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.