Passive immunization against TNF allowed non-tumor-bearing C3H/HEN mice and tumor-bearing C57BL/6 mice to tolerate significantly more doses of IL-2 before death (p less than 0.005 and p less than 0.001, respectively). The antitumor effect of IL-2 against both 3-d and 10-d pulmonary metastases was maintained in mice treated concurrently with neutralizing antibodies to TNF. In one experiment with 10-d pulmonary metastases, increased administration of IL-2 made possible by passive immunization against TNF significantly improved the antitumor response compared to equitoxic doses of IL-2 and control antibody. The results indicate that TNF is a mediator of IL-2 toxicity but contributes minimally to the antitumor effects of IL-2. Strategies to inhibit TNF may improve the therapeutic index of IL-2 as a neoplastic agent.

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