TGFB1 and malignant glioma: Along with PD-L1 and PD-L2 expression, PC from normal human brain and human malignant glioma (both PDGFRβ+, desmin+, SMA+, and NG2+) have been shown to secrete various factors with immunosuppressive properties, such as NO, PGE2, and TGF-β (95).