Israeli scientists from the Weizmann Institute of Science have discovered a new method of fighting the most aggressive type of breast cancer. It turned out that this type of disease encourages neighboring immune cells to build molecular bridges between themselves, which restrains immunity. The study is published in the scientific journal Cell Reports. The team identified a protein CD84 (SLAMF5), which serves to build bridges between cells. Experts analyzed the genetic sequences of neoplasms taken from women with triple-negative breast cancer. They found that the level of CD84 expression in the tumor microenvironment was much higher than normal. It turned out that although breast cancer cells themselves express very low levels of CD84, they cause neighboring immune cells to express it in large amounts and build bridges between themselves, suppressing the immune response. Building bridges causes the cells to produce a small protein that is known as a key suppressor of the immune response. When this protein is expressed in the tumor microenvironment, it is picked up by the immune system's T cells - the warrior cells that are supposed to destroy cancer cells - by suppressing their activity and preventing them from attacking the tumor. The researchers studied the progression of breast cancer in mice that had been genetically modified to not secrete the CD84 protein and found that these individuals developed significantly smaller neoplasms. The discovery prompted the team to test an antibody they had previously developed that successfully prevented the formation of molecular bridges. Injections given twice a week to mice with developing breast cancer significantly slowed tumor growth and in some cases even led to complete recovery.