Establishing a Xenograft Model with CD-1 Nude Mice to Study Human Skin Wound Repair

BACKGROUND

A significant gap exists in the translatability of small-animal models to human subjects. One important factor is poor laboratory models involving human tissue. Thus, the authors have created a viable postnatal human skin xenograft model using athymic mice.

METHODS

Discarded human foreskins were collected following circumcision. All subcutaneous tissue was removed from these samples sterilely. Host CD-1 nude mice were then anesthetized, and dorsal skin was sterilized. A 1.2-cm-diameter, full-thickness section of dorsal skin was excised. The foreskin sample was then placed into the full-thickness defect in the host mice and sutured into place. Xenografts underwent dermal wounding using a 4-mm punch biopsy after engraftment. Xenografts were monitored for 14 days after wounding and then harvested.

RESULTS

At 14 days postoperatively, all mice survived the procedure. Grossly, the xenograft wounds showed formation of a human scar at postoperative day 14. Hematoxylin and eosin and Masson trichome staining confirmed scar formation in the wounded human skin. Using a novel artificial intelligence algorithm using picrosirius red staining, scar formation was confirmed in human wounded skin compared with the unwounded skin. Histologically, CD31 + immunostaining confirmed vascularization of the xenograft. The xenograft exclusively showed human collagen type I, CD26 + , and human nuclear antigen in the human scar without any staining of these human markers in the murine skin.

CONCLUSION

The proposed model demonstrates wound healing to be a local response from tissue resident human fibroblasts and allows for reproducible evaluation of human skin wound repair in a preclinical model.

CLINICAL RELEVANCE STATEMENT

Radiation-induced fibrosis is a widely prevalent clinical phenomenon without a well-defined treatment at this time. This study will help establish a small-animal model to better understand and develop novel therapeutics to treat irradiated human skin.

Mouse Models for Human Skin Transplantation: A Systematic Review

Immunodeficient mouse models with human skin xenografts have been developed in the past decades to study different conditions of the skin. Features such as follow-up period and size of the graft are of different relevance depending on the purpose of an investigation. The aim of this study is to analyze the different mouse models grafted with human skin. A systematic review of the literature was performed in line with the PRISMA statement using MEDLINE/PubMed databases from January 1970 to June 2020. Articles describing human skin grafted onto mice were included. Animal models other than mice, skin substitutes, bioengineered skin, postmortem or fetal skin, and duplicated studies were excluded. The mouse strain, origin of human skin, graft dimensions, follow-up of the skin graft, and goals of the study were analyzed. Ninety-one models were included in the final review. Five different applications were found: physiology of the skin (25 models, mean human skin graft size 1.43 cm2 and follow-up 72.92 days), immunology and graft rejection (17 models, mean human skin graft size 1.34 cm2 and follow-up 86 days), carcinogenesis (9 models, mean human skin graft size 1.98 cm2 and follow-up 253 days), skin diseases (25 models, mean human skin graft size 1.55 cm2 and follow-up 86.48 days), and would healing/scars (15 models, mean human skin graft size 2.54 cm2 and follow-up 129 days). The follow-up period was longer in carcinogenesis models (253 ± 233.73 days), and the skin graft size was bigger in wound healing applications (2.54 ± 3.08 cm2). Depending on the research application, different models are suggested. Careful consideration regarding graft size, follow-up, immunosuppression, and costs should be analyzed and compared before choosing any of these mouse models. To our knowledge, this is the first systematic review of mouse models with human skin transplantation.

Ovine model of burn wounds grafted with ovine cadaver skin

Shortage in autograft to cover burn wounds involves a frequent use of cadaver skin (CS) as a temporary cover to prevent infection, dehydration and preparation of wounds for subsequent autografting. We aimed to establish an ovine model of burn wound healing using ovine CS (OCS). Quality and efficacy of fresh and frozen OCS overlaid on to excised 3rd degree flame burn wounds in sheep were evaluated in comparison to autograft. Histologically, autografted wounds maintained normal skin structure at different time points. Wounds overlaid with fresh OCS graft showed signs of rejection starting from day 7. At day 14, the epidermis was mostly rejected. The rejection was completed by day 20 with signs of immunoreaction and presence of many immune cells. Frozen OCS was rejected in the same pattern. Immediately prior to grafting, the thickness was comparable between freshly prepared and frozen OCS for 10 or 40 days. Significant reduction in viability was detected in OCS frozen for 40 days. Both fresh or frozen ovine OCS were rejected within 10 days that mimics CS rejection time in humans (∼8.4 days), suggesting that ovine model of burn wound grafted with OCS can successfully be used in burn wound research mimicking clinical scenario.

