Tumorigenicity of persistent leukemic cells and their sensitivity to CTL-mediated killing. (A) Survival curves of naive mice injected intraperitoneally with the leukemic cell line (DA1-3B) or with leukemic cells that had persisted in other animals for 1 month (DA1-3b/d35) or 1 year (DA1-3b/d365). (B) Sensitivity of DA1-3b cells to CTL-mediated killing measured by lactate dehydrogenase (LDH) release (Cytotox) or by detecting caspase activation (FCC) using flow cytometry. E/T indicates effector-target ratio. (C) Sensitivity to CTL-mediated killing of DA1-3b cells or control YAC-1 or EL4 cells and inhibition of lysis with anti-MHC I or II. (D) CTL-mediated killing of DA1-3b cells treated with CMA, anti-FAS-L, or anti-TRAIL. (E) CTLs were isolated 1 month after challenge from mice vaccinated with irradiated DA1-3b/IL12 cells and tested for their ability to kill leukemic cells that had persisted in other animals for 1 month (DA1-3b/d35), 2 months (DA1-3b/d60), 3 months (DA1-3b/d90), 4 months (DA1-3b/d120), and 1 year (DA1-3b/d365). (F) The procedure described for panel E was followed except that the CTLs were isolated from mice 12 months after challenge (CTL/d365). (G) CTLs were isolated from mice 1 month after challenge, incubated at a 20:1 ratio with leukemic cells that persisted in other animals for up to 1 year, and production of IFN-γ and TNF-α was measured. All experiments were performed in quadruplicate and repeated at least 3 times. Error bars indicate standard deviation.