In vitro synergic effect of interferon gamma combined with liposomes containing muramyl tripeptide on human monocyte cytotoxicity against fresh allogeneic and autologous tumor cells.

Abstract

The purpose of the present study was to investigate whether human recombinant interferon-gamma (hrIFN-gamma) can act synergically with various activators in increasing the cytotoxicity of cancer patient monocytes against fresh autologous and allogeneic tumor cells. Fresh target cells were obtained by means on the mechanical and enzymatic dissociation of human renal carcinomas. A 375 and SW 626 cell lines were used as positive controls. Monocytes from renal cancer patients and normal volunteers were activated in vitro with lipopolysaccharide, muramyl tripeptide (MTP-PE) or liposomes containing MTP-PE (MTP-PE liposomes), with or without a pre-incubation with hrIFN-gamma and were tested for cytotoxicity by means of a 72-hr 111indium-release assay. All of the patients were tumor free at the time of the study. Cancer patient peripheral blood monocytes were activated in vitro by different immunomodulators and became cytotoxic to freshly dissociated autologous or allogeneic tumor cells. A synergic effect producing maximal cytotoxicity was obtained with an appropriately scheduled combination of hrIFN-gamma (10 U/ml) and MTP-PE liposomes (50 nm/ml), free lipopolysaccharide (10 micrograms/ml) or MTP-PE (100 micrograms/ml). The synergic cytotoxicity was observed against fresh allogeneic and autologous tumor cells, as well as against cultured cells. All of these data support the possibility of a combined treatment using hrIFN-gamma and MTP-PE liposomes in human studies, particularly when it is borne in mind that liposomes can prevent the direct toxicity of many immunomodulators and that the low levels of hrIFN-gamma required for the synergic activation are not toxic in vivo.