We first established single-cell-derived clones of 4T1 mammary tumours that express either influenza haemagglutinin (HA) antigen (4T1-HA), HA and a dominant-negative form (DN) of the IFN-γ receptor (IFN-γR) (4T1-HAγRDN) or HA and control vector (4T1-HAc). Here, IFNGR1 is linked to breast cancer.