Comparison of the effects between animal-derived trypsin and recombinant trypsin on human skin cells proliferation, gene and protein expression

Residual protein analysis by SDS-PAGE in clinically manufactured BM-MSC products

Residual substances that are considered hazardous to the recipient must be removed from final cellular therapeutic products manufactured for clinical purposes. In doing so, quality rules determined by competent authorities (CAs) for the clinical use of tissue- and cell-based products can be met. In our study, we carried out residual substance analyses, and purity determination studies of trypsin and trypsin inhibitor in clinically manufactured bone marrow-derived mesenchymal stromal/stem cell products, using the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) method. Despite being a semiquantitative method, SDS-PAGE has several benefits over other methods for protein analysis, such as simplicity, convenience of use, and affordability. Due to its convenience and adaptability, SDS-PAGE is still a commonly used method in many laboratories, despite its limits in dynamic range and quantitative precision. Our goal in this work was to show that SDS-PAGE may be used effectively for protein measurement, especially where practicality and affordability are the major factors. The results of our study suggest a validated method to guide tissue and cell manufacturing sites for making use of an agreeable, accessible, and cost-effective method for residual substance analyses in clinically manufactured cellular therapies.

Quality management overview for the production of a tissue-engineered human skin substitute in Malaysia

Treatments for skin injuries have recently advanced tremendously. Such treatments include allogeneic and xenogeneic transplants and skin substitutes such as tissue-engineered skin, cultured cells, and stem cells. The aim of this paper is to discuss the general overview of the quality assurance and quality control implemented in the manufacturing of cell and tissue product, with emphasis on our experience in the manufacturing of MyDerm®, an autologous bilayered human skin substitute. Manufacturing MyDerm® requires multiple high-risk open manipulation steps, such as tissue processing, cell culture expansion, and skin construct formation. To ensure the safety and efficacy of this product, the good manufacturing practice (GMP) facility should establish a well-designed quality assurance and quality control (QA/QC) programme. Standard operating procedures (SOP) should be implemented to ensure that the manufacturing process is consistent and performed in a controlled manner. All starting materials, including tissue samples, culture media, reagents, and consumables must be verified and tested to confirm their safety, potency, and sterility. The final products should also undergo a QC testing series to guarantee product safety, efficacy, and overall quality. The aseptic techniques of cleanroom operators and the environmental conditions of the facility are also important, as they directly influence the manufacturing of good-quality products. Hence, personnel training and environmental monitoring are necessary to maintain GMP compliance. Furthermore, risk management implementation is another important aspect of QA/QC, as it is used to identify and determine the risk level and to perform risk assessments when necessary. Moreover, procedures for non-conformance reporting should be established to identify, investigate, and correct deviations that occur during manufacturing. This paper provides insight and an overview of the QA/QC aspect during MyDerm® manufacturing in a GMP-compliant facility in the Centre for Tissue Engineering and Regenerative Medicine, Faculty of Medicine, Universiti Kebangsaan Malaysia.

A method for harvesting viable cells from wound dressings

Wound fluid has been well studied for exploring protein biomarkers contained in it. However, cells in wound fluid have not received much attention due to the difficulty in their collection. Our study aimed to establish a method for collecting viable cells from discarded wound dressings. A protocol was designed to wash out nonadherent cells and detach adherent cells from silicone-faced foam wound dressings using trypsin-EDTA. The optimal concentration and incubation time of trypsin-EDTA for collecting equivalent proportions of different cell types to the original cell population were determined in vitro. Cell composition and gene expression changes in monocytes, lymphocytes, neutrophils, fibroblasts and keratinocytes were confirmed using immunocytochemistry and RNA-sequencing ex vivo. Full-thickness wounds were created on 9-week-old male C57BL/6J mice. Wound fluid was collected, and half of it was applied to the wound dressings. The original cell population in the wound fluid and the cell population collected from wound dressings were compared. In the in vitro study, 0.25% trypsin-EDTA and 2.5-min incubation time were considered optimal for collecting adherent cells from wound dressings. In the ex vivo study, among all cell types, only CD3+ lymphocytes showed a significantly higher cell proportion in the collected group. The relative gene expression of the five selected cells showed no significant changes (p-value >0.05, |log2 fold change| < 1.5, differential gene expression analysis). Viable nonadherent and adherent cells were collected from wound dressings without altering gene expression and could be used in future studies for cellular analysis of wound fluid.

