Rapid culture of human keratinocytes in an autologous, feeder-free system with a novel growth medium

BACKGROUND AIMS

The ability to culture human keratinocytes is beneficial in the treatment of skin injury and disease, as well as for testing chemicals in vitro as a substitute for animal testing.

RESULTS

We have identified a novel culture medium for the rapid growth of keratinocytes from human skin. "Kelch's medium" supports keratinocyte growth that is as rapid as in the classical Rheinwald and Green method, but without the need for cholera toxin or xenogeneic feeder cells. It enables keratinocytes to out-compete co-cultured autologous fibroblasts so that separation of the epidermis from the dermis is no longer required before keratinocyte culture. Enzymatic digests of whole human skin can therefore be used to generate parallel cultures of autologous keratinocytes, fibroblasts and melanocytes simply by using different cell culture media.

CONCLUSIONS

This new keratinocyte medium and the simplified manufacturing procedures it enables are likely to be beneficial in skin engineering, especially for clinical applications.

Epidermolysis Bullosa: A Review of the Tissue-Engineered Skin Substitutes Used to Treat Wounds

Skin wound healing is a crucial process for regenerating healthy skin and avoiding the undesired consequences associated with open skin wounds. For epidermolysis bullosa (EB), a debilitating group of fragile skin disorders currently without a cure, skin blistering can often be severe and heal poorly, increasing susceptibility to life-threatening complications. To prevent these, investigational therapies have been exploring the use of tissue-engineered skin substitutes (TESSs) aimed at replacing damaged skin and promoting long-term wound closure. These products have either been developed in house or commercially sourced and are composed of allogeneic or autologous human skin cells, often with some form of bioscaffolding. They can be broadly classified based on their cellular composition: keratinocytes (epidermal substitutes), fibroblasts (dermal substitutes) or a combination of both (composite substitutes). Encouraging long-term wound healing has been achieved with epidermal substitutes. However, these substitutes have not demonstrated the same efficacy for all patients, which may be due to the molecular heterogeneity observed between EB subtypes. Autologous composite TESSs, which more closely resemble native human skin, are therefore being investigated and may hold promise for treating an extended range of patients. Additionally, future TESSs for EB are focused on using gene-corrected patient skin cells, which have already demonstrated remarkable long-term wound healing capabilities. In this review, we provide an overview of the different TESSs that have been investigated in clinical studies to treat patients with EB, as well as their long-term wound healing results. Where available, we describe the methods used to develop these products to inform future efforts in this field.

Distinctive Subpopulations of Stromal Cells Are Present in Human Lymph Nodes Infiltrated with Melanoma

Metastasis of human tumors to lymph nodes (LN) is a universally negative prognostic factor. LN stromal cells (SC) play a crucial role in enabling T-cell responses, and because tumor metastases modulate their structure and function, this interaction may suppress immune responses to tumor antigens. The SC subpopulations that respond to infiltration of malignant cells into human LNs have not been defined. Here, we identify distinctive subpopulations of CD90⁺ SCs present in melanoma-infiltrated LNs and compare them with their counterparts in normal LNs. The first population (CD90⁺ podoplanin⁺ CD105⁺ CD146⁺ CD271⁺ VCAM-1⁺ ICAM-1⁺ α-SMA⁺) corresponds to fibroblastic reticular cells that express various T-cell modulating cytokines, chemokines, and adhesion molecules. The second (CD90⁺ CD34⁺ CD105⁺ CD271⁺) represents a novel population of CD34⁺ SCs embedded in collagenous structures, such as the capsule and trabeculae, that predominantly produce extracellular matrix. We also demonstrated that these two SC subpopulations are distinct from two subsets of human LN pericytes, CD90⁺ CD146⁺ CD36⁺ NG2^- pericytes in the walls of high endothelial venules and other small vessels, and CD90⁺ CD146⁺ NG2⁺ CD36^- pericytes in the walls of larger vessels. Distinguishing between these CD90⁺ SC subpopulations in human LNs allows for further study of their respective impact on T-cell responses to tumor antigens and clinical outcomes.

microRNAs in Ex Vivo Human Adipose Tissue Derived Mesenchymal Stromal Cells (ASC) Undergo Rapid Culture-Induced Changes in Expression, Including miR-378 which Promotes Adipogenesis

