Immunization with the tumor line "E.G7 OVA LOSS", but not OVA protein, protects mice against E.G7 tumor growth. C57BL/6 mice were immunized twice, one week apart, with irradiated "E.G7 OVA LOSS" cells (A), native OVA (B), heat-denatured OVA (C), irradiated E.G7 cells (D) or buffer (E). Seven days later, they were challenged with live E.G7 cells and tumor growth was measured. Each line denotes the kinetics of tumor growth in a single mouse.