A Skin Rejection Grading System for Vascularized Composite Allotransplantation in a Preclinical Large Animal Model

On-patient medical record and mRNA therapeutics using intradermal microneedles

Medical interventions often require timed series of doses, thus necessitating accurate medical record-keeping. In many global settings, these records are unreliable or unavailable at the point of care, leading to less effective treatments or disease prevention. Here we present an invisible-to-the-naked-eye on-patient medical record-keeping technology that accurately stores medical information in the patient skin as part of microneedles that are used for intradermal therapeutics. We optimize the microneedle design for both a reliable delivery of messenger RNA (mRNA) therapeutics and the near-infrared fluorescent microparticles that encode the on-patient medical record-keeping. Deep learning-based image processing enables encoding and decoding of the information with excellent temporal and spatial robustness. Long-term studies in a swine model demonstrate the safety, efficacy and reliability of this approach for the co-delivery of on-patient medical record-keeping and the mRNA vaccine encoding severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This technology could help healthcare workers make informed decisions in circumstances where reliable record-keeping is unavailable, thus contributing to global healthcare equity.

Immune responses in rodent whole eye transplantation: elucidation and preliminary investigations into rejection diagnosis and monitoring

Background

Whole Eye Transplantation (WET) offers potential for vision restoration but is hindered by the complex challenge of immune rejection. Understanding and closely monitoring these immunological responses is crucial for advancing WET. This study delves into the timeline and nature of immune responses in a rodent model of WET without immunosuppression, aiming to elucidate a detailed picture of the immune landscape post-transplantation and establish innovative diagnostic and monitoring methods.

Methods

We employed a multi-faceted approach to analyze immune responses post-WET, including assessments of gross changes in corneal transparency, thickness, and skin condition. Histopathological examinations of both ocular and surrounding skin tissues provided insights into cellular changes, complemented by ocular RT-qPCR for molecular analysis. Serological analysis was employed to quantify cytokines, chemokines, and donor-specific antibodies, aiming to identify potential biomarkers correlating with WET rejection and to validate the presence of antibody-mediated rejection. These methodologies collectively contribute to the development of non-invasive diagnostic and monitoring strategies for WET.

Results

Our study revealed a rapid and acute immune response following WET, characterized by an early innate immune response dominated by complement involvement, and infiltration of neutrophils and monocytes by post-operative day (POD) 2. This was succeeded by an acute T-cell-mediated immune reaction, predominantly involving T helper 1 (Th1) cells and cytotoxic T lymphocytes (CTLs). The presence of donor specific antibody (DSA) and indications of pyroptosis in the early phases of rejection were observed. Notably, the early elevation of serum CXCL10 by POD4, coupled with ocular CD3+ cell infiltration, emerged as a potential early biomarker for WET rejection. Additionally, corneal transparency grading proved effective as a non-invasive monitoring tool.

Conclusion

This study offers a first-time comprehensive exploration of immune responses in WET, unveiling rapid and complex rejection mechanisms. The identification of early biomarkers and the development of non-invasive monitoring techniques significantly advance our understanding of WET rejection. Additionally, these findings establish an essential baseline for future research in this evolving field.

Autologous porcine VRAM flap model for VCA research

INTRODUCTION

As research advances in vascularized composite allotransplantation (VCA), large animal models are essential for translational studies related to immune rejection and graft survival. However, procurement of large flaps can cause significant defects, complicating wound closure and increasing postoperative risks. This study details the surgical techniques and outcomes of autologous vertical rectus abdominis myocutaneous (VRAM) flap transplantation and neck flap isolation with induced ischemia in a swine model. The purpose of this study was to identify the most effective control procedure for use in future VRAM flap allotransplantation research.

METHODS

We performed two left heterotopic autologous VRAM flap transplants and two right anterolateral neck flap isolations using female Yucatan pigs. Postoperatively, animals were monitored for complications and flap healing, with punch biopsies taken on POD1, 5, and at the end of the study for histological analysis. Transcutaneous oxygen and temperature were also recorded.

