An exciting new study, led by a team of Australian researchers, has uncovered how the immune system can keep cancer cells in a dormant state. It's hoped the breakthrough insight will offer new pathways for research into immunotherapy techniques that can essentially stop a tumor's growth for an indefinite period of time.

While much modern cancer research is investigating ways to destroy these deadly cells, a new study has examined a potentially different approach to battling the nasty disease. Scientists have long understood that, in some instances, malignant cancer cells can sit in stasis for prolonged periods of time without spreading or causing disease-related symptoms. This process is called the cancer-immune equilibrium, and while it is known to be mediated by the body's immune system, we do not know exactly how it works.

"What we haven't understood are the mechanisms responsible for keeping tumors under control and in this state of dormancy," says Jason Waithman, one of the authors of the new study. "All we knew was that this 'black box' of cancer control existed – and that if we could understand this process better, we could potentially learn how to exploit it in more patients, thus saving more lives."

The new research homed in on a type of immune cell called a tissue-resident memory (TRM) T cell. TRM cells were only identified around 20 years ago, and they presented as functionally different from other types of immune cells. In order to study the effect of TRM cells on cancer-immune equilibrium, a mouse melanoma model was developed alongside a new imaging technique allowing scientists to observe the movement of these immune cells in real-time.

"Using a special microscope, we could see individual melanoma cells sitting in the skin of the mouse, and could watch the T cells move through the skin, find the melanoma cells and control the growth of those cells," explains Simone Park, one of the researchers who developed the novel imaging technique for the study.

TRM cells (in light green) surrounding and keeping the melanoma cells (in red) in check Peter Doherty Institute

The next step was to observe what happens to the melanoma cells when the TRM cells were depleted. The results were notable, with tumor outgrowth triggered after the TRM cells were removed. The researchers concluded TRM cells to play a fundamental role in suppressing cancer progression and maintaining cancer–immune equilibrium.

Further work is necessary to better understand exactly how these TRM cells are keeping cancer cells dormant, but the researchers are confident these results are transferable to humans. Prior research has found that cancer patients with increased levels of TRM cells have demonstrated better general treatment outcomes.

"The next step in this research is to delve into the mechanism further so we can make this process happen more often," says Waithman. "We hope this research will lead to novel ways for us to maintain cancer in a dormant state and, effectively, cure people."

The new study was published in the journal Nature.

Sources: Peter Doherty Institute, Telethon Kids Institute