Exosomes participate in intercellular communication, but most data published are based on exosomes released from in vitro cultured cells that do not communicate with neighboring cells located in the same microenvironment as the exosomal-producing cells in vivo. In this study, our data show that co-culture of leukocytes isolated from breast tumor tissue leads to uptake of fibronectin (FN) on or in the tumor exosomes (Exo fib+). The induction of FN and exosomal uptake is tumor tissue derived and leukocyte specific, because leukocytes isolated from the peripheral blood of nave mice failed to induce FN uptake by tumor exosomes. Furthermore, depletion of both CD25 + cells and Gr-1 + cells from tumor-associated leukocytes causes a reduction of Exo fib+, suggesting that tumor-associated CD25 + cells and Gr-1 + cells participate in FN production and uptake by tumor exosomes, resulting in Exo fib+. As a result of tumor cells absorbing Exo fib+, two major events are induced: focal adhesion kinase/Src-dependent signaling pathways are activated, and the production of proinflammatory cytokines and metalloproteinase 9 is enhanced in response to absorbing exosomes. This, in turn, enhances tumor cell invasion in vitro and in vivo. Collectively, our findings provide evidence that exosomes released from freshly excised tumor tissue cells that have communicated/ interacted with immune cells gain new immune evasion capacity. © 2012 American Society for Investigative Pathology.