RESULTS

Both autologous flaps survived after vessel anastomosis, with effective closure of abdominal defects using suturable mesh, and no postoperative complications were observed. Histology revealed mild dermal edema and perivascular inflammation on POD5. In the neck flap group, both flaps survived temporary ischemia, however, postoperative complications included dorsal flap necrosis and wound dehiscence, requiring reoperation. No gross inflammation or edema was observed following surgery and histologically there was only mild dermal edema on POD5.

DISCUSSION

We have developed a low-risk, technically feasible porcine autologous VRAM flap transplantation model and our findings support its use in future VCA studies.

Lymph Node Inclusion in a Modified Osteomyocutaneous Allograft for Vascularized Composite Allotransplantation: Establishment and Feasibility Assessment in a Pig Model

Background

Representative translational animal models play a key role in vascularized composite allotransplantation (VCA) research. A composite porcine hindlimb flap, previously described, is a relevant preclinical model. However, its bulkiness and the absence of critical immunologic tissues make it less suitable for investigating the unique immunologic features of VCA. We aimed to further develop this model by reducing its bulkiness and by including donor-draining lymph nodes.

Methods

We conducted an anatomic study by harvesting 11 porcine osteomyocutaneous flaps (4 conventional and 7 modified techniques), which were characterized by computed tomography. Furthermore, 8 allotransplantations were performed in Swiss landrace pigs. After the procedure, animals were assigned to a model development and control group (N = 4 per group). No immunosuppression was given, and animals were followed up until grade 3 rejection.

Results

With the modified technique, the flap weight was significantly reduced with a mean weight of 831 g, corresponding to 1.8% total body weight versus 1710 g in the conventional technique, representing 4.2% of total body weight (P < 0.0001). The muscle/bone ratio was reduced from 8.24 (conventional) to 2.92 (modified), (P = 0.03). Histologically, graft-draining lymph nodes showed typical changes related to rejection and no signs of ischemia after in vivo transplantation.

Conclusions

By modifying the surgical technique, the bulkiness of the flap was markedly reduced, without impairing its vascularization and reliably including vascularized graft-draining lymph nodes. Our modified VCA model in the pig presents distinct advantages for surgery as well as immunologic analysis, warranting a large-scale use for experimental reconstructive transplantation studies.

Immune Rejection of Cartilage in a Swine Vascularized Composite Allotransplantation Model

BACKGROUND

Cartilage is a crucial tissue in vascularized composite allotransplantation (VCA) and plays a pivotal role in restoring motor function, especially in joint allotransplantation. Nevertheless, our understanding of immune rejection in cartilage remains limited and contentious. This study seeks to investigate the immune rejection of cartilage in a large animal model of VCA.

METHODS

Cartilage, including articular cartilage and meniscus, as well as skin, muscle and lymph node, was retrieved from a swine heterotopic VCA graft when the skin of the graft suffered from grade III-IV rejection. Histologic examination, transmission electron microscopy and immunofluorescent staining were used to investigate immune rejection.

RESULTS

Histologic examination revealed the infiltration of inflammatory cells and tissue destruction in cartilage. Transmission electron microscopy confirmed tissue damage and necrosis in cartilage. However, cartilage exhibited milder tissue damage when compared to rejected skin and muscle. Immunofluorescent staining revealed the activation of both the innate and adaptive immune systems, accompanied by an up-regulation of cell death biomarkers, including apoptosis and pyroptosis, in the rejected cartilage.

CONCLUSION

Our study demonstrates that cartilage is not immunologically privileged and undergoes immune rejection concurrently with skin and muscle in the VCA graft, though with less severe inflammation and rejection.

Efficacy of 1060 nm Diode Laser for Non-Invasive Subcutaneous Fat Reduction in Mini-Pigs

Purpose

To evaluate the efficacy and safety of abdominal fat reduction in mini-pigs, utilizing at 1060 nm diode laser with a wavelength of 1060 nm.

