Label-free monitoring of T cell activation by the impedance-based xCELLigence system

Real-time detection of T cell activation by visualizing TCR nanoclusters with a cholesterol derived aggregation-induced emission probe

Successful T-cell based immunotherapy usually depends on the activation of T cells. Most of commonly used methods for assessing T cell activity rely on the antibody-based technology, which focus on detecting protein-centered activation markers, including CD25, cytokines and so on. However, these methods always involve tedious sample-preparation process, labor-consuming and costly, which could not be utilized in real-time detection. The T cell receptor (TCR) clustering is another kind of essential T cell activation marker on the membrane, which increases during the activation state of T cells. We herein developed a cholesterol derived aggregation-induced emission (AIE) fluorescent probe (R-TPE-PEG-Chol) for detecting T cell activation in real-time. Five probes were first designed and synthesized and among them COOH-TPE-PEG-Chol displayed the best imaging effects, which had no significant impact on the key physiological functions of T cells. In addition, we have proved that COOH-TPE-PEG-Chol was introduced onto the naïve T cell membrane in its molecularly dissolved form without fluorescent emission. While during T cell activation, the formation of TCR nanoclusters would induce aggregation of membrane cholesterol, which could provoke the fluorescence signal of the COOH-TPE-PEG-Chol due to the AIE characteristic. Moreover, the enhancement of the fluorescence intensity was positively related to the activation state of T cells. Our study demonstrated the concept of cholesterol-derived AIE fluorescent probes for deciphering the spatiotemporal arrangements of TCR on the membrane during T cell activation, and consequently provided a novel and complementary strategy for detecting T cell activation in real-time.

In vitrodifferentiation of human cardiac fibroblasts into myofibroblasts: characterization using electrical impedance

Cardiac arrhythmias represent about 50% of the cardiovascular diseases which are the first cause of mortality in the world. Implantable medical devices play a major role for treating these arrhythmias. Nevertheless the leads induce an unwanted biological phenomenon called fibrosis. This phenomenon begins at a cellular level and is effective at a macroscopic scale causing tissue remodelling with a local modification of the active cardiac tissue. Fibrosis mechanism is complex but at the cellular level, it mainly consists in cardiac fibroblasts activation and differentiation into myofibroblasts. We developed a simplifiedin vitromodel of cardiac fibrosis, with human cardiac fibroblasts whom differentiation into myofibroblasts was promoted with TGF-β1. Our study addresses an unreported impedance-based method for real-time monitoring ofin vitrocardiac fibrosis. The objective was to study whether the differentiation of cardiac fibroblasts in myofibroblasts had a specific signature on the cell index, an impedance-based feature measured by the xCELLigence system. Primary human cardiac fibroblasts were cultured along 6 days, with or without laminin coating, to study the role of this adhesion protein in cultures long-term maintenance. The cultures were characterized in the presence or absence of TGF-β1 and we obtained a significant cell index signature specific to the human cardiac fibroblasts differentiation.

Bio-impedance measurement allows displaying the early stages of neutrophil extracellular traps

Neutrophils are the most abundant immune cells in the blood. Besides common immune defense mechanisms, releasing their DNA covered with antimicrobial proteases and histones represent another strong defense mechanism: neutrophil extracellular traps. In vitro the two most common inducers of these, so called, NETs are calcium ionophores (CI) and PMA (Phorbol 12-myristate 13-acetate). Following stimulation monitoring of NET release is necessary. For now, the methods of choice are quantification of free DNA by fluorescent dyes or analysis of immunofluorescence images. As a new method we tested bio-impedance monitoring of neutrophils after stimulation with the two inducers PMA and CI in gold-electrode coated plates. Bio-impedance (cell index) was measured over time. Results were compared to the monitoring of NETs by the fluorescent DNA-binding dye Sytox Green and immunofluorescence analysis. Cell index peaked about 25 min faster following CI stimulation than following PMA stimulation. The activation in Sytox Green Assay was significantly later detectable for PMA (+ approx. 90 min) but not for CI stimulation. The earlier and faster activation by CI was also confirmed by immunofluorescence staining. Our data suggest that bio-impedance measurement allows an easy online tracking of early neutrophil activation. This offers new opportunities to monitor early phases and stimuli-dependent dynamics of NETosis.

