Transplantation Of Human Skin Research Articles

Behavioral and axon histomorphometric analyses after intraneural transplantation of human skin- and nerve-derived Schwann cells in nude rats.

We have recently isolated and expanded skin-derived Schwann cells (Sk-SCs) from human skin and showed that they are largely similar to nerve-derived Schwann cells (N-SCs). Here, we extend our investigation into functional assessments of the nude rats that received human Sk-SCs and N-SCs after intraneural delivery into crushed and decellularized tibial nerve in adult nude rats. Sk-SCs, N-SCs, dermal fibroblasts, or control culture medium was injected into the crushed and decellularized tibial nerve using in situ repeated freeze-thaw cycles. Animals were then subjected to a ladder rung walking test, nociceptive von Frey testing, and walking gait analysis weekly. Animals were euthanized 6 weeks after surgery, gastrocnemius and soleus muscles were weighed, distal nerves were harvested, and whole semithin cross-sections were analyzed using segmentation software. N-SC-injected and dermal fibroblast-injected animals improved significantly at 4 to 6 weeks postinjury in nociceptive assessment compared with medium-injected controls. Sk-SCs recovered more rapidly in tibial functional index at 2 weeks postinjury compared with medium-injected controls. No significant difference was observed for the ladder rung walking test or muscle weight ratio. Histologically, the number of myelinated axons was significantly higher in all cell injection groups compared with medium-injected controls. No significant difference was observed in g ratio, axon diameter, or myelin thickness. Cell injection significantly improved axon regeneration across an in situ decellularized nerve segment. However, a more human cell-permissive animal model is required to delineate functional differences between cell types for preclinical transplantation studies.

577 The role of YAP1 in regeneration of human skin and in pathological states

To study the role of YAP1 in regeneration of human skin we have developed a unique model of a full-layer human skin xenograft, containing epidermis, dermis, adipose tissue, as well as hair follicles, sebaceous and sweat glands. On days 40, 75 and 110 after transplantation of human skin to NOD/SCID mice, biopsies were studied immunohistochemically and compared with intact skin and with biopsies of cutaneous papilloma and chronic wound. Morphometric parameters, distribution and content of markers were studied using ImageJ and Cell Profiler.

Spatiotemporal in vivo tracking of polyclonal human regulatory T cells (Tregs) reveals a role for innate immune cells in Treg transplant recruitment

Regulatory T cells (Tregs) are emerging as a new cell-based therapy in solid organ transplantation. Adoptive transfer of Tregs has been shown preclinically to protect from graft rejection, and the safety of Treg therapy has been demonstrated in clinical trials. Despite these successes, the in vivo distribution and persistence of adoptively transferred Tregs remained elusive, which hampers clinical translation. Here we isolated human Tregs using a GMP-compatible protocol and lentivirally transduced them with the human sodium iodide symporter to render them traceable in vivo by radionuclide imaging. Engineered human Tregs were characterized for phenotype, survival, suppressive capacity, and reporter function. To study their trafficking behavior, they were subsequently administered to humanized mice with human skin transplants. Traceable Tregs were quantified in skin grafts by non-invasive nano-single-photon emission computed tomography (nanoSPECT)/computed tomography (CT) for up to 40 days, and the results were validated ex vivo. Using this approach, we demonstrated that Treg trafficking to skin grafts was regulated by the presence of recipient Gr-1+ innate immune cells. We demonstrated the utility of radionuclide reporter gene-afforded quantitative Treg in vivo tracking, addressing a fundamental need in Treg therapy development and offering a clinically compatible methodology for future Treg therapy imaging in humans.

