SEMA4D and head and neck squamous cell carcinoma: Sema4D is also involved in immune response by interacting with the tumor microenvironment; soluble Sema4D level has been found to increase when coculturing with tumor-associated macrophages in a gastric carcinoma cell line [20]; the function of CD8+ T cell is inhibited when it fails to release soluble Sema4D in non-small-cell lung cancer [26]; in addition, inhibition of myeloid-derived suppressor cells is associated with Sema4D secretion in human head and neck squamous cell carcinoma [16].