To test this hypothesis directly, we used the non-immunogenic HCmel31 tumour cells, which we engineered to express a retroviral antigen (Friend helper murine leukaemic virus isolate FB29 envelope glycoprotein gp70), previously shown to elicit adaptive anti-tumour responses even in the absence of prior immunisation [30, 37]. This evidence concerns the gene ERVW-1 and neoplasm.