FIGURE 1.

Schematic diagram showing the in vivo selection of WF-0, WF-1, WF-2, and WF-3 cell lines. The peritoneal cells of the C57BL/6 mice were collected, transduced with retrovirus encoding human papillomavirus type 16 (HPV-16) E6 and E7 genes, followed by transfection with DNA encoding human c-Ha-ras gene, and named WF cells. The WF cells were injected intraperitoneally into athymic mice repeatedly. Eventually, athymic mice developed ascites. The tumor cells from ascites in athymic mice previously challenged with WF cells were isolated, expanded in vitro, and named WF-0. When WF-0 cells were injected into C57BL/6 mice, <10% of WF-0 tumor-challenged C57BL/6 mice developed ascites. Tumor cells from the ascites of C57BL/6 mice were isolated and expanded in vitro. These expanded cell lines were called WF-1. The mice were further challenged intraperitoneally with WF-1. The outgrown ascites in mice challenged with WF-1 were further cultured in vitro. These expanded cell lines were called WF-2. The mice were challenged intraperitoneally with WF-2. Cells harvested from the ascites of mice challenged with WF-2 were further cultured in vitro. These expanded cell lines were called WF-3.