Major new ‘don’t eat me’ signal discovered in cancer cells

● Researchers found blocking a protein led to a reduction in tumour growth

A major “don’t eat me” signal which cancer cells appear to use to stop the immune system from attacking them has been discovered by US researchers.

Normally, immune cells detect cancer cells and engulf them, but researchers have previously discovered proteins on the surface of cells that can tell them not to do this.

This is useful to ward off attacks on normal, healthy cells, but scientists have found that cancer cells are using these signals to hide.

Researchers at the Stanford University School of Medicine have now discovered a new protein, called CD24, that acts as a potent “don’t eat me” signal “capable of directly protecting cancer cells from attack”.

They believe the discovery holds “particular promise” and is even a possible cure for sufferers of hard-to-treat ovarian and breast cancers, which affect thousands of women each year in the UK.

When the researchers blocked the CD24 signal in mice implanted with human cancers, they found that this allowed the immune cells, called macrophages, to attack the cancer cells.

This led to a reduction in tumour growth and increase in survival time in the mice.

Researchers from the university have previously shown that the proteins PD-L1, CD47 and the beta-2-microglobulin subunit of the major histocompatibility class 1 complex are all used by cancer cells to protect themselves from immune cells.

Antibodies that block CD47 are in clinical trials, while treatments that target PD-L1 or the PD-L1 receptor are being used in clinics.

A paper describing the research is published in Nature.

Senior author Irving Weissman, professor of pathology and of developmental biology and director of the Stanford Institute for Stem Cell Biology and Regenerative Medicine, said: “Finding that not all patients responded to anticd47 antibodies helped fuel our research at Stanford to test whether non-responder cells and patients might have alternative ‘don’t eat me’ signals.”

Lead author Amira Barkal, an MD-PHD student, said: “Ovarian cancer and breast cancer are two of the most deadly diseases affecting women, and both are very aggressive cancers that are notoriously difficult to treat in the clinic.

“We are excited about the potential of these findings to provide a new strategy to treat and maybe even cure ovarian cancer and breast cancers.”