Summary
Forty-five mice of the C3H inbred line were inoculated intracutaneously with a small dose of a spindle cell sarcoma (Sa 1) that had been originally induced with methylcholanthrene in an animal of the same line. All of the inoculated animals developed tumors, and 25 recovered spontaneously. These 25 mice were reinoculated with, and found immune to, sarcoma 1. Nineteen of these immunized animals were now submitted to intracutaneous inoculation of a rhabdomyosarcoma (Sa 2) that had also been induced with methylcholanthrene in an animal of the same inbred line. At the same time, 17 control animals were inoculated with equal, or smaller, doses of the same neoplasm (Sa 2). Fourteen of the 19 immunized mice, and 12 of the 17 controls developed tumors (rhabdomyosarcomas). In addition; 6 animals immunized against sarcoma 1, and 6 normal control mice were inoculated intracutaneously with a mammary carcinoma (Ca 1) that had originated spontaneously in a female of the same inbred line. Five of the immunized animals, and 6 control mice developed progressively growing carcinomas at the site of inoculation.
It results from these experiments that tumors may be immunologically different in spite of the fact that they originated in homozygous animals. This observation may be explained by assuming that immunity acquired against tumors is directed specifically against the tumor, as such, that had been used for immunization, and that tumor immunity is not caused by genetic differences between the cells of the host and those of the animal in which the tumor originated. The implications of these and previous (6, 7, 18–21) observations are discussed. Acquired immunity to tumors, and natural resistance are discussed and compared with those observed in various communicable diseases. Finally, a classification of tumor immunity is suggested.
