Natural killer (NK) cells provide a powerful weapon mediating immune defense against viral infections, tumor growth, and metastatic spread. NK cells demonstrate great potential for cancer immunotherapy; they can rapidly and directly kill cancer cells in the absence of MHC-dependent antigen presentation and can initiate a robust immune response in the tumor microenvironment (TME). Nevertheless, current NK cell-based immunotherapies have several drawbacks, such as the requirement for ex vivo expansion of modified NK cells, and low transduction efficiency. Furthermore, to date, no clinical trial has demonstrated a significant benefit for NK-based therapies in patients with advanced solid tumors, mainly due to the suppressive TME. To overcome current obstacles in NK cell-based immunotherapies, we describe here a non-viral lipid nanoparticle-based delivery system that encapsulates small interfering RNAs (siRNAs) to gene silence the key intrinsic inhibitory NK cell molecules, SHP-1, Cbl-b, and c-Cbl. The nanoparticles (NPs) target NK cells in vivo, silence inhibitory checkpoint signaling molecules, and unleash NK cell activity to eliminate tumors. Thus, the novel NP-based system developed here may serve as a powerful tool for future NK cell-based therapeutic approaches.

Natural killer (NK) cells are a potent weapon of the immune system against viral infections and tumor growth. The actomyosin network generates forces through the activity of actin filaments and myosin motors. This machinery is responsible for the conversion of mechanical forces into biochemical signals in a process termed mechanotransduction. However, the mechanism by which mechanotransduction controls the immune response, and specifically lymphocyte activity, is poorly understood. Here, we demonstrate that actomyosin retrograde flow (ARF) controls NK cell response through a novel interaction between beta-actin with the SH2-domain containing protein tyrosine phosphatase-1 (SHP-1), converting its conformation state, thereby regulating NK cell cytotoxicity. Actin dynamics govern SHP-1 conformational structure dictating its catalytic activity. Indeed, blocking actin dynamics results in reduced SHP-1 activity, by confining SHP-1 to its inactivated “closed” conformation. This reduced enzymatic activity of SHP-1 leads to increased phosphorylation of SHP-1 substrates, an elevation of intracellular calcium flux, and NK cell cytotoxicity. Using multidisciplinary approaches including functional and advanced molecular imaging, we followed the signaling events in individual NK cells from the moment of target cell encounter until the final outcome – target cell killing or NK cell inhibition. Our data suggest that SHP-1 plays a major role as a sensor of ARF-generated forces in the process of mechanotransduction, and reveal a novel mechanism by which regulation of SHP-1 by ARF dictates NK cell killing decisions. Our data identify ARF as a master regulator of the lymphocyte response.