S1PR1 and glioblastoma: TGF-β may result in T-cell sequestration in the bone marrow among GBM patients through down-regulation of S1P1,35 but it should be noted that TGF-β blockade did not result in less T-cell sequestration.35 Glioma cell line studies have also shown that glioma cells produce TGF-β1 for retention of stemness of glioma initiating cells (GICs) through an induced expression of various genes including Sox2, a stemness gene.36,37 Furthermore, TGF-β1 has been shown to promote cell migration and invasiveness in glioma and may be involved in angiogenesis.38–40