Targeting of immunomodulators to mononuclear phagocytes for therapy of cancer

Macrophages activated to the tumoricidal state can recognize and destroy neoplastic cells and leave normal cells unharmed. Systemic activation of macrophages can be achieved by the administration of liposomes containing immunomodulators. Similar to any particle, liposomes are cleared from the circulation by phagocytic cells. The multiple administration of such liposomes has produced eradication of cancer metastases in several rodent-tumor systems. The destruction of metastases by macrophages is limited by the ratio of effector to target cells. Thus, once metastases are large, therapeutic efficacy is diminished. For this reason, various methods to reduce the tumor burden in metastases by modalities such as chemotherapy or radiotherapy should preceed treatment with liposomes-immunomodulators. In this way, tumoricidal macrophages should be an effective modality for treatment of tumor cells which are resistant to conventional therapies.