Measuring containment of viable infectious cell sorting in high-velocity cell sorters

Guidelines for establishing a cytometry laboratory

The purpose of this document is to provide guidance for establishing and maintaining growth and development of flow cytometry shared resource laboratories. While the best practices offered in this manuscript are not intended to be universal or exhaustive, they do outline key goals that should be prioritized to achieve operational excellence and meet the needs of the scientific community. Additionally, this document provides information on available technologies and software relevant to shared resource laboratories. This manuscript builds on the work of Barsky et al. 2016 published in Cytometry Part A and incorporates recent advancements in cytometric technology. A flow cytometer is a specialized piece of technology that require special care and consideration in its housing and operations. As with any scientific equipment, a thorough evaluation of the location, space requirements, auxiliary resources, and support is crucial for successful operation. This comprehensive resource has been written by past and present members of the International Society for Advancement of Cytometry (ISAC) Shared Resource Laboratory (SRL) Emerging Leaders Program https://isac-net.org/general/custom.asp?page=SRL-Emerging-Leaders with extensive expertise in managing flow cytometry SRLs from around the world in different settings including academia and industry. It is intended to assist in establishing a new flow cytometry SRL, re-purposing an existing space into such a facility, or adding a flow cytometer to an individual lab in academia or industry. This resource reviews the available cytometry technologies, the operational requirements, and best practices in SRL staffing and management.

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.

Fluorescence activated cell sorting via a focused traveling surface acoustic beam

Fluorescence activated cell sorting (FACS) has become an essential technique widely exploited in biological studies and clinical applications. However, current FACS systems are quite complex, expensive, bulky, and pose potential sample contamination and biosafety issues due to the generation of aerosols in an open environment. Microfluidic technology capable of precise cell manipulation has great potential to reinvent and miniaturize conventional FACS systems. In this work, we demonstrate a benchtop scale FACS system that makes use of a highly focused traveling surface acoustic wave beam to sort out micron-sized particles and biological cells upon fluorescence interrogation at ∼kHz rates. The highly focused acoustic wave beam has a width of ∼50 μm that enables highly accurate sorting of individual particles and cells. We have applied our acoustic FACS system to isolate fluorescently labeled MCF-7 breast cancer cells from diluted whole blood samples with the purity of sorted MCF-7 cells higher than 86%. The cell viability before and after acoustic sorting is higher than 95%, indicating excellent biocompatibility that should enable a variety of cell sorting applications in biomedical research.

Qualification of academic facilities for small-scale automated manufacture of autologous cell-based products

Academic centers, hospitals and small companies, as typical development settings for UK regenerative medicine assets, are significant contributors to the development of autologous cell-based therapies. Often lacking the appropriate funding, quality assurance heritage or specialist regulatory expertise, qualifying aseptic cell processing facilities for GMP compliance is a significant challenge. The qualification of a new Cell Therapy Manufacturing Facility with automated processing capability, the first of its kind in a UK academic setting, provides a unique demonstrator for the qualification of small-scale, automated facilities for GMP-compliant manufacture of autologous cell-based products in these settings. This paper shares our experiences in qualifying the Cell Therapy Manufacturing Facility, focusing on our approach to streamlining the qualification effort, the challenges, project delays and inefficiencies we encountered, and the subsequent lessons learned.

Evaluation of cell sorting aerosols and containment by an optical airborne particle counter

Understanding aerosols produced by cell sorting is critical to biosafety risk assessment and validation of containment efficiency. In this study an Optical Airborne Particle Counter was used to analyze aerosols produced by the BD FACSAria and to assess the effectiveness of its aerosol containment. The suitability of using this device to validate containment was directly compared to the Glo-Germ method put forth by the International Society for Advancement of Cytometry (ISAC) as a standard for testing. It was found that high concentrations of aerosols ranging from 0.3 µm to 10 µm can be detected in failure mode, with most less than 5 µm. In most cases, while numerous aerosols smaller than 5 µm were detected by the Optical Airborne Particle Counter, no Glo-Germ particles were detected, indicating that small aerosols are under-evaluated by the Glo-Germ method. The results demonstrate that the Optical Airborne Particle Counter offers a rapid, economic, and quantitative analysis of cell sorter aerosols and represents an improved method over Glo-Germ for the task of routine validation and monitoring of aerosol containment for cell sorting.