Mechanical strain in the mouse astrocytic lamina increases after exposure to recombinant trypsin

The responses of astrocytes in the optic nerve head (ONH) to mechanical and biochemical stimuli are important to understanding the degeneration of retinal ganglion cell axons in glaucoma. The ONH in glaucoma is vulnerable to stress produced by the intraocular pressure (IOP). Notably, after three days of elevated IOP in a mouse model, the junctions between the astrocytic processes and the peripapillary sclera were altered and the structural compliance of the ONH increased. In order to simulate this aspect of glaucomatous remodeling, explanted mouse eyes were treated with TrypLE, a recombinant trypsin enzyme. Treatment with TrypLE caused the periphery of the astrocytic lamina to contract radially by 0.044 ± 0.038. Transmission electron microscopy showed that TrypLE caused a separation of the end-feet of the astrocyte processes from the basement membrane at the junction with the sclera. Inflation testing after treatment with TrypLE caused an increased strain response in the astrocytic lamina compared to the strain response before treatment. The greatest increase was in the radial Green-Lagrange strain, Err = 0.028 ± 0.009, which increased by 340%. The alterations in the microstructure and in the strain response of the astrocytic lamina reported in mouse experimental glaucoma were partially reproduced by experimental treatment of mouse eyes with TrypLE. The results herein suggest that separation of junctions between the astrocyte processes and the sclera may be instrumental in increasing the structural compliance of the ONH after a period of elevated IOP. STATEMENT OF SIGNIFICANCE: Astrocytes of the optic nerve of the eye spread out from edge to edge across the optic nerve in a region referred to as the astrocytic lamina. In an experimental model of glaucoma caused by elevated eye-pressure, there is disruption of the connections between astrocytes and the edge of the astrocytic lamina. We caused a similar event in the lamina by incubating explanted mouse eyes with an enzyme. Disruption of the astrocyte connections to the edge of their tissue caused the tissue to stretch more when we increased the eye-pressure, compared to the control tissue. This work is the first on the tissue of the optic nerve to demonstrate the importance of cell connections in preventing the over-stretching of the astrocytic lamina.

Replacement of Trypsin by Proteases for Medical Applications

Background

Cell culture has a crucial role in many applications in biotechnology. The production of vaccines, recombinant proteins, tissue engineering, and stem cell therapy all need cell culture. Most of these activities needed adherent cells to move, which should be trypsinized several times until received on a large scale. Although trypsin is manufactured from the bovine or porcine pancreas, the problem of contamination by unwanted animal proteins, unwanted immune reactions, or contamination to pathogen reagents is the main problem.

Objectives

This study investigated microbial proteases as a safe alternative for trypsin replacement in cell culture experiments for the detachment of adherent cells.

Methods

The bacteria were isolated from the leather industry effluent based on their protease enzymes. After sequencing their 16S ribosomal deoxyribonucleic acid, their protease enzymes were purified, and their enzyme activities were assayed. The alteration of enzymatic activities using different substrates and the effect of substrate concentrations on enzyme activities were determined. The purified proteases were evaluated for cell detachment in the L929 fibroblast cells compared to trypsin. The separated cells were cultured again, and cell proliferation was determined by the MTT assay.

Results

The results showed that the isolated bacteria were Bacillus pumilus, Stenotrophomonas sp., Klebsiella aerogenes, Stenotrophomonas maltophilia, and Bacillus licheniformis. Among the isolated bacteria, the highest and the lowest protease activity belonged to Stenotrophomonas sp. and K. aerogenes, with 60.34 and 11.09 U/mL protease activity, respectively. All the isolated microbial proteases successfully affected L929 fibroblast cells' surface proteins and detached the cells. A significant induction in cell proliferation was observed in the cells treated with K. aerogenes protease and B. pumilus protease, respectively (P < 0.05).

Conclusions

The obtained results suggested that microbial proteases can be used as safe and efficient alternatives to trypsin in cell culture in biopharmaceutical applications.

Optimizing large-scale autologous human keratinocyte sheets for major burns-Toward an animal-free production and a more accessible clinical application

Background and Aims

Autologous keratinocyte sheets constitute an important component of the burn wound treatment toolbox available to a surgeon and can be considered a life‐saving procedure for patients with severe burns over 50% of their total body surface area. Large‐scale keratinocyte sheet cultivation still fundamentally relies on the use of animal components such as inactivated murine 3T3 fibroblasts as feeders, animal‐derived enzymes such as trypsin, as well as media components such as fetal bovine serum (FBS). This study was therefore aimed to optimize autologous keratinocyte sheets by comparing various alternatives to critical components in their production.

