Differential Efficacies of Recombinant Murine Interferon-γ and Recombinant Human Interleukin 2 Against EL4-Bearing Mice

The effects of treating tumor-bearing mice with recombinant murine interferon-γ (rMuIFN-γ) and recombinant human interleukin-2 (rIL2) were compared using EL4 thymoma with the same mouse model. Successive administration of rMu IFN-γ (10⁴ units) starting 1 day after tumor inoculation was highly effective, while rIL2 (5 × 10⁴ Jurkat units) starting 7 days later produced potent suppression of tumor growth leading to complete cure in about 50% of the mice treated with either of two agents. These results showed that the effectiveness of these lymphokines differed depending on the time of their administration. Furthermore, the therapeutic effect of rIL2 against tumor-bearing mouse was poorer in T-cell-deficient nude mice than in B6 mice and NK-cell-deficient beige mice, whereas the effect of rMuIFN-γ was poorer in beige mice than in B6 and nude mice. These results suggest that the role of NK cells in the tumor regression caused by the treatment of rMuIFN-γ is much more important than that of other activated lymphocytes, and that the antitumor activity of rIL2 may be due to the generation of T-cell--related lymphocytes. Our results reveal that combination therapy with rMuIFN-γ and rIL2 can induce a synergistic effect on EL4-bearing mice.