Monocyte-Conditioned Medium Factor as Auto-activation Signal for Monocyte Tumor Cytotoxicity

Abstract

The usefulness of tumoricidal macrophages as cancer treatment modality has been studied previously. Recently, cancer researchers have gained much interest in the use of biological response modifiers; therefore we, like others [1, 2], wanted to study the feasibility of using tumoricidal macrophages as an additional modality for the treatment of cancer. We studied the effects of two immunomodulators, lipopolysaccharide (LPS) and human recombinant interferon-γ (IFN-γ) on the development of tumor cytotoxicity in freshly isolated and cultured human monocytes. In our system, freshly isolated monocytes showed very low levels of tumor cytotoxicity when the effector cells were cultured in a medium supplemented with autologous serum. Enhanced tumor cytotoxicity was only observed when LPS was added to the culture medium; IFN-γ did not enhance tumor cytotoxicity at all. The addition of both LPS and IFN-γ did result in cytotoxicity levels equivalent to those obtained with LPS alone, indicating neither additive nor synergistic effects of the two immunomodulators.