Survival of vaccinated vs. mock-vaccinated mice. Ten C57BL/6 male mice were vaccinated i.p. with 1 × 106 RAG × EL-4 semi-allogeneic somatic cell hybrids [irradiated with 30 Gy (3,000 rad) in a 137Cs irradiator]. As a control, ten age-matched mice were mock-vaccinated i.p. with 0.5 mL PBS. Four weeks after vaccination or mock-vaccination each mouse was challenged by i.p. injection with 1 × 103 EL-4 and mice were monitored daily for ten more weeks. Mice with enlarging abdominal tumors were euthanized and the presence of tumor was confirmed at necropsy (P < 0.0001 between the two survival curves).