For instance, melanoma stem cells use CTLA-4 to induce tumor cell proliferation and inhibit apoptosis, while cutaneous squamous cell carcinoma stem cells activate CTLA-4 expression through CD80, hindering the activity of cytotoxic T-lymphocytes (CTLs) and aiding tumor cells in evading immune surveillance. The gene discussed is CTLA4; the disease is cutaneous squamous cell carcinoma.