REPOPULATION OF FUNCTIONAL MULTILINEAGE HUMAN HAEMATOPOIETIC CELLS IN NON-IRRADIATED NBSGW MICE

Introduction: Humanised mouse models provide a platform to investigate human immune biology in vivo, reducing the need for large animal studies. Importantly they can overcome biological differences between humans and other species, reducing the uncertainty in progressing to clinical studies. In transplantation research, humanised immune system (HIS) models have provided pre-clinical evidence for human-specific therapies such as biologics and regulatory T cell therapy, which are now in clinical trials. Most HIS models lack multilineage leukocyte development, limiting accurate representation of the full alloresponse in transplantation. To address this, we assessed immune reconstitution and human skin transplant rejection in NOD,B6.SCID Il2rγ−/− KitW41/W41 (NBSGW) mice, which are capable of long-term multilineage haemopoiesis without irradiation due to the presence of an inactivating mutation in the stem cell growth factor receptor. Materials and Methods: Human cord blood CD133+ haematopoietic stem cells (HSCs) were injected intravenously into non-irradiated NBSGW mice (n=20). Engraftment in blood and lymphoid organs was assessed over 20 weeks. In a separate group, HSC-engrafted mice (HIS-NBSGW) underwent allogeneic human skin transplantation 10-12 weeks post-injection (Figure 1).At the point of skin transplant rejection (or after 100 days) blood, spleen, bone marrow (BM), thymus and skin were analysed by multiparameter flow cytometry and NanoString gene expression analysis. Results and Discussion: High levels of human CD45+ cell chimerism developed reliably in the blood, BM and spleen after HSC transplantation in a dose-dependent manner (Figure 2).Multilineage engraftment was achieved, consisting of human myeloid cells, B and T lymphocytes at multiple recognised stages of development. Expression of Human Leukocyte Antigen (HLA) Class I and II molecules was identified on CD3- thymocytes. Antigen-presenting cells (APCs), B cells and T cells were found to be functional in in vitro assays. In mice with multilineage human leukocyte reconstitution, allogeneic human skin grafts rejected. Rejection was associated with RNA markers of upregulated immune function and elevated production of IgM, IgG and Th1, Th2 and Th17-related cytokines (Figure 3).Conclusion: The HIS-NBSGW model provides a technically straightforward research system utilising adult mice, which does not require irradiation, co-transplantation of human haematopoietic stromal tissues, or provision of human cytokines. By producing functional multilineage immune cells, it is a useful method for assessing HSC function in vivo and a framework for assessing human transplant responses encompassing the breadth of innate, cellular and humoural immunity. Clarendon Fund, University of Oxford. MRC Discovery Award, Ref: MC_PC_15069.

Transplant of Tissue-Engineered Artificial Autologous Human Skin in Andalusia: An Example of Coordination and Institutional Collaboration

A new model of tissue-engineered artificial autologous human skin developed in Andalusia is currently being transplanted into patients suffering from large burns within the Andalusian Public Healthcare System. This product is considered an advanced therapy medicinal product (ATMP) in Europe, and its clinical use implies meeting transplant and medicinal product legal requirements, being the Guidelines of Good Manufacturing Practice for ATMPs of particular importance. The preclinical research and clinical translation of the product have represented a technical, regulatory, and organizational challenge, which has taken 10 years since the first preclinical experiments were designed. Twelve patients with large burns, including 3 pediatric patients, have hitherto received artificial autologous skin grafts with an overall survival rate of 75% and positive clinical, homeostatic, and histologic results. Achieving such a milestone within our Healthcare System was possible through a multidisciplinary approach and the joint efforts of multiple publicly funded institutions and units under the coordination of the Andalusian Initiative for Advanced Therapies. In this article, we present the organizational model set up to facilitate collaboration and logistics among the professionals involved, totaling more than 80 people. The similarities between the tissue-engineered artificial autologous human skin transplant and other organ and tissue transplants, in terms of logistic requirements, reveal how regional and hospital transplant coordination have played a crucial role.

Ethical rejections of xenotransplantation? The potential and challenges of using human-pig chimeras to create organs for transplantation.

