Why do cases of cancer become more common as we get older? Scientists interested in explaining the so-called “Silver Tsunami” phenomenon look to immune cells for an answer. From Monash University, researchers show how age-related inflammation, or “inflamm-aging,” could be to blame for increased incidence of cancer as people get older.
Life expectancy in the United States and worldwide is significantly higher than it was half a century ago. Experts estimate that by 2050, more than 20 percent of the population will be older than 65. This means that over 20 percent of the population will be at an increased risk of cancer, all because weak immune cells grow in number and strong immune cells fade away.
Specifically, Monash University scientists describe “virtual memory T cells” and “true naïve T cells.” The former are prone to losing their ability to become activated, leaving them essentially useless in fighting pathogens and preventing cancer. Researchers found that these cells make up just five percent of T cells in young animal models and younger humans, but they increase significantly with old age.
True naïve T cells, unlike virtual memory T cells, keep their ability to become activated and participate in an immune response, but this population of cells decreases significantly as people get older. Researchers found that these cells go from 90 percent of the T cell population to just 30 percent. So as people age, they lose the cells that they need to fight off infection and prevent cancer, and they gain the cells too weak to put up a fight.
Accumulation of the virtual memory T cell population paired with the progressive loss of true naïve T cells is the perfect storm to explain the increased incidence of cancer associated with older age. Additionally, these changes prevent older people from mounting an effective immune response to vaccines, and reduce the chances of success with cancer immunotherapy.
"In cancer immunotherapy, a patient's own T cells are stimulated to kill cancer cells and it has been hugely successful for certain forms of cancer,” explained Nicole La Gruta. “Unfortunately, older patients or people over 65 years of age respond less well than younger ones.”
A potential solution is to selectively target each population of T cells to reduce the incidence of cancer in older people. For example, reduce the amount of virtual memory T cells and/or increase the amount of true naïve T cells. This approach could improve treatment and prevention of cancer.
“We may be able to tailor cancer immunotherapy specifically for the needs of an older patient's immune system- this is where medicine must head to meet the needs of our ageing society,” La Gruta explained.
Norman E. Sharpless, MD, wrote about cancer and aging in a January Cancer Currents Blog: “It’s clear that we need to better understand how the biological underpinnings of aging affect the onset and trajectory of cancer to address this looming public health challenge.”
The present study was published in the journal Cell Reports.