The effect of cellular isolation and cryopreservation on the expression of markers identifying subsets of regulatory T cells

Flow Cytometric Immunophenotyping: Minimal Differences in Fresh and Cryopreserved Peripheral Blood Mononuclear Cells versus Whole Blood

Background/Objectives: Flow cytometry is a convenient tool in immunophenotyping for monitoring the status of immunological conditions and diseases. The aim of this study was to investigate the effect of isolation and cryopreservation by flow cytometric analysis on subpopulations of CD4+ T helper (Th), T regulatory (Treg), CD8+ T cytotoxic (Tc), CD56+ NK, CD19+ B and monocytes. Freshly isolated and cryopreserved peripheral blood mononuclear cells (PBMCs) were compared to fresh whole blood. Methods: Peripheral blood was collected from healthy donors and prepared for flow cytometric analysis using the same panels of antibodies throughout the study. Results: Comparisons between fresh (F)- and cryopreserved (C)-PBMCs showed no major differences in percentages of CD4+, Th1, Th2 and CD4+CD25+CD127low Treg cells. No differences in percentage of CD8+ or subpopulations of naive/stem, central or effector memory cells were observed between F- and C-PBMCs. The percentage of CD56+ NK cells, CD19+ B cells or classical and nonclassical monocytes did not differ between F-and C-PBMCs either. On the contrary, whole blood had lower percentages of Th and NK cells but higher percentages of Th1, Th17, Th1Th17, Tregs, Tc and B cells compared to C-PBMCs, while it had a higher proportion of Tc compared to F-PBMCs. Conclusions: Flow cytometric immunophenotyping minimally differs between freshly isolated and cryopreserved PBMCs. This implies the possibility of cryostorage of cohorts for later analysis. Importantly, care must be taken when comparing results from whole blood with isolated and cryopreserved PBMCs. Collectively, these results can contribute to the standardization of flow cytometric protocols in both clinical and research settings.

Association of Immune Cell Subsets with Incident Hip Fracture: The Cardiovascular Health Study

In this study, we aimed to evaluate the association of innate and adaptive immune cell subsets in peripheral blood mononuclear cells (PBMCs) with hip fracture. To conduct this study, we used data from the Cardiovascular Health Study (CHS), a U.S. multicenter observational cohort of community-dwelling men and women aged ≥ 65 years. Twenty-five immune cell phenotypes were measured by flow cytometry from cryopreserved PBMCs of CHS participants collected in 1998-1999. The natural killer (NK), γδ T, T helper 17 (Th17), and differentiated/senescent CD4+CD28- T cell subsets were pre-specified as primary subsets of interest. Hip fracture incidence was assessed prospectively by review of hospitalization records. Multivariable Cox hazard models evaluated associations of immune cell phenotypes with incident hip fracture in sex-stratified and combined analyses. Among 1928 persons, 259 hip fractures occurred over a median 9.7 years of follow-up. In women, NK cells were inversely associated with hip fracture [hazard ratio (HR) 0.77, 95% confidence interval (CI) 0.60-0.99 per one standard deviation higher value] and Th17 cells were positively associated with hip fracture [HR 1.18, 95% CI 1.01-1.39]. In men, γδ T cells were inversely associated with hip fracture [HR 0.60, 95% CI 0.37-0.98]. None of the measured immune cell phenotypes were significantly associated with hip fracture incidence in combined analyses. In this large prospective cohort of older adults, potentially important sex differences in the associations of immune cell phenotypes and hip fracture were identified. However, immune cell phenotypes had no association with hip fracture in analyses combining men and women.

