Effect of immunotherapy with IL-2 against growth of L1210 Fas⁺ and L1210 Fas⁻ tumor cells in syngeneic host. L1210 Fas⁺ and Fas⁻ tumor cells (1 × 10⁶) were injected sc into group of five syngeneic (DBA/2) mice. The mice were injected with PBS (control) or with IL-2 (10,000 U/mouse, 3 times a day for 1 week followed by once a day for additional 7 days). The mice were observed for tumor growth and survival. The experiment was terminated after 60 days.