Successful Immunotherapy of Murine Experimental Hepatic Metastases with Lymphokine-activated Killer Cells and Recombinant Interleukin 2

Lymphokine-activated killer (LAK) cells are generated in vitro by the incubation of normal murine splenocytes in interleukin 2. We have shown previously that the systemic injection of LAK cells in conjunction with recombinant interleukin 2 can reduce the number of established pulmonary metastases in mice. In an attempt to study this approach in the treatment of hepatic metastases, we developed a technique for the induction of hepatic metastases in mice based on the intrasplenic injection of tumor cells and have tested the effects of LAK cells and recombinant interleukin 2 produced in Escherichia coli (RIL-2) therapy on these metastases. Treatment with LAK cells alone in 14 consecutive experiments rarely produced significant reduction in metastases over control (mean percentage reduction, 12%). Therapy with RIL-2 alone produced a dosedependent reduction in the number of liver metastases. In 20 consecutive experiments when RIL-2 was administered i.p. three times a day at doses varying from 1, 000 to 5, 000, 10, 000 to 15, 000, and 25, 000 units, a statistically significant (P < 0.05) reduction in liver metastases was seen in 2 of 12, 2 of 4, and 8 of 12 determinations, respectively (percentage reduction, 0 to 97; mean, 42%). At doses greater than 25, 000 units, the reduction in metastases was highly reproducible (percentage reduction, 66 to 95; mean, 83%) and was statistically significant in 14 of 14 determinations. When LAK cells were given i.v. in addition to RIL-2 administration in 16 consecutive experiments, the percentage reduction in liver metastases was markedly increased over that seen with RIL-2 alone (mean percentage reduction, 77% at doses of 5, 000 to 25, 000 units of RIL-2 and mean reduction, 97% for doses greater than 25, 000 units of RIL-2). At doses of 5, 000, 10, 000, 25, 000, and greater than 25, 000 units of RIL-2 plus LAK cells, significant reduction of liver metastases (P < 0.05) was achieved in 3 of 7, 2 of 2, 8 of 8, and 6 of 6 determinations, respectively. When animals were given fresh splenocytes or splenocytes cultured in complete medium without RIL-2 instead of LAK cells, no reduction in liver metastases was seen except for that attributable to the administration of RIL-2 alone. Sublethal total body irradiation of the mice prior to therapy abrogated the therapeutic effects of RIL-2, but the effects of treatment with LAK cells plus RIL-2 were maintained. Thus, treatment with RIL-2 alone or in combination with LAK cells is effective in reducing the number of established hepatic micrometastases in a murine model. These studies are in accord with our previous observations concerning the effective therapy of established pulmonary metastases with RIL-2 plus LAK cells and provide a rationale for the extension of these observations to the treatment of metastatic cancer in humans.