Characterisation of functional biotinylated TNF-alpha targeted to the membrane of apoptotic melanoma cells.

The physiologic clearance of apoptotic cells prevents inflammation at the site of cell death and limits the immunogenicity of tumors. In this study we report the functional characterisation of biotinylated tumor necrosis factor-alpha (TNF-alpha) after anchorage to apoptotic melanoma cells via a biotin-avidin-biotin bridge. Flow cytometric and morphological analysis showed that biotinylated TNF-alpha efficiently bound to apoptotic membrane blebs of dying cells. Membrane-bound TNF-alpha (12 fg/cell) killed sensitive WEHI164 cells 250-fold more effectively than equivalent amounts of the soluble cytokine. Furthermore, macrophages engulfing apoptotic cells with membrane-bound TNF-alpha secreted significantly higher amounts of soluble TNF-alpha and lower amounts of interleukin-10 (IL-10). Therefore the bridging of TNF-alpha potentiates its biological function and influences the outcome of the phagocytic clearance of apoptotic tumor cells.