Caspase-independent cell lysis is unaffected by P-gp expression. P-gp^+ve and P-gp^−ve CEM cell lines were labeled with ¹²⁵IUdR (A, C) and ⁵¹Cr (B, D) for 1 hour, washed in growth media, and incubated for 16 hours in 96-well plates (2 × 10⁴ cells/well) with a sublytic concentration of pfp (30 U) and increasing amounts of GzB (0.2, 0.5, 2.0 μg/mg) (A, B) or with pfp alone (300 U) (C, D). In some wells, cells were preincubated for 30 minutes with 20 μmol/L ZVAD-fmk or control ZFA-fmk inhibitor and/or anti–P-gp MoAb MRK 16 (50 μg/mL) as indicated in Table 1. Data are calculated as the mean ± SE of triplicate samples and are representative of at least two different experiments.