EMBO Reports (2018) 19: e46337[OpenUrl][1][FREE Full Text][2] Gene editing and stem cell biotechnologies are being applied to create chimeric animals with human organs, which could alleviate the current shortage of human organs for transplantation. While the medical benefits of xenotransplantation appear to be significant, we discuss specific ethical, medical, cultural, and financial challenges and potential solutions that need to be addressed before clinical trials using organs from human‐animal chimeras should begin. > The use of animal organs to replace defective organs in human patients dates back at least to 1838 when the first pig‐to‐human corneal transplant was performed. Organ transplantation has a long history. The use of animal organs to replace defective organs in human patients dates back at least to 1838 when the first pig‐to‐human corneal transplant was performed. The first human skin transplant was done in 1869, the first successful kidney transplant between fraternal twins took place in 1954, and the first heart transplant was performed in 1967. Aortic valve replacement with a porcine heart valve was first reported 2 years later in 1969 and continues to be used to this day. Notwithstanding, of the clinical successes, organ transplantation has been held back by a huge shortage of people willing to donate their organs. Currently, more than 115,000 people are organ transplant candidates in the USA; 75,000 of these are on the national organ waiting list (https://optn.transplant.hrsa.gov). About 25% of patients on the list die before an organ becomes available. Xenotransplantation—using organs from animals for transplantation—has great potential to alleviate this organ shortage. However, tissue rejection and infections have greatly limited the effectiveness of cross‐species transplantations. Recent advances in biotechnology, including gene editing and stem cell science, may provide the key elements needed to create animals that grow human organs for transplantation. Research is currently focusing on growing human hearts, … [1]: {openurl}?query=rft.jtitle%253DEMBO%2BReports%26rft_id%253Dinfo%253Adoi%252F10.15252%252Fembr.201846337%26rft_id%253Dinfo%253Apmid%252F29991538%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [2]: /lookup/ijlink?linkType=FULL&journalCode=embor&resid=19/8/e46337&atom=%2Fembor%2F19%2F8%2Fe46337.atom

1429 VEGF mediates rejuvenation of aged human skin xenografts in young mice

Previously we have shown that transplantation of aged human skin onto young SCID mice results in a rejuvenated human epidermal phenotype. Here, we demonstrate that the rejuvenation of old human skin xenotransplants onto young SCID/beige mouse skin well extends beyond the epidermis and leads to statistically significant improvements in multiple skin aging-associated read-outs assessed by quantitative histomorphometry, which showed e.g. thickening of the epidermis, along with basal layer keratinocyte proliferation, increased vascularization, significantly more collagen type I and III and elastic fibers, and number of epidermal melanocytes in aged human skin xenotransplants.Gene expression RNA-Seq analyses of DEGs showed in 1week versus pre-transplant numerous transcripts related to hypoxia, VEGF and angiogenesis, inflammation, the Notch, TGF-β and IGF pathways, genes related to reinnervation, as well as keratins and epidermal regulators. qRT-PCR confirmed an upregulation of VEGFA and HIF1A, as well as angiogenesis-related genes. Proinflammatory infiltrates expressing CXCL1 and CXCL5 were also confirmed by these data. Skin rejuvenation was primarily mediated by the angiogenesis-promoting growth factor, VEGF, since injection of anti-VEGF blocking antibodies alone, but not of TGF-ß, IGF-1- or HGF-neutralizing antibodies, sufficed to prevent the rejuvenation of old human skin in vivo. Conversely, intradermal injection of VEGF-loaded nanoparticles reversed the aged human skin phenotype when aged human skin was grafted onto old mice. Our study shows that a remarkable degree of rejuvenation of aged human skin is possible in vivo and that VEGF-mediated signaling i a key pathway in this process.

Expression of a Chimeric Antigen Receptor Specific for Donor HLA Class I Enhances the Potency of Human Regulatory T Cells in Preventing Human Skin Transplant Rejection.

