Nonselective destruction of murine neoplastic cells by syngeneic tumoricidal macrophages

The purpose of these studies was to select in vitro tumor cells that were resistant to macrophage-mediated lysis. Seven different heterogeneous murine neoplasms (four fibrosarcomas, a melanoma, a rhabdomyosarcoma, and an osteogenic sarcoma) and one cloned line of a fibrosarcoma were incubated in vitro with syngeneic tumoricidal macrophages. Surviving tumor cells were recovered and expanded to undergo subsequent interaction with tumoricidal macrophages. After six sequential interactions, all cell lines were examined for their susceptibility to lysis mediated by murine peritoneal exudate macrophages activated with liposomes containing muramyl tripeptide phosphatidylethanolamine. In all eight systems, no significant differences were detected between the parent tumor cells and cells that survived the sequential interactions. Neither macrophage infiltration into s.c. tumors nor the experimental or spontaneous metastatic potentials of the parental tumors differed from the lines established by cells surviving macrophage-mediated lysis. Collectively, the data suggest that tumor cell destruction by activated macrophages is nonselective and does not lead to the development of resistant tumor cells nor to cells with altered metastatic properties.