Active specific immunotherapy with vaccinia colon oncolysate enhances the immunomodulatory and antitumor effects of interleukin-2 and interferon alpha in a murine hepatic metastasis model.

The role of cytokines as primary or adjuvant antineoplastic agents has been well established. Interleukin-2 (IL-2) and the interferons have, particularly, proven to be effective antitumor agents when given alone, and seem to act synergistically on the eradication of metastases from immunogenic tumors. Active specific immunotherapy, in the form of viral oncolysates, has also shown effectiveness in cancer therapy. Bearing this in mind, we decided to combine these agents in an adjuvant triple regimen and compare their effectiveness to other treatments in terms of tumor burden and survival in a murine colon cancer hepatic metastases model. BALB/c mice were injected with CC-36, a weakly immunogenic murine colon adenocarcinoma, intrasplenically, to produce artificial liver metastases. The animals were divided into one control group and seven treatment groups receiving either vaccinia colon oncolysate (VCO), IL-2, interferon-alpha (IFN alpha) alone, or combinations of these agents. Half the animals were followed for survival and the other half were sacrificed at the end of the experiment for quantification of tumor burden. The blood of the sacrificed animals was utilized in a series of immunological tests in order to demonstrate the cytolytic potential of the peripheral blood lymphocytes (PBL) in each treatment group, as well as to characterize phenotypically the cells acting as effectors. The triple-adjuvant regimen group was by far the most effective treatment group, demonstrating 100% survival and a significant reduction in tumor burden when compared to other groups. Furthermore, the PBL from the animals in this group showed 69.4% lysis of the CC-36 target cells in vitro. These effector lymphocytes were characterized as ASMG1-/Lyt2.2+ cytolytic lymphocytes. We conclude that these lymphocytes were stimulated by the administration of VCO and further augmented by the immunomodulation of the cytokines given in the triple regimen, and that such a regimen might prove beneficial in the treatment of established hepatic metastases from weakly immunogenic tumors.