Colorectal tumors are swarming with white blood cells, but whether these cells help or hinder the cancer is hotly debated. While some studies have shown that white blood cells heroically restrict tumor growth and combat colorectal cancer, equally compelling evidence casts the white blood cells as malignant co-conspirators — bolstering the tumor and helping it spread.

Now, new research clarifies the role of these intestinal white blood cells, known as 𝛄𝛅 T cells, in colorectal cancer. It turns out that the cells have a double-edged function: They rein in early-stage tumors but, as the disease progresses, undergo biochemical changes and switch sides, strengthening the tumor. The findings, published in Science, shed further light on the role of 𝛄𝛅 T cells in tumor growth, and may open new paths toward colorectal cancer therapies.

“𝛄𝛅 T cells that live in the gut act to prevent tumor formation,” says Bernardo Reis, a research associate in the laboratory of Daniel Mucida at The Rockefeller University. “But once tumors form, gut 𝛄𝛅 T cell populations change, enter the tumor, and promote tumor growth.”

Altered T cell receptors

The intestinal lining may be the body’s most vulnerable port of entry. Composed of but a single layer of epithelial cells, this busy digestive region must absorb useful substances like nutrients, and reject harmful ones like foodborne pathogens, within a limited working space. 𝛄𝛅 T cells mind the gaps, perpetually scanning the epithelium to maintain the integrity of the intestinal lining and prevent pathogens from invading the rest of the body.

Reis set out to investigate conflicting claims over whether these cells help or hinder the growth of intestinal tumors. But as is often the case in biology, there was no simple answer.

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