Patients and Methods

The laser system non-invasively disrupts adipose tissue; its effectiveness and safety were evaluated by ultrasound imaging and histological analysis. Laser irradiation was performed with various powers, and the cooling function was activated to prevent skin surface damage.

Results

The dermal tissue temperature increased to at least 43°C during laser exposure, leading to a decrease in abdominal fat thickness after 30 days. Blood tests revealed no significant changes in kidney and liver function but showed increased blood levels of nonessential free acids (NEFAs), likely due to the release of fatty tissue-derived free fatty acids. Histological evaluation demonstrated rapid transformation of adipose tissue into collagen, muscle fibers, and intracellular fibrous tissue.

Conclusion

The 1060 nm laser showed promise as a non-invasive and safe tool for reducing abdominal fat.

A local drug delivery system prolongs graft survival by dampening T cell infiltration and neutrophil extracellular trap formation in vascularized composite allografts

Introduction

The standard treatment for preventing rejection in vascularized composite allotransplantation (VCA) currently relies on systemic immunosuppression, which exposes the host to well-known side effects. Locally administered immunosuppression strategies have shown promising results to bypass this hurdle. Nevertheless, their progress has been slow, partially attributed to a limited understanding of the essential mechanisms underlying graft rejection. Recent discoveries highlight the crucial involvement of innate immune components, such as neutrophil extracellular traps (NETs), in organ transplantation. Here we aimed to prolong graft survival through a tacrolimus-based drug delivery system and to understand the role of NETs in VCA graft rejection.

Methods

To prevent off-target toxicity and promote graft survival, we tested a locally administered tacrolimus-loaded on-demand drug delivery system (TGMS-TAC) in a multiple MHC-mismatched porcine VCA model. Off-target toxicity was assessed in tissue and blood. Graft rejection was evaluated macroscopically while the complement system, T cells, neutrophils and NETs were analyzed in graft tissues by immunofluorescence and/or western blot. Plasmatic levels of inflammatory cytokines were measured using a Luminex magnetic-bead porcine panel, and NETs were measured in plasma and tissue using DNA-MPO ELISA. Lastly, to evaluate the effect of tacrolimus on NET formation, NETs were induced in-vitro in porcine and human peripheral neutrophils following incubation with tacrolimus.

Results

Repeated intra-graft administrations of TGMS-TAC minimized systemic toxicity and prolonged graft survival. Nevertheless, signs of rejection were observed at endpoint. Systemically, there were no increases in cytokine levels, complement anaphylatoxins, T-cell subpopulations, or neutrophils during rejection. Yet, tissue analysis showed local infiltration of T cells and neutrophils, together with neutrophil extracellular traps (NETs) in rejected grafts. Interestingly, intra-graft administration of tacrolimus contributed to a reduction in both T-cellular infiltration and NETs. In fact, in-vitro NETosis assessment showed a 62-84% reduction in NETs after stimulated neutrophils were treated with tacrolimus.

Conclusion

Our data indicate that the proposed local delivery of immunosuppression avoids off-target toxicity while prolonging graft survival in a multiple MHC-mismatch VCA model. Furthermore, NETs are found to play a role in graft rejection and could therefore be a potential innovative therapeutic target.

Nafamostat mesylate decreases skin flap necrosis in a mouse model of type 2 diabetes by protecting the endothelial glycocalyx

