CD274 and neoplasm: Later, the tumor-cell inhibitory marker PD-L1 (CD274, previously known as B7-H1) was discovered in 1999-2000 [80] and PD-L2 (CD273, previously known as B7-DC) in 2001 [81] and was considered even much better control over immune cell checkpoint-based therapeutic targets [82] (Figure 2).