Comprehensive evaluation of the effects of long-term cryopreservation on peripheral blood mononuclear cells using flow cytometry

Human peripheral blood mononuclear cells (PBMCs) originate from hematopoietic stem cells in the bone marrow, which mainly includes lymphocytes (T cells, B cells, and natural killer cells) and monocytes. Cryopreserved PBMCs providing biobank resources are crucial for clinical application or scientific research. Here, we used flow cytometry to explore the influence of long-term cryopreservation on the quality of PBMCs with the aim of providing important evidence for the effective utilization of biobank resources. The PBMCs were isolated from the peripheral blood, which was collected from volunteers in the hospital. After long-term cryopreservation in liquid nitrogen, we analyzed the changes in cell numbers, viability, and multiple subtypes of PBMCs and studied the apoptosis, proliferation, activation, function, and status of T cells in comparison with freshly isolated PBMCs by flow cytometry, and then further tracked the effects of long-term cryopreservation on the same sample. Although the different cell types in the PBMCs dynamically changed compared with those in the freshly isolated samples, PBMC recovery and viability remained stable after long-term cryopreservation, and the number of most innate immune cells (e.g., monocytes and B cells) was significantly reduced compared to that of the freshly isolated PBMCs or long-term cryopreserved PBMCs; more importantly, the proportion of T cell subtypes, apoptosis, proliferation, and functional T cells, except for Tregs, were not affected by long-term cryopreservation. However, the proportions of activated T, naïve T, central memory T, effector T, and effector memory T cells dynamically changed after long-term cryopreservation. This article provides important evidence for the effective utilization of biobank resources. Long-term cryopreserved PBMCs can be partly used as biological resources for clinical research or basic studies, but the effect of cryopreservation on PBMCs should be considered when selecting cell samples, especially in research relating to activating or inhibiting function.

CyTOF® for the Masses

Mass cytometry has revolutionized immunophenotyping, particularly in exploratory settings where simultaneous breadth and depth of characterization of immune populations is needed with limited samples such as in preclinical and clinical tumor immunotherapy. Mass cytometry is also a powerful tool for single-cell immunological assays, especially for complex and simultaneous characterization of diverse intratumoral immune subsets or immunotherapeutic cell populations. Through the elimination of spectral overlap seen in optical flow cytometry by replacement of fluorescent labels with metal isotopes, mass cytometry allows, on average, robust analysis of 60 individual parameters simultaneously. This is, however, associated with significantly increased complexity in the design, execution, and interpretation of mass cytometry experiments. To address the key pitfalls associated with the fragmentation, complexity, and analysis of data in mass cytometry for immunologists who are novices to these techniques, we have developed a comprehensive resource guide. Included in this review are experiment and panel design, antibody conjugations, sample staining, sample acquisition, and data pre-processing and analysis. Where feasible multiple resources for the same process are compared, allowing researchers experienced in flow cytometry but with minimal mass cytometry expertise to develop a data-driven and streamlined project workflow. It is our hope that this manuscript will prove a useful resource for both beginning and advanced users of mass cytometry.

Alignment of practices for data harmonization across multi-center cell therapy trials: a report from the Consortium for Pediatric Cellular Immunotherapy

Immune effector cell (IEC) therapies have revolutionized our approach to relapsed B-cell malignancies, and interest in the investigational use of IECs is rapidly expanding into other diseases. Current challenges in the analysis of IEC therapies include small sample sizes, limited access to clinical trials and a paucity of predictive biomarkers of efficacy and toxicity associated with IEC therapies. Retrospective and prospective multi-center cell therapy trials can assist in overcoming these barriers through harmonization of clinical endpoints and correlative assays for immune monitoring, allowing additional cross-trial analysis to identify biomarkers of failure and success. The Consortium for Pediatric Cellular Immunotherapy (CPCI) offers a unique platform to address the aforementioned challenges by delivering cutting-edge cell and gene therapies for children through multi-center clinical trials. Here the authors discuss some of the important pre-analytic variables, such as biospecimen collection and initial processing procedures, that affect biomarker assays commonly used in IEC trials across participating CPCI sites. The authors review the recent literature and provide data to support recommendations for alignment and standardization of practices that can affect flow cytometry assays measuring immune effector function as well as interpretation of cytokine/chemokine data. The authors also identify critical gaps that often make parallel comparisons between trials difficult or impossible.