The success rate of flap tissue reconstruction has increased in recent years owing to advancements in microsurgical techniques. However, complications, such as necrosis, are still more prevalent in diabetic patients compared to non-diabetic individuals, presenting an ongoing challenge. To address this issue, many previous studies have examined vascular anastomoses dilation and stability, primarily concerning surgical techniques or drugs. In contrast, in the present study, we focused on microvascular damage of the peripheral microvessels in patients with diabetes mellitus and the preventative impact of nafamostat mesylate. Herein, we aimed to investigate the effects of hyperglycemia on glycocalyx (GCX) levels in mice with type 2 diabetes. We examined the endothelial GCX (eGCX) in skin flap tissue of 9-12-week-old type 2 diabetic mice (db/db mice) using a perforator skin flap and explored treatment with nafamostat mesylate. The growth rates were compared after 1 week. Heterotype (db/+) mice were used as the control group. Morphological examination of postoperative tissues was performed at 1, 3, 5, and 7 days post-surgery. In addition, db/db mice were treated with 30 mg/kg/day of nafamostat mesylate daily and were evaluated on postoperative day 7. Seven days after surgery, all db/db mice showed significant partial flap necrosis. Temporal observation of the skin flaps revealed a stasis-like discoloration and necrosis starting from the contralateral side of the remaining perforating branch. The control group did not exhibit flap necrosis, and the flap remained intact. In the quantitative assessment of endothelial glycans using lectins, intensity scoring showed that the eGCX in the db/db group was significantly thinner than that in the db/+ group. These results were consistent with the scanning electron microscopy findings. In contrast, treatment with nafamostat mesylate significantly improved the flap engraftment rate and suppressed eGCX injury. In conclusion, treatment with nafamostat mesylate improves the disrupted eGCX structure of skin flap tissue in db/db mice, potentially ameliorating the impaired capillary-to-venous return in the skin flap tissue.

Transcriptome profiling of immune rejection mechanisms in a porcine vascularized composite allotransplantation model

Background

Vascularized composite allotransplantation (VCA) offers the potential for a biological, functional reconstruction in individuals with limb loss or facial disfigurement. Yet, it faces substantial challenges due to heightened immune rejection rates compared to solid organ transplants. A deep understanding of the genetic and immunological drivers of VCA rejection is essential to improve VCA outcomes.

Methods

Heterotopic porcine hindlimb VCA models were established and followed until reaching the endpoint. Skin and muscle samples were obtained from VCA transplant recipient pigs for histological assessments and RNA sequencing analysis. The rejection groups included recipients with moderate pathological rejection, treated locally with tacrolimus encapsulated in triglycerol-monostearate gel (TGMS-TAC), as well as recipients with severe end-stage rejection presenting evident necrosis. Healthy donor tissue served as controls. Bioinformatics analysis, immunofluorescence, and electron microscopy were utilized to examine gene expression patterns and the expression of immune response markers.

Results

Our comprehensive analyses encompassed differentially expressed genes, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes pathways, spanning various composite tissues including skin and muscle, in comparison to the healthy control group. The analysis revealed a consistency and reproducibility in alignment with the pathological rejection grading. Genes and pathways associated with innate immunity, notably pattern recognition receptors (PRRs), damage-associated molecular patterns (DAMPs), and antigen processing and presentation pathways, exhibited upregulation in the VCA rejection groups compared to the healthy controls. Our investigation identified significant shifts in gene expression related to cytokines, chemokines, complement pathways, and diverse immune cell types, with CD8 T cells and macrophages notably enriched in the VCA rejection tissues. Mechanisms of cell death, such as apoptosis, necroptosis and ferroptosis were observed and coexisted in rejected tissues.

Conclusion

Our study provides insights into the genetic profile of tissue rejection in the porcine VCA model. We comprehensively analyze the molecular landscape of immune rejection mechanisms, from innate immunity activation to critical stages such as antigen recognition, cytotoxic rejection, and cell death. This research advances our understanding of graft rejection mechanisms and offers potential for improving diagnostic and therapeutic strategies to enhance the long-term success of VCA.

