New insight on how some tumors may escape attack by the immune system could lead to earlier diagnosis of breast, lung, colon and other cancers, as well as new ways to treat the malignancies.
Dr Thomas Spies and colleagues at the Fred Hutchinson Cancer Research Centre in Seattle have found that many of these tumours produce high levels of a protein called MIC. Their laboratory experiments using simple blood tests have shown that high levels of MIC could indicate the presence, or reoccurrence of cancer.
However, the new findings are preliminary and much more research is needed to confirm them, Spies said.
The investigation into how tumours can avoid being wiped out by immune cells found that MIC can bind to receptors on important cancer-fighting T cells and prevent them from targeting and destroying cancer.
Normally, low levels of MIC which are produced by cells stressed by bacteria or viruses would stimulate an attack, but the high levels of tumor-derived MIC appear to inhibit the immune system’s ability to destroy cancer cells.
‘This protein is essentially silencing those T cells,’ Spies said. The findings run contrary to expectation, because it was assumed that MIC on the surface of tumor cells would tell the immune system that those cells are foreign and should be destroyed. But the cancer appears to be one step ahead of the game. Spies said, ‘The tumor seems to be exploiting the system.’
The experiments involved tumor cells and T cells taken from 39 patients with cancers of the breast, lung, colon, ovaries or skin melanoma.
If the findings are supported by additional research, they might lay the foundation for a new cancer drug that would work by inhibiting the release of MIC or somehow blocking its effect on immune cells, Spies said.
‘The problem with tumors is that they counter the immune system on so many levels,’ Spies said. ‘This is just one instance.’
In an accompanying editorial, Dr. Wayne Yokoyama of Washington University in St. Louis, Missouri, said the findings provide a ‘new hint as to how to catch the tumor cells that have long eluded both the immune system and immunologists.’
This report has been published in the October 17th issue of Nature.
(Source: Reuters Health and ASCO)