Building a spectral cytometry toolbox: Coupling fluorescent proteins and antibodies to microspheres.

Fluorescent proteins (FPs) have become an essential tool for biological research. Since the isolation and description of GFP, hundreds of fluorescent proteins have been discovered and created with various characteristics. The excitation of these proteins ranges from ultra-violet (UV) up to near infra-RED (NIR). Using conventional cytometry with each detector assigned to each fluorochrome, great care must be taken when selecting the optimal bandpass filters to minimalize the spectral overlap. In the last 8 years, several companies have released full spectrum flow cytometers which eliminates the need to change optical filters for analyzing FPs. This addressed at least part of the problem however, the laser wavelengths in commercial instruments are generally not ideal for all fluorescent proteins yet do allow the separation of at least six FPs. Another technical challenge is to have convenient single color controls. If four different FPs are being used in an experiment, single color controls will be needed to compensate or unmix the data. In the case of cultured cells this will involve having each of the FPs expressed in cell lines separately with a parental cell line expressing none. In the case of in vivo experiments, colonies of animals may need to be maintained expressing each FP along with a wildtype animal. This represents a considerable expense and inconvenience. An appealing alternative is to produce and purify FPs and covalently couple to polystyrene microspheres. Such microspheres are ready to use and can be stored at 4°C for months or even years without any deterioration in fluorescence. The same procedure can be used to couple antibodies to these particles. Here we describe this procedure which can be executed in any lab without any special equipment or skills.

Transcriptome sequencing and multi-plex imaging of prostate cancer microenvironment reveals a dominant role for monocytic cells in progression.

BACKGROUND: Prostate cancer is caused by genomic aberrations in normal epithelial cells, however clinical translation of findings from analyses of cancer cells alone has been very limited. A deeper understanding of the tumour microenvironment is needed to identify the key drivers of disease progression and reveal novel therapeutic opportunities. RESULTS: In this study, the experimental enrichment of selected cell-types, the development of a Bayesian inference model for continuous differential transcript abundance, and multiplex immunohistochemistry permitted us to define the transcriptional landscape of the prostate cancer microenvironment along the disease progression axis. An important role of monocytes and macrophages in prostate cancer progression and disease recurrence was uncovered, supported by both transcriptional landscape findings and by differential tissue composition analyses. These findings were corroborated and validated by spatial analyses at the single-cell level using multiplex immunohistochemistry. CONCLUSIONS: This study advances our knowledge concerning the role of monocyte-derived recruitment in primary prostate cancer, and supports their key role in disease progression, patient survival and prostate microenvironment immune modulation.

Procedures for Flow Cytometry-Based Sorting of Unfixed Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infected Cells and Other Infectious Agents.

In response to the recent COVID-19 pandemic, many laboratories are involved in research supporting SARS-CoV-2 vaccine development and clinical trials. Flow cytometry laboratories will be responsible for a large part of this effort by sorting unfixed antigen-specific lymphocytes. Therefore, it is critical and timely that we have an understanding of risk assessment and established procedures of infectious cell sorting. Here we present procedures covering the biosafety aspects of sorting unfixed SARS-CoV-2-infected cells and other infectious agents of similar risk level. These procedures follow the ISAC Biosafety Committee guidelines and were recently approved by the National Institutes of Health Institutional Biosafety Committee for sorting SARS-CoV-2-infected cells. © 2020 International Society for Advancement of Cytometry.

Novel Impactor and Microsphere-Based Assay Used to Measure Containment of Aerosols Generated in a Flow Cytometer Cell Sorter.

Today's state-of-the-art cell sorting flow cytometers are equipped with aerosol containment systems designed to evacuate aerosols from the sort chamber during a sort. This biosafety device is especially important when the sort operator is sorting infectious or potentially infections samples. Hence, it is critical to evaluate the performance for this system in normal operation and in "failure" mode to determine the efficacy of containment. In the past decade, the most popular published method for evaluating containment has been the Glo-Germ bead procedure. These highly fluorescent and multisize particles can easily be detected on a microscope slide and enumerated using a fluorescent microscope. Collecting particles on this slide is accomplished using an Aerotech impactor. This sampler collects potentially escaping aerosols from the sort chamber before enumerating any particles. Although the Glo-Germ procedure has been adopted by many labs, there are several drawbacks with the procedure that have limited its adoption by cell sorter laboratories: The Aerotech impactor is a reusable device that requires rigorous cleaning between measurements. The surface area of the collection slide is large and difficult to scan on a fluorescence microscope. These beads produce a wide variation in sizes resulting in inconsistency in flow rates. Here, we describe a novel and replacement method utilizing a Cyclex-d impactor and Dragon Green beads. This method was compared for sensitivity of detection of escaped aerosols with a published method for aerosol detection which utilizes a UV-APS aerodynamic particle sizer and a UV-excitable dye. One of the advantages of the Cyclex-d system is the narrow-defined field of collection as compared to the standard Glo-Germ bead procedure, this means a smaller sampling area is used in the Cyclex-d impactor as compared to the AeroTech impactor. In addition, the sensitivity of detection was found to be better using the Cyclex-d collection device as compared to the standard Glo-Germ bead procedure. © 2018 International Society for Advancement of Cytometry.

A rapid method to verify single-cell deposition setup for cell sorters.

