CTLA4 and central nervous system cancer: Single-cell sequencing analysis revealed that the expression profile of Siglec-5, Siglec-7, and Siglec-9 were mutually exclusive with that of Siglec-16 in the glioma TME, and that Siglec-16 might suppress antitumor immunity via mechanisms different from PD-1, PD-L1 and CTLA4 (24).