PDCD1 and Miyoshi myopathy: The role of the PD-1/PD-L1 pathway in mediating immune escape of malignant plasma cells [95], combined with the fact that PD-L1 is highly expressed on plasma cells isolated from patients with MM but not on normal plasma cells [96,97,98,99], led to an increased interest in the use of anti-PD-1/PD-L1 therapy in MM.