Macrophages surrounding lymph nodes block the progression of melanoma, other cancers

Source: EurekAlert, April 2016

Researchers at Massachusetts General Hospital (MGH) have identified a type of immune cell that appears to block the progress of melanoma and other cancers in animal models. These subcapsular sinus (SCS) macrophages form a protective coating around lymph nodes, preventing the entry of tiny structures that transport bits of tumor tissue and help the cancer to grow and spread. However, the SCS macrophage barrier appears to be temporary, as it breaks down as the tumor progresses and in response to some cancer treatment drugs.

“Macrophages found within tumors are typically seen as promoting cancer growth, for example, by helping form new blood vessels which deliver nutrients to tumor cells," says Mikael Pittet, PhD, of the MGH Center for Systems Biology, who led the study appearing in the April 8, 2016 issue of Science. “My lab studies how tumors communicate with the immune system in the entire body, and we became particularly interested in knowing whether tumors also interact with macrophages that reside away from the tumor."

One potential means by which molecular signals could be transferred from tumors to immune cells are tiny membrane-bound compartments called tumor-derived extracellular vesicles (tEVs), which are known to bind to and activate many different cell types. Measuring tEV levels can be used to predict treatment response and survival, but assessing the impact of tEVs in living animals has been difficult. The MGH team combined genetic and imaging approaches in a novel way to track tEVs and their targets.