(A, B) EGFP fluorescence (A) and Cre immunoreactivity (B) in HEK 293T cells infected with LV-Cre-EGFP recombinant virus in vitro. All the cells which express EGFP also express Cre. (C, D) Immunohistochemistry for Cre, in HEK 293T cells 16 hrs after exposure to the AAV-Cre virus (1C) and in uninfected HEK 293T cells (1D). Cre is present in the nucleus of large numbers of cells infected with the virus but is absent from uninfected cells. Scale bars A and B = 25 μm, C = 50 μm, D = 100 μm.