In a recent study, scientists found that a high-fat diet may impair the immune system and accelerateIn previous research, obesity increased the risk of over 12 different cancers; it also led to a worse diagnosis and survival rate. This research also helped scientists learn how obesity increases tumor growth; underlying causes include metabolic changes and chronic inflammation. In the , researchers found that obesity actually gives cancer cells the upper hand over immune cells when fighting for fuel.
Researchers at the Harvard Medical School used mice to analyze how cancer cells would react to a high-fat diet. The study published in the journal Cell reveals new information about obesity and cancer. This new information could change the future of immunotherapy.
The team found that a high-fat diet reduced the amount and antitumor activity of CD8+T cells, an important immune cell, within tumors. Scientists discovered that this happens because cancer cells alter their metabolism in response to higher fat accessibility. Thus, they have a better capability of eating up fat molecules, which starves the T cells of fuel, increasing.
“Putting the same tumor in obese and nonobese settings reveals that cancer cells rewire their metabolism in response to a high-fat diet,” said Marcia Haigis, professor of cell biology in the Blavatnik Institute at HMS and co-senior author of the study. “This finding suggests that a therapy that would potentially work in one setting might not be as effective in another, which needs to be better understood given the obesity epidemic in our society.”
Implications for this research on the future of immunotherapy
“Cancer immunotherapies are making an enormous impact on patients’ lives, but they do not benefit everyone,” said co-senior author Arlene Sharpe, the HMS George Fabyan Professor of Comparative Pathology and chair the Department of Immunology in the Blavatnik Institute.
“We now know there is a metabolic tug-of-war between T cells and tumor cells that changes with obesity,” Sharpe said. “Our study provides a roadmap to explore this interplay, which can help us to start thinking about cancer immunotherapies and combination therapies in new ways.”
For the study, the team analyzed how obesity affected various types of cancer in mice such as breast, melanoma, and colorectal. Researchers fed the mice either normal or high-fat diets; mice eating higher fat gained weight and experienced other signs of obesity. Then, they studied the various cell types and molecules within and around the tumors, known as the tumor microenvironment.
How cancer cells reacted to higher levels of fat
Unsurprisingly, the team discovered that tumor growth occurred more quickly in mice on high-fat diets. However, they found this only happened for immunogenic cancers, which have large amounts of immune cells. The immune system also recognizes them more easily, making them more likely to respond.
The study revealed that obesity-related tumor growth depended solely on CD8+ T cell activity; these immune cells target and kill cancer cells. Diet did not impact tumor growth rate if researchers removed CD8+ T cells from the mice. Interestingly, they found that high-fat diets caused the immune cells to decrease in the tumor microenvironment. However, the immune cells didn’t change anywhere else in the body.
What the team discovered
The cells left in the tumor showed less strength, dividing more slowly and becoming lethargic. However, when the researchers grew these cells in a lab, they showed normal activity levels. To the team, this implied that something in the tumor caused cells to malfunction.
Furthermore, the team found that in obese mice, the microenvironment had no major free fatty acids, a key fuel for cells. The rest of the body still contained fatty acids, as you would expect in obesity.