Novel approach for enhancing skin allograft survival by bioadhesive nanoparticles loaded with rapamycin

Skin graft rejection is a significant challenge in skin allografts for skin defects, particularly in extensive burn injury patients when autografts are insufficient. Enhancing the survival duration of allogeneic skin grafts can improve the success rate of subsequent autologous skin grafting, thereby promoting the therapeutic efficacy for wound healing. Rapamycin (Rapa), a potent immunosuppressant with favorable efficacy in organ transplantation, is limited by its systemic administration-associated toxicity and side effects. Therefore, addressing the short survival time of allogeneic skin grafts and minimizing the toxicity related to systemic application of immunosuppressive agents is an urgent requirement. Here, we present a topical formulation based on bioadhesive poly (lactic acid)-hyperbranched polyglycerol nanoparticles (BNPs) with surface-modified encapsulation of Rapamycin (Rapa/BNPs), applied for local immunosuppression in a murine model of allogeneic skin grafts. Our Rapa/BNPs significantly prolong nanoparticle retention, reduce infiltration of T lymphocytes and macrophages, decrease the level of pro-inflammatory cytokines and ultimately extend skin allograft survival with little systemic toxicity compared to free Rapa or Rapamycin-loaded non-bioadhesive nanoparticles (Rapa/NNPs) administration. In conclusion, Rapa/BNPs effectively deliver local immunosuppression and demonstrate potential for enhancing skin allograft survival while minimizing localized inflammation, thus potentially increasing patient survival rates for various types of skin defects.

Minimally and Non-invasive Approaches to Rejection Identification in Vascularized Composite Allotransplantation

OBJECTIVE

Rejection is common and pernicious following Vascularized Composite Allotransplantation (VCA). Current monitoring and diagnostic modalities include the clinical exam which is subjective and biopsy with dermatohistopathologic Banff grading, which is subjective and invasive. We reviewed literature exploring non- and minimally invasive modalities for diagnosing and monitoring rejection (NIMMs) in VCA.

METHODS

PubMed, Cochrane, and Embase databases were queried, 3125 unique articles were reviewed, yielding 26 included studies exploring 17 distinct NIMMs. Broadly, NIMMs involved Imaging, Liquid Biomarkers, Epidermal Sampling, Clinical Grading Scales, and Introduction of Additional Donor Tissue.

RESULTS

Serum biomarkers including MMP3 and donor-derived microparticles rose with rejection onset. Epidermal sampling non-invasively enabled measurement of cytokine & gene expression profiles implicated in rejection. Both hold promise for monitoring. Clinical grading scales were useful diagnostically as was reflection confocal microscopy. Introducing additional donor tissue showed promise for preemptively identifying rejection but requires additional allograft tissue burden for the recipient.

CONCLUSION

NIMMs have the potential to dramatically improve monitoring and diagnosis in VCA. Many modalities show promise however, additional research is needed and a multimodal algorithmic approach should be explored.

Heterotopic intestine and abdominal wall transplantation in a miniature swine: A model for graft immunology

In order to accurately monitor graft immunology, we have developed a method for performing intestine and abdominal wall transplantation heterotopically in miniature swine. The procedure consisted of simultaneous segmental terminal ileum and full-thickness abdominal wall transplantation in Lanyu miniature swine, with the intestinal and the abdominal wall grafts being placed on the recipient's bilateral rear flank. Five transplantations were technically successful. One animal died on the first post-transplant day due to anesthesia-related issues, three abdominal wall and four intestinal grafts survived, while one abdominal wall graft failed due to vascular thrombosis. Acute cellular rejection (ACR) of the intestinal graft could occur preceding, simultaneously with or following ACR of the abdominal wall graft. Our experimental model demonstrates the technical feasibility of heterotopic intestine and abdominal wall transplantation in miniature swine without grafting in gastrointestinal continuity. This model could be suitable for further studies of graft immunology.

Methods of ex vivo analysis of tissue status in vascularized composite allografts

Vascularized composite allotransplantation can improve quality of life and restore functionality. However, the complex tissue composition of vascularized composite allografts (VCAs) presents unique clinical challenges that increase the likelihood of transplant rejection. Under prolonged static cold storage, highly damage-susceptible tissues such as muscle and nerve undergo irreversible degradation that may render allografts non-functional. Skin-containing VCA elicits an immunogenic response that increases the risk of recipient allograft rejection. The development of quantitative metrics to evaluate VCAs prior to and following transplantation are key to mitigating allograft rejection. Correspondingly, a broad range of bioanalytical methods have emerged to assess the progression of VCA rejection and characterize transplantation outcomes. To consolidate the current range of relevant technologies and expand on potential for development, methods to evaluate ex vivo VCA status are herein reviewed and comparatively assessed. The use of implantable physiological status monitoring biochips, non-invasive bioimpedance monitoring to assess edema, and deep learning algorithms to fuse disparate inputs to stratify VCAs are identified.