Biosensors for Detecting Lymphocytes and Immunoglobulins

Lymphocytes (B, T and natural killer cells) and immunoglobulins are essential for the adaptive immune response against external pathogens. Flow cytometry and enzyme-linked immunosorbent (ELISA) kits are the gold standards to detect immunoglobulins, B cells and T cells, whereas the impedance measurement is the most used technique for natural killer cells. For point-of-care, fast and low-cost devices, biosensors could be suitable for the reliable, stable and reproducible detection of immunoglobulins and lymphocytes. In the literature, such biosensors are commonly fabricated using antibodies, aptamers, proteins and nanomaterials, whereas electrochemical, optical and piezoelectric techniques are used for detection. This review describes how these measurement techniques and transducers can be used to fabricate biosensors for detecting lymphocytes and the total content of immunoglobulins. The various methods and configurations are reported, along with the advantages and current limitations.

Hypercapnia and Hypoxia Stimulate Proliferation of Astrocytes and Neurons In Vitro

We compared proliferative activity and hypoxic tolerance in a co-culture of neurons and astrocytes in vitro after preliminary exposure to normobaric hypoxia and/or permissive hypercapnia in vivo. Preliminary hypoxic exposure increased the cell index throughout the 72-h period of observation, the effect of hypercapnia was observed on days 1 and 3 of the experiment, and the effect of hypercapnic hypoxia was noted only on day 1. Preliminary hypoxic exposure has a protective effect on nerve cells under conditions of chemical hypoxia. This suggests that hypercapnia and hypoxia activate proliferative activity of nerve cells, which can be viewed as a mechanism of their neuroprotective effectiveness.

A novel cell-based assay for dynamically detecting neutrophil extracellular traps-induced lung epithelial injuries

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS) are common lung disorders characterized by alveolar-capillary barrier disruption and dyspnea, which can cause substantial morbidity and mortality. Currently, a cluster of acute respiratory illnesses, known as novel coronavirus (2019-nCoV)-infected pneumonia (NCIP), which allegedly originally occurred in Wuhan, China, has increased rapidly worldwide. The critically ill patients with ARDS have high mortality in subjects with comorbidities. Previously, the excessive recruitment and activation of neutrophils (polymorphonuclear leukocytes [PMNs]), accompanied by neutrophil extracellular traps (NETs) formation were reported being implicated in the pathogenesis of ALI/ARDS. However, the direct visualization of lung epithelial injuries caused by NETs, and the qualitative and quantitative evaluations of this damage are still lacking. Additionally, those already reported methods are limited for their neglect of the pathological role exerted by NETs and focusing only on the morphological features of NETosis. Therefore, we established a cell-based assay for detecting NETs during lung epithelial cells-neutrophils co-culture using the xCELLigence system, a recognized real-time, dynamic, label-free, sensitive, and high-throughput apparatus. Our results demonstrated that lung epithelial injuries, reflected by declines in cell index (CI) values, could be induced by lipopolysaccharide (LPS)-activated PMNs, or NETs in a time and dose-dependent manner. NETs generation was verified to be the major contributor to the cytotoxicity of activated PMNs; protein components of NETs were the prevailing cytotoxic mediators. Moreover, this cell-based assay identified that PMNs from severe pneumonia patients had a high NETs formative potential. Additionally, acetylsalicylic acid (ASA) and acetaminophen (APAP) were discovered alleviating NETs formation. Thus, this study not only presents a new methodology for detecting the pathophysiologic role of NETs but also lays down a foundation for exploring therapeutic interventions in an effort to cure ALI/ARDS in the clinical setting of severe pneumonia, including the emerging of NCIP.

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A real-time, dynamical and label-free assay for detecting NETs is established using the xCELLigence system.

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This establishment relies on the co-culture of lung epithelia and neutrophils, focusing on evaluating NETs’ effects.

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This cell-based assay has feasibility and practicality in clinical applications.

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This methodology builds a solid foundation for exploring therapies for ALI/ARDS, including the emerging NCIP.

Early Diagnosis of Pathogen Infection by Cell-Based Activation Immunoassay

Diagnostic identification of pathogens is usually accomplished by isolation of the pathogen or its substances, and should correlate with the time and site of infection. Alternatively, immunoassays such as enzyme-linked immunosorbent assay (ELISA) tests for quantification of serum antibodies are expedient and are usually employed for retrospective diagnostic of a particular infective agent. Here, the potential of cell-based immunoassays for early pathogen detection was evaluated by quantification of specific, antigen-activated, low-frequency IFNγ-secreting cells in mouse spleens following infection with various pathogens. Using enzyme-linked immunospot (ELISPOT) assays, specific responses were observed within 3–6 days following infection with F. tularensis, B. anthracis, Y. pestis, or Influenza virus. Blood samples collected from F. tularensis-infected mice revealed the presence of IFNγ-producing activated cells within one week post infection. When non-human primates were infected with B. anthracis, cellular response was observed in peripheral blood samples as early as five days post infection, 3–5 days earlier than serum antibodies. Finally, the expression pattern of genes in splenocytes of F. tularensis-infected mice was inspected by a transcriptomic approach, enabling the identification of potential host targets for the future development of genetic-based cellular immunoassays. Altogether, the data demonstrate the potential of cell-based immunoassays for early pathogen detection.

