PDCD1 and plasma cell myeloma: Later, in 2002, the potential to target PD-1/PD-L1 as an ICI gathered sustained attention after a syngeneic mouse model demonstrated that administration of anti-PD-L1 Ab inhibited the growth of mouse myeloma cells, and that growth was completely blocked when myeloma cells were transplanted into PD-1 deficient mice [23].