Methods

Human skin samples were retrieved from remnant operative tissues. Cell isolation efficiency and viability were investigated by comparing the efficacy of porcine‐derived trypsin and animal‐free enzymes (Accutase and TrypLESelect). The subsequent expansion of the cells and the keratinocyte sheet formation was analyzed, comparing various cell culture substrates (inactivated murine 3T3 fibroblasts, inactivated human fibroblasts, Collagen I or plain tissue culture plastic), as well as media containing serum or chemically defined animal‐free media.

Results

The cell isolation step showed clear cell yield advantages when using porcine‐derived trypsin, compared to animal‐free alternatives. The keratinocyte sheets produced using animal‐free serum were similar to those produced using 3T3 feeder layer and FBS‐containing medium, particularly in mechanical integrity as all grafts were liftable. In addition, sheets grown on collagen in an animal‐free medium showed indications of advantages in homogeneity, speed, reduced variability, and differentiation status compared to the other growth conditions investigated. Most importantly, the procedure was compatible with the up‐scaling requirements of major burn wound treatments.

Conclusion

This study demonstrated that animal‐free components could be used successfully to reduce the risk profile of large‐scale autologous keratinocyte sheet production, and thereby increase clinical accessibility.

Cell secretomes for wound healing and tissue regeneration: Next generation acellular based tissue engineered products

Wound represents a significant socioeconomic burden for both affected individuals and as a whole healthcare system. Accordingly, stem cells have garnered attention due to their differentiation capacity and ability to aid tissue regeneration by releasing biologically active molecules, found in the cells' cultivated medium which known as conditioned medium (CM) or secretomes. This acellular approach provides a huge advantage over conventional treatment options, which are mainly used cellular treatment at wound closure. Interestingly, the secretomes contained the cell-secreted proteins such as growth factors, cytokines, chemokines, extracellular matrix (ECM), and small molecules including metabolites, microvesicles, and exosomes. This review aims to provide a general view on secretomes and how it is proven to have great potential in accelerating wound healing. Utilizing the use of secretomes with its secreted proteins and suitable biomaterials for fabrications of acellular skin substitutes can be promising in treating skin loss and accelerate the healing process.

Xeno-free workflow exhibits comparable efficiency and quality of keratinocytes isolated from human skin biopsies

INTRODUCTION

Regenerative solutions of the skin represent a hope for burn victims with extensive skin loss and chronic wound patients. The development of xeno-free workflow is crucial for clinical application in compliance with the directives of the European Medicines Agency. This study aimed at evaluating the outcome of the xeno-free isolation workflow of keratinocytes from human skin biopsy.

METHODS

Skin biopsies were obtained from volunteers. The epidermis was digested with TrypLE™ Select, which was deactivated by dilution or with trypsin, deactivated by media with fetal bovine serum. Freshly isolated cells were compared for total cell number, viability, activity of caspase 3, gene expression and the presence of the keratinocyte surface markers cytokeratin 14. The cells were cultured in xeno-free conditions for one week and characterized regarding the number and viability as well as the metalloproteinase secretion.

RESULTS

The number of obtained cells was similar in both workflows. The cell viability was less in the TrypLE group, with slight reduction of the cell surface marker cytokeratin 14. Caspase 3 activity was comparable as well as the gene expression of the apoptotic markers BAX, BCL2 and SLUG, as well as the keratinocyte markers cytokeratin 14, stratifin and filaggrin. Upon culture, the number of keratinocytes, their viability and secretion of matrix metalloproteinases 1 and 10 were equal in both groups.

CONCLUSION

This study reports the possibility of isolating functioning and viable keratinocytes through a xeno-free workflow for clinical application.

Cell-based influenza vaccine: current production, halal status assessment, and recommendations towards Islamic-compliant manufacturing

Influenza virus is a life-threatening pathogen that infects millions of people every year, with annual mortality in the hundreds of thousands. The scenario for controlling infection has worsened with increasing numbers of vaccine hesitancy cases reported worldwide due to objections on safety, religious and other grounds. Uses of haram (impermissible) and mashbooh (doubtful) ingredients in vaccine production has raised doubts among Muslim consumers and consequently stimulated serious vaccine hesitancy. To address this major problem, we have reviewed and recommended some alternatives appropriate for manufacturing cell-based influenza vaccine which comply with Islamic laws and consumers' needs. Intensive assessments of current influenza vaccine production in both scientific and Islamic views have led to the identification of four main ingredients deemed impermissible in novel sharia-compliant (approved by Islamic laws) vaccine manufacturing. Only some of these impermissible components could be replaced with halal (permissible) alternatives, while others remain impermissible due to unavailability and unsuitability.

