Excision of the foreign expression cassettes from GLV-1h68 enhances virus replication efficiency. (A) Viral growth curves. GI-101A cells were infected with GLV-1h68 or its derivatives at an MOI of 0.01 or 10, and harvested at 24, 48, and 72 hpi. Viral titers were determined in CV-1 cells. The values are the mean of triplicate samples, and the bars indicate SD. The data represents two independent experiments. Statistical analysis was performed using two-way ANOVA. *, **, and *** indicate P < 0.05, 0.01, and 0.001, respectively, when compared with the GLV-1h68 group. (B) Plaque size comparison. Human breast tumor GI-101A cells were infected with 200 pfu of each virus strain for three days, and stained with crystal violet. The values are the mean of more than 58 plaques, and the bars indicate SD. Representative of two independent experiments. Statistical analysis was performed using unpaired t-test. GLV-1h71, GLV-1h73, and GLV-1h74 formed significantly larger plaques then did GLV-1h68. *** indicates P < 0.001 when compared to GLV-1h68. (C) Correlation between the promoter scores of GLV-1h68 and its derivative with their virus yields in the GI-101A cell culture (48 hpi, MOI 0.01).