CD28 and squamous cell carcinoma: Oral and squamous cell carcinoma samples were divided into four combinations based on the median value of gene expression levels for eight pairs of genes (CD274-CTLA4, CD274-ICOS, CD274-TNFRSF4, CD274-CD27, CD274-BTLA, CD274-ADORA2A, CD274-CD40LG, and CD274-CD28).