There is clinical interest in using human adipose tissue-derived mesenchymal stromal cells (ASC) to treat a range of inflammatory and regenerative conditions. Aspects of ASC biology, including their regenerative potential and paracrine effect, are likely to be modulated, in part, by microRNAs, small RNA molecules that are embedded as regulators of gene-expression in most biological pathways. However, the effect of standard isolation and expansion protocols on microRNA expression in ASC is not well explored. Here, by using an untouched and enriched population of primary human ASC, we demonstrate that there are rapid and significant changes in microRNA expression when ASC are subjected to standard isolation and expansion methods. Functional studies focusing on miR-378 indicate that these changes in expression may have an impact on phenotype and function. Specifically, we found that increased levels of miR-378 significantly promoted adipogenesis in late passage ASC. These results are informative to maximizing the potential of ASC for use in various clinical applications, and they have implications for targeting microRNAs as a therapeutic strategy for obesity or metabolic disease.

Ex Vivo Human Adipose Tissue Derived Mesenchymal Stromal Cells (ASC) Are a Heterogeneous Population That Demonstrate Rapid Culture-Induced Changes

Human adipose-derived mesenchymal stromal cells (ASC) are showing clinical promise for the treatment of a range of inflammatory and degenerative conditions. These lipoaspirate-derived cells are part of the abundant and accessible source of heterogeneous stromal vascular fraction (SVF). They are typically isolated and expanded from the SVF via adherent cell culture for at least 2 weeks and as such represent a relatively undefined population of cells. We isolated ex vivo ASC directly from lipoaspirate using a cocktail of antibodies combined with immunomagnetic bead sorting. This method allowed for the rapid enrichment of a defined and untouched ex vivo ASC population (referred to as MACS-derived ASC) that were then compared to culture-derived ASC. This comparison found that MACS-derived ASC contain a greater proportion of cells with activity in in vitro differentiation assays. There were also significant differences in the secretion levels of some key paracrine molecules. Moreover, when the MACS-derived ASC were subjected to adherent tissue culture, rapid changes in gene expression were observed. This indicates that culturing cells may alter the clinical utility of these cells. Although MACS-derived ASC are more defined compared to culture-derived ASC, further investigations using a comprehensive multicolor flow cytometry panel revealed that this cell population is more heterogeneous than previously appreciated. Additional studies are therefore required to more precisely delineate phenotypically distinct ASC subsets with the most therapeutic potential. This research highlights the disparity between ex vivo MACS-derived and culture-derived ASC and the need for further characterization.

Visualization and Quantification of Mesenchymal Cell Adipogenic Differentiation Potential with a Lineage Specific Marker

Several dyes are currently available for use in detecting differentiation of mesenchymal cells into adipocytes. Dyes, such as Oil Red O, are cheap, easy to use and widely utilized by laboratories analyzing the adipogenic potential of mesenchymal cells. However, they are not specific to changes in gene transcription. We have developed a gene-specific differentiation assay to analyze when a mesenchymal cell has switched its fate to an adipogenic lineage. Immuno-labelling against fatty acid binding protein-4 (FABP4), a lineage-specific marker of adipogenic differentiation, enabled visualization and quantification of differentiated cells. The ability to quantify adipogenic differentiation potential of mesenchymal cells in a 96 well microplate format has promising implications for a number of applications. Hundreds of clinical trials involve the use of adult mesenchymal stromal cells and it is currently difficult to correlate therapeutic outcomes within and especially between such clinical trials. This simple high-throughput FABP4 assay provides a quantitative assay for assessing the differentiation potential of patient-derived cells and is a robust tool for comparing different isolation and expansion methods. This is particularly important given the increasing recognition of the heterogeneity of the cells being administered to patients in mesenchymal cell products. The assay also has potential utility in high throughput drug screening, particularly in obesity and pre-diabetes research.

From bench to bedside: use of human adipose-derived stem cells

Since the discovery of adipose-derived stem cells (ASC) in human adipose tissue nearly 15 years ago, significant advances have been made in progressing this promising cell therapy tool from the laboratory bench to bedside usage. Standardization of nomenclature around the different cell types used is finally being adopted, which facilitates comparison of results between research groups. In vitro studies have assessed the ability of ASC to undergo mesenchymal differentiation as well as differentiation along alternate lineages (transdifferentiation). Recently, focus has shifted to the immune modulatory and paracrine effects of transplanted ASC, with growing interest in the ASC secretome as a source of clinical effect. Bedside use of ASC is advancing alongside basic research. An increasing number of safety-focused Phase I and Phase IIb trials have been published without identifying any significant risks or adverse events in the short term. Phase III trials to assess efficacy are currently underway. In many countries, regulatory frameworks are being developed to monitor their use and assure their safety. As many trials rely on ASC injected at a distant site from the area of clinical need, strategies to improve the homing and efficacy of transplanted cells are also being explored. This review highlights each of these aspects of the bench-to-bedside use of ASC and summarizes their clinical utility across a variety of medical specialties.

