Enhanced Calcium Signal Induces NK Cell Degranulation but Inhibits Its Cytotoxic Activity

pHLIP-fused PD-L1 engages avelumab to elicit NK cytotoxicity under acidic conditions

Natural killer (NK) cells represent key player in immune surveillance to eliminate transformed or malignant cells. One of mechanisms of action of NK cells is antibody-dependent cell-mediated cytotoxicity (ADCC) by recognizing tumor antigens on the surface of cancer cells. However, the heterogeneity of tumor antigens and the scarcity of membrane surface targets significantly restrict this strategy. Recently, we constructed a new cargo by tethering a low pH insertion peptide (pHLIP) to the C terminus of the ectodomain of programed death ligand-1 (PD-L1) and demonstrated its ability to modulate immune responses. Herein, the potential application of PD-L1-pHLIP in cancer therapy was determined. pHLIP tethering had no effect on the binding capacity of PD-L1 protein to an anti-PD-L1 antibody (i.e. avelumab). Association of pHLIP rendered PD-L1 segment display on the surface of cellular membrane in the acidic buffer instead of the neutral solution. Importantly, plate-coated or beads-coupled PD-L1-pHLIP enable robust activation and expression of cytotoxic mediators of NK cells via engaging avelumab. Overall, this work provides proof of concept that recombinant PD-L1 protein decorated on the cellular membrane driven by pHLIP in combination with appropriate monoclonal antibody has potentials to elicit NK cytotoxicity, which may represent a novel and promising therapeutic avenue in cancer.

Identification, sorting and profiling of functional killer cells via the capture of fluorescent target-cell lysate

Assays for assessing cell-mediated cytotoxicity are largely target-cell-centric and cannot identify and isolate subpopulations of cytotoxic effector cells. Here we describe an assay compatible with flow cytometry for the accurate identification and sorting of functional killer-cell subpopulations in co-cultures. The assay, which we named PAINTKiller (for 'proximity affinity intracellular transfer identification of killer cells'), relies on the detection of an intracellular fluorescent protein 'painted' by a lysed cell on the surface of the lysing cytotoxic cell (specifically, on cell lysis the intracellular fluorescein derivative carboxyfluorescein succinimidyl ester is captured on the surface of the natural killer cell by an antibody for anti-fluorescein isothiocyanate linked to an antibody for the pan-leucocyte surface receptor CD45). The assay can be integrated with single-cell RNA sequencing for the analysis of molecular pathways associated with cell cytotoxicity and may be used to uncover correlates of functional immune responses.

Networked Cluster Formation via Trigonal Lipid Modules for Augmented Ex Vivo NK Cell Priming

Current cytokine-based natural killer (NK) cell priming techniques have exhibited limitations such as the deactivation of biological signaling molecules and subsequent insufficient maturation of the cell population during mass cultivation processes. In this study, we developed an amphiphilic trigonal 1,2-distearoyl-sn-glycero-3-phosphorylethanolamine (DSPE) lipid-polyethylene glycol (PEG) material to assemble NK cell clusters via multiple hydrophobic lipid insertions into cellular membranes. Our lipid conjugate-mediated ex vivo NK cell priming sufficiently augmented the structural modulation of clusters, facilitated diffusional signal exchanges, and finally activated NK cell population with the clusters. Without any inhibition in diffusional signal exchanges and intrinsic proliferative efficacy of NK cells, effectively prime NK cell clusters produced increased interferon-gamma, especially in the early culture periods. In conclusion, the present study demonstrates that our novel lipid conjugates could serve as a promising alternative for future NK cell mass production.

Reduction of Ca2+ Entry by a Specific Block of KCa3.1 Channels Optimizes Cytotoxic Activity of NK Cells against T-ALL Jurkat Cells

Degranulation mediated killing mechanism by NK cells is dependent on store-operated Ca2+ entry (SOCE) and has optimum at moderate intracellular Ca2+ elevations so that partial block of SOCE optimizes the killing process. In this study, we tested the effect of the selective blocker of KCa3.1 channel NS6180 on SOCE and the killing efficiency of NK cells from healthy donors and NK-92 cells against T-ALL cell line Jurkat. Patch-clamp analysis showed that only one-quarter of resting NK cells functionally express KCa3.1 current, which increases 3-fold after activation by interleukins 15 and 2. Nevertheless, blockage of KCa3.1 significantly reduced SOCE and intracellular Ca2+ rise induced by IL-15 or target cell recognition. NS6180 (1 μM) decreased NK degranulation at zero time of coculture with Jurkat cells but already after 1 h, the degranulation reached the same level as in the control. Monitoring of target cell death by flow cytometry and confocal microscopy demonstrated that NS6180 significantly improved the killing ability of NK cells after 1 h in coculture with Jurkat cells and increased the Jurkat cell fraction with apoptotic and necrotic markers. Our data evidence a strong dependence of SOCE on KCa3.1 activity in NK cells and that KCa3.1 specific block can improve NK cytotoxicity.

Epigenetic modulation and prostate cancer: Paving the way for NK cell anti-tumor immunity

Immunoepigenetics is a growing field, as there is mounting evidence on the key role played by epigenetic mechanisms in the regulation of tumor immune cell recognition and control of immune cell anti-tumor responses. Moreover, it is increasingly acknowledgeable a tie between epigenetic regulation and prostate cancer (PCa) development and progression. PCa is intrinsically a cold tumor, with scarce immune cell infiltration and low inflammatory tumor microenvironment. However, Natural Killer (NK) cells, main anti-tumor effector immune cells, have been frequently linked to improved PCa prognosis. The role that epigenetic-related mechanisms might have in regulating both NK cell recognition of PCa tumor cells and NK cell functions in PCa is still mainly unknown. Epigenetic modulating drugs have been showing boundless therapeutic potential as anti-tumor agents, however their role in immune cell regulation and recognition is scarce. In this review, we focused on studies addressing modulation of epigenetic mechanisms involved in NK cell-mediated responses, including both the epigenetic modulation of tumor cell NK ligand expression and NK cell receptor expression and function in different tumor models, highlighting studies in PCa. The integrated knowledge from diverse epigenetic modulation mechanisms promoting NK cell-mediated immunity in various tumor models might open doors for the development of novel epigenetic-based therapeutic options for PCa management.

Differential effects on natural killer cell production by membrane-bound cytokine stimulations

Robust manufacturing production of natural killer (NK) cells has been challenging in allogeneic NK cell-based therapy. Here, we compared the impact of cytokines on NK cell expansion by developing recombinant K562 feeder cell lines expressing membrane-bound cytokines, mIL15, mIL21, and 41BBL, individually or in combination. We found that 41BBL played a dominant role in promoting up to 500,000-fold of NK cell expansion after a 21-day culture process without inducing exhaustion. However, 41BBL stimulation reduced the overall cytotoxic activity of NK cells when combined with mIL15 and mIL21. Additionally, long-term stimulation with mIL15 and mIL21, but not 41BBL, increased CD56 expression and CD56bright population, which is unexpectedly correlated with the NK cell cytotoxicity. By conducting single-cell sequencing, we identified distinct subpopulations of NK cells induced by different cytokines, including an adaptive-like CD56brightCD16-CD49a+ subset induced by mIL15. Through gene expression analysis, we found that cytokines modulated signaling pathways and target genes involved in cell cycle, senescence, self-renewal, migration, and maturation, in a different manner. Together, our study demonstrated cytokine signal pathways play different roles in NK cell expansion and differentiation, which shed light on NK cell process design to improve productivity and product quality. This article is protected by copyright. All rights reserved.