Hybrid Collagen Hydrogel/Chondroitin-4-Sulphate Fortified with Dermal Fibroblast Conditioned Medium for Skin Therapeutic Application

The current strategy for rapid wound healing treatment involves combining a biomaterial and cell-secreted proteins or biomolecules. This study was aimed at characterizing 3-dimensional (3D) collagen hydrogels fortified with dermal fibroblast-conditioned medium (DFCM) as a readily available acellular skin substitute. Confluent fibroblasts were cultured with serum-free keratinocyte-specific medium (KM1 and KM2) and fibroblast-specific medium (FM) to obtain DFCM. Subsequently, the DFCM was mixed with collagen (Col) hydrogel and chondroitin-4-sulphate (C4S) to fabricate 3D constructs termed Col/C4S/DFCM-KM1, Col/C4S/DFCM-KM2, and Col/C4S/DFCM-FM. The constructs successfully formed soft, semi-solid and translucent hydrogels within 1 h of incubation at 37 °C with strength of <2.5 Newton (N). The Col/C4S/DFCM demonstrated significantly lower turbidity compared to the control groups. The Col/C4S/DFCM also showed a lower percentage of porosity (KM1: 35.15 ± 9.76%; KM2: 6.85 ± 1.60%; FM: 14.14 ± 7.65%) compared to the Col (105.14 ± 11.87%) and Col/C4S (143.44 ± 27.72%) constructs. There were no changes in both swelling and degradation among all constructs. Fourier transform infrared spectrometry showed that all groups consisted of oxygen–hydrogen bonds (O-H) and amide I, II, and III. In conclusion, the Col/C4S/DFCM constructs maintain the characteristics of native collagen and can synergistically deliver essential biomolecules for future use in skin therapeutic applications.

Effect of Kelulut Honey on the Cellular Dynamics of TGFβ-Induced Epithelial to Mesenchymal Transition in Primary Human Keratinocytes

Over-induction of epithelial to mesenchymal transition (EMT) by tumor growth factor beta (TGFβ) in keratinocytes is a key feature in keloid scar. The present work seeks to investigate the effect of Kelulut honey (KH) on TGFβ-induced EMT in human primary keratinocytes. Image analysis of the real time observation of TGFβ-induced keratinocytes revealed a faster wound closure and individual migration velocity compared to the untreated control. TGFβ-induced keratinocytes also have reduced circularity and display a classic EMT protein expression. Treatment of 0.0015% (v/v) KH reverses these effects. In untreated keratinocytes, KH resulted in slower initial wound closure and individual migration velocity, which sped up later on, resulting in greater wound closure at the final time point. KH treatment also led to greater directional migration compared to the control. KH treatment caused reduced circularity in keratinocytes but displayed a partial EMT protein expression. Taken together, the findings suggest the therapeutic potential of KH in preventing keloid scar by attenuating TGFβ-induced EMT.

Safety and efficacy of dermal fibroblast conditioned medium (DFCM) fortified collagen hydrogel as acellular 3D skin patch

Skin substitutes are one of the main treatments for skin loss, and a skin substitute that is readily available would be the best treatment option. However, most cell-based skin substitutes require long production times, and therefore, patients endure long waiting times. The proteins secreted from the cells and tissues play vital roles in promoting wound healing. Thus, we aimed to develop an acellular three-dimensional (3D) skin patch with dermal fibroblast conditioned medium (DFCM) and collagen hydrogel for immediate treatment of skin loss. Fibroblasts from human skin samples were cultured using serum-free keratinocyte-specific media (KM1 or KM2) and serum-free fibroblast-specific medium (FM) to obtain DFCM-KM1, DFCM-KM2, and DFCM-FM, respectively. The acellular 3D skin patch was soft, semi-solid, and translucent. Collagen mixed with DFCM-KM1 and DFCM-KM2 showed higher protein release compared to collagen plus DFCM-FM. In vitro and in vivo testing revealed that DFCM and collagen hydrogel did not induce an immune response. The implantation of the 3D skin patch with or without DFCM on the dorsum of BALB/c mice demonstrated a significantly faster healing rate compared to the no-treatment group 7 days after implantation, and all groups had complete re-epithelialization at day 17. Histological analysis confirmed the structure and integrity of the regenerated skin, with positive expression of cytokeratin 14 and type I collagen in the epidermal and dermal layer, respectively. These findings highlight the possibility of using fibroblast secretory factors together with collagen hydrogel in an acellular 3D skin patch that can be used allogeneically for immediate treatment of full-thickness skin loss.

