In a new study, researchers have identified a previously unknown mechanism that promotes the growth and spread of cancer. This mechanism involves a key role for immune cells and a new function for small regulatory molecules called microRNAs. This discovery points to a new strategy for treating cancer and possibly immune system diseases. Researchers from The Ohio State University Comprehensive Cancer Center and Children’s Hospital Los Angeles found that tumor cells release tiny vesicles that are taken up by healthy immune cells, causing the immune cells to excrete chemicals that promote the growth and spread of tumor cells. The study used lung cancer cells as subjects and demonstrated that these vesicles contain microRNAs, molecules that play a powerful regulatory role, and that the behavior of immune cells is altered after ingestion of these molecules. In humans, this process involves a fundamental immune system receptor called Toll-like receptor 8 (TLR8). MicroRNAs help control the type and amount of proteins expressed by cells and are usually achieved by binding to the mRNAs that express the proteins. The key findings of this study are as follows: (1) Lung tumor cells release vesicles called exosomes, which contain microRNA-21 and microRNA-29a. immune cells located adjacent to normal tissue and tumor tissue – macrophages – take up these exosomes. (3) In the case of human macrophages, microRNA-21 and microRNA-29a bind to TLR8, resulting in the secretion of tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) by macrophages, two cytokines that promote the production of inflammation . (3) Increased levels of these two cytokines correlate with increased tumor numbers in the lungs of model animals, as decreased levels of these two cytokines lead to decreased tumor numbers in the lungs, implying that they also play a role in tumor metastasis.