Effect of Recombinant Human Interleukin 2 on the Growth of a BALB/c Sarcoma Induced by Moloney Murine Sarcoma Virus

The effect of in vivo administration of recombinant interleukin 2 (rIL2) on the growth of a primary female BALB/c sarcoma induced by Moloney marine sarcoma virus (M‐MSV) was studied. Although low‐dose administration of (6,000 JU/mouse × 14 days) rIL2 had no effect on the growth of the tumors, high‐dose (15,000–80,000 JU/mouse × 14 days) intraperitoneal inoculation of rIL2 induced tumor regression, dose‐dependently. Tumors in mice which received 80,000 JU/mouse/day of rIL2 regressed completely 2 weeks after the initiation of treatment. The survival rates of the treated groups were significantly higher than those of the control group. A time course experiment disclosed that the effect of rIL2 was restricted only to the group in which rIL2 treatment started 8 days after the inoculation of M‐MSV. The cytotoxic activity of regional lymph node lymphocytes from rIL2‐treated mice was demonstrated against primary culture of M‐MSV‐induced sarcoma but not against syngeneic tumor induced by methylcholanthrene (Meth A). The effect of rIL2 was partially blocked by the administration of anti‐IL2 receptor antibody. Immunohistochemical examination revealed that infiltration of Thy1.2(+)Lyt1(+)2(‐) (helper/inducer subset) lymphocytes into the tumor tissue was prominent in mice which received high‐dose rIL2. The results indicated that IL2 induced regression of M‐MSV‐induced sarcoma mainly through activation of IL2‐receptor‐positive helper T cells in the tumor tissues and of killer cells in the draining lymph nodes.