Proteomic Analysis of Human Dermal Fibroblast Conditioned Medium (DFCM)

Growth factors and extracellular matrix (ECM) proteins are involved in wound healing. Human dermal fibroblasts secrete wound-healing mediators in culture medium known as dermal fibroblast conditioned medium (DFCM). However, the composition and concentration of the secreted proteins differ with culture conditions and environmental factors. We cultured human skin fibroblasts in vitro using serum-free keratinocyte-specific media (EpiLife™ Medium [KM1] and defined keratinocyte serum-free medium [KM2]) and serum-free fibroblast-specific medium (FM) to obtain DFCM-KM1, DFCM-KM2 and DFCM-FM, respectively. We identified and compared their proteomic profiles using bicinchoninic acid assay (BCA), 1-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (1D SDS-PAGE), enzyme-linked immunosorbent assay (ELISA), matrix-assisted laser desorption ionisation-time-of-flight mass spectrometry (MALDI-TOF/TOF MS/MS) and liquid chromatography MS (LC-MS/MS). DFCM-KM1 and DFCM-KM2 had higher protein concentrations than DFCM-FM but not statistically significant. MALDI-TOF/TOF MS identified the presence of fibronectin, serotransferrin, serpin and serum albumin. LC-MS/MS and bioinformatics analysis identified 59, 46 and 58 secreted proteins in DFCM-KM1, DFCM-KM2 and DFCM-FM, respectively. The most significant biological processes identified in gene ontology were cellular process, metabolic process, growth and biological regulation. STRING® analysis showed that most secretory proteins in the DFCMs were associated with biological processes (e.g. wound healing and ECM organisation), molecular function (e.g. ECM binding) and cellular component (e.g. extracellular space). ELISA confirmed the presence of fibronectin and collagen in the DFCMs. In conclusion, DFCM secretory proteins are involved in cell adhesion, attachment, proliferation and migration, which were demonstrated to have potential wound-healing effects by in vitro and in vivo studies.

Development and validation of a simple method for the extraction of human skin melanocytes

Primary melanocytes in culture are useful models for studying epidermal pigmentation and efficacy of melanogenic compounds, or developing advanced therapy medicinal products. Cell extraction is an inevitable and critical step in the establishment of cell cultures. Many enzymatic methods for extracting and growing cells derived from human skin, such as melanocytes, are described in literature. They are usually based on two enzymatic steps, Trypsin in combination with Dispase, in order to separate dermis from epidermis and subsequently to provide a suspension of epidermal cells. The objective of this work was to develop and validate an extraction method of human skin melanocytes being simple, effective and applicable to smaller skin samples, and avoiding animal reagents. TrypLE™ product was tested on very limited size of human skin, equivalent of multiple 3-mm punch biopsies, and was compared to Trypsin/Dispase enzymes. Functionality of extracted cells was evaluated by analysis of viability, morphology and melanin production. In comparison with Trypsin/Dispase incubation method, the main advantages of TrypLE™ incubation method were the easier of separation between dermis and epidermis and the higher population of melanocytes after extraction. Both protocols preserved morphological and biological characteristics of melanocytes. The minimum size of skin sample that allowed the extraction of functional cells was 6 × 3-mm punch biopsies (e.g., 42 mm²) whatever the method used. In conclusion, this new procedure based on TrypLE™ incubation would be suitable for establishment of optimal primary melanocytes cultures for clinical applications and research.

