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 nine pairs of genes (CD8A-CD274, CD8A-CTLA4, CD8A-ICOS, CD8A-TNFRSF4, CD8A-CD27, CD8A-BTLA, CD8A-ADORA2A, CD8A-CD40LG, and CD8A-CD28).