Cytopathic effects of recombinant vaccinia viruses on tumor cell growth. (a) MDA-MB-231 and MX-7 cells were infected with various concentration of VVs (0.06–2 PFU/cell) for 72 h. The relative survival of infected tumor cells was detected by MTT test. The data represent the mean ± SD. (b) Visualization of lytic (apoptotic) morphology of infected MDA-MB-231 cells. Cells were infected with VV-GMCSF-dGF, VV-GMCSF-Lact, and VV-GMCSF-Apo. At 6, 24, and 48 h after infection, cells were analyzed by inverted microscope (phase-contrast) and photographed. Representative photomicrographs of three independent experiments.