IL-12 antitumor activity in vivo. (A) Volume of tumors grown intraperitoneally in PBS- and IL-12–treated animals 23 days after NCI-H929 cell inoculation. The differences in size between tumors removed from PBS- and IL-12–treated mice were evaluated by Mann-Whitney U test. Boxes represent values between the 25th and 75th percentiles; whisker lines, highest and lowest values for each group; horizontal lines, median values. (B) Human angiogenesis PCR array on tumors explanted from IL-12– versus PBS-treated animals 23 days after NCI-H929 cell inoculation. Left panel enlists the gene whose expression has been abolished in tumors from IL-12– versus PBC-treated mice. Histogram in right panel shows fold expression changes of genes up-regulated in tumors from IL-12– versus PBC-treated mice. (C) Histologic and immunohistochemical features of tumors developed in PBS-treated (i-iii) and hrIL-12–treated (iv-vi) SCID/NOD mice 23 days after NCI-H929 tumor cell injection. NCI-H929 tumors are mostly formed by undifferentiated, proliferating (mitotic features indicated by arrows) blast cells that are large and pleomorphic and sometimes binucleated or endowed with very prominent nucleoli (i). These tumors are supplied by a distinct network of mature microvessels, as assessed by laminin staining (ii), and show frequent PCNA expression (iii). In hrIL-12–treated mice, these morphologic features are frequently altered by the appearance of ischemic-hemorrhagic foci of necrosis (N; iv) associated with defective microvascularization (v) and decreased tumor cell proliferation (vi). Histologic and immunohistochemical analyses were performed under a Zeiss LSM 510 Meta laser scanning confocal microscope (Zeiss, Oberkochen, Germany). ×400 field (×40 objective and ×10 ocular lens; 0.180 mm² per field).