INHIBITION OF CT-26 MURINE ADENOCARCINOMA GROWTH IN THE RECTUM OF MICE TREATED WITH RECOMBINANT HUMAN INTERLEUKIN-6

In the present study we evaluated the antitumor effects of recombinant human interleukin-6 (rhIL-6), expressed in Chinese hamster ovary cell s, in a murine primary tumor model. We showed that treatment with rhIL -6 substantially inhibited the implantation and growth rates of CT-26 adenocarcinoma tumor cells in the rectal submucosa of syngeneic mice. This effect was achieved by injecting rhIL-6 for 7 consecutive days st arting 1 day prior to tumor inoculation. No obvious antitumor effect w as noted when rhILd injections started 5 days after tumor inoculation. Analysis of the mechanisms by which rhILd exerts its antitumor effect s did not reveal a direct antitumor effect on CT-26 tumor cells or the up-regulation of major histocompatibility complex antigens on these c ells. However, infiltration of lymphocytes at the tumor site was obser ved. Increase of carcinoembryonic antigen by IL-6 was clearly seen in human HT-29 colon carcinoma cells. The possible application of these r esults for adjuvant immunotherapy of selected colorectal patients and prevention of reimplantation of tumor cells disseminated during surger y is discussed.