By carrying a ‘don’t eat me’ sign, cancer cells have frequently avoided being chewed up by immune cells. But a new study shows that cancer cells actually also carry an ‘eat me’ sign on them.
And the trick will be to figure out why they would do that and use that against them.
Don’t eat me = CD47
The 'don’t eat me’ sign is also known as CD47. And about a year ago, a team of Stanford scientists found that drugs that block CD47 can eliminate tumors in mice with leukemia and lymphoma.
Many normal cells in the body also have CD47, but surprisingly these cells don’t get taken out by the CD47-blocking drug.
They thought that there had to be an 'eat me' signal that the cancer cells were also carrying in addition to CD47, says co-author Ravindra Majeti.
Eat me = calreticulin (CRT)
Something like that happens all the time. When normal body cells become infected, damaged or otherwise unuseful, they start carrying on them a protein called calreticulin (CRT) that tells immune cells to engulf and digest – or phagocytose – them.
So that same Stanford team, this time led by Chao, discovered that CRT is also found on a variety of cancers, including several leukemias, non-Hodgkin's lymphoma and bladder, brain and ovarian cancers.
They showed that immune cells decide whether or not to eat cancer cells depending on both ‘eat me’ and ‘don’t eat me’ signals. CRT on tumors causes immune cells to go straight for the cancer cells, preoccupying themselves with those instead of eating normal cells.
But surprisingly… in patients, the more aggressive the tumor, the more CRT (eat me) they have, basically announcing bon appetite to the immune cells.
But uh, why would cancer cells carry this suicide protein in the first place, and why would the worst cancers make more of it? That remains to be seen.
"We want to know how it contributes to the disease process and what is happening in the cell that causes the protein to move to the cell surface," Majeti says. "Any of these mechanisms offer potential new ways to treat the disease by interfering with those processes."
The study was published in Science Translational Medicine earlier today.
Image by Caro's Lines via Flickr