C. parvum immuntherapy of transplanted rat tumours

C.parvum (Wellcome CN 6134) has been tested for tumour suppression against a range of syngeneically transplanted rat tumours, both carcinogen-induced and of spontaneous origin. Subcutaneous growth was not prevented by distant subcutaneous or intravenous injection of the preparation, although growth rates were sometimes depressed or accelerated. In contrast, C. parvum injected in admixture with tumour cells consistently suppressed their growth and with highly immunogenic tumours induced systemic tumour immunity, C. parvum injected intravenously retarded development of pulmonary tumour deposits, and intrapleural injection suppressed growth of pleural tumours and malignant effusions. Host immunosuppression failed to abrogate the tumour-suppressive effect of locally applied C. parvum, but host macrophage depletion with silica totally abolished the response. These studies indicate that in the rat, tumour suppression is most consistently achieved by regional application of C. parvum, and that this response is more dependent upon local macrophage stimulation than generation of systemic immune responses.