Cryopreservation and post-thaw characterization of dissociated human islet cells

The objective of this study is to optimize the cryopreservation of dissociated islet cells and obtain functional cells that can be used in single-cell transcriptome studies on the pathology and treatment of diabetes. Using an iterative graded freezing approach we obtained viable cells after cooling in 10% dimethyl sulfoxide and 6% hydroxyethyl starch at 1°C/min to -40°C, storage in liquid nitrogen, rapid thaw, and removal of cryoprotectants by serial dilution. The expression of epithelial cell adhesion molecule declined immediately after thaw, but recovered after overnight incubation, while that of an endocrine cell marker (HPi2) remained high after cryopreservation. Patch-clamp electrophysiology revealed differences in channel activities and exocytosis of various islet cell types; however, exocytotic responses, and the biophysical properties of voltage-gated Na+ and Ca2+ channels, are sustained after cryopreservation. Single-cell RNA sequencing indicates that overall transcriptome and crucial exocytosis genes are comparable between fresh and cryopreserved dispersed human islet cells. Thus, we report an optimized procedure for cryopreserving dispersed islet cells that maintained their membrane integrity, along with their molecular and functional phenotypes. Our findings will not only provide a ready source of cells for investigating cellular mechanisms in diabetes but also for bio-engineering pseudo-islets and islet sheets for modeling studies and potential transplant applications.

Comparison of peripheral blood mononuclear cell isolation techniques and the impact of cryopreservation on human lymphocytes expressing CD39 and CD73

CD39 and CD73 are ecto-nucleotidases present on human peripheral blood mononuclear cells (PBMCs) and are emerging biomarkers on these cells in various disorders including cancer. Many factors influence PBMC quality, so it is essential to validate sample processing methods prior to incorporation in clinical studies. This study examined the impact of both PBMC cryopreservation and PBMC isolation using SepMate density gradient centrifugation on CD39 and CD73 expressing subsets. First, PBMCs were isolated from the peripheral blood of 11 healthy donors by routine Ficoll-Paque density gradient centrifugation, cryopreserved and compared with freshly isolated PBMCs by flow cytometry. The proportions of T and B cells expressing combinations of CD39 and CD73 were relatively stable over 6-month cryopreservation, although some T cell combinations revealed small but significant changes. Second, peripheral blood was collected from six healthy donors to compare PBMCs isolated by SepMate or Ficoll-Paque density gradient centrifugation. Compared with Ficoll-Paque, the more rapid SepMate method yielded 9.1% less PBMCs but did not alter cell viability or proportions of T and B cells expressing combinations of CD39 and CD73. The present study reveals that cryopreservation is suitable for studying T and B cells expressing combinations of CD39 and CD73. However, caution should be exercised when observing small differences in these cryopreserved subsets between different cohorts. Further, SepMate and Ficoll-Paque methods of PBMC isolation show similar results for T and B cell subset analysis; however, SepMate is a faster and easier approach.

A Method of Assessment of Human Natural Killer Cell Phenotype and Function in Whole Blood

