CD274 and carcinoma: Until now, besides in different human carcinomas, PD-L1 has also been reported to be expressed on OIIRR-associated periodontal tissue cell types including human osteoblasts [24], which has a similar phenotype as cementoblasts, human osteoclasts [25], human periodontal ligament cells [26], human gingival fibroblasts [27] and human gingival keratinocytes [22].