Investigating human microskin grafting technique in a new experimental model

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.

Micrografting chronic lower extremity ulcers with mechanically disaggregated skin using a micrograft preparation system

OBJECTIVE

The Rigenera system is a new standardised micrograft preparation system. It works by means of automated mechanical disaggregation of small tissue samples, extracting only the smallest cells (<50µm). The aim of this study was to retrospectively evaluate patients affected by chronic ulcers and who were treated with the micrograft preparation method.

METHOD

Chronic ulcers have been included regardless of the cause. The specimen was collected with a 3mm diameter biopsy punch and immediately dissociated by means of the Rigenera System. The obtained suspension was placed on a scaffold of equine collagen.

RESULTS

We included 15 patients (four males, 11 females) with a mean age of 72.2±8.41 (mean±standard deviation) years. In seven patients the ulcers were related to the complications of diabetes, post-traumatic in a further three diabetic patients, vasculitis in one patient, and four patients had venous leg ulcers (VLUs). The median main diameter was 5.0cm and the median estimated area was 43.96cm². The ulcers were present from a mean of 4.50±2.30 months before inclusion in this study. At the second week the wounds were reduced by 37.33%±19.35%, at the week eight, nine patients (60.0%) were healed, and at week 16, 13 (86.7%) were healed. The quality of scars was good and did not deteriorate at the six month follow-up.

CONCLUSION

The simplicity of the approach, the minimal invasiveness of the specimen collection, and the good quality of scarring of healed wounds, confirmed in the follow-up, makes this micrograft preparation method a useful tool to use on large or complex wounds.

One-stage, simultaneous skin grafting with artificial dermis and basic fibroblast growth factor successfully improves elasticity with maturation of scar formation

The efficacy of one-stage artificial dermis and skin grafting was tested in a nude rat model. Reconstruction with artificial dermis is usually a two-stage procedure with 2- to 3-week intermission. If one-stage use of artificial dermis and split-thickness skin grafting are effective, the overall burden on patients and the medical cost will markedly decrease. The graft take rate, contraction rate, tissue elasticity, histology, morphometric analysis of the dermal thickness, fibroblast counting, immunohistochemistry of α-smooth muscle actin, matrix metalloproteinase-2, CD31, and F4/80, as well as gelatin zymography, real-time reverse transcriptase polymerase chain reaction for matrix metalloproteinase-2, and electron microscopy, were investigated from day 3 to 3 months postoperatively. The graft take rate was good overall in one-stage artificial dermis and skin grafting groups up to 3 weeks, and the contraction rate was greater in the two-staged artificial dermis and skin grafting group than in the skin grafting alone or one stage of artificial dermis and skin grafting groups. Split-thickness skin grafting with artificial dermis and basic fibroblast growth factor at a concentration of 1 μg/cm(2) showed significantly greater elasticity by Cutometer, and the dermal thickness was significantly thinner, fibroblast counting was significantly greater, and the α-smooth muscle actin expression level was more notable with a more mature blood supply in the dermis and more organized dermal fibrils by electron microscopy at 3 weeks. Thus, one-stage artificial dermis and split-thickness skin grafting with basic fibroblast growth factor show a high graft take rate and better tissue elasticity determined by Cutometer analysis, maturity of the dermis, and increased fibroblast number and blood supply compared to a standard two-stage reconstruction.

The micrograft concept for wound healing: strategies and applications

The standard of care for wound coverage is to use an autologous skin graft. However, large or chronic wounds become an exceptionally challenging problem especially when donor sites are limited. It is important that the clinician be aware of various treatment modalities for wound care and incorporate those methods appropriately in the proper clinical context. This report reviews an alternative to traditional meshed skin grafting for wound coverage: micrografting. The physiological concept of micrografting, along with historical context, and the evolution of the technique are discussed, as well as studies needed for micrograft characterization and future applications of the technique.