The majority of data on human Natural Killer (NK) cell phenotype and function has been generated using cryopreserved peripheral blood mononuclear cells (PBMCs). However, cryopreservation can have adverse effects on PBMCs. In contrast, investigating immune cells in whole blood can reduce the time, volume of blood required, and potential artefacts associated with manipulation of the cells. Whole blood collected from healthy donors and cancer patients was processed by three separate protocols that can be used independently or in parallel to assess extracellular receptors, intracellular signaling protein phosphorylation, and intracellular and extracellular cytokine production in human NK cells. To assess extracellular receptor expression, 200 μL of whole blood was incubated with an extracellular staining (ECS) mix and cells were subsequently fixed and RBCs lysed prior to analysis. The phosphorylation status of signaling proteins was assessed in 500 μL of whole blood following co-incubation with interleukin (IL)-2/12 and an ECS mix for 20 min prior to cell fixation, RBC lysis, and subsequent permeabilization for staining with an intracellular staining (ICS) mix. Cytokine production (IFNγ) was similarly assessed by incubating 1 mL of whole blood with PMA-ionomycin or IL-2/12 prior to incubation with ECS and subsequent ICS antibodies. In addition, plasma was collected from stimulated samples prior to ECS for quantification of secreted IFNγ by ELISA. Results were consistent, despite inherent inter-patient variability. Although we did not investigate an exhaustive list of targets, this approach enabled quantification of representative ECS surface markers including activating (NKG2D and DNAM-1) and inhibitory (NKG2A, PD-1, TIGIT, and TIM-3) receptors, cytokine receptors (CD25, CD122, CD132, and CD212) and ICS markers associated with NK cell activation following stimulation, including signaling protein phosphorylation (p-STAT4, p-STAT5, p-p38 MAPK, p-S6) and IFNγ in both healthy donors and cancer patients. In addition, we compared extracellular receptor expression using whole blood vs. cryopreserved PBMCs and observed a significant difference in the expression of almost all receptors. The methods presented permit a relatively rapid parallel assessment of immune cell receptor expression, signaling protein activity, and cytokine production in a minimal volume of whole blood from both healthy donors and cancer patients.

Innate and adaptive immune cell subsets as risk factors for coronary heart disease in two population-based cohorts

BACKGROUND AND AIMS

Cell-mediated immunity is implicated in atherosclerosis. We evaluated whether innate and adaptive immune cell subsets in peripheral blood are risk factors for coronary heart disease.

METHODS

A nested case-cohort study (n = 2155) was performed within the Multi-Ethnic Study of Atherosclerosis (MESA) and the Cardiovascular Health Study (CHS). Cases of incident myocardial infarction (MI) and incident angina (n = 880 total cases) were compared with a cohort random sample (n = 1275). Immune cell phenotypes (n = 34, including CD14⁺ monocytes, natural killer cells, γδ T cells, CD4⁺, CD8⁺ and CD19⁺ lymphocyte subsets) were measured from cryopreserved cells by flow cytometry. Cox proportional hazards models with adjustment for cardiovascular disease risk factors were used to evaluate associations of cell phenotypes with incident MI and a composite phenotype of incident MI or incident angina (MI-angina) over a median 9.3 years of follow-up. Th1, Th2, Th17, T regulatory (CD4⁺CD25⁺CD127^-), naive (CD4⁺CD45RA⁺), memory (CD4⁺CD45RO⁺), and CD4⁺CD28^- cells were specified as primary hypotheses. In secondary analyses, 27 additional cell phenotypes were investigated.

RESULTS

After correction for multiple testing, there were no statistically significant associations of CD4⁺ naive, memory, CD28^-, or T helper cell subsets with MI or MI-angina in MESA, CHS, or combined-cohort meta analyses. Null associations were also observed for monocyte subsets, natural killer cells, γδ T cells, CD19⁺ B cell and differentiated CD4⁺ and CD8⁺ cell subsets.

CONCLUSIONS

The proportions of peripheral blood monocyte and lymphocyte subsets are not strongly related to the future occurrence of MI or angina in adults free of autoimmune disease.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Rigor and Reproducibility of Cytometry Practices for Immuno-Oncology: A multifaceted challenge

