CD9 and neoplasm: This model is supported by (1) multiple studies demonstrating that tetraspanin-deficiency affects proliferation, migration, cytokine production, and antigen presentation, (2) CD9 upregulation on NK cells after TGFβ incubation leading to immunosuppressive NK cells (91), (3) regulation of TGFβ by tetraspanins (94, 95), and (4) own unpublished observations demonstrating that human lymphocytes cultured with tumor cells change expression of multiple tetraspanins.