A compendium of single extracellular vesicle flow cytometry

Flow cytometry (FCM) offers a multiparametric technology capable of characterizing single extracellular vesicles (EVs). However, most flow cytometers are designed to detect cells, which are larger than EVs. Whereas cells exceed the background noise, signals originating from EVs partly overlap with the background noise, thereby making EVs more difficult to detect than cells. This technical mismatch together with complexity of EV-containing fluids causes limitations and challenges with conducting, interpreting and reproducing EV FCM experiments. To address and overcome these challenges, researchers from the International Society for Extracellular Vesicles (ISEV), International Society for Advancement of Cytometry (ISAC), and the International Society on Thrombosis and Haemostasis (ISTH) joined forces and initiated the EV FCM working group. To improve the interpretation, reporting, and reproducibility of future EV FCM data, the EV FCM working group published an ISEV position manuscript outlining a framework of minimum information that should be reported about an FCM experiment on single EVs (MIFlowCyt-EV). However, the framework contains limited background information. Therefore, the goal of this compendium is to provide the background information necessary to design and conduct reproducible EV FCM experiments. This compendium contains background information on EVs, the interaction between light and EVs, FCM hardware, experimental design and preanalytical procedures, sample preparation, assay controls, instrument data acquisition and calibration, EV characterization, and data reporting. Although this compendium focuses on EVs, many concepts and explanations could also be applied to FCM detection of other particles within the EV size range, such as bacteria, lipoprotein particles, milk fat globules, and viruses

Stability of monodisperse phospholipid-coated microbubbles formed by flow-focusing at high production rates

Monodisperse microbubble ultrasound contrast agents may dramatically increase the sensitivity and efficiency in ultrasound imaging and therapy. They can be produced directly in a microfluidic flow-focusing device, but questions remain as to the interfacial chemistry, such as the formation and development of the phospholipid monolayer coating over time. Here, we demonstrate the synthesis of monodisperse bubbles with radii of 2–10 μm at production rates ranging from 104 to 106 bubbles/s. All bubbles were found to dissolve to a stable final radius 2.55 times smaller than their initial radius, independent of the nozzle size and shear rate, indicating that the monolayer self-assembles prior to leaving the nozzle. The corresponding decrease in surface area by a factor 6.6 reveals that lipid molecules are adsorbed to the gas–liquid interface in the disordered expanded state, and they become mechanically compressed by Laplace pressure-driven bubble dissolution to a more ordered condensed state with near zero surface tension. Acoustic characterization of the stabilized microbubbles revealed that their shell stiffness gradually increased from 0.8 to 2.5 N/m with increasing number of insonations through the selective loss of the more soluble lipopolymer molecules. This work therefore demonstrates high-throughput production of clinically relevant monodisperse contrast microbubbles with excellent control over phospholipid monolayer elasticity and microbubble resonance

Hand-opening feedback for myoelectric forearm prostheses: Performance in virtual grasping tasks influenced by different levels of distraction

Sensory feedback and the required attentional demands are important aspects in prosthesis acceptance. In this study, hand-opening feedback is provided and the performance in a virtual grasping task is investigated. Simultaneously, a secondary task was performed to investigate the attentional demands. Ten nondisabled subjects performed the tasks with and without feedback about the hand opening through an array of eight vibrotactile stimulators on the forearm. Activation of one stimulator corresponded to one hand-opening position. For the dual-task experiments, subjects simultaneously performed a secondary auditory counting task. The addition of vibrotactile feedback increased the performance (expressed in percentages of correct hand positions, mean absolute errors in position, and percentages of deviations up to one hand-opening position), but the duration of the tasks was also increased. Three levels of distraction (no distraction, counting task, count and subtract task) were applied, which did not influence the performance in the grasping tasks except for the highest level of distraction. We concluded that the proposed method to provide hand-opening feedback through an array of eight vibrotactile stimulators is successful because the performance in a grasping task increases but it is not significantly attention demanding

Quantification of Light Scattering Detection Efficiency and Background in Flow Cytometry

