GFRA1 and breast carcinoma: To strengthen the suggestion that GFRα1 expression is central to efficient retargeted virus infection of breast cancer cells, we transfected MCF7 cells with GFRα1-specific or non-targeting control short interfering RNA (siRNA) pools, exposed these and uninfected cells at 72 h to KNTc-gD:GDNFΔ38 (2 pfu/cell) or KNTc-gD:wt virus (0.2 pfu/cell), and assessed virus entry by staining for the viral immediate-early protein ICP4 at 6 hpi.