(AGI) Rome, Aug 22 - Researchers at the Bambino Gesu' Children's Hospital in Rome and their colleagues at the Department of Experimental Medicine at the University of Genoa have discovered a mechanism through which cancer cells can "trick" the body's immune system and prevent it from attacking them. As shown in the study published on the Journal of Allergy and Clinical Immunology, the "switch" is triggered when immune natural killer (NK) cells - which play an important role in destroying tumor or infected cells - come into contact with cancer cells, resulting in the body's defense mechanism being lowered. NK cells in cancer patients produce an inhibiting receptor on their surface called PD-1, which acts as a switch, turning the cells off and on. When NK cells are out to kill tumors, they are switched off if the PD-1 receptor interacts with molecules on the external surface of cancer cells (PDL-1), thus allowing the tumor to grow freely. The PD-1 receptor was first discovered on T-lymphocytes, other important "soldiers" in the battle waged by the immune system against cancer cells. Tumors, especially extremely aggressive ones, often succeed in fending off attacks by T-lymphocytes, but they remain vulnerable to NK cells. If even these cells are inhibited by the PD-1 receptor, the body's defenses against tumors are practically non-existent and the cancer continues to grow. The Italian study, explained Emanuela Marcenaro from the University of Genova, has proven that the PD-1 receptor's inhibiting action can be prevented, and did so not only in the lab, "but also in patients affected by common tumors, such as melanoma and lung cancer. A specific monoclonal antibody binds with the PD-1 receptor and 'coats' it, thus preventing it from reacting with the PDL-1 and generate the signal thturning off NK cells." Ms Marcenaro also pointed out the new element in their study: "We have shown that the PD-1 switch is also present on cancer patients' NK cells, which we know play an extremely important role in our defence against tumors." The study, which was made possible by the contribution of the Italian Association for Cancer Research (AIRC), was conducted on patients suffering from ovarian cancer. The treatment is potentially viable for paediatric cancer patients. (AGI). .