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The field of organ transplantation is experiencing a transformative shift with the rise of Advanced Therapy Medicinal Products (ATMPs), which include gene therapies, somatic cell therapies, and tissue-engineered products. These therapies offer new, potentially curative treatments for longstanding medical challenges, impacting numerous patients. However, their adoption is hindered by complex regulatory frameworks, high production costs, and inconsistent access across Europe. The ESOT ATMP Task Force's position paper analyzes these challenges from research to clinical application, advocating for a coordinated strategy to position Europe as a leader in ATMP development. It proposes specific actions such as streamlining regulatory pathways to accelerate approvals, boosting funding for ATMP research, and creating specialized facilities for development and implementation. The paper also highlights the critical roles of patient engagement and real-world evidence in optimizing clinical and regulatory practices., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Berishvili, Piemonti, de Koning, Lindstedt, Scholz, Scott, Auxenfans, Johnson, Martin, Gunther, Mey, Potena and Thaunat.)

Corneal disease is the second cause of blindness in developing countries, where the number of corneal grafts needed by far exceeds the number available. In industrialized countries, although corneas are generally available for keratoplasty, onto inflamed and vascularized host beds they are often rejected despite immune-suppression. A non-immunogenic, transparent, cytocompatible stroma is therefore required, which can be lyophilized for long-term conservation. Decellularization methods were tested on porcine corneal stromas before validation on human corneas. Decellularization and lyophilization led to opacification of the stroma, which could be reversed by soaking in 100% glycerol. Cell-depleted transparized stromas were then lyophilized (LTDC) to allow their long-term conservation and water content was measured. The ultrastructure of LTDC corneas was examined by transmission electron microscopy (TEM). Histocompatibility antigens were undetectable on LTDC stromas by antibody staining. Finally, cytocompatibility of LTDC stromas was demonstrated on an ex vivo model of anterior lamellar keratoplasty. Differential staining was used to monitor colonization of LTDC stromas by cells from the receiving cornea. Only SDS-based decellularization produced acellular porcine stromas. The lowest SDS concentration tested (0.1%) was validated on human corneas. Unlike lyophilized corneas, LTDC stromas without residual water, express no histocompatibility markers, although TEM revealed the presence of cellular debris in an ultrastructural arrangement of collagen fibers very close to that of native corneas. This structure is compatible with colonization by cells from the receiver cornea in an ex vivo lamellar graft model. Our procedure produced non-immunogenic, transparent stromas with conserved ultrastructure compatible with long-term conservation.

Soft tissue reconstruction is a challenge in plastic surgery, when replacing lost materials and correcting contour defects. Many permanent and temporary fillers have been used to restore the volume of these lesions, but often with poor results and even complications. Adipose-derived stem/stromal cells (ASCs) and adipose tissue engineering have been suggested as valuable alternatives. In order to inject these cultured cells, it was essential to find a suitable vehicle. The purpose of this study was to evaluate Cytocare(®), an injectable medical device, composed of hyaluronic acid plus amino acids, vitamins and mineral salts. First, ASC viability and bioavailability in the 3 different available Cytocare(®) formulations using the MTT test were assessed; then an animal experiment, testing the tolerance after intradermal injections of both Cytocare(®) alone and with ASCs was carried out. Our in vitro results demonstrate a high biocompatibility of Cytocare(®) resulting in a better viability of ASCs when cultured in Cytocare(®) compared to culture medium (p < 0.05, Mann and Whitney). Cytocare(®) also permits their bioavailability and proliferation, making it a potential transfer vehicle that can retain the cells before their integration around the recipient site. Finally, our animal experiment shows that the ASC + Cytocare(®) combination is well tolerated. In conclusion, Cytocare(®) can be used as a biocompatible scaffold for cultured ASCs in therapeutic treatments, ensuring ASC bioavailability, as well as evidence of excellent tolerance in nude mice., (Copyright © 2015 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.)

Background: Adipose tissue engineering has been hampered by the inability to culture mature adipocytes. Adipose-derived stem cell (ASC) culture opens the way for the preparation of human 3-D hypodermis in large quantities. These models play a role in obesity-related active molecules and slimming agent screening. Moreover, they contribute to a better understanding of the mechanisms underpinning obesity., Materials and Methods: Freshly extracted ASC from fat tissue were characterized by flow cytometry for CD73, CD90, CD105, HLA-ABC, CD14 and CD45 markers and by Western blot for pref-1. Their differentiation in mature adipocytes was followed by lipid and adiponectin secretion or by oil red O staining and radioimmunoassay. Neosynthesized extracellular matrix (ECM) of 3-D hypodermis was investigated by immunohistochemistry (collagen type I, V and VI) and transmission electron microscopy., Results: Our results demonstrate that the culture of preadipocytes in proliferation medium for 15 days followed by 16 days of culture in differentiation medium allowed production of the thickest single-layer hypodermis in which preadipocytes and mature adipocytes coexist and synthesize adiponectin and ECM components. Functionality of our 3-D single-layer hypodermis was demonstrated both by a 3.5-fold glycerol production after its stimulation with norepinephrine (adrenergic agonist) and by its slimming after caffeine treatment versus the nontreated 3-D hypodermis., Conclusion: This economic 3-D model, easy to prepare and giving reproducible results after the treatment of actives, is useful for pharmacotoxicological trials as an alternative to animal experimentation., (Copyright © 2011 S. Karger AG, Basel.)