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.

Tracking cross-contamination transfer dynamics at a mock retail deli market using GloGerm

Ready-to-eat (RTE) deli meats are considered a food at high risk for causing foodborne illness. Deli meats are listed as the highest risk RTE food vehicle for Listeria monocytogenes. Cross-contamination in the retail deli market may contribute to spread of pathogens to deli meats. Understanding potential cross-contamination pathways is essential for reducing the risk of contaminating various products. The objective of this study was to track cross-contamination pathways through a mock retail deli market using an abiotic surrogate, GloGerm, to visually represent how pathogens may spread through the deli environment via direct contact with food surfaces. Six contamination origination sites (slicer blade, meat chub, floor drain, preparation table, employee's glove, and employee's hands) were evaluated separately. Each site was inoculated with 20 ml of GloGerm, and a series of standard deli operations were completed (approximately 10 min of work). Photographs were then taken under UV illumination to visualize spread of GloGerm throughout the deli. A sensory panel evaluated the levels of contamination on the resulting contaminated surfaces. Five of the six contamination origination sites were associated with transfer of GloGerm to the deli case door handle, slicer blade, meat chub, preparation table, and the employee's gloves. Additional locations became contaminated (i.e., deli case shelf, prep table sink, and glove box), but this contamination was not consistent across all trials. Contamination did not spread from the floor drain to any food contact surfaces. The findings of this study reinforce the need for consistent equipment cleaning and food safety practices among deli workers to minimize cross-contamination.

How to develop a standard operating procedure for sorting unfixed cells

Written standard operating procedures (SOPs) are an important tool to assure that recurring tasks in a laboratory are performed in a consistent manner. When the procedure covered in the SOP involves a high-risk activity such as sorting unfixed cells using a jet-in-air sorter, safety elements are critical components of the document. The details on sort sample handling, sorter set-up, validation, operation, troubleshooting, and maintenance, personal protective equipment (PPE), and operator training, outlined in the SOP are to be based on careful risk assessment of the procedure. This review provides background information on the hazards associated with sorting of unfixed cells and the process used to arrive at the appropriate combination of facility design, instrument placement, safety equipment, and practices to be followed.

Flow cytometry: retrospective, fundamentals and recent instrumentation

Flow cytometry is a complete technology given to biologists to study cellular populations with high precision. This technology elegantly combines sample dimension, data acquisition speed, precision and measurement multiplicity. Beyond the statistical aspect, flow cytometry offers the possibility to physically separate sub-populations. These performances come from the common endeavor of physicists, biophysicists, biologists and computer engineers, who succeeded, by providing new concepts, to bring flow cytometry to current maturity. The aim of this paper is to present a complete retrospective of the technique and remind flow cytometry fundamentals before focusing on recent commercial instrumentation.

Flow cytometry: retrospective, fundamentals and recent instrumentation

Flow cytometry is a complete technology given to biologists to study cellular populations with high precision. This technology elegantly combines sample dimension, data acquisition speed, precision and measurement multiplicity. Beyond the statistical aspect, flow cytometry offers the possibility to physically separate sub-populations. These performances come from the common endeavor of physicists, biophysicists, biologists and computer engineers, who succeeded, by providing new concepts, to bring flow cytometry to current maturity. The aim of this paper is to present a complete retrospective of the technique and remind flow cytometry fundamentals before focusing on recent commercial instrumentation.