Regulatory T cell (Treg) therapy using recipient-derived Tregs expanded exvivo is currently being investigated clinically by us and others as a means of reducing allograft rejection following organ transplantation. Data from animal models has demonstrated that adoptive transfer of allospecific Tregs offers greater protection from graft rejection compared to polyclonal Tregs. Chimeric antigen receptors (CAR) are clinically translatable synthetic fusion proteins that can redirect the specificity of T cells toward designated antigens. We used CAR technology to redirect human polyclonal Tregs toward donor-MHC class I molecules, which are ubiquitously expressed in allografts. Two novel HLA-A2-specific CARs were engineered: one comprising a CD28-CD3ζ signaling domain (CAR) and one lacking an intracellular signaling domain (ΔCAR). CAR Tregs were specifically activated and significantly more suppressive than polyclonal or ΔCAR Tregs in the presence of HLA-A2, without eliciting cytotoxic activity. Furthermore, CAR and ΔCAR Tregs preferentially transmigrated across HLA-A2-expressing endothelial cell monolayers. In a human skin xenograft transplant model, adoptive transfer of CAR Tregs alleviated the alloimmune-mediated skin injury caused by transferring allogeneic peripheral blood mononuclear cells more effectively than polyclonal Tregs. Our results demonstrated that the use of CAR technology is a clinically applicable refinement of Treg therapy for organ transplantation.

Systemic depletion of macrophages in the subacute phase of wound healing reduces hypertrophic scar formation.

Hypertrophic scars are caused by trauma or burn injuries to the deep dermis and can cause cosmetic disfigurement and psychological issues. Studies suggest that M2-like macrophages are pro-fibrotic and contribute to hypertrophic scar formation. A previous study from our lab showed that M2 macrophages were present in developing hypertrophic scar tissues in vivo at 3-4 weeks after wounding. In this study, the effect of systemic macrophage depletion on scar formation was explored at subacute phase of wound healing. Thirty-six athymic nude mice that received human skin transplants were randomly divided into macrophage depletion group and control group. The former received intraperitoneal injections of clodronate liposomes while the controls received sterile saline injections on day 7, 10, and 13 postgrafting. Wound area, scar thickness, collagen abundance and collagen bundle structure, mast cell infiltration, myofibroblast formation, M1, and M2 macrophages together with gene expression of M1 and M2 related factors in the grafted skin were investigated at 2, 4, and 8 weeks postgrafting. The transplanted human skin from the control group developed contracted, elevated, and thickened scars while the grafted skin from the depletion group healed with significant less contraction and elevation. Significant reductions in myofibroblast number, collagen synthesis, and hypertrophic fiber morphology as well as mast cell infiltration were observed in the depletion group compared to the control group. Macrophage depletion significantly reduced M1 and M2 macrophage number in the depletion group 2 weeks postgrafting as compared to the control group. These findings suggest that systemic macrophage depletion in subacute phase of wound healing reduces scar formation, which provides evidence for the pro-fibrotic role of macrophages in fibrosis of human skin as well as insight into the potential benefits of specifically depleting M2 macrophages in vivo.

Robust Lentiviral Gene Delivery But Limited Transduction Capacity of Commonly Used Adeno-Associated Viral Serotypes in Xenotransplanted Human Skin.

Skin is an easily accessible organ, and therapeutic gene transfer to skin remains an attractive alternative for the treatment of skin diseases. Although we have previously documented potent lentiviral gene delivery to human skin, vectors based on adeno-associated virus (AAV) rank among the most promising gene delivery tools for in vivo purposes. Thus, we compared the potential usefulness of various serotypes of recombinant AAV vectors and lentiviral vectors for gene transfer to human skin in a xenotransplanted mouse model. Vector constructs encoding firefly luciferase were packaged in AAV capsids of serotype 1, 2, 5, 6, 8, and 9 and separately administered by intradermal injection in human skin transplants. For all serotypes, live bioimaging demonstrated low levels of transgene expression in the human skin graft, and firefly luciferase expression was observed primarily in neighboring tissue outside of the graft. In contrast, gene delivery by intradermally injected lentiviral vectors was efficient and led to extensive and persistent firefly luciferase expression within the human skin graft only. The study demonstrates the limited capacity of single-stranded AAV vectors of six commonly used serotypes for gene delivery to human skin in vivo.

Long-term expression pattern of melanocyte markers in light- and dark-pigmented dermo-epidermal cultured human skin substitutes.