Tissue engineered human oral mucosa has the potential to be applied to the closure of surgical wounds after tissue deficits due to facial trauma, malignant lesion surgery or preposthetic procedure. It can also be used to elucidate the biology and pathology of oral mucosa and as a model alternative to animals for safety testing of oral care products. Using the technology previously developed in our laboratory for the production of a skin equivalent, we were able to reconstruct a nonkeratinized full-thickness human oral mucosal equivalent closely mimicking human native oral mucosa. The successive coculture of human lamina propria fibroblasts and human oral epithelial cells isolated from the nonkeratinized region of oral cavity in a porous collagen-glycosaminoglycan (GAG)-chitosan scaffold gave rise to a lamina propria equivalent (LPE) and then to an oral mucosa equivalent (OME). The results of the histology, immunohistology and transmission electron microscopy of this OME demonstrated the presence of a nonkeratinized pluristratified and differentiated epithelium as in native nonkeratinized human oral mucosa expressing both K13 and K3/76. This epithelium was firmly anchored to the LPE by a continuous and ultrastructurally well-organized basement membrane. In the LPE, fibroblasts synthesized new extracellular matrix where the average collagen fibre diameter was 28.4 nm, close to that of native oral mucosa. The proliferative capacity of the basal cells was demonstrated by the expression of Ki67.

Skin and cornea both feature an epithelium firmly anchored to its underlying connective compartment: dermis for skin and stroma for cornea. A breakthrough in tissue engineering occurred in 1975 when skin stem cells were successfully amplified in culture by Rheinwald and Green. Since 1981, they are used in the clinical arena as cultured epidermal autografts for the treatment of patients with extensive burns. A similar technique has been later adapted to the amplification of limbal-epithelial cells. The basal layer of the limbal epithelium is located in a transitional zone between the cornea and the conjunctiva and contains the stem cell population of the corneal epithelium called limbal-stem cells (LSC). These cells maintain the proper renewal of the corneal epithelium by generating transit-amplifying cells that migrate from the basal layer of the limbus towards the basal layer of the cornea. Tissue-engineering protocols enable the reconstruction of three-dimensional (3D) complex tissues comprising both an epithelium and its underlying connective tissue. Our in vitro reconstruction model is based on the combined use of cells and of a natural collagen-based biodegradable polymer to produce the connective-tissue compartment. This porous substrate acts as a scaffold for fibroblasts, thereby, producing a living dermal/stromal equivalent, which once epithelialized results into a reconstructed skin/hemicornea. This paper presents the reconstruction of surface epithelia for the treatment of pathological conditions of skin and cornea and the development of 3D tissue-engineered substitutes based on a collagen-GAG-chitosan matrix for the regeneration of skin and cornea.

Since the culture of keratinocytes on feeder layers, research to produce skin equivalents has been motivated by the challenge of treating large burns and chronic wounds and by European regulations which both require proof of the innocuousness and the effectiveness of cosmetic products, and which forbid animal testing. The dynamism in fundamental research, dermocosmetology and the pharmaceutical industry has led to the evolution and complexification of reconstructed skin. The Collagen-GAG-Chitosan sponge, as well as the self-assembly model, allow dermal reconstruction in which the neosynthesized extracellular matrix contains all of the desired macromolecules. It is deposited forming an ultrastructurally organised architecture. The quality of the dermis obtained allows the development and regeneration of a pluristratified and differentiated epidermis firmly anchored by an organised dermal-epidermal junction. Evolution of reconstructed skin into models which are more and more similar to the physiological skin results in higher graft take rates in the treatment of burns and chronic wounds, and brings to research, to dermocosmetology and to the pharmaceutical industry, a wide range of products such as pigmented, endothelialized, immunocompetent, and now adipose reconstructed skins. The present review will mainly concentrate on the latest developments in skin engineering and will mostly concern the studies carried out by our groups.