Studying single cells reveals biology that cannot be explored using bulk techniques. Cell sorters provide the opportunity of separating single cells either for cell culture or for downstream molecular applications such as qPCR to study specific gene expression and single cell mRNA sequencing. Some of these molecular studies can be expensive so the investigator will often want reassurance that the cell sorter can reliably deposit a single droplet into each well of a 96-well or 384-well plate. Such plates may contain very small volumes of fluid as reducing the volume of fluid used can reduce the cost of the assay. To miss some of the wells could leave the data set incomplete requiring costly repetition. To verify this by microscopy is at best very time consuming and at worst impossible. Here, an inexpensive colorimetric method is described for verifying whether a well, in either a 96- or 384-well plate, did receive a single sorted droplet from a cell sorter into the fluid at the bottom of the well. The droplet consists of particles suspended in an enzymatic solution, horseradish peroxidase, which is deposited into microtiter plate wells containing a substrate, 3,3',5,5'-tetramethylbenzidine. This method requires no special equipment or expertise and is rapid enough to be performed directly prior to the single-cell sorting experiment. © 2016 International Society for Advancement of Cytometry.

International Society for the Advancement of Cytometry cell sorter biosafety standards.

Flow cytometric cell sorting of biological specimens has become prevalent in basic and clinical research laboratories. These specimens may contain known or unknown infectious agents, necessitating precautions to protect instrument operators and the environment from biohazards arising from the use of sorters. To this end the International Society of Analytical Cytology (ISAC) was proactive in establishing biosafety guidelines in 1997 (Schmid et al., Cytometry 1997;28:99-117) and subsequently published revised biosafety standards for cell sorting of unfixed samples in 2007 (Schmid et al., Cytometry Part A J Int Soc Anal Cytol 2007;71A:414-437). Since their publication, these documents have become recognized worldwide as the standard of practice and safety precautions for laboratories performing cell sorting experiments. However, the field of cytometry has progressed since 2007, and the document requires an update. The new Standards provides guidance: (1) for laboratory design for cell sorter laboratories; (2) for the creation of laboratory or instrument specific Standard Operating Procedures (SOP); and (3) on procedures for the safe operation of cell sorters, including personal protective equipment (PPE) and validation of aerosol containment.

Fluorescent Protein Production, Purification, and Coupling to Microspheres.

Fluorescent proteins (FPs) have become an essential tool for biological research. Since the isolation and description of green FP, hundreds of FPs have been discovered and created with various characteristics. The excitation of these proteins ranges from ultraviolet (UV) up to near infrared (NIR). Using conventional cytometry, with each detector assigned to a fluorochrome, great care must be taken when selecting the optimal bandpass filters to minimalize the spectral overlap as the emission spectra of FPs are broad. Full-spectrum flow cytometers eliminate the need to change optical filters for analyzing FPs, which simplifies instrument setup. In experiments where more than one FP is used, single-color controls are required. These can be cells expressing each of the proteins separately. In the case of the confetti system, for instance, when four FPs are used, all these proteins will need to be expressed separately so that compensation or spectral unmixing can be performed, and this can be inconvenient and expensive. An appealing alternative is to produce FPs in Escherichia coli, purify them, and covalently couple them to carboxylate polystyrene microspheres. Such microspheres are ready to use and can be stored at 4°C for months or even years without any deterioration in fluorescence. The same procedure can be used to couple antibodies or other proteins to these particles. Here, we describe how to express and purify FPs, how to couple them to microspheres, and how to evaluate the fluorescent properties of the particles. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Escherichia coli expression and purification of recombinant mPlum Basic Protocol 2: Coupling fluorescent proteins to polystyrene microspheres Support Protocol 1: Comparing the cell-bound and bead-bound fluorescence signatures Support Protocol 2: Comparing spectral signatures via the similarity index, complexity matrix, and spillover spread matrix of fluorescent protein-coupled beads.

Inhibition of Hematopoietic Cell Kinase Activity Suppresses Myeloid Cell-Mediated Colon Cancer Progression.

Aberrant activation of the SRC family kinase hematopoietic cell kinase (HCK) triggers hematological malignancies as a tumor cell-intrinsic oncogene. Here we find that high HCK levels correlate with reduced survival of colorectal cancer patients. Likewise, increased Hck activity in mice promotes the growth of endogenous colonic malignancies and of human colorectal cancer cell xenografts. Furthermore, tumor-associated macrophages of the corresponding tumors show a pronounced alternatively activated endotype, which occurs independently of mature lymphocytes or of Stat6-dependent Th2 cytokine signaling. Accordingly, pharmacological inhibition or genetic reduction of Hck activity suppresses alternative activation of tumor-associated macrophages and the growth of colon cancer xenografts. Thus, Hck may serve as a promising therapeutic target for solid malignancies.

Long-term maintenance of virus-specific effector memory CD8+ T cells in the lung airways depends on proliferation.

Recent studies have shown that virus-specific effector memory T cells can be recovered from the lung airways long after clearance of a respiratory virus infection. These cells are thought to play an important role in the recall response to secondary viral infection. It is currently unclear whether these cells actually persist at this site or are maintained by continual proliferation and recruitment. In this study, we have analyzed the mechanisms underlying the persistence of memory CD8(+) T cells in the lung airway lumina following recovery from a respiratory virus infection. The data identify two distinct populations of memory cells. First, a large population Ag-specific CD8(+) T cells is deposited in the airways during the acute response to the virus. These cells persist in a functional state for several weeks with minimal further division. Second, a smaller population of Ag-specific CD8(+) T cells is maintained in the lung airways by homeostatic proliferation and migration to lung airways after viral clearance. This rate of proliferation is identical to that observed in the spleen, suggesting that these cells may be recent immigrants from the lymphoid organs. These data have significant implications for vaccines designed to promote cellular immunity at mucosal sites such as the lung.