Therapy of disseminated NK-resistant tumor by the synergistic effects of recombinant interleukin-2 and tumor necrosis factor.

Tumor necrosis factor and interleukin-2 each in recombinant form have antitumor activity against established tumors if used in high enough dosages. The problem associated with such high dosages is the high degree of toxicity and expense encountered. Therefore, this study was undertaken to look at the antitumor efficacy of these two lymphokines when used together at dosages well below the toxic levels. Our results using recombinant human interleukin-2 (IL-2) and recombinant human tumor necrosis factor (TNF) against established methylcholanthrene-induced fibrosarcoma (MCA sarcoma) pulmonary metastases showed that TNF and IL-2 therapy at low nontoxic dosages alone did not produce significant tumor regression, but when combined at the same dosage synergize producing significant antitumor effects in mice induced with MCA sarcoma. This was also evident from histopathological examination of the lungs where the maximum tumor reduction along with the maximum lymphocytic infiltration into tumor was seen when TNF and IL-2 were combined. In this tumor regression, inherent immunity of the treated mice was needed, since in those mice in which we induced immunosuppression by using radiation, tumor regression was not seen when TNF and IL-2 therapy was combined in the doses efficacious in immunocompetent mice. Tumor regression is also dependent on the sequence of administration of IL-2 and TNF, since when IL-2 was administered before TNF, the tumor regression was more significant than when TNF was administered before IL-2 or when both were administered simultaneously to mice with established pulmonary tumors. Therefore the synergistic effect of IL-2 and TNF could be used as an efficacious but inexpensive and nontoxic alternative to therapy with lymphokine activated killer (LAK) cells + IL-2.