provide strong experimental support for the concept that the efficacy and durability of T cell immunotherapy for infections and cancer may be improved by utilising specific T cell subsets.”

by Lillian Sando



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