Transplantation of pigmented tissue-engineered human autologous skin substitutes represents a promising procedure to cover skin defects. We have already demonstrated that we can restore the patient's native light or dark skin color by adding melanocytes to our dermo-epidermal skin analogs. In this long-term study, we investigated if melanocytes in our skin substitutes continue to express markers as BCL2, SOX9, and MITF, known to be involved in survival, differentiation, and function of melanocytes. Human epidermal melanocytes and keratinocytes, as well as dermal fibroblasts from light- and dark-pigmented skin biopsies were isolated and cultured. Bovine collagen hydrogels containing fibroblasts were prepared, and melanocytes and keratinocytes were seeded in a 1:5 ratio onto the gels. Pigmented dermo-epidermal skin substitutes were transplanted onto full-thickness wounds of immuno-incompetent rats and analyzed for the expression of melanocyte markers after 15 weeks. Employing immunofluorescence staining techniques, we observed that our light and dark dermo-epidermal skin substitutes expressed the same typical melanocyte markers including BCL2, SOX9, and MITF 15 weeks after transplantation as normal human light and dark skin. These data suggest that, even in the long run, our light and dark dermo-epidermal tissue-engineered skin substitutes contain melanocytes that display a characteristic expression pattern as seen in normal pigmented human skin. These findings have crucial clinical implications as such grafts transplanted onto patients should warrant physiological numbers, distribution, and function of melanocytes.

Anti-CD28 Antagonism Using a Monovalent Fab Antibody for the Prolongation of Human Skin Allograft Survival.

Background. T cells play a principal detrimental role in alloresponses after transplantation. Costimulation through CD28 induces T cells activation, cytokine production, proliferation, and differentiation, whereas the absence of CD28 signalling leads to T cell apoptosis or anergy. Importantly, the development of effector or regulatory responses after initial antigen exposure may be influenced by the balance between CD28 and cytotoxic T lymphocyte antigen 4 (CTLA-4) costimulatory signalling. Influencing this balance by blocking costimulation through CD28 is theoretically advantageous to agonistic signaling through CTLA4 (for example using CTLA4-Ig) as this would not interfere with CTLA4 and PDL-1 co-inhibitory signaling. In the current study we have investigated the hypothesis that a non-activating monovalent anti-CD28 antibody would prevent rejection of human skin allografts in vivo. Methods. Using a humanised mouse system, we treated mice that had received human skin transplants with FR104 (5 mg/kg), CTLA4-Ig (10mg/kg) or vehicle control intravenously twice a week for three weeks. All mice were started on the treatment regimen three weeks post-adoptive transfer of allogeneic human peripheral blood mononuclear cells (PBMCs) to ensure adequate levels of human leukocyte chimerism. Results. FR104 significantly prolonged skin allograft survival in humanised mice compared with CTLA4-Ig (median survival time, MST=63 vs. 31 (p=0.002)) or Saline (MST=31). While FR104 treatment significantly impacted the level of human leukocyte chimerism in the peripheral blood, it remained above the required reconstitution level known to induce skin rejection. The number of graft infiltrating CD4+ (47.8±24.8 vs 83.3±5.1 cells/HPF, P<0.02) and CD8+ (50.0±11.9 vs 111±34.0 cells/HPF, P<0.04) cells was significantly reduced by FR104 treatment as compared to CTLA-4 Ig treatment. No differences were noted in the number of graft infiltrating Foxp3+ cells between FR104 and CTLA4-Ig groups. FR104 significantly suppressed the serum cytokine production of IL-2, IFNγ, TNFα and IL-10. Conclusion. FR104 is an effective immunosuppressant in vivo. By sparing CTLA-4 and PDL-1 coinhibitory signals, FR104 may theoretically lead to improved therapeutic responses compared with CTLA-4-Ig.

