Natural killer (NK) cells can protect from tumor-transformed cells using a fine-tuned machinery of activating and inhibiting receptors. An important activating receptor is Fc gamma receptor IIIa (FcγRIIIA or CD16A), which can trigger antibody-dependent cellular cytotoxicity (ADCC) when recognizing antibody-opsonized target cells. One strategy to boost ADCC responses may be achieved by inhibiting activation-induced shedding of CD16A from the NK cell surface. However, previous preclinical studies have shown contrasting results regarding the effectiveness and limitations of this approach. Here, microchip-based live cell-imaging was used to assess the consequences of CD16A shedding inhibition on the dynamics of NK cell cytotoxicity. The bispecific innate cell engager acimtamig (AFM13) was superior to IgG1 monoclonal antibodies in ADCC and in increasing the fraction of cytotoxic NK cells and serial killers. Under conditions where CD16A shedding was inhibited, acimtamig still triggered ADCC; however, the ability to promote serial killing was reduced and associated with impaired NK cell detachment from target cells. These results demonstrate that CD16A shedding represents an intrinsic feature of NK cell biology that is critical to sustain the antitumoral cytotoxicity of NK cells. This has implications for CD16A engineering of NK cell products and their combination with CD16A-directed NK cell engagers.

Miniaturization of cell culture substrates enables controlled analysis of living cells in confined micro-scale environments. This is particularly suitable for imaging individual cells over time, as they can be monitored without escaping the imaging field-of-view (FoV). Glass materials are ideal for most microscopy applications. However, with current methods used in life sciences, glass microfabrication is limited in terms of either freedom of design, quality, or throughput. In this work, we introduce laser-induced deep etching (LIDE) as a method for producing glass microwell arrays for live single cell imaging assays. We demonstrate novel microwell arrays with deep, high-aspect ratio wells that have rounded, dimpled or flat bottom profiles in either single-layer or double-layer glass chips. The microwells are evaluated for microscopy-based analysis of long-term cell culture, clonal expansion, laterally organized cell seeding, subcellular mechanics during migration and immune cell cytotoxicity assays of both adherent and suspension cells. It is shown that all types of microwells can support viable cell cultures and imaging with single cell resolution, and we highlight specific benefits of each microwell design for different applications. We believe that high-quality glass microwell arrays enabled by LIDE provide a great option for high-content and high-resolution imaging-based live cell assays with a broad range of potential applications within life sciences. 

Allogeneic natural killer (NK) cell transfer is a potential immunotherapy to eliminate and control cancer. A promising source are CD34 + hematopoietic progenitor cells (HPCs), since large numbers of cytotoxic NK cells can be generated. Effective boosting of NK cell function can be achieved by interleukin (IL)-15. However, its in vivo half-life is short and potent trans-presentation by IL-15 receptor α (IL-15Rα) is absent. Therefore, ImmunityBio developed IL-15 superagonist N-803, which combines IL-15 with an activating mutation, an IL-15Rα sushi domain for trans-presentation, and IgG1-Fc for increased half-life. Here, we investigated whether and how N-803 improves HPC-NK cell functionality in leukemia and ovarian cancer (OC) models in vitro and in vivo in OC-bearing immunodeficient mice. We used flow cytometry-based assays, enzyme-linked immunosorbent assay, microscopy-based serial killing assays, and bioluminescence imaging, for in vitro and in vivo experiments. N-803 increased HPC-NK cell proliferation and interferon (IFN)γ production. On leukemia cells, co-culture with HPC-NK cells and N-803 increased ICAM-1 expression. Furthermore, N-803 improved HPC-NK cell-mediated (serial) leukemia killing. Treating OC spheroids with HPC-NK cells and N-803 increased IFNγ-induced CXCL10 secretion, and target killing after prolonged exposure. In immunodeficient mice bearing human OC, N-803 supported HPC-NK cell persistence in combination with total human immunoglobulins to prevent Fc-mediated HPC-NK cell depletion. Moreover, this combination treatment decreased tumor growth. In conclusion, N-803 is a promising IL-15-based compound that boosts HPC-NK cell expansion and functionality in vitro and in vivo. Adding N-803 to HPC-NK cell therapy could improve cancer immunotherapy.

