For example, once exosomes derived from macrophages collected from patients with glioblastoma multiforme (GBM) are taken up by the GBM cells, an miRNA (miR-21) residing in these exosomes can inhibit expression of a tumor suppressor gene PDCD4 (programmed cell death 4) in these cells, allowing the cells to grow further 80. Here, PDCD4 is linked to glioblastoma.