A New Humanized Mouse Model for Alopecia Areata

Although alopecia areata (AA) is not life threatening, it may lead to severe psychological disturbances, reducing the quality of life in all ages. Thus, a new animal model is needed for shedding more light onto the pathogenesis of this cell-mediated, organ-specific autoimmune disease to identify more effective therapeutic strategies. Recently, we succeeded in developing a new humanized mouse model of AA, which includes transplantation of healthy human scalp skin obtained from normal volunteers on to severe-combined immunodeficient mice. This is followed by intradermal injection of either autologous or allogeneic peripheral blood mononuclear cells, which had been cultured with high dose of IL-2 and enriched for natural killer group 2D-positive (NKG2D+) and CD56+ cells. This protocol leads to rapid and predictable development of focal hair loss, with all the characteristic clinical, histological, and immunohistochemical features of AA. This humanized mouse AA model underscores the functional importance of NKG2D+ and CD56+ cells in AA pathogenesis and promises to be instrumental for identifying novel AA treatment strategies.

Antagonistic effect of the inflammasome on thymic stromal lymphopoietin expression in the skin

Innate immune sensors control key cytokines that regulate T-cell priming and T-cell fate. This is particularly evident in allergic reactions, which represent ideal systems to study the interplay of innate and adaptive immunity. In patients with contact dermatitis, inflammasome-mediated IL-1 activation is responsible for a TH1 immune response. Surprisingly, the IL-1 signaling pathway was also proposed to control the activation of thymic stromal lymphopoietin (TSLP), a cytokine implicated in development of the T(H)2 response in patients with atopic dermatitis (AD) and asthma. We sought to assess the effect of the inflammasome on TSLP expression levels and the development of AD. We studied the effect of the inflammasome activator 2,4-dinitrofluorobenzene, and IL-1β on TSLP mRNA expression levels in mouse and human cell lines (in vitro assays), as well as in live mice and on human skin transplants. We also assessed the effect of 2,4-dinitrofluorobenzene on TSLP and the TH2 response in mice in which the inflammasome and IL-1 signaling pathways were blocked, either genetically or pharmacologically, in 2 models of AD. We provide in vitro and in vivo evidence that inflammasome activation has an inhibitory role on TSLP mRNA expression and T(H)2 cell fate in the skin. We also show that solvents influence the activation of TSLP and IL-1β and direct the T-cell fate to a given hapten. Our observations strongly suggest that the TH1 versus TH2 cell fate decision is regulated at multiple levels and starts with innate immune events occurring within peripheral epithelial tissues.

Inhibition of p38 kinase suppresses the development of psoriasis-like lesions in a human skin transplant model of psoriasis

Inhibition of p38 kinase suppresses the development of psoriasis-like lesions in a human skin transplant model of psoriasis

Ex vivo-expanded human regulatory T cells prevent the rejection of skin allografts in a humanized mouse model.

Composite tissue transplantation effectively reconstructs the most complex defects, but its use is limited because of harmful immunosuppression and the high susceptibility of skin to rejection. Development of tolerance is an ideal solution, and protocols using regulatory T cells (Tregs) to achieve this have been promising in experimental animal models. The aim of this study was to investigate the ability of human Tregs to regulate immune responses to a human skin allograft in vivo. We isolated and expanded naturally occurring CD127loCD25+CD4+ human Tregs from peripheral blood mononuclear cells (PBMCs) and examined their phenotype and suppressive activity in vitro. Using a clinically relevant chimeric humanized mouse system, we transplanted mice with human skin grafts followed by allogeneic populations of PBMCs with or without Tregs derived from the same PBMC donor. Ex vivo-expanded Tregs maintain the appropriate Treg markers and retain suppressive activity against allostimulated and polyclonally stimulated autologous PBMCs in vitro. Mice receiving allogeneic PBMCs alone consistently reject human skin grafts, whereas those also receiving Tregs display stable long-term human skin transplant survival along with a reduction in the CD8+ human cellular graft infiltrate. We show for the first time the unique ability of human Tregs to prevent the rejection of a skin allograft in vivo, highlighting the therapeutic potential of these cells clinically.

NOD-scid IL2rgamma(null) mouse model of human skin transplantation and allograft rejection.