Measuring the aggregation of CHO cells prior to single cell cloning allows a more accurate determination of the probability of clonality

The manufacturing process for biotherapeutics is closely regulated by the Food and Drug Administration (FDA), European Medicines Agency (EMA) and other regulatory agencies worldwide. To ensure consistency of the product of a manufacturing cell line, International Committee on Harmonization guidelines (Q5D, 1997) state that the cell substrate should be derived from a single cell progenitor, i.e., clonal.Cell lines in suspension culture may naturally revert to cell adhesion in the form of doublets, triplets and higher order structures of clustered cells. We can show evidence of a single colony from limiting dilution cloning or in semi-solid media, but we cannot determine the number of cells from which the colony originated. To address this, we have used the ViCELL® XR (Beckman Coulter, High Wycombe, UK) cell viability analyzer to determine the proportion of clusters of two or more cells in a sample of the cell suspension immediately prior to cloning. Here, we show data to define the accuracy of the ViCELL for characterizing a cell suspension and summarize the statistical model combining two or more rounds of cloning to derive the probability of clonality. The resulting statistical model is applied to cloning in semi-solid medium, but could equally be applied to a limiting dilution cloning process. We also describe approaches to reduce cell clusters to generate a cell line with a high probability of clonality from a CHO host lineage. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:593-601, 2018.

Secretion of wound healing mediators by single and bi-layer skin substitutes

Limitations of current treatments for skin loss caused by major injuries leads to the use of skin substitutes. It is assumed that secretion of wound healing mediators by these skin substitutes plays a role in treating skin loss. In our previous study, single layer keratinocytes (SK), single layer fibroblast (SF) and bilayer (BL; containing keratinocytes and fibroblasts layers) skin substitutes were fabricated using fibrin that had shown potential to heal wounds in preclinical studies. This study aimed to quantify the secretion of wound healing mediators, and compare between single and bi-layer skin substitutes. Skin samples were digested to harvest fibroblasts and keratinocytes, and expanded to obtain sufficient cells for the construction of skin substitutes. Acellular fibrin (AF) construct was used as control. Substitutes i.e. AF, SK, SF and BL were cultured for 2 days, and culture supernatant was collected to analyze secretion of wound healing mediators via multiplex ELISA. Among 19 wound healing mediators tested, BL substitute secreted significantly higher amounts of CXCL1 and GCSF compared to SF and AF substitute but this was not significant with respect to SK substitute. The BL substitute also secreted significantly higher amounts of CXCL5 and IL-6 compared to other substitutes. In contrast, the SK substitute secreted significantly higher amounts of VCAM-1 compared to other substitutes. However, all three skin substitutes also secreted CCL2, CCL5, CCL11, GM-CSF, IL8, IL-1α, TNF-α, ICAM-1, FGF-β, TGF-β, HGF, VEGF-α and PDGF-BB factors, but no significant difference was seen. Secretion of these mediators after transplantation may play a significant role in promoting wound healing process for the treatment of skin loss.

Clinical Translation of Cell Therapy, Tissue Engineering, and Regenerative Medicine Product in Malaysia and Its Regulatory Policy

With the worldwide growth of cell and tissue therapy (CTT) in treating diseases, the need of a standardized regulatory policy is of paramount concern. Research in CTT in Malaysia has reached stages of clinical trials and commercialization. In Malaysia, the regulation of CTT is under the purview of the National Pharmaceutical Control Bureau (NPCB), Ministry of Health (MOH). NPCB is given the task of regulating CTT, under a new Cell and Gene Therapy Products framework, and the guidelines are currently being formulated. Apart from the laboratory accreditation, researchers are advised to follow Guidelines for Stem Cell Research and Therapy from the Medical Development Division, MOH, published in 2009.

Novel flow cytometric analysis of the blood-brain barrier

The blood-brain barrier (BBB) is primarily comprised of brain microvascular endothelial cells (BMVEC) and astrocytes and serves as a physical and chemical barrier that separates the periphery from the brain. We describe a flow cytometric method using our in vitro model of the human BBB to characterize BMVEC surface junctional proteins critical for maintenance of barrier function, cell viability, and leukocyte adhesion. For this methodology, BMVEC are cocultured with astrocytes in a transwell tissue culture insert to establish the barrier, after which time the BBB are treated with specific agents, and the BMVEC collected for flow cytometric analyses. We use a standard and optimized method to recover the BMVEC from the coculture model that maintains junctional protein expression and cell viability. A novel leukocyte adhesion assay enables a quantitative analysis of peripheral blood mononuclear cell (PBMC) interactions with the BMVEC and can be used to assess the adhesion of many cell types to the BBB. Furthermore, this method enables the concomitant analysis of a large number of adhesion molecules and tight junction proteins on both the BMVEC and adherent PBMC under homeostatic and pathologic conditions. Flow cytometry is an extremely powerful tool, and this technique can also be applied to assess variables not performed in this study, including cell cycle progression, and calcium flux.