Tumor incidence in mice after inoculation of HSV amplicon vector into pre-established EL4 tumor. (A) Viable EL4 cells (10⁶) were implanted SC on one side of the hind limb of the C57BL/6 mice (8 weeks old). Tumors were allowed to develop to a size of 5 to 6 mm in diameter. HSV amplicon virus (2 × 10⁶amplicon-containing particles) was inoculated on day 7 and again on day 14, and tumor growth was monitored every 3 days. The graph represents the percentage of tumor-bearing mice over time. (▴) HSV-B7.1; (▪) HSVrantes; (•) HSV-B7.1 + HSVrantes; (▵) HSVlac. The number of animals used in each group is shown in (B). Results of three separate experiments are pooled. Mice in which primary tumor had regressed were selected for rechallenge with 10⁶ viable EL4 cells and tumor growth was observed for another month. Mice were killed when the tumor diameter exceeded 22 mm. (C) Statistical analysis was performed using Fisher’s exact test comparing all four arms to each other.