Transplantation of human skin on immunodeficient mice that support engraftment with functional human immune systems would be an invaluable tool for investigating mechanisms involved in wound healing and transplantation. Nonobese diabetic (NOD)-scid interleukin-2 gamma chain receptor (NSG) readily engraft with human immune systems, but human skin graft integrity is poor. In contrast, human skin graft integrity is excellent on CB17-scid bg (SCID.bg) mice, but they engraft poorly with human immune systems. Human skin grafts transplanted onto immunodeficient NSG, SCID.bg, and other immunodeficient strains were evaluated for graft integrity, preservation of graft endothelium, and their ability to be rejected after engraftment of allogeneic peripheral blood mononuclear cells. Human skin transplanted onto NSG mice develops an inflammatory infiltrate, consisting predominately of host Gr1(+) cells, that is detrimental to the survival of human endothelium in the graft. Treatment of graft recipients with anti-Gr1 antibody reduces this cellular infiltrate, preserves graft endothelium, and promotes wound healing, tissue development, and graft remodeling. Excellent graft integrity of the transplanted skin includes multilayered stratified human epidermis, well-developed human vasculature, human fibroblasts, and passenger leukocytes. Injection of unfractionated, CD4 or CD8 allogeneic human peripheral blood mononuclear cell induces a rapid destruction of the transplanted skin graft. NSG mice treated with anti-Gr1 antibody provide a model optimized for both human skin graft integrity and engraftment of a functional human immune system. This model provides the opportunity to investigate mechanisms orchestrating inflammation, wound healing, revascularization, tissue remodeling, and allograft rejection and can provide guidance for improving outcomes after clinical transplantation.

The quality of human skin xenografts on SCID mice: a noninvasive bioengineering approach

Animal models are important tools for studies in skin physiology and pathophysiology. Due to substantial differences in skin characteristics such as thickness and number of adnexa, the results of animal studies cannot always be directly transferred to the human situation. Therefore, transplantation of human skin on to SCID (severe combined immunodeficiency) mice might offer a promising tool to perform studies in viable human skin without the direct need for human volunteers. To characterize the physiological and anatomical changes of a human skin transplant on a SCID animal host. In this study human skin was transplanted on to 32 SCID mice and followed for 6 months. Barrier function was assessed by transepidermal water loss (TEWL; tewametry) and moisture content of the stratum corneum was studied by measurement of electrical capacitance (corneometry). The results showed considerable deviations of TEWL values and skin hydration between the grafts and human skin in vivo. The human skin showed epidermal hyperkeratosis and moderate sclerosis of the corium 4 and 6 months after transplantation on to SCID mice. Our results indicate that human skin does not completely preserve its physiological and morphological properties after transplantation on to SCID mice. Therefore, results from experiments using this model system need to be discussed cautiously.

Immunopathology of human T cell responses to skin, artery and endothelial cell grafts in the human peripheral blood lymphocyte/severe combined immunodeficient mouse.

Blood vessels and their endothelial lining are major stimulators and targets of the rejection response. The immunological properties of human endothelial cells differ significantly from those of other species and new models are needed for proper study of human vessels in the transplant setting. We have employed the human peripheral blood lymphocyte/severe combined immunodeficiency (huPBL/SCID) mouse for this purpose. We describe here our results involving transplantation of human skin, human artery and cultured human endothelial cells. We also describe our more limited experience using porcine skin and artery transplantation to study human T cells responses to pig endothelium.

The SCID-hu xenogeneic transplantation model: complex but telling.

Animal models based on knock-out or transgenic technology are widely used in basic and applied biomedical research. An alternative to these approaches is the generation of xenogeneic transplantation models allowing the in-vivo investigation of cell types and organs. In the field of dermatology transplantation of human skin onto mice lacking functional B and T cells (SCID mice) and subsequent manipulation of these grafts yielded new insights in many different aspects of skin biology. This review highlights some of the applications of this versatile model focussing on phenomena relevant for the subject of dermatology.