How do cancer cells prevent immune attack against them?

United States – Scientists at the Southwestern Medical Center in Texas have shown that cancer cells release acid in a much higher concentration than previously thought, forming an “acid wall” that prevents immune cells from attacking tumors.

Scientists have known for nearly a century that tumors are slightly more acidic (their pH, that is, a measure of acidity, is less than 7) than most healthy tissues in the body.

“The new study revealed a previously unknown acidity that circulates around cancer cells,” said study leader Jinming Gao, a professor at the Harold C. Simmons Comprehensive Cancer Center.

Several years ago, Gao and his colleagues designed a group of nanoparticles that fluoresce at specific pH levels. They found that a substance called pegcytacyanin, which glows at a pH of 5.3, fluoresces more brightly in the presence of tumors.

In 2023, pegcitacyanin received a revolutionary treatment designation by the US Food and Drug Administration, in a move that will accelerate the development of promising drugs.

Now, these nanoparticles have passed phase II clinical trials in patients as a tool for image-guided cancer surgery.

However, it was not clear why pegcitacyanin fluoresced, Gao said, as the acidity of the tumor was thought to be too mild to trigger its activation.

Later, the research team found that this acidity results from the secretion of lactic acid, which cancer cells produce as waste following digesting glucose, or blood sugar.

When the team conducted experiments on tumor tissue, it was found that cancer cells pump acid, especially away from neighboring cancer cells, outside the cell, forming an area with higher acidity at the edge of the tumor.

Samples of human tumors showed that this acidic wall was practically devoid of CD8+ T immune cells within the tumors, which are known to fight cancer, indicating that extreme acidity may thwart immune cell attack without harming cancer cells.

The findings might pave the way for new cancer treatment methods that alter the acidic environment surrounding tumors.

Source: Medical Express