Unlabelled: Our objective was to optimize a medium for preadipocyte differentiation into adipocytes., Methods: The differentiation medium contains fixed components as well as 7 variable ones. To perform this study, different experiments were designed and the study was carried out in 4 stages. The first two stages tested the influence of serum, dexamethasone, hydrocortisone and an cAMP activator. In the third stage, two new variables were added: rosiglitazone and insulin. In the final stage, the medium selected in stage 3 was validated. The differentiation selection criteria consisted of the number of mature adipocytes and adiponectin secretion., Results: We have shown that each variable was indispensable and that positive interactions occurred between some variables. No negative interactions were found and it was possible to optimize the concentration of each variable., Conclusions: We selected the following medium, which provides optimal adipocyte size and adiponectin secretion: DMEM/HAMF12+10% Foetal Clone Serum (FCS)+2 nM triiodothyronine+10 nM hydrocortisone +0.5 mM IsoButyl Methyl Xanthine (IBMX)+500 nM dexamethasone+1 microM rosiglitazone+0.15 UI/ml insulin+antibiotics.

Large-scale culture of primary keratinocytes allows the production of large epidermal sheet surfaces for the treatment of extensive skin burns. This method is dependent upon the capacity to establish cultures of proliferating keratinocytes in conditions compatible with their clonal expansion while maintaining their capacity to differentiate into the typical squamous pattern of human epidermis. Feeder layers are critical in this process because the fibroblasts that compose this layer serve as a source of adhesion, growth and differentiation factors. In this report, we have characterise the expression patterns of p63 isoforms in primary keratinocytes cultured on two different feeder layer systems, murine 3T3 and human fibroblasts. We show that with the latter, keratinocytes express a higher ratio of Delta N to TAp63 isoform, in relation with higher clonogenic potential. These results indicate that human fibroblasts represent an adequate feeder layer system to support the culture of primary human keratinocytes.

Introduction: Repairing contour defects is a challenge in plastic surgery. Different filling materials have been used with inadequate results and complications. The autologous fat transfer is the standard technique at the moment, but adipose tissue reserves are limited. The aim of our study was to compare in vivo on an animal model, preadipocytes cultured in a collagen scaffold versus adipose tissue transferred by the usual surgical technique., Materials and Methods: In order to compare adipocytes resulting from the differentiation of preadipocytes with those of purified adipose tissue, we implanted them in 10 nude mice. The preadipocytes were implanted using a collagen scaffold as intermediary and the adipose tissue following the plastic surgery protocol described by SR Coleman. After 8 weeks, tissue fragments were explanted and analysed after staining with HPS, Oil Red O and labelling with human anti-vimentin antibodies., Results: The scaffold seeded with preadipocytes had the macroscopic appearance of adipose tissue with peripheral neovascularisation. The preadipocytes had been transformed into mature adipocytes. Purified adipose tissue also presented peripheral neovascularisation. Numerous mature adipocytes were found. There was an abundant murine extracellular matrix since anti-vimentin labelling was negative., Conclusion: This experimental study showed that adipose tissue engineering is feasible and gives comparable results to fat grafting. It allows a better understanding of the sequence of events following the transfer of adipose tissue. It provides not only volume but also undeniable stimulation, leading to significant thickening of the extracellular matrix.

Abstract: Skin and cornea both feature an epithelium firmly anchored to its underlying connective compartment: dermis for skin and stroma for cornea. A breakthrough in tissue engineering occurred in 1975 when skin stem cells were successfully amplified in culture by Rheinwald and Green. Since 1981, they are used in the clinical arena as cultured epidermal autografts for the treatment of patients with extensive burns. A similar technique has been later adapted to the amplification of limbal-epithelial cells. The basal layer of the limbal epithelium is located in a transitional zone between the cornea and the conjunctiva and contains the stem cell population of the corneal epithelium called limbal-stem cells (LSC). These cells maintain the proper renewal of the corneal epithelium by generating transit-amplifying cells that migrate from the basal layer of the limbus towards the basal layer of the cornea. Tissue-engineering protocols enable the reconstruction of three-dimensional (3D) complex tissues comprising both an epithelium and its underlying connective tissue. Our in vitro reconstruction model is based on the combined use of cells and of a natural collagen-based biodegradable polymer to produce the connective-tissue compartment. This porous substrate acts as a scaffold for fibroblasts, thereby, producing a living dermal/stromal equivalent, which once epithelialized results into a reconstructed skin/hemicornea. This paper presents the reconstruction of surface epithelia for the treatment of pathological conditions of skin and cornea and the development of 3D tissue-engineered substitutes based on a collagen–GAG–chitosan matrix for the regeneration of skin and cornea. [Copyright &y& Elsevier]