Subsequent studies in patients showed the presence of expanded CD4 CTLs in several tumour types, such as lung cancer (65), colorectal cancer (66), hepatocellular carcinoma (67, 68), breast cancer (69, 70), head and neck cancer (71), osteosarcoma (72) and malignant melanoma (73), as assessed by deep single-cell RNA sequencing analyses of tumour-infiltrating lymphocytes. The gene discussed is CD4; the disease is melanoma.