The rapid advancement of immunotherapy strategies has created a need for technologies that can reliably and reproducibly identify rare populations, detect subtle changes in modulatory signals, and assess antigenic expression patterns that are time-sensitive. Accomplishing these tasks requires careful planning and the employment of tools that provide greater sensitivity and specificity without demanding extensive time. Flow Cytometry has earned its place as a preferred analysis platform. This technology offers a flexible path to the interrogation of protein expression patterns and detection of functional properties in cell populations of interest. Mass Cytometry is a newcomer technology that has generated significant interest in the field. By incorporating mass spectrometry analysis to the traditional principles of flow cytometry, this innovative tool promises to significantly expand the ability to detect multiple proteins on a single cell. The use of these technologies in a manner that is consistent and reproducible through multiple sample sets demands careful attention to experiment design, reagent selection, and instrumentation. Whether applying flow or mass cytometry, reaching successful, reliable results involves many factors. Sample preparation, antibody titrations, and appropriate controls are major biological considerations that impact cytometric analysis. Additionally, instrument voltages, lasers, and run quality assessments are essential for ensuring comparability and reproducibility between analyses. In this article, we aim to discuss the critical aspects that impact flow cytometry, and will touch on important considerations for mass cytometry as well. Focusing on their relevance to immunotherapy studies, we will address the importance of appropriate sample processing and will discuss how selection of suitable panels, controls, and antibodies must follow a carefully designed plan. We will also comment on how educated use of instrumentation plays a significant role in the reliability and reproducibility of results.Through this work, we hope to contribute to the effort toward establishing higher standards for rigor and reproducibility of cytometry practices by researchers, operators, and general cytometry users employing cytometry-based assays in their work. © 2019 International Society for Advancement of Cytometry.

Validation of CyTOF Against Flow Cytometry for Immunological Studies and Monitoring of Human Cancer Clinical Trials

Flow cytometry is a widely applied approach for exploratory immune profiling and biomarker discovery in cancer and other diseases. However, flow cytometry is limited by the number of parameters that can be simultaneously analyzed, severely restricting its utility. Recently, the advent of mass cytometry (CyTOF) has enabled high dimensional and unbiased examination of the immune system, allowing simultaneous interrogation of a large number of parameters. This is important for deep interrogation of immune responses and particularly when sample sizes are limited (such as in tumors). Our goal was to compare the accuracy and reproducibility of CyTOF against flow cytometry as a reliable analytic tool for human PBMC and tumor tissues for cancer clinical trials. We developed a 40+ parameter CyTOF panel and demonstrate that compared to flow cytometry, CyTOF yields analogous quantification of cell lineages in conjunction with markers of cell differentiation, function, activation, and exhaustion for use with fresh and viably frozen PBMC or tumor tissues. Further, we provide a protocol that enables reliable quantification by CyTOF down to low numbers of input human cells, an approach that is particularly important when cell numbers are limiting. Thus, we validate CyTOF as an accurate approach to perform high dimensional analysis in human tumor tissue and to utilize low cell numbers for subsequent immunologic studies and cancer clinical trials.

Aberrant determination of phenotypic markers in chronic lymphocytic leukemia (CLL) lymphocytes after cryopreservation

The cryopreservation of peripheral blood mononuclear cells (PBMCs) is a routine research laboratory process, enabling long-term storage of primary patient blood samples. Retrospective analysis of these samples has the potential to identify markers that may be associated with prognosis and response to treatment. To draw valid biological conclusions from this type of analysis, it is essential to ensure that any observed changes are directly related to the pathology of the disease rather than the preservation process itself. Therefore, we have investigated 15 cell surface markers that are relevant to chronic lymphocytic leukemia (CLL) on matched fresh and thawed samples to determine the effect of cryopreservation on their detection. We found that the number of CLL cells positive for the markers CD22, CD40, CD49d, CD54, CD69, and CXCR3 was decreased significantly after cryopreservation. In addition, the mean fluorescence intensity of 10 of the 15 markers changed significantly after cryopreservation. These findings demonstrate that care must be taken when interpreting this type of analysis on thawed samples.

