Natural killer (NK) cells have the potential to be effective killers of
tumor cells. They are governed by inhibitory and activating receptors like NKG2D, whose
ligands are normally upregulated in cells that are stressed, like
cancer cells. Advanced
cancer cells, however, have ways to reduce these
ligands' expression, leaving them less detectable by NK cells. Along with these receptors, NK cells also require activating
cytokines, like
interleukin 12 (IL-12). The goal of this study is to develop a novel bi-functional fusion
protein for enhanced NK cell activation. The proposed
protein combines the extracellular domain of the NKG2D
ligand Mouse UL-16-binding
protein-like transcript 1 (MULT1E) and mouse
IL-12 (mIL-12). It is hypothesized that when expressed by
tumor cells, the
protein will activate NK and other killer cells using the
NKG2D receptor, and deliver mIL-12 to the NK cells where it can interact with the IL-12R and enhance cytotoxicity. The fusion
protein, when expressed by engineered
tumor cells, indeed activated NK cells in vitro as assayed by increased production of
interferon-γ and cytotoxicity and significantly reduced
tumor growth in vivo. Although the study is preliminary, the data suggest that the MULT1E/
mIL-12 bi-functional fusion
protein is an effective activator of NK cells for
cancer treatment.