ARG1 and glioblastoma: The secretion of immunosuppressive mediator Prostaglandin E2 (PGE2) induced by irradiation from glioblastoma CSCs even enhanced cell survival and proliferation, causing tumour recurrence afterward [111], and macrophage migration inhibitory factor increased the production of the immune-suppressive enzyme arginase-1 and stimulated myeloid-derived suppressor cell function in glioblastoma [112].