CD8A and neoplasm: While Osteopontin can enhance activation and survival of T cells in graft-versus-host disease (93), in cancer models, Osteopontin is a newly identified immune checkpoint expressed by intra-tumoral myeloid cells that upregulates PD-L1 expression (94) and directly inhibits activation and proliferation of tumor-reactive CD8+ T cells, thereby blocking anti-tumor immunity (95).