Development of SPR Imaging-Impedance Sensor for Multi-Parametric Living Cell Analysis

Label-free evaluation and monitoring of living cell conditions or functions by means of chemical and/or physical sensors in a real-time manner are increasingly desired in the field of basic research of cells and clinical diagnosis. In order to perform multi-parametric analysis of living cells on a chip, we here developed a surface plasmon resonance (SPR) imaging (SPRI)-impedance sensor that can detect both refractive index (RI) and impedance changes on a sensor chip with comb-shaped electrodes. We then investigated the potential of the sensor for label-free and real-time analysis of living cell reactions in response to stimuli. We cultured rat basophilic leukemia (RBL)-2H3 cells on the sensor chip, which was a glass slide coated with comb-shaped electrodes, and detected activation of RBL-2H3 cells, such as degranulation and morphological changes, in response to a dinitro-phenol-conjugated human serum albumin (DNP-HSA) antigen. Moreover, impedance analysis revealed that the changes of impedance derived from RBL-2H3 cell activation appeared in the range of 1 kHz–1 MHz. Furthermore, we monitored living cell-derived RI and impedance changes simultaneously on a sensor chip using the SPRI-impedance sensor. Thus, we developed a new technique to monitor both impedance and RI derived from living cells by using a comb-shaped electrode sensor chip. This technique may enable us to clarify complex living cell functions which affect the RI and impedance and apply this to medical applications, such as accurate clinical diagnosis of type I allergy.

Impedance-based analysis of Natural Killer cell stimulation

The use of impedance-based label free cell analysis is increasingly popular and has many different applications. Here, we report that a real-time cell analyzer (RTCA) can be used to study the stimulation of Natural Killer (NK) cells. Engagement of NK cells via plate-bound antibodies directed against different activating surface receptors could be measured in real time using the label-free detection of impedance. The change in impedance was dependent on early signal transduction events in the NK cells as it was blocked by inhibitors of Src-family kinases and by inhibiting actin polymerization. While CD16 was the only receptor that could induce a strong change in impedance in primary NK cells, several activating receptors induced changes in impedance in expanded NK cells. Using PBMCs we could detect T cell receptor-mediated T cell activation and CD16-mediated NK cell activation in the same sample. Performing a dose-response analysis for the Src-family kinases inhibitor PP1 we show that T cells are more sensitive to inhibition compared to NK cells. Our data demonstrate that the RTCA can be used to detect physiological activation events in NK cells in a label-free and real-time fashion.

Impedance-Based Living Cell Analysis for Clinical Diagnosis of Type I Allergy

Non-invasive real time evaluation of living cell conditions and functions are increasingly desired in the field of clinical diagnosis. For diagnosis of type I allergy, the identification of antigens that induces activation of mast cells and basophils is crucial to avoid symptoms of allergic diseases. However, conventional tests, such as detection of antigen-specific IgE antibody and skin tests, are either of low reliability or are invasive. To overcome such problems, we hereby applied an impedance sensor for label-free and real-time monitoring of mast cell reactions in response to stimuli. When IgE-sensitized RBL-2H3 cells cultured on the electrodes were stimulated with various concentrations of antigens, dose-dependent cell index (CI) increases were detected. Moreover, we confirmed that the impedance sensor detected morphological changes rather than degranulation as the indicator of cell activation. Furthermore, the CI of human IgE receptor-expressing cells (RBL-48 cells) treated with serum of a sweat allergy-positive patient, but not with serum from a sweat allergy-negative patient, significantly increased in response to purified human sweat antigen. We thus developed a technique to detect the activation of living cells in response to stimuli without any labeling using the impedance sensor. This system may represent a high reliable tool for the diagnosis of type I allergy.

