Direct targeting of genetically modified tumour cells to FcγRI triggers potent tumour cytotoxicity

Abstract

Expression of the type I receptor for Fc domain of immunoglobulin (Ig)G (FcγRI or CD64) is restricted to myeloid effector cells, such as monocytes, macrophages and a subset of dendritic cells. Previous work has indicated a role for FcγRI in antibody-dependent phagocytosis and lysis of tumour cells. We hypothesised that tagging of tumour cells with an anti-FcγRI single chain Fv (sFv) may facilitate targeting to this receptor on effector cells, thereby initiating tumour cytotoxicity. A vector encoding the sFv for an FcγRI-specific antibody (H22), linked to the transmembrane domain of platelet-derived growth factor was constructed. Transfected tumour cells expressed high surface levels of functional H22-sFv, which greatly enhanced susceptibility for phagocytosis and lysis by monocytes and macrophages. The expression of H22-sFv evoked the ability of tumour cells to directly activate monocytes, as evidenced by phosphorylation of mitogen-activated protein kinase and secretion of the inflammatory cytokines interleukin (IL)-1β, tumour necrosis factor-α and IL-6. Moreover, growth of tumour cells in mice expressing H22-sFv was profoundly delayed (or absent) in transgenic mice expressing human FcγRI. These results demonstrated that tumour cells can be readily modified to activate cell effector mechanisms, a strategy that may be useful for in vivo targeting in patients. © 2005 Blackwell Publishing Ltd.