Knowledge of the sensitivity of a flow cytometer is essential for data interpretation and comparison. However, light scatter sensitivity currently cannot be quantified due to a lack of a standardized unit. Analogous to the QB approach for fluorescence, we show that it is possible to derive the detection efficiency Q and background B for light scatter detectors, using the scattering cross section (σs) in nm2 as a standardized unit. Side scatter of a mixture of polystyrene beads with known diameter and refractive index was measured at different illumination powers on a customized BD FACSCanto. Poisson statistics was used to derive the number of statistical photoelectrons from the measured coefficient of variation of the bead populations. The resulting light scatter sensitivity was expressed as Q in photoelectrons/nm2, B in nm2, and a resolution limit (R) in nm2. As expected, Q scales linearly with the illumination power (R2 = 0.999), and B is constant over the illumination power (difference < 15%). The resulting R decreased from 1.75·105 nm2 at 20 mW, to 4.03·104 nm2 at 200 mW, which resembles the light scattering of a 450 nm and a 314 nm polystyrene bead, respectively. Comparison of R with the side scatter histograms confirmed that R describes the lower limit at which light scatter signals can be fully discriminated from the background noise. In conclusion, as a proof of principle, we derived Q, B, and R for a scatter detector of a flow cytometer where photon noise associated with the light scattering signal originating from the particle is the dominant source of the measured variation. To quantify the sensitivity of scatter detectors with nanoparticle (<100 nm) sensitivity, our approach requires monodisperse (variation coefficient < 2%) nanoparticles that scatter light isotropically. © 2020 The Authors. Cytometry Part A published by Wiley Periodicals LLC on behalf of International Society for Advancement of Cytometry

Comparison of Generic Fluorescent Markers for Detection of Extracellular Vesicles by Flow Cytometry

Extracellular vesicles (EVs) in biofluids are potential biomarkers of disease. To explore the clinical relevance of EVs, a specific generic EV marker would be useful, one that does not require antibodies and binds to all EVs. Here we evaluated 5 commonly used generic markers for flow cytometry. +)]. Side scatter triggering was applied as a reference, and the influence of non-EV components (proteins and lipoproteins) was evaluated. +EVs, respectively. Di-8-ANEPPS detected platelet EVs only if soluble protein was first removed. Because all generic markers stained proteins, at best 33% of platelet EVs in plasma were detected. The calcein markers and CFSE were either insensitive to EVs in both samples or associated with swarm detection. None of the generic markers detected all and only EVs in plasma. Side scatter triggering detected the highest concentration of plasma EVs on our A60-Micro, followed by lactadherin. The choice between scatter or lactadherin primarily depends on the analytical sensitivity of the flow cytometer use

Detection of extracellular vesicles in plasma and urine of prostate cancer patients by flow cytometry and surface plasmon resonance imaging

Large (> 1 μm) tumor-derived extracellular vesicles (tdEVs) enriched from the cell fraction of centrifuged whole blood are prognostic in metastatic castration-resistant prostate cancer (mCRPC) patients. However, the highest concentration of tdEVs is expected in the cell-free plasma fraction. In this pilot study, we determine whether mCRPC patients can be discriminated from healthy controls based on detection of tdEVs (< 1μm, EpCAM+) and/or other EVs, in cell-free plasma and/or urine. The presence of marker+ EVs in plasma and urine samples from mCRPC patients (n = 5) and healthy controls (n = 5) was determined by flow cytometry (FCM) and surface plasmon resonance imaging (SPRi) using an antibody panel and lactadherin. For FCM, the concentrations of marker positive (+) particles and EVs (refractive index <1.42) were determined. Only the lactadherin+ particle and EV concentration in plasma measured by FCM differed significantly between patients and controls (p = 0.017). All other markers did not result in signals exceeding the background on both FCM and SPRi, or did not differ significantly between patients and controls. In conclusion, no difference was found between patients and controls based on the detection of tdEVs. For FCM, the measured sample volumes are too small to detect tdEVs. For SPRi, the concentration of tdEVs is probably too low to be detected. Thus, to detect tdEVs in cell-free plasma and/or urine, EV enrichment and/or concentration is required. Furthermore, we recommend testing other markers and/or a combination of markers to discriminate mCRPC patients from healthy controls

Absolute sizing and label-free identification of extracellular vesicles by flow cytometry

Blood contains extracellular vesicles (EVs), which are biological nanoparticles with clinical applications. In blood plasma, EVs are outnumbered by similar-sized lipoprotein particles (LPs), leading to controversial data such as non-specific binding of antibodies to LPs. Flow cytometry is a clinically applicable technique to characterize single EVs in body fluids. However, flow cytometry data have arbitrary units, impeding standardization, data comparison, and data interpretation, such as differentiation between EVs and LPs. Here we present a new method, named flow cytometry scatter ratio (Flow-SR), to relate the ambiguous light scattering signals of flow cytometry to the diameter and refractive index (RI) of single nanoparticles between 200-500 nm in diameter. Flow-SR enables label-free differentiation between EVs and LPs and improves data interpretation and comparison. Because Flow-SR is easy to implement, widely applicable, and more accurate and faster than existing techniques to size nanoparticles in suspension, Flow-SR has numerous applications in nanomedicin

A Systematic Approach to Improve Scatter Sensitivity of a Flow Cytometer for Detection of Extracellular Vesicles

