Relationship of macrophage content, immunogenicity, and metastatic potential of a murine osteosarcoma of recent origin

The purpose of these studies was to determine whether the high macrophage content (>50 per cent) of the⁹⁰Sr-induced osteogenic sarcoma J (Os-J) of recent origin correlated with its immunogenicity or low metastatic potential. Cloning experiments demonstrated that the Os-J tumor is heterogeneous with regard to the production of experimental pulmonary metastases. Immunization-challenge studies in syngeneic mice and comparisons of tumor growth in normal or nude mice established that the slow growing Os-J tumor is poorly immunogenic. In vitro studies demonstrated that the Os-J tumor is highly susceptible to macrophages-mediated lysis. This may explain the slow growth of the tumor in normal recipients with an intact mononuclear phagocyte system, as compared with the more rapid emergence of tumors in macrophage-suppressed mice. However, spontaneous metastases of the Os-J tumor were not observed either in normal or macrophage-suppressed mice. Although a high macrophage infiltration of neoplasms could slow tumor growth, this was not associated with the immunogenicity of the neoplasm and did not appear to limit the spontaneous metastasis of this essentially benign neoplasm.