The extend to which immunotherapy is successful depends on different factors. It has long been known that successful immunotherapy is associated with the presence of tumor-killing CDB+ T cells in the tumor. But the tumor tissue also contains body cells that suppress the immune system against a tumor. In their study, the researchers show that after recognizing cancer cells, CDB+ T cells required tumor-killing M1-like macrophages to make a tumor disappear. 

The way it works is that tumor-killing CD8+ T cells produce signalling substances that bring macrophages present in the human body into the tumor and close to the T cell. Here, these macrophages get fully activated and develop into true 'cell soldiers': the tumor-killing M1-like macrophages. They fight the tumor by making substances that suppress the growth of tumor cells, but also by ‘eating’ the tumor cells. In addition, M1-like macrophages produce signalling substances that in turn attract new CD8+ T cells to the tumor, thereby boosting the antitumor response. 

This current research was conducted in mice but also applies to people. The researchers show that CD8+ T cells and M1-like macrophages are also present in the tumor tissues of patients, who respond better to immunotherapy. 

“The research represents an important step in tackling tumors that have already reached maturity. At the same time, it is also a call to be very cautious with treatments that suppress the recruitment of macrophages” says Oncode Investigator Sjoerd van der Burg. "We are considering developing a drug to recruit and activate these types of macrophages directly in the tumor without the presence of CD8+ T cells."

Read the full publication in Cancer Cell.

This research was made possible with the support of KWF and Oncode Institute.