A role for T lymphocytes in the antitumour action of systemic C. parvum.

The frequency of tumours arising from s.c. injection of a syngeneic chemically-induced fibrosarcoma (Fsa) was not influenced by systemic administration of C. parvum (day + 3) except when doses less than the TD50 were injected. Then the number of takes was increased. The tumour normally grows progressively however regression was frequent in intact mice treated with C. parvum. Tumour regression did not occur in T cell-depleted mice treated in the same way. Splenic T cell-enriched populations of cells taken from Fsa-bearing C. parvum-treated mice caused tumour regression when adoptively transferred to Fsa-bearing T cell-depleted mice. Although this assay measures systemic rather than intratumoral T cell activity, it is proposed that C. parvum-induced regression of the fibrosarcoma is to a large extent due to enhanced T cell reactivity.