Label-free identification of activated T lymphocytes through tridimensional microsensors on chip

Label-free approaches to assess cell properties ideally suit the requirements of cell-based therapeutics, since they permit to characterize cells with minimal perturbation and manipulation, at the benefit of sample recovery and re-employment for treatment. For this reason, label-free techniques would find sensible application in adoptive T cell-based immunotherapy. In this work, we describe the label-free and single-cell detection of in vitro activated T lymphocytes in flow through an electrical impedance-based setup. We describe a novel platform featuring 3D free-standing microelectrodes presenting passive upstream and downstream extensions and integrated into microfluidic channels. We employ such device to measure the impedance change associated with T cell activation at electrical frequencies maximizing the difference between non-activated and activated T cells. Finally, we harness the impedance signature of unstimulated T cells to set a boundary separating activated and non-activated clones, so to characterize the selectivity and specificity of the system. In conclusion, the strategy here proposed highlights the possible employment of impedance to assess T cell activation in label-free.

Dynamic monitoring of GPER-mediated estrogenic effects in breast cancer associated fibroblasts: An alternative role of estrogen in mammary carcinoma development

Cancer associated fibroblasts (CAFs) are crucial contributors to breast cancer development. Estrogen affects mammary stroma in both physiological and pathophysiological conditions. We show here that estrogen (G-protein coupled) receptor (GPER) could be detected by immunohistochemistry in stromal fibroblasts of primary breast cancers. The presence of GPER expression was further confirmed by immunofluorescence and quantitative PCR in CAFs isolated from primary breast cancers. Based on dynamic monitoring by real time cell analyzer (RTCA) system, 17-β-estradiol (E2) as well as GPER specific agonist G1 were observed to trigger transient cell index increasing within an hour in a dosage-dependent manner in breast CAFs. In addition, E2 and G1 stimulated intracellular calcium modulation and phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 within seconds and minutes in CAFs, respectively. Moreover, E2 and G1 promoted cell proliferation of breast CAFs measured by RTCA monitoring, cell viability assay and cell cycle analysis, and this promotion could be blocked by a GPER-selective antagonist G15. Interestingly, dynamic RTCA monitoring indicated that E2 increased adhesion of resuspended cells, and microscopy confirmed that E2 stimulated cell spreading. Both the adhesion and spreading were proposed to be mediated by GPER, since G1 also stimulated these effects similar to E2, and G15 reduced them. Moreover, GPER was found to mediate migration that was increased by E2 and G1 but reduced by G15 in RTCA cell migration assay and transwell assay. Accordingly, GPER mediates not only rapid actions but also slow effects including adhesion/spreading, proliferation and migration in breast CAFs. Estrogen is likely to affect tumor associated stroma and contributes to mammary carcinoma development through CAFs.

Primary Macrophage Chemotaxis Induced by Cannabinoid Receptor 2 Agonists Occurs Independently of the CB2 Receptor

Activation of CB₂ has been demonstrated to induce directed immune cell migration. However, the ability of CB2 to act as a chemoattractant receptor in macrophages remains largely unexplored. Using a real-time chemotaxis assay and a panel of chemically diverse and widely used CB₂ agonists, we set out to examine whether CB₂ modulates primary murine macrophage chemotaxis. We report that of 12 agonists tested, only JWH133, HU308, L-759,656 and L-759,633 acted as macrophage chemoattractants. Surprisingly, neither pharmacological inhibition nor genetic ablation of CB₂ had any effect on CB₂ agonist-induced macrophage chemotaxis. As chemotaxis was pertussis toxin sensitive in both WT and CB₂^-/- macrophages, we concluded that a non-CB₁/CB₂, G_i/o-coupled GPCR must be responsible for CB₂ agonist-induced macrophage migration. The obvious candidate receptors GPR18 and GPR55 could not mediate JWH133 or HU308-induced cytoskeletal rearrangement or JWH133-induced β-arrestin recruitment in cells transfected with either receptor, demonstrating that neither are the unidentified GPCR. Taken together our results conclusively demonstrate that CB₂ is not a chemoattractant receptor for murine macrophages. Furthermore we show for the first time that JWH133, HU308, L-759,656 and L-759,633 have off-target effects of functional consequence in primary cells and we believe that our findings have wide ranging implications for the entire cannabinoid field.

A simple in vitro method for evaluating dendritic cell-based vaccinations

Background

Dendritic cell (DC) therapy is a promising therapy for cancer-targeting treatments. Recently, DCs have been used for treatment of some cancers. We aimed to develop an in vitro assay to evaluate DC therapy in cancer treatment using a breast cancer model.

