The relationship of immune status to the efficacy of immunotherapy in preventing tumour recurrence in mice.

The immunotherapeutic value of tumour extracts or B.C.G. in preventing either the occurrence of primary tumours or the recurrence of tumours in surgically resected animals has been examined. A transplantable methylcholanthrene induced tumour in DBA/2J mice was used. Neither tumour extract nor chemically modified extract was effective in preventing tumour growth in immunized animals, even though the mice demonstrated measurable levels of cell mediated tumour immunity at the time of tumour challenge. The frequency of tumour recurrence after resection of small tumours (about 1·0 g) was significantly lowered by treatment of the mice with a combination of B.C.G. and either modified or unmodified tumour extract. The frequency of recurrence after resection of large tumours (about 2·5 g) was not affected by any form of immunotherapy although the survival time of treated animals was significantly prolonged. The immunological status of animals with small and large tumours was examined and it was shown that mice with 1·0 g tumours have unimpaired mitogen responsiveness and measurable tumour specific immunity, whereas mice bearing large tumours (2·5 g) have a markedly impaired immune system.