Figure 2

Tumor cells surviving topotecan or paclitaxel are sensitized to effector T cells. (A) In vitro exposure to paclitaxel or topotecan enhances the sensitivity of ID8-E6E7 cells to activated E7-specific T cells. Bars show cytotoxicity after exposure to 2 different doses of paclitaxel and topotecan (IC₅₀ and 10 fold IC₅₀) for the same E:T ratio (20:1). Experiments were performed twice with similar results. (B) Treatment of ID8 cells with topotecan or paclitaxel sensitizes them to Fas agonistic antibody. ID8 cells (untreated or treated with topotecan or paclitaxel at IC₅₀ as described) were incubated with the Fas agonistic antibody and recombinant protein G or with isotype matched antibody and recombinant protein G for 24 hours, harvested, stained with trypan blue and the viable cells were counted (hemocytometer). The bars show the mean level of cytotoxicity and standard errors of three independent experiments. (C) The addition of Fas agonistic antibody to paclitaxel (upper left), carboplatin (upper right), topotecan (lower left) or gemcitabine (lower right) in vitro targets the resistant ID8 tumor cells and shifts the plateau phase of the dose-response curve for paclitaxel and topotecan downwards. The sigmoid curves represent the fit of the obtained data to a logistic regression dose response curve.