Histological and mechanical evaluation of antifreeze peptide (Afp1m) cryopreserved skin grafts post transplantation in a rat model

The objective of this study was to evaluate the use of Afp1m as a cryopreservative agent for skin by examining the transplanted skin histological architecture and mechanical properties following subzero cryopreservation. Thirty four (34) rats with an average weight of 208 ± 31 g (mean ± SD), were used. Twenty four (n = 24) rats were equally divided into four groups: (i) immediate non-cryopreserved skin autografts (onto same site), (ii) immediate non-cryopreserved skin autografts (onto different sites), (iii) skin autografts cryopreserved with glycerol for 72 h and (iv) skin autografts cryopreserved with Afp1m for 72 h at -4 °C. Rounded shaped full-thickness 1.5-2.5 cm in diameter skin was excised from backs of rats for the autograft transplantation. Non-cryopreserved or cryopreserved auto skin graft were positioned onto the wound defects and stitched. Non-transplanted cryopreserved and non-cryopreserved skin strips from other ten rats (n = 10) were allowed for comparative biomechanical test. All skin grafts were subjected to histological and mechanical examinations at the end of day 21. Histological results revealed that tissue architecture especially the epidermal integrity and dermal-epidermal junction of the Afp1m cryopreserved skin grafts exhibited better histological appearance, good preservation of tissue architecture and structural integrity than glycerolized skin. However, there was no significant difference among these groups in other histological criteria. There were no significant differences among the 4 groups in skin graft mechanical properties namely maximum load. In conclusion, Afp1m were found to be able to preserve the microstructure as well as the viability and function of the skin destined for skin transplantation when was kept at -4 °C for 72 h.

Multiparametric and semiquantitative scoring systems for the evaluation of mouse model histopathology--a systematic review

BACKGROUND

Histopathology has initially been and is still used to diagnose infectious, degenerative or neoplastic diseases in humans or animals. In addition to qualitative diagnoses semiquantitative scoring of a lesion`s magnitude on an ordinal scale is a commonly demanded task for histopathologists. Multiparametric, semiquantitative scoring systems for mouse models histopathology are a common approach to handle these questions and to include histopathologic information in biomedical research.

RESULTS

Inclusion criteria for scoring systems were a first description of a multiparametric, semiquantiative scoring systems which comprehensibly describe an approach to evaluate morphologic lesion. A comprehensive literature search using these criteria identified 153 originally designed semiquantitative scoring systems for the analysis of morphologic changes in mouse models covering almost all organs systems and a wide variety of disease models. Of these, colitis, experimental autoimmune encephalitis, lupus nephritis and collagen induced osteoarthritis colitis were the disease models with the largest number of different scoring systems. Closer analysis of the identified scoring systems revealed a lack of a rationale for the selection of the scoring parameters or a correlation between scoring parameter value and the magnitude of the clinical symptoms in most studies.

CONCLUSION

Although a decision for a particular scoring system is clearly dependent on the respective scientific question this review gives an overview on currently available systems and may therefore allow for a better choice for the respective project.

Cryopreservation of tissue-engineered epithelial sheets in trehalose

Tissue-engineered epidermal membranes are useful for clinical wound healing. To facilitate these products in the clinic, optimized storage methods need to be developed. We studied the efficiency of extracellular trehalose at various concentrations for cryopreserving human tissue-engineered epidermal membranes compared with that of dimethyl-sulfoxide (DMSO) used by most organ banks for cryopreserving skin grafts and artificial skin substitutes. Keratinocyte (KC) viability, proliferation and marker expression following cryopreservation in trehalose were examined with similar results to those using DMSO. Trehalose concentration (0.4m) was optimized according to the described cellular activities following cryopreservation. Artificial epidermal substitutes were then cryopreserved in trehalose at the optimized concentration. Cell viability, growth factor secretion and wound healing properties of cryopreserved artificial epidermal substitutes using nude mice were examined and compared with those of DMSO cryopreservation. Cryopreservation with trehalose enhanced human KC viability in suspension and artificial skin substitutes. In addition, trehalose cryopreservation provided fast recovery of EGF and TGF-β1 secretion by KCs after thawing. When transplanted into nude mice, trehalose-cryopreserved artificial skin repaired skin defects in a similar manner to that of a non-cryopreserved control. Moreover, trehalose-cryopreserved artificial skin resulted in engraftment and wound closure that was significantly enhanced compared with that of DMSO-cryopreserved epidermal membranes. The results indicate that the use of trehalose improves cryopreservation of tissue-engineered epithelial sheets.