CD4 and central nervous system cancer: Interestingly, in glioma (U251-MG, T98G, U-87 MG, A172, LN-229, and LN-18) cells, triptolide downregulates PD-L1 protein expression induced by IFN-γ on the cell surface, helping to reverse T cell inhibition, particularly affecting CD4+ T cells, and counteracting immunosuppression within the tumor microenvironment [974].