Cell-targeted platinum nanoparticles and nanoparticle clusters

The facile preparation of cell-targeted platinum nanoparticles (PtNPs) is described, using designed peptides that as a single molecule control PtNP cluster growth, stabilise clusters in aqueous suspension and enable attachment of a versatile range of cell-targeting ligands.

MicroRNA regulation in human CD8+ T cell subsets--cytokine exposure alone drives miR-146a expression

Background

microRNAs (miRNAs) are emerging as key regulators of the immune system, but their role in CD8+ T cell differentiation is not well explored. Some evidence suggests that signals from cell surface receptors influence the expression of miRNAs in CD8+ T cells, and may have consequent effects on cell phenotype and function. We set out to investigate whether common gamma chain cytokines modulated human CD8+ T cell expression of miR-146a, which previous studies have associated with different stages of CD8+ differentiation. We also investigated how changes in miR-146a related to other miRNAs that alter with CD8+ differentiation status.

Methods

We treated human CD8+ T cells with the cytokines IL-2, IL-7 or IL-15 either at rest or after stimulation with anti-CD3 and anti-CD28. For some experiments we also purified human CD8+ T cell subsets ex vivo. Flow cytometry was used in parallel to assess cell surface memory marker expression. Total RNA from these cells was subjected to microarray analysis and real-time PCR for miRNA expression. Nucleofection studies were performed to assess potential mRNA targets of miR-146a.

Results

We find that miR-146a is up-regulated in naïve CD8+ T cells exposed to IL-2 or IL-15, even in the absence of an activating T cell receptor stimulus, but not when IL-7 is also present. miR-146a expression correlates with a memory phenotype in both ex vivo and in vitro cultured cells although in our hands overexpression of miR-146a was not sufficient alone to drive a full memory phenotype. In ex vivo analysis, miR-146a was one of a small number of miRNAs that was differentially expressed between naïve and memory CD8+ T cells.

Conclusions

miR-146a is emerging as a critical regulator of immune system. Our data shows that miR-146a expression is strongly influenced by the cytokine milieu even in the absence of a T cell receptor stimulus. Our results have implications for studies designed to assess the function of miR-146a, help to define a fingerprint of miRNA expression in CD8+ T cell subsets and may be useful when designing optimal protocols for T cell expansion as efficacy of T cell immunotherapy is correlated with an ‘early’ memory phenotype.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0292-0) contains supplementary material, which is available to authorized users.

Characterization of mesenchymal progenitor cell populations directly derived from human dermis

Mesenchymal stem cell (MSC) and progenitor cell (MPC) populations in human dermis remain poorly characterized, despite their importance to wound repair and the pathogenesis of many skin diseases. To identify MSC/MPC populations in human dermis we developed an 11-marker flow cytometry technique that enabled sorting of mesenchymal cell populations for functional assays, using adipose-derived stem cells (ASCs) from human adipose tissue as a positive control. Two populations of dermal cells had similar phenotypes to ASCs: both were CD34(+) CD73(+) CD105(-)/low, and lacked expression of c-kit (CD117) and hematopoietic or vascular markers (CD31, CD45, CD146, and HLA-DR). However, whereas ASCs were CD36(+/-) CD90(+), dermal mesenchymal progenitor cells (DMPCs) were split between a dominant CD36(-) CD90(+) population (DMPC1) and a small CD36(+) CD90(-) population (DMPC2). Both these populations were capable of differentiating into adipocytes, but only DMPC1 localized to a perivascular location, similar to that reported for ASCs. Re-gating of the flow cytometry data revealed that both DMPC1 and DMPC2 were part of CD45(-) CD73(+) CD146(-) populations with variable expression of CD34. This suggests that CD34 may not be a stable marker of DMPC populations in human dermis, consistent with data from MSCs in human bone marrow, and with the loss of CD34 we observed from both ASCs and DMPCs on cell culture. These data enable future study of DMPCs in health and disease, and may also explain why some mesenchymal cell lines derived from human dermis exhibit characteristics of MSCs.