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Cancer research has considerably progressed with the improvement of in vitro study models, helping to understand the key role of the tumor microenvironment in cancer development and progression. Over the last few years, complex 3D human cell culture systems have gained much popularity over in vivo models, as they accurately mimic the tumor microenvironment and allow high-throughput drug screening. Of particular interest, in vitrohuman 3D tissue constructs, produced by the self-assembly method of tissue engineering, have been successfully used to model the tumor microenvironment and now represent a very promising approach to further develop diverse cancer models. In this review, we describe the importance of the tumor microenvironment and present the existing in vitro cancer models generated through the self-assembly method of tissue engineering. Lastly, we highlight the relevance of this approach to mimic various and complex tumors, including basal cell carcinoma, cutaneous neurofibroma, skin melanoma, bladder cancer, and uveal melanoma.

Over the last century, the clinical management of severe skin burns significantly progressed with the development of burn care units, topical antimicrobials, resuscitation methods, early eschar excision surgeries, and skin grafts. Despite these considerable advances, the present treatment of severe burns remains burdensome, and patients are highly susceptible to skin engraftment failure, infections, organ dysfunction, and hypertrophic scarring. Recent researches have focused on mesenchymal stromal cell (MSC) therapy and hold great promises for tissue repair, as reported in several animal studies and clinical cases. In the present review, we will provide an up-to-date outlook of the pathophysiology of severe skin burns, clinical treatment modalities and current limitations. We will then focus on MSCs and their potential in the burn wound healing both in in vitro and in vivo studies. A specific attention will be paid to the cell preconditioning approach, as a means of improving the MSC efficacy in the treatment of major skin burns. In particular, we will debate how several preconditioning cues would modulate the MSC properties to better match up with the burn pathophysiology in the course of the cell therapy. Finally, we will discuss the clinical interest and feasibility of a MSC-based therapy in comparison to their paracrine derivatives, including microvesicles and conditioned media for the treatment of major skin burn injuries.

Background & Aim Deep and extensive skin wounds and burns are treated with autologous Split-Thickness Skin Grafts, with a possible combination of adjuvant therapy, or grafted with Cultured Epidermal Autografts (CEAs) when donor sites are limited. Despite many years of use and the allowing of patient survival, CEA still fail to provide satisfactory clinical outcomes due to poor engraftment rates and reduced skin functionality. In the past few decades, Mesenchymal Stromal Cells (MSCs) therapy have been proposed as a novel therapeutic tool to promote wound healing through anti-inflammatory, pro-trophic and pro-remodeling effects. MSCs are also able to interact with their environment and modify their secretory profile depending on cellular, molecular or physical environment. Our team recently shown that, IL-1β-primed gingival MSCs promoted wound healing in vitro, and in vivo through the secretion of a mix of secreted products and extracellular vesicles. Paracrine mechanism involving MMPs and TGF-βs signaling has been shown to be implicated in MSC primed effect on wound healing. Preliminary results also indicated that IL-6 could also been involved. Therefore, in the present work, we investigated whether other source of MSC could respond similarly to Interleukin 1β to favor wound healing through the secretion of extracellular vesicles and secreted products. Methods, Results & Conclusion Naive and IL-1β-primed MSCs from gingival or bone marrow sources were evaluated in in vitro models of migration, inflammation and Dermal-Epidermal Junction (DEJ) formation. Extracellular vesicles and IL-6 expression were analyzed by NTA and ELISA respectively in the Conditioned Media (CM) of MSC culture. To investigate the mechanism of action of IL-6 in particular, we used human recombinant IL-6 at the concentration found in IL-CM by ELISA and specific blocking antibody in our different in vitro models. Preliminary results indicated that both MSC sources responds similarly to Interleukin-1β priming and have been shown to promote skin cell migration, favor extracellular matrix deposition and reduce inflammation. In vivo studies will be performed to confirm the results observed in vitro. Overall, these results underline the benefit of the IL-1β priming strategy in the treatment of severe skin defects using MSC and epidermal substitute. We hope that this approach could soon improve the current medical treatment of full-thickness burn wounds.

Our laboratory has developed a scaffold-free cell-based method of tissue engineering to produce bilayered tissue-engineered skin substitutes (TESs) from epidermal and dermal cells. However, TES pigmentation is absent or heterogeneous after grafting, due to a suboptimal number of melanocytes in culture. Our objectives were to produce TESs with a sufficient quantity of melanocytes from different pigmentation phototypes (light and dark) to achieve a homogeneous color and to evaluate whether the resulting pigmentation was photoprotective against ultraviolet radiation (UVR)-induced DNA damage in the dermis and the epidermis. TESs were cultured using different concentrations of melanocytes (100, 200, and 1,500 melanocytes/mm2 ), and pigmentation was evaluated in vitro and after grafting onto an athymic mouse excisional model. Dermal and epidermal DNA damage was next studied, exposing pigmented TESs to 13 and 32.5 J/cm2 UVR in vitro. We observed that melanocyte cell density increased with culture time until reaching a plateau corresponding to the cell distribution of native skin. Pigmentation of melanocyte-containing TESs was similar to donor skin, with visible melanin transfer from melanocytes to keratinocytes. The amount of melanin in TESs was inversely correlated to the UVR-induced formation of cyclobutane pyrimidine dimer in dermal fibroblasts and keratinocytes. Our results indicate that the pigmentation conferred by the addition of melanocytes in TESs protects against UVR-induced DNA damage. Therefore, autologous pigmented TESs could ensure photoprotection after grafting.