Characterization of aerosols produced by cell sorters and evaluation of containment

Despite the recognition of potential aerosol hazards associated with cell sorting by the flow cytometry community, there has been no previous study that has thoroughly characterized the aerosols that can be produced by cell sorters. In this study, an aerodynamic particle sizer was used to determine the concentration and aerodynamic diameter (AD) of aerosols produced by a FACS Aria II cell sorter under various conditions. Aerosol containment and evacuation were also evaluated using this novel methodology. The results showed that high concentrations of aerosols in the range of 1-3 μm can be produced in fail mode and that with decreased sheath pressure, aerosol concentration decreased and AD increased. Although the engineering controls of the FACS Aria II for containment were effective, sort chamber evacuation of aerosols following a simulated nozzle obstruction was ineffective. However, simple modifications to the FACS Aria II are described that greatly improved sort chamber aerosol evacuation. The results of this study will facilitate the risk assessment of cell sorting potentially biohazardous samples by providing much needed data regarding aerosol production and containment.

Practical issues in high-speed cell sorting

Modern flow cytometric cell sorters are all capable of so-called "high-speed sorting." However, there is confusion about exactly how fast a "high-speed" cell sorter can sort cells. There are many considerations in achieving the fastest sorting speed, as well as the highest quality sort results--cell recovery, purity, and functionality. This requires the same considerations required for "slow-speed sorting"; however, a more precise implementation is required for high-speed sorting. The modern cell sorters enable high-speed sorting because of advances in high-speed electronics and data processing. We discuss the practical considerations of high-speed sorting in terms of the theory and practical aspects of the mechanical and software components of sorting, statistics of sorting, cell preparation and viability, instrument setup, sort strategies, and biosafety.

Standard safety practices for sorting of unfixed cells

Cell sorting of viable biological specimens has become widespread in laboratories involved in basic and clinical research. As these samples can contain infectious agents, precautions to protect instrument operators and the environment from hazards arising from the use of sorters are paramount. This unit presents a revised and updated version of the biosafety guidelines for sorting of unfixed cells established in 1977 by the International Society of Analytical Cytology (ISAC), whose recommendations have become recognized worldwide as the standard practices and safety precautions for laboratories performing viable cell-sorting experiments. The unit contains background information on the biohazard potential of sorting and the hazard classification of infectious agents as well as recommendations on (1) sample handling, (2) operator training and personal protection, (3) laboratory design, (4) cell sorter setup, maintenance, and decontamination, and (5) testing the instrument for the efficiency of aerosol containment.

Evidence-based biosafety: a review of the principles and effectiveness of microbiological containment measures

We examined the available evidence on the effectiveness of measures aimed at protecting humans and the environment against the risks of working with genetically modified microorganisms (GMOs) and with non-GMO pathogenic microorganisms. A few principles and methods underlie the current biosafety practice: risk assessment, biological containment, concentration and enclosure, exposure minimization, physical containment, and hazard minimization. Many of the current practices are based on experience and expert judgment. The effectiveness of biosafety measures may be evaluated at the level of single containment equipment items and procedures, at the level of the laboratory as a whole, or at the clinical-epidemiological level. Data on the containment effectiveness of equipment and laboratories are scarce and fragmented. Laboratory-acquired infections (LAIs) are therefore important for evaluating the effectiveness of biosafety. For the majority of LAIs there appears to be no direct cause, suggesting that failures of biosafety were not noticed or that containment may have been insufficient. The number of reported laboratory accidents associated with GMOs is substantially lower than that of those associated with non-GMOs. It is unknown to what extent specific measures contribute to the overall level of biosafety. We therefore recommend that the evidence base of biosafety practice be strengthened.

