PDCD1 and myeloid sarcoma: Mechanistic studies suggest that PD-1/PD-L signaling actively modulates the onset and progressive course of MS via the regulation of various types of immune cells, such as effector T-cells, DCs, Tregs, and NK T-cells (Latchman et al., 2004; Chang et al., 2008; Schreiner et al., 2008; Brandl et al., 2010).