A Practical Cryopreservation and Staining Protocol for Immunophenotyping in Population Studies

Large population-based cohort studies, through their prospective collection of a broad range of health information, represent an invaluable resource for novel insights into the pathogenesis of human diseases. Collection and cryopreservation of viable cells from blood samples is becoming increasingly common in large cohorts as these cells are a valuable resource for immunophenotyping and functional studies. The cryopreservation of peripheral blood mononuclear cells (PBMCs), thawing, and immunophenotyping protocols used to immunophenotype 9938 participants in the Health and Retirement Study (HRS) are described. The extensive quality control involved in a large-scale immunophenotyping epidemiological study is also outlined. The existing literature on the effect of cryopreservation on various immune cell subsets including T, B, NK cells, monocytes, and dendritic cells is provided. © 2018 by John Wiley & Sons, Inc.

Optimizing recovery of frozen human peripheral blood mononuclear cells for flow cytometry

Introduction

Live peripheral blood mononuclear cells (PBMCs) can be frozen and thawed for later analyses by adding and removing a cryoprotectant, such as dimethyl sulfoxide (DMSO). Laboratories across the world use various procedures, but published evidence of optimal thawing procedures is scarce.

Materials and methods

PBMCs were separated from blood collected from healthy Danish blood donors, and stored at -80°C after adding of DMSO. The essential steps in the thawing procedure were modified and performance was evaluated by flow cytometry with respect to the percentage and total yield of viable PMBCs.

Results

The best-performing washing medium was Roswell Park Memorial Institute (RPMI) 1640 at 37°C with 20% fetal bovine serum. When using 10 mL washing medium in a 15-mL Falcon tube, samples should be centrifuged for at least 10 minutes at 500 g. We failed to detect any differences between the tested methods of mixing PBMCs with washing medium. Likewise, neither the thawing duration nor centrifugation temperature (20°C and 37°C) had any effect. PBMCs could be incubated (rested) for up to eight hours in a 37°C 5% CO₂ incubator without affecting cell counts, but incubating PBMCs for 16 hours significantly decreased viability and recovery. In general, high viability was not necessarily associated with high recovery.

Conclusion

Changing the thawing procedure significantly impacted PBMC viability and live cell recovery. Evaluating both viability and live PBMC recovery are necessary to evaluate method performance. Investigation of differential loss of PBMC subtypes and phenotypic changes during thawing and incubation requires further evaluation.

The effects of cryopreservation on the expression of canine regulatory T-cell markers

BACKGROUND

Regulatory T (Treg) cells have been described as key regulators in various immunological processes and are of growing interest in veterinary allergy. Cryopreservation of immune cells is performed routinely in human basic science research and in clinical studies. As such, it allows batch testing of collected samples at a single time point, resulting in a significant reduction in sample variability. Data which describe the effects of cryopreservation on Treg cell frequency and functionality in the canine species are important to inform future research.

HYPOTHESIS/OBJECTIVES

The purpose of this study was to establish a robust freeze/thaw procedure and flow cytometric staining protocol for canine Treg cells, and to compare the frequencies of different canine Treg cell phenotypes before and after cryopreservation.

ANIMALS

Nine privately owned dogs.

METHODS

Peripheral blood mononuclear cells were isolated and Treg cells stained and analysed by flow cytometry, before and after three months of cryopreservation. The recovery percentages and the corresponding correlations (fresh versus cryopreserved) for CD4⁺ CD25⁺ , CD4⁺ FOXP3⁺ and CD4⁺ CD25⁺ FOXP3⁺ cell populations were calculated.

RESULTS

A high recovery rate of 97.2 (r = 0.94, P < 0.0001), 93.9 (r = 0.77, P < 0.01) and 101.7% (r = 0.99, P < 0.0001) for CD4⁺ CD25⁺ , CD4⁺ FOXP3⁺ and CD4⁺ CD25⁺ FOXP3⁺ cell populations, respectively, was observed.

CONCLUSIONS

This study demonstrates an optimized protocol for freezing, thawing and quantifying canine Treg cells. These results indicate that cryopreservation does not substantially affect the expression of surface and intracellular markers of canine Treg cells; however, additional studies will be necessary to assess whether functionality of the cells is also maintained.