Validation of RNA-based molecular clonotype analysis for virus-specific CD8+ T-cells in formaldehyde-fixed specimens isolated from peripheral blood

Recent advances in the field of molecular clonotype analysis have enabled detailed repertoire characterization of viably isolated antigen-specific T cell populations directly ex vivo. However, in the absence of a biologically contained FACS facility, peripheral blood mononuclear cell (PBMC) preparations derived from patients infected with agents such as HIV must be formaldehyde fixed to inactivate the pathogen; this procedure adversely affects nucleic acid template quality. Here, we developed and validated a method to amplify and sequence mRNA species derived from formaldehyde fixed PBMC specimens. Antigen-specific CD8+ cytotoxic T-lymphocyte populations were identified with standard fluorochrome-conjugated peptide-major histocompatibility complex class I tetramers refolded around synthetic peptides representing immunodominant epitopes from HIV p24 Gag (KRWII[M/L]GLNK/HLA B*2705) and CMV pp65 (NLVPMVATV/HLA A*0201 and TPRVTGGGAM/HLA B*0702), and acquired in separate laboratories with or without fixation. In the presence of proteinase K pre-treatment, the observed antigen-specific CD8+ T-cell repertoire determined by molecular clonotype analysis was statistically no different whether derived from fixed or unfixed PBMC. However, oligo-dT recovery methods were not suitable for use with fixed tissue as significant skewing of clonotypic representation was observed. Thus, we have developed a reliable RNA-based method for molecular clonotype analysis that is compatible with formaldehyde fixation and therefore suitable for use with primary human samples isolated by FACS outside the context of a biological safety level 3 containment facility.

International Society for Analytical Cytology biosafety standard for sorting of unfixed cells

BACKGROUND

Cell sorting of viable biological specimens has become very prevalent in laboratories involved in basic and clinical research. As these samples can contain infectious agents, precautions to protect instrument operators and the environment from hazards arising from the use of sorters are paramount. To this end the International Society of Analytical Cytology (ISAC) took a lead in establishing biosafety guidelines for sorting of unfixed cells (Schmid et al., Cytometry 1997;28:99-117). During the time period these recommendations have been available, they have become recognized worldwide as the standard practices and safety precautions for laboratories performing viable cell sorting experiments. However, the field of cytometry has progressed since 1997, and the document requires an update.

METHODS

Initially, suggestions about the document format and content were discussed among members of the ISAC Biosafety Committee and were incorporated into a draft version that was sent to all committee members for review. Comments were collected, carefully considered, and incorporated as appropriate into a draft document that was posted on the ISAC web site to invite comments from the flow cytometry community at large. The revised document was then submitted to ISAC Council for review. Simultaneously, further comments were sought from newly-appointed ISAC Biosafety committee members.

RESULTS

This safety standard for performing viable cell sorting experiments was recently generated. The document contains background information on the biohazard potential of sorting and the hazard classification of infectious agents as well as recommendations on (1) sample handling, (2) operator training and personal protection, (3) laboratory design, (4) cell sorter set-up, maintenance, and decontamination, and (5) testing the instrument for the efficiency of aerosol containment.

CONCLUSIONS

This standard constitutes an updated and expanded revision of the 1997 biosafety guideline document. It is intended to provide laboratories involved in cell sorting with safety practices that take into account the enhanced hazard potential of high-speed sorting. Most importantly, it states that droplet-based sorting of infectious or hazardous biological material requires a higher level of containment than the one recommended for the risk group classification of the pathogen. The document also provides information on safety features of novel instrumentation, new options for personal protective equipment, and recently developed methods for testing the efficiency of aerosol containment.

Biosafety concerns for shared flow cytometry core facilities

Many researchers who need flow cytometry for their projects have neither sufficient funds nor the work volume to justify the purchase of an analytic cytometer or cell sorter. In shared flow cytometry facilities, costs for instrument purchases, cytometer maintenance, and personnel are pooled to provide economic services for a multitude of users when they are required. Owing to the diverse nature of the samples that are submitted to core facilities, the biohazard potential of the samples can vary dramatically. For the safety of facility personnel and users, it is critical that information about hazards contained in the samples be transmitted to instrument operators before flow cytometry experiments are started. During 1999 the former Biosafety Committee of the International Society for Analytical Cytology formulated a framework biosafety questionnaire for shared facilities designed to request information about the hazard potential of experimental samples from investigators who wish to use the facility. In this report we review safety issues that are pertinent to flow cytometry core facilities by discussing the individual components of this biosafety questionnaire.