💊 Macrophages caught in the act of devouring live cancer cells!

For the first time, researchers have filmed macrophages – those immune cells that clean the body – devouring live melanoma cells. This scene, captured by an Australian team from the Garvan Institute, reveals a natural defense mechanism against cancer that was previously unknown. A discovery that could transform our understanding of the immune system and pave the way for new treatments.

These macrophages are often described as the body's garbage collectors: they eliminate cellular waste and pathogens. However, they are also very abundant in tumors, where they can account for up to 30% of the tumor mass. Their exact role in cancer was debated, with some evidence suggesting they could either help or hinder tumor progression. This new study sheds light on their protective function.


Researchers at the Garvan Institute identified a specific subpopulation of macrophages, which carry the protein CD169 on their surface. To test their role, the scientists selectively eliminated these cells in mice with melanoma. Result: the tumors grew significantly, indicating that these macrophages play a key role in controlling tumor growth. A discovery that highlights a new player in the immune system's fight against cancer.

In order to visualize this process in real time, the researchers used an advanced imaging method called two-photon intravital microscopy. This allows observing cellular activity in a living organism without disturbing it. Thanks to this technique, they were able to film CD169+ macrophages engulfing live melanoma cells, thus confirming their ability to directly attack cancer.

Contrary to what was previously thought, this macrophage attack does not depend on T and B lymphocytes, the immune cells traditionally recognized for fighting cancer. This surprised the researchers, who assumed these lymphocytes were necessary. CD169+ macrophages thus act independently, on the front line. After engulfing cancer cells, they present fragments of them on their surface, acting as sentinels to alert the rest of the immune system.

This discovery could have important implications for immunotherapy. Today, checkpoint inhibitor treatments are only effective in about half of melanoma patients. A major problem comes from so-called "cold" tumors, which prevent T lymphocytes from penetrating and attacking. CD169+ macrophages could help transform these tumors into accessible targets by attracting T cells, thus making immunotherapy more effective.


The next steps will be to understand how these macrophages interact with T lymphocytes. Ultimately, scientists plan to develop drugs capable of stimulating their activity, for example by making them more voracious or increasing their number. Combined with current immunotherapies, these approaches could benefit a larger number of patients.

Furthermore, since macrophages are present in most tumors, these treatments could apply to other cancers besides melanoma.