SUCCESSFUL IMMUNOTHERAPY OF MURINE EXPERIMENTAL HEPATIC METASTASES WITH LYMPHOKINE-ACTIVATED KILLER CELLS AND RECOMBINANT INTERLEUKIN-2

Abstract

Lymphokine-activated killer (LAK) cells are generated in vitro by the incubation of normal murine splenocytes in interleukin 2. 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, a technique was developed for the induction of hepatic metastases in mice based on the intrasplenic injection of tumor cells [sarcoma MCA 105] 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 dose-dependent reduction in the number of liver metastases. In 20 consecutive experiments when RIL-2 was administered i.p. 3 times a day at doses varying from 1000-5000, 10,000-15,000 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, 66-95; 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 5000-25,000 units of RIL-2 and mean reduction, 97% for doses greater than 25,000 units of RIL-2). At doses of 5000, 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.