Since the 1980s, deep and extensive skin wounds and burns are treated with autologous split-thickness skin grafts, or cultured epidermal autografts, when donor sites are limited. However, the clinical use of cultured epidermal autografts often remains unsatisfactory because of poor engraftment rates, altered wound healing, and reduced skin functionality. In the past few decades, mesenchymal stromal cells (MSCs) have raised much attention because of their anti-inflammatory, protrophic, and pro-remodeling capacities. More specifically, gingival MSCs have been shown to possess enhanced wound healing properties compared with other tissue sources. Growing evidence also indicates that MSC priming could potentiate therapeutic effects in diverse in vitro and in vivo models of skin trauma. In this study, we found that IL-1β-primed gingival MSCs promoted cell migration, dermal-epidermal junction formation, and inflammation reduction in vitro, as well as improved epidermal substitute engraftment in vivo. IL-1β-primed gingival MSCs had different secretory profiles from naive gingival MSCs, characterized by an overexpression of transforming growth factor-β and matrix metalloproteinase (MMP) pathway agonists. Eventually, MMP-1, MMP-9, and transforming growth factor-β1 appeared to be critically involved in IL-1β-primed gingival MSC mechanisms of action.

Cultured epithelial autografts (CEAs) represent a life-saving surgical technique for full-thickness skin burns covering more than 60% total body surface area. However, CEAs present numerous drawbacks leading to heavy cosmetic and functional sequelae. In our previous study, we showed that human plasma-based fibrin matrices (hPBM) could improve the reparative potential of CEAs. Therefore, in the present work, we sought to investigate the role of hPBM compared with fibrin from purified fibrinogen (FPF) or plastic support on epidermal substitute formation and engraftment. The use of hPBM for epidermal substitute culture improved keratinocyte migration, proliferation, and epidermal substitute organization to a better extent than FPF in vitro. Both fibrin matrices favored greater dermal-epidermal junction protein deposition and prevented their degradation. Keratinocyte differentiation was also decreased using both fibrin matrices. Basement membrane protein deposition was mainly influenced by matrix whereas growth factors released from fibrin especially by hPBM were shown to enhance in vitro keratinocyte migration, proliferation, and epidermal substitute organization. Ultimately, epidermal substitutes grown on hPBM displayed better engraftment rates than those cultured on FPF or on plastic support in a NOD-SCID model of acute wound with the formation of a functional dermal-epidermal junction. Together, these results show the positive impact of fibrin matrices and their released growth factor on epidermal substitute phenotype and grafting efficiency. Fibrin matrices, and especially hPBM, may therefore be of interest to favor the treatment of full-thickness burn patients.

Human mesenchymal stromal cells (hMSCs) are adult-source cells that have been extensively evaluated for cell-based therapies. hMSCs delivered by intravascular injection have been reported to accumulate at the sites of injury to promote tissue repair and can also be employed as vectors for the delivery of therapeutic genes. However, the full potential of hMSCs remains limited as the cells are lost after injection due to anoikis and the adverse pathologic environment. Encapsulation of cells has been proposed as a means of increasing cell viability. However, controlling the release of therapeutic cells over time to target tissue still remains a challenge today. Here, we report the design and development of thermo-rheological responsive hydrogels that allow for precise, time dependent controlled-release of hMSCs. The encapsulated hMSCs retained good viability from 76% to 87% dependent upon the hydrogel compositions. We demonstrated the design of different blended hydrogel composites with modulated strength (S parameter) and looseness of hydrogel networks (N parameter) to control the release of hMSCs from thermo-responsive hydrogel capsules. We further showed the feasibility for controlled-release of encapsulated hMSCs within 3D matrix scaffolds. We reported for the first time by a systematic analysis that there is a direct correlation between the thermo-rheological properties associated with the degradation of the hydrogel composite and the cell release kinetics. This work therefore provides new insights into the further development of smart carrier systems for stem cell therapy.

Background & Aim In spite of several research advances in the field of skin tissue engineering and regenerative medicine, little progress has been made in the management of major burns. Since the 1980s, deep and extensive skin wounds and burns are treated with autologous Split-Thickness Skin Grafts, or Cultured Epidermal Autografts (CEAs) when donor sites are limited. While CEAs allow patient survival in most critical cases, poor engraftment rates and reduced skin functionality limit the clinical use of CEAs. In the past few decades, Mesenchymal Stromal Cells (MSCs) therapy has emerged as a new strategy to promote wound healing through anti-inflammatory, anti-microbial, pro-trophic and pro-remodeling effects. MSCs are also able to interact with their environment and modify their secretory profile depending on cellular, molecular or physical priming cues. Thus, the present work aims to assess the benefit and mechanism of action of Interleukin-1β (IL-1β) primed MSCs or their secretory products on wound healing and epidermal substitute engraftment. Methods, Results & Conclusion Naive and IL-1β-primed MSCs or their Conditioned Media (CM) were evaluated in in vitro models of migration, inflammation and Dermal-Epidermal Junction (DEJ) formation, and in an in vivo skin excisional and epidermal substitute grafting mouse model. We showed that the IL-1β priming potentiates the MSC efficacy through the reduction of inflammation and the promotion of cell migration, DEJ remodeling and epidermal substitute engraftment. These positive effects were partly mediated by MSC paracrine secretions which targeted downstream p38MAPK, SMAD and MMP signalings. Among priming-induced secreted factors, MMP-1, MMP-9, HGF and TGF-β1 were found to play key roles in the resolution of wound healing. These results underline the benefit of the IL-1β priming strategy in the treatment of severe skin defects using MSC and epidermal substitute. We hope that this approach could soon improve the current medical treatment of full-thickness burn wounds.