BCG immunotherapy of a rat sarcoma.

Growth of syngeneic transplants of a 3-methylcholanthrene induced rat sarcoma was suppressed when tumour cells were injected in admixture with BCG. Rejection of these mixed inocula resulted in the suppression of growth of a simultaneous challenge with cells of the same tumour at a contralateral subcutaneous site and conditions for immunotherapy were evaluated with respect to the maximum tumour cell challenge rejected and the optimum time of treatment. These studies established that viable tumour cells were more effective than radiation attenuated cells for the immunizing stimulus. Also, the maximum tumour challenge totally rejected in this way was of the order of 10(6) cells, and with this rapidly growing tumour, treatment had to be initiated within 4 days of tumour injection. These observations are relevant to current proposals for adjuvant immunotherapy of human malignant disease where conditions of minimal residual disease are not being fulfilled.