IL-12 gene transfer combined with Ad.CD/5-FC increases splenic NK cell activity and IFN-γ production. (A) Cytotoxicity of NK cells in Renca tumor-bearing mice treated with various adenoviral vectors (see Figure 4 legend). Mice in which tumor growth was completely or partially inhibited were chosen from the treatment groups on day 21 after tumor cell inoculation. Splenocytes were isolated from the treated mice (n = 3 per group) and used as effector cells. A standard 4-h 51Cr release assay was performed using YAC-1 cells labeled with 51Cr as target cells. The percentage specific lysis was determined. Data are means ± SD. (B) Mouse splenocytes (n = 3 per group) were isolated from the treatment groups on day 21 as described above, and incubated with Renca cells inactivated by pretreatment with 50 μg/ml mitomycin C for 20 min at 37°C. Culture supernatants were obtained from the incubated cells at the indicated times. Amounts of IFN-γ in the supernatants were measured using ELISA. Bars represent mean ± SD.