CD274 and neoplasm: For example, Siglec-15 is an immune checkpoint that inhibits antigen-specific T cell responses, and is expressed, independent of PD-L1 status, on both tumor and tumor-infiltrating myeloid cells (110), and a mAb for Siglec-15 is currently being evaluated in a phase I/II study for advanced or metastatic solid tumors (NCT03665285).