Local delivery of CpG(A)-STAT3 siRNA into xenotransplanted leukemia induces tumor cell death and stimulated neutrophil infiltration. (A-B) Effects of IT delivery of CpG(A)-STAT3 siRNA on tumor cell apoptosis and neutrophil infiltration. Mice xenotransplanted with MV4-11 leukemia were treated by 4 IT injections of CpG(A)-siRNA targeting STAT3 or Luc as a negative control. Tumors were harvested 1 day after the last treatment, frozen, and sectioned. (A) Tissue cryosections were immunofluorescently stained using antibodies to neutrophils (7/4, green) and activated caspase-3 (red). Slides were counterstained using Hoechst 33342 to visualize nuclei (blue) and analyzed by fluorescent microscopy. Shown are representative results from 2 independent experiments using tumor sections from 4 mice per group; arrows indicate contact sites between neutrophils and cells undergoing apoptosis. (B) Quantification of neutrophil infiltration using at least 20 randomly chosen fields. Statistically significant differences between treatment groups (from 2-way ANOVA) are indicated by asterisks. Data are shown as means ± SEM (n = 4). ***P < .001.