Extracellular vesicles (EVs) are commonly studied by flow cytometry. Due to their small size and low refractive index, the scatter intensity of most EVs is below the detection limit of common flow cytometers. Here, we aim to improve forward scatter (FSC) and side scatter (SSC) sensitivity of a common flow cytometer to detect single 100 nm EVs. The effects of the optical and fluidics configuration on scatter sensitivity of a FACSCanto (Becton Dickinson) were evaluated by the separation index (SI) and robust coefficient of variation (rCV) of polystyrene beads (BioCytex). Improvement is defined as increased SI and/or reduced rCV. Changing the obscuration bar improved the rCV 1.9-fold for FSC. A 10-fold increase in laser power improved the SI 19-fold for FSC and 4.4-fold for SSC, whereas the rCV worsened 0.8-fold and improved 1.5-fold, respectively. Confocalization worsened the SI 1.2-fold for FSC, and improved the SI 5.1-fold for SSC, while the rCV improved 1.1-fold and worsened 1.5-fold, respectively. Replacing the FSC photodiode with a photomultiplier tube improved the SI 66-fold and rCV 4.2-fold. A 2-fold reduction in sample stream width improved both SI and rCV for FSC by 1.8-fold, and for SSC by 1.3- and 2.2-fold, respectively. Decreasing the sample flow velocity worsened rCVs. Decreasing the flow channel dimensions and the pore size of the sheath filter did not substantially change the SI or rCV. Using the optimal optical configuration and fluidics settings, the SI improved 3.8∙104-fold on FSC and 30-fold on SSC, resulting in estimated detection limits for EVs (assuming a refractive index of 1.40) of 246 and 91 nm on FSC and SSC, respectively. Although a 50-fold improvement on FSC is still necessary, these adaptions have produced an operator-friendly, high-throughput flow cytometer with a high sensitivity on both SSC and FSC. © 2020 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry

Reduced Antibody Acquisition with Increasing Age following Vaccination with BNT162b2: Results from Two Longitudinal Cohort Studies in The Netherlands.

Vaccine-induced protection against severe COVID-19, hospitalization, and death is of the utmost importance, especially in the elderly. However, limited data are available on humoral immune responses following COVID-19 vaccination in the general population across a broad age range. We performed an integrated analysis of the effect of age, sex, and prior SARS-CoV-2 infection on Spike S1-specific (S1) IgG concentrations up to three months post-BNT162b2 (Pfizer/BioNTech; Comirnaty) vaccination. In total, 1735 persons, eligible for COVID-19 vaccination through the national program, were recruited from the general population (12 to 92 years old). Sixty percent were female, and the median vaccination interval was 35 days (interquartile range, IQR: 35-35). All participants had seroconverted to S1 one month after two vaccine doses. S1 IgG was higher in participants with a history of SARS-CoV-2 infection (median: 4535 BAU/mL, IQR: 2341-7205) compared to infection-naive persons (1842 BAU/mL, 1019-3116), p &lt; 0.001. In infection-naive persons, linear mixed effects regression showed a strong negative association between age and S1 IgG (p &lt; 0.001) across the entire age range. Females had higher S1 IgG than males (p &lt; 0.001). In persons with an infection history, age nor sex was associated with S1 IgG concentrations. The lower magnitude of S1 antibodies in older persons following COVID-19 vaccination will affect long-term protection

Reduced Antibody Acquisition with Increasing Age following Vaccination with BNT162b2: Results from Two Longitudinal Cohort Studies in The Netherlands.

Vaccine-induced protection against severe COVID-19, hospitalization, and death is of the utmost importance, especially in the elderly. However, limited data are available on humoral immune responses following COVID-19 vaccination in the general population across a broad age range. We performed an integrated analysis of the effect of age, sex, and prior SARS-CoV-2 infection on Spike S1-specific (S1) IgG concentrations up to three months post-BNT162b2 (Pfizer/BioNTech; Comirnaty) vaccination. In total, 1735 persons, eligible for COVID-19 vaccination through the national program, were recruited from the general population (12 to 92 years old). Sixty percent were female, and the median vaccination interval was 35 days (interquartile range, IQR: 35-35). All participants had seroconverted to S1 one month after two vaccine doses. S1 IgG was higher in participants with a history of SARS-CoV-2 infection (median: 4535 BAU/mL, IQR: 2341-7205) compared to infection-naive persons (1842 BAU/mL, 1019-3116), p &lt; 0.001. In infection-naive persons, linear mixed effects regression showed a strong negative association between age and S1 IgG (p &lt; 0.001) across the entire age range. Females had higher S1 IgG than males (p &lt; 0.001). In persons with an infection history, age nor sex was associated with S1 IgG concentrations. The lower magnitude of S1 antibodies in older persons following COVID-19 vaccination will affect long-term protection