Immunological studies on mouse mammary tumors. I. Induction of resistance to tumor isograft in C3H/He mice

An isografted tumor MM2, originating from a spontaneous mammary tumor in a C3H/He/mouse, killed 4- to 5-week-old mice within 30 days through intraperitoneal injection of 2 × 104 cells per mouse. It was shown that resistance to the isograft was induced by injection of 1.5 × 105 or 2.0 × 105 tumor cells sensitized with serum (5 μg antibody N) of rabbits immunized with the tumor. Four weeks after injection of the sensitized MM2 cells, 173 C3H/He mice were challenged intraperitoneally with fresh unsensitized MM2 in doses of 5 × 105 to 1 × 106 cells per mouse. Of these, 119 mice survived without any sign of tumor growth while all untreated mice died. The mean survival time for untreated mice was 18.1 days (± 1.7) when inoculated with 5 × 105 cells and 16.2 days (± 1.8) when inoculated with 1 × 106 cells. After the second challenge with the same number of fresh unsensitized cells, 117 out of 119 mice survived without any sign of tumor growth. All of 15 mice randomly selected from these resistant mice were tested for acceptance of skin grafts from normal C3H/He mice. The grafts showed no rejection even 150 days after the second graft. After hyperimmunization of these resistant mice, the serum of the spleen extract taken from the mice inhibited growth of tumors when the tumors were premixed in vitro and injected intraperitoneally into C3H/He mice.