Macrophage colony‐stimulating factor enhances rituximab‐dependent cellular cytotoxicity by monocytes

Recent studies suggest that monocytes are the dominant effectors by which rituximab induces cell death in B‐cell lymphoma. Because macrophage colony‐stimulating factor (M‐CSF) can enhance the cytotoxicity of monocytes, the authors examined whether this growth factor can enhance their ability to kill lymphoma cells in vitro. Monocytes derived from a healthy volunteer were cultured for 48 h in the presence or absence of M‐CSF. Monocytes stimul ated with M‐CSF were significantly more cytotoxic to Daudi B‐cell lymphomas than unstimulated monocytes. Flow cytometry revealed that M‐CSF increased monocyte expression of Fcγ receptors III and I by 1.6‐ and 1.5‐fold, whereas the expression of Fcγ receptor II remained unchanged. These results suggest that pretreatment with M‐CSF can improve the therapeutic efficacy of rituximab against intractable CD20+ lymphoma. (Cancer Sci 2007; 98: 1368–1372)