Vaccine produced in the cell-free system protected mice from tumor challenge comparably to the Id-KLH vaccine. In 3 independent experiments mice were immunized biweekly with 3 vaccinations of the indicated vaccine and were challenged with 400 38C13 tumor cells (or 1200 tumor cells in panel C) 2 weeks following the third vaccination. (A) First tumor challenge experiment (n = 10 mice per group). (B) Second tumor challenge experiment (n = 10 mice per group). For both groups, *statistical significance (P < .05 compared with DsbC control) determined by comparing survival curves using the log-rank test. (C) Third tumor challenge experiment (n = 10 except n = 9 for scFv and Im9-38ScFv and n = 7 for hGM-Im9-scFv). *significance (P < .05) by the log-rank test compared with both 38C13 scFv (V_H-V_L) and A20 scFv (V_H-V_L). Actual P values for all experiments are listed in the text.