PDCD1 and myeloid sarcoma: Although inflammatory conditions induce PD-L1 expression in microglia, astrocytes, and infiltrating mononuclear cells [29], pathological studies on post-mortem brain tissues confirmed that more than half of infiltrating CD8+ T cells lack PD-1 expression and are thus insensitive to PD-L1/L2, pointing to a potential therapeutic implication of PD-1 augmentation for MS patients [30].