TGFB1 and head and neck squamous cell carcinoma: In addition to CD4+ T cells, other types of cells, such as retinal pigment epithelial cells [10], corneal endothelial cells [11], tumor apoptotic bodies [12], head and neck squamous cell carcinoma cells [13] and colorectal cancer cells [14], are able to express membrane-bound TGF-β and inhibit T cell function or induce Treg cell development in a TGF-β-dependent manner.