Methods

DCs were induced from murine bone marrow mononuclear cells in Roswell Park Memorial Institute (RPMI) 1640 medium supplemented with GM-CSF (20 ng/mL) and IL-4 (20 ng/mL). Immature DCs were primed with breast cancer stem cell (BCSC)-derived antigens. BCSCs were sorted from 4T1 cell lines based on aldehyde dehydrogenase expression. A mixture of DCs and cytotoxic T lymphocytes (CTLs) were used to evaluate the inhibitory effect of antigen-primed DCs on BCSCs. BCSC proliferation and doubling time were recorded based on impedance-based cell analysis using the xCELLigence system. The specification of inhibitory effects of DCs and CTLs was also evaluated using the same system.

Results

The results showed that impedance-based analysis of BCSCs reflected cytotoxicity and inhibitory effects of DCs and CTLs at 72 hours. Differences in ratios of DC:CTL changed the cytotoxicity of DCs and CTLs.

Conclusion

This study successfully used impedance-based cell analysis as a new in vitro assay to evaluate DC efficacy in cancer immunotherapy. We hope this technique will contribute to the development and improvement of immunotherapies in the near future.

Size does matter! Label-free detection of small molecule-protein interaction

This review is focused on methods for detecting small molecules and, in particular, the characterisation of their interaction with natural proteins (e.g. receptors, ion channels). Because there are intrinsic advantages to using label-free methods over labelled methods (e.g. fluorescence, radioactivity), this review only covers label-free techniques. We briefly discuss available techniques and their advantages and disadvantages, especially as related to investigating the interaction between small molecules and proteins. The reviewed techniques include well-known and widely used standard analytical methods (e.g. HPLC-MS, NMR, calorimetry, and X-ray diffraction), newer and more specialised analytical methods (e.g. biosensors), biological systems (e.g. cell lines and animal models), and in-silico approaches.

Mangiferin has an additive effect on the apoptotic properties of hesperidin in Cyclopia sp. tea extracts

A variety of biological pro-health activities have been reported for mangiferin and hesperidin, two major phenolic compounds of Honeybush (Cyclopia sp.) tea extracts. Given their increasing popularity, there is a need for understanding the mechanisms underlying the biological effects of these compounds. In this study, we used real-time cytotoxicity cellular analysis of the Cyclopia sp. extracts on HeLa cells and found that the higher hesperidin content in non-fermented "green" extracts correlated with their higher cytotoxicity compared to the fermented extracts. We also found that mangiferin had a modulatory effect on the apoptotic effects of hesperidin. Quantitative PCR analysis of hesperidin-induced changes in apoptotic gene expression profile indicated that two death receptor pathway members, TRADD and TRAMP, were up regulated. The results of this study suggest that hesperidin mediates apoptosis in HeLa cells through extrinsic pathway for programmed cell death.

Autotaxin-lysophosphatidic acid signaling axis mediates tumorigenesis and development of acquired resistance to sunitinib in renal cell carcinoma

PURPOSE

Sunitinib is currently considered as the standard treatment for advanced renal cell carcinoma (RCC). We aimed to better understand the mechanisms of sunitinib action in kidney cancer treatment and in the development of acquired resistance.

EXPERIMENTAL DESIGN

Gene expression profiles of RCC tumor endothelium in sunitinib-treated and -untreated patients were analyzed and verified by quantitative PCR and immunohistochemistry. The functional role of the target gene identified was investigated in RCC cell lines and primary cultures in vitro and in preclinical animal models in vivo.

RESULTS

Altered expression of autotaxin, an extracellular lysophospholipase D, was detected in sunitinib-treated tumor vasculature of human RCC and in the tumor endothelial cells of RCC xenograft models when adapting to sunitinib. ATX and its catalytic product, lysophosphatidic acid (LPA), regulated the signaling pathways and cell motility of RCC in vitro. However, no marked in vitro effect of ATX-LPA signaling on endothelial cells was observed. Functional blockage of LPA receptor 1 (LPA1) using an LPA1 antagonist, Ki16425, or gene silencing of LPA1 in RCC cells attenuated LPA-mediated intracellular signaling and invasion responses in vitro. Ki16425 treatment also dampened RCC tumorigenesis in vivo. In addition, coadministration of Ki16425 with sunitinib prolonged the sensitivity of RCC to sunitinib in xenograft models, suggesting that ATX-LPA signaling in part mediates the acquired resistance against sunitinib in RCC.

CONCLUSIONS

Our results reveal that endothelial ATX acts through LPA signaling to promote renal tumorigenesis and is functionally involved in the acquired resistance of RCC to sunitinib.