Experimental animals can be made resistant to implantation of syngeneic tumors and induction of tumors by viruses. I n a few studies established tumors were inhibited by immunotherapy. Such results suggest that immunotherapeutic methods might be useful in clinical cancer. I n animals, immunity is usually induced by living tumor cells or tumor-causing viruses. In man, a tumor vaccine must not expose the patient to risk of cancer implantation or cancer induction and must maintain its antigenicity. We have studied the immunogenic efficacy of various preparations which are potentially applicable to man, using methylcholanthreneinduced sarcomas in syngeneic C57BL/6 mice. As a positive control, transplantation immunity was induced by implanting live tumor cells and then excising the resulting tumors. This made mice resistant to 10 or 100 times the minimum number of tumor cells which produced tumors (MTD) in non-immunized controls, but did not protect against 1000 times the MTD. One million fresh gamma-irradiated cells (10,000 rads 6OCo) were equally effective. Such cells are morphologically intact and metabolize for a limited time but do not propagate. After irradiation, cells could be stored at -70 C with only partial loss of immunogenicity, but if stored at -20 C they were ineffective. Tumor cells irradiated to a dose of 100,000 rads were also effective, but less so than the 10,000 rads preparation. Lesser but significant protection was effected by implanting Millipore chambers containing living tumor cells. This chamber prevents egress of the tumor cells, but apparently it does allow the tumor-specific transplantation antigens (TSTA) to reach the immunologically reactive hosts cells in an effective condition and amount.
ECENT LARORATORY STUDIES A n w L Y DEMON-R strate that experimental animals can be made immunologically resistant to implantainduction of tumors by viruses.G~s~33 In a few studies, syngeneic or autochthonous tumors were rejected or inhibited by active immunotherapy.20J6 Such results have reawakened hope that immunotherapeutic methods might be useful in clinical cancer. tion of syngeneic tunlor~7,13,1C,21,22,~4,28 and Piesented a t the twenty-fourth annual scicntihc SCSsion of the James Ewing Society, Portland, Oregon, May 6-8, 1951.