Glass materials have excellent optical and chemical properties for microscopy-based live cell assays but state-of-the-art methods for microfabrication of Lab-on-Chip (LoC) devices are often limited by either complex manufacturing and/or low quality results. In this work, we have evaluated glass microwell array chips produced using a recently introduced laser-based microfabrication method. Three different types of microwell designs have been tested for imaging and screening of on-chip cell cultures and live cell assays.

Myelodysplastic syndrome (MDS) is a clonal heterogeneous stem cell disorder driven by multiple genetic and epigenetic alterations resulting in ineffective hematopoiesis. MDS has a high frequency of immune suppressors, including myeloid-derived suppressor cells (MDSCs), that collectively result in a poor immune response. MDSCs in MDS patients express CD155 that ligates the T-cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT) and delivers an inhibitory signal to natural killer (NK) cells. To mediate a productive immune response against MDS, negative regulatory checkpoints, like TIGIT, expressed on MDS NK cells must be overcome. NK cells can be directed to lyse MDS cells by bispecific killer engagers (BiKEs) that ligate CD16 on NK cells and CD33 on MDS cells. However, such CD16 x CD33 (1633) BiKEs do not induce the proliferative response in MDS NK cells needed to sustain their function. Here, we show that the addition of an NK stimulatory cytokine, interleukin-15 (IL-15), into the BiKE platform leads to productive IL-15 signaling without TIGIT upregulation on NK cells from MDS patients. Lower TIGIT expression allowed NK cells to resist MDSC inhibition. When compared with 1633 BiKE, 161533 trispecific killer engager (TriKE)-treated NK cells demonstrated superior killing kinetics associated with increased STAT5 phosphorylation. Furthermore, 161533 TriKE-treated MDS NK cells had higher proliferation and enhanced NK-cell function than 1633 BiKE-treated cells without the IL-15 linker. Collectively, our data demonstrate novel characteristics of the 161533 TriKE that support its application as an immunotherapeutic agent for MDS patients.

Cross-talk between NK cells and dendritic cells (DCs) is important in Th1 immune responses, including antitumor immunity and responses to infections. DCs also play a crucial role in polarizing Th2 immunity, but the impact of NK cell-DC interactions in this context remains unknown. In this study, we stimulated human monocyte-derived DCs in vitro with different pathogen-associated molecules: LPS or polyinosinic-polycytidylic acid, which polarize a Th1 response, or soluble egg Ag from the helminth worm Schistosoma mansoni, a potent Th2-inducing Ag. Th2-polarizing DCs were functionally distinguishable from Th1-polarizing DCs, and both showed distinct morphology and dynamics from immature DCs. We then assessed the outcome of autologous NK cells interacting with these differently stimulated DCs. Confocal microscopy showed polarization of the NK cell microtubule organizing center and accumulation of LFA-1 at contacts between NK cells and immature or Th2-polarizing DCs but not Th1-polarizing DCs, indicative of the assembly of an activating immune synapse. Autologous NK cells lysed immature DCs but not DCs treated with LPS or polyinosinic-polycytidylic acid as reported previously. In this study, we demonstrated that NK cells also degranulated in the presence of Th2-polarizing DCs. Moreover, time-lapse live-cell microscopy showed that DCs that had internalized fluorescently labeled soluble egg Ag were efficiently lysed. Ab blockade of NK cell-activating receptors NKp30 or DNAM-1 abrogated NK cell lysis of Th2-polarizing DCs. Thus, these data indicate a previously unrecognized role of NK cell cytotoxicity and NK cell-activating receptors NKp30 and DNAM-1 in restricting the pool of DCs involved in Th2 immune responses.