Phenotypical characterization of 6–21-week gestational age human dermis and epidermal cell isolation methods for in vitro studies on epidermal progenitors

Directed differentiation of human pluripotent stem cells into epidermal stem and progenitor cells

BACKGROUND

Pluripotent stem cells (PSCs) produced by somatic cell reprogramming self-renew in culture and can differentiate into any cell type, representing a powerful tool for disease modeling, drug screening, regenerative medicine, and the discovery of personalized therapies to treat tissue-specific pathologies. We previously reported the directed differentiation of human PSCs into epidermal stem and progenitor cells (ESPCs) and 3D epidermis to model the inherited syndrome Fanconi anemia (FA), wherein epidermal cell-junctional defects discovered using this system were validated in patient populations. Here, we describe in detail the corresponding protocol for generating PSC-derived keratinocytes using a distinct, normal PSC line (209.2 PSC).

METHODS AND RESULTS

Our approach modifies previous protocols to minimize spontaneous cell death and terminal differentiation, eliminate cell stress-inducing keratinocyte selection steps, and reduce total protocol duration and cost. Independent donor-derived PSC lines were converted into ESPCs through the addition of relevant morphogens and a ROCK inhibitor. Results for the 209.2 PSC line highlight consistencies in 2D and also variable features in 3D epidermis compared to the previously published FA-PSC lines. 209.2 PSC-derived ESPCs exhibited a basal cell phenotype while maintaining the capacity to form epidermal organotypic rafts with morphology consistent with fetal epidermis. Transcriptional analyses demonstrated 209.2 ESPCs express epidermis-selective markers and not early endoderm markers, thus supporting an immature stage of p63+ epidermal development.

CONCLUSIONS

This protocol provides an accelerated path for the generation of human ESPCs and 3D epidermal models to study normal epidermal development and homeostasis, elucidate mechanisms of epidermal disease pathogenesis, and provides a platform for developing personalized therapies.

Isolation and Characterization of a Human Fetal Mesenchymal Stem Cell Population: Exploring the Potential for Cell Banking in Wound Healing Therapies

Various cell-based therapies are in development to address chronic and acute skin wound healing, for example for burns and trauma patients. An off-the-shelf source of allogeneic dermal cells could be beneficial for innovative therapies accelerating the healing in extensive wounds where the availability of a patient’s own cells is limited. Human fetal-derived dermal fibroblasts (hFDFs) show high in vitro division rates, exhibit low immunological rejection properties, and present scarless wound healing in the fetus, and previous studies on human fetal tissue-derived cell therapies have shown promising results on tissue repair. However, little is known about cell lineage stability and cell differentiation during the cell expansion process, required for any potential therapeutic use. We describe an isolation method, characterize a population, and investigate its potential for cell banking and thus suitability as a potential product for cell grafting therapies. Our results show hFDFs and a bone marrow-derived mesenchymal stem cell (BM-MSC) line shared identification markers and in vitro multilineage differentiation potential into osteogenic, chondrogenic, and adipogenic lineages. The hFDF population exhibited similar cell characteristics as BM-MSCs while producing lower pro-inflammatory cytokine IL-6 levels and higher levels of the wound healing factor hepatocyte growth factor. We demonstrate in vitro differentiation of hFDFs, which may be a problem in maintaining long-term lineage stability, potentially limiting their use for cell banking and therapy development.

An in vitro feasibility investigation considering primary human melanocytes for spray- grafting of freshly isolated autologous skin cells for burn treatment and a clinical case report

A skin cell-spray grafting technique that enables the on-site application of freshly isolated autologous single cell suspensions was already applied in many cases on caucasian patients with low skin coloration. Our project hypothesis is that these suspensions contain keratinocytes and vital melanocytes, that are of particular interest for the treatment of patients of darker skin color. To test this, we applied an in vitro model, wherein the feasibility of i) isolating and ii) spraying of freshly isolated autologous melanocyte-keratinocyte cell suspensions was investigated. Primary human epidermal keratinocytes (HEKs) and melanocytes (MCs) were isolated from skin biopsies (n=8). Biochemical parameter, cell counts, cell morphology, growth behavior and immunofluorescence results were compared in two groups using MC cultures and co-cultures of MCs with HEKs. Case information on using the method clinically with one patient is included. The sprayed mixed cell suspensions proliferated in all groups without measurable loss of viability, and MCs exhibited a regular cell morphology in monoculture up to passage 4°. The sprayed MCs and HEKs demonstrated in vitro glucose and lactate metabolism that was comparable to the pipetted controls. In co-culture, well distributed CK14+ HEKs and NKI/beteb+ MCs could be demonstrated, which interacted in the in vitro model. The ratio of HEKs : MCs in our primary cultures were microscopically counted (n=8 each) as mean +/- SD 1,211,000 (+/- 574,343) HEK : 99,625 (+/- 59,025) MC; i.e., a ratio of approx. 12 : 1. Using the isolation method clinically for a patient with dark skin coloration after suffering severe second-degree burns shows a satisfying re-pigmentation of the resulting wound post healing. Freshly isolated spray-on melanocyte/keratinocyte suspensions provide for a considerable amount of viable HEKs and MCs. Using MCs in spray-grafting suspensions could represent a promising approach for treating severe partial-thickness burns and innovative therapy developments that also aim to address cosmetic aspects.

Fetal fibroblasts and keratinocytes with immunosuppressive properties for allogeneic cell-based wound therapy

Fetal skin heals rapidly without scar formation early in gestation, conferring to fetal skin cells a high and unique potential for tissue regeneration and scar management. In this study, we investigated the possibility of using fetal fibroblasts and keratinocytes to stimulate wound repair and regeneration for further allogeneic cell-based therapy development. From a single fetal skin sample, two clinical batches of keratinocytes and fibroblasts were manufactured and characterized. Tolerogenic properties of the fetal cells were investigated by allogeneic PBMC proliferation tests. In addition, the potential advantage of fibroblasts/keratinocytes co-application for wound healing stimulation has been examined in co-culture experiments with in vitro scratch assays and a multiplex cytokines array system. Based on keratin 14 and prolyl-4-hydroxylase expression analyses, purity of both clinical batches was found to be above 98% and neither melanocytes nor Langerhans cells could be detected. Both cell types demonstrated strong immunosuppressive properties as shown by the dramatic decrease in allogeneic PBMC proliferation when co-cultured with fibroblasts and/or keratinocytes. We further showed that the indoleamine 2,3 dioxygenase (IDO) activity is required for the immunoregulatory activity of fetal skin cells. Co-cultures experiments have also revealed that fibroblasts-keratinocytes interactions strongly enhanced fetal cells secretion of HGF, GM-CSF, IL-8 and to a lesser extent VEGF-A. Accordingly, in the in vitro scratch assays the fetal fibroblasts and keratinocytes co-culture accelerated the scratch closure compared to fibroblast or keratinocyte mono-cultures. In conclusion, our data suggest that the combination of fetal keratinocytes and fibroblasts could be of particular interest for the development of a new allogeneic skin substitute with immunomodulatory activity, acting as a reservoir for wound healing growth factors.

Isolation and characterization of multipotent cells from human fetal dermis

We report that cells from human fetal dermis, termed here multipotent fetal dermal cells, can be isolated with high efficiency by using a nonenzymatic, cell outgrowth method. The resulting cell population was consistent with the definition of mesenchymal stromal cells by the International Society for Cellular Therapy. As multipotent fetal dermal cells proliferate extensively, with no loss of multilineage differentiation potential up to passage 25, they may be an ideal source for cell therapy to repair damaged tissues and organs. Multipotent fetal dermal cells were not recognized as targets by T lymphocytes in vitro, thus supporting their feasibility for allogenic transplantation. Moreover, the expansion protocol did not affect the normal phenotype and karyotype of cells. When compared with adult dermal cells, fetal cells displayed several advantages, including a greater cellular yield after isolation, the ability to proliferate longer, and the retention of differentiation potential. Interestingly, multipotent fetal dermal cells expressed the pluripotency marker SSEA4 (90.56 ± 3.15% fetal vs. 10.5 ± 8.5% adult) and coexpressed mesenchymal and epithelial markers (>80% CD90(+)/CK18(+) cells), coexpression lacking in the adult counterparts isolated under the same conditions. Multipotent fetal dermal cells were able to form capillary structures, as well as differentiate into a simple epithelium in vitro, indicating skin regeneration capabilities.