Cytostasis of different tumours by a murine PPD-reactive CD4+ T lymphocyte clone is mediated by interferon-gamma and tumour necrosis factor alone or synergistically

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Abstract
We have shown that a murine CD4+ PPD-reactive T lymphocyte clone was weakly cytotoxic towards the syngeneic tumour B16 melanoma and MC6A fibrosarcoma which had been coated with PPD using a monoclonal antibody-PD heteroconjugate. Cell-free supernatants produced by PPD-stimulated T lymphocyte clones were however highly cytostatic for the two tumour targets when assayed over 48-72 h. In this study we have demonstrated good titres of tumour necrosis factor (TNF) and interferon-gamma (IFN-.gamma.) in the supernatants, which accounted for their observed cytostatic activity on the tumour targets. The high level of cytostasis seen with the B16 melanoma using the supernatants could be attributed to their sensitivity to the cytostasis seen with the B16 melanoma using the supernatants could be attributed to their sensitivity to the cytostatic activity of IFN-.gamma.; the lower levels of cytostasis seen with the IFN-.gamma.-resistant MC6A target was the result of IFN-.gamma. increasing the sensitivity of this target to TNF. Antibodies to IFN-.gamma. were able to neutralize the majority of the cytostatic activity of the supernatants on both targets, consistent with the role demonstrated for this lymphokine.