Donor programmed cell death 1 ligand 1 is required for organ transplant tolerance in major histocompatibility complex-mismatched mixed chimeras although programmed cell death 1 ligand 1 and major histocompatibility complex class II are not required for inducing chimerism

Induction of major histocompatibility complex (MHC) human leukocyte antigen (HLA)-mismatched mixed chimerism is a promising approach for organ transplantation tolerance; however, human leukocyte antigen-mismatched stable mixed chimerism has not been achieved in the clinic. Tolerogenic dendritic cell (DC) expression of MHC class II (MHC II) and programmed cell death 1 ligand 1 (PD-L1) is important for immune tolerance, but whether donor-MHC II or PD-L1 is required for the induction of stable MHC-mismatched mixed chimerism and transplant tolerance is unclear. Here, we show that a clinically applicable radiation-free regimen can establish stable MHC-mismatched mixed chimerism and organ transplant tolerance in murine models. Induction of MHC-mismatched mixed chimerism does not require donor cell expression of MHC II or PD-L1, but donor-type organ transplant tolerance in the mixed chimeras (MC) requires the donor hematopoietic cells and the organ transplants to express PD-L1. The PD-L1 expressed by donor hematopoietic cells and the programmed cell death 1 expressed by host cells augment host-type donor-reactive CD4+ and CD8+ T cell anergy/exhaustion and differentiation into peripheral regulatory T (pTreg) cells in association with the organ transplant tolerance in the MC. Conversely, host-type Treg cells augment the expansion of donor-type tolerogenic CD8+ DCs that express PD-L1. These results indicate that PD-L1 expressed by donor-type tolerogenic DCs and expansion of host-type pTreg cells in MHC-mismatched MCs play critical roles in mediating organ transplant tolerance.

Cellular activation pathways and interaction networks in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an evolving field of reconstructive surgery that has revolutionized the treatment of patients with devastating injuries, including those with limb losses or facial disfigurement. The transplanted units are typically comprised of different tissue types, including skin, mucosa, blood and lymphatic vasculature, muscle, and bone. It is widely accepted that the antigenicity of some VCA components, such as skin, is particularly potent in eliciting a strong recipient rejection response following transplantation. The fine line between tolerance and rejection of the graft is orchestrated by different cell types, including both donor and recipient-derived lymphocytes, macrophages, and other immune and donor-derived tissue cells (e.g., endothelium). Here, we delineate the role of different cell and tissue types during VCA rejection. Rejection of VCA grafts and the necessity of life-long multidrug immunosuppression remains one of the major challenges in this field. This review sheds light on recent developments in decoding the cellular signature of graft rejection in VCA and how these may, ultimately, influence the clinical management of VCA patients by way of novel therapies that target specific cellular processes.

Real-Time Monitoring Using Multiplexed Multi-Electrode Bioelectrical Impedance Spectroscopy for the Stratification of Vascularized Composite Allografts: A Perspective on Predictive Analytics

Vascularized composite allotransplantation addresses injuries to complex anatomical structures such as the face, hand, and abdominal wall. Prolonged static cold storage of vascularized composite allografts (VCA) incurs damage and imposes transportation limits to their viability and availability. Tissue ischemia, the major clinical indication, is strongly correlated with negative transplantation outcomes. Machine perfusion and normothermia can extend preservation times. This perspective introduces multiplexed multi-electrode bioimpedance spectroscopy (MMBIS), an established bioanalytical method to quantify the interaction of the electrical current with tissue components, capable of measuring tissue edema, as a quantitative, noninvasive, real-time, continuous monitoring technique to provide crucially needed assessment of graft preservