Increased NDV replication leads to more cell apoptosis. A Western blot analysis of the expression of apoptosis-related proteins (BAX, Bcl2 and caspase-3) in HeLa cells at 48 hpi (0.1 MOI; La Sota). B qRT-PCR analysis of apoptosis-related gene expression in HeLa cells at 48 hpi (0.1 MOI; La Sota). C Flow cytometry analysis of cell apoptosis at 48 hpi (0.1, 1 or 2 MOI); data are pooled from replicates of at least three independent experiments. D Overall description of how NDV selectively infects proliferating cells to kill tumor cells. Data are presented as the mean ± SD of triplicate samples from a single experiment and are representative of three independent experiments. *P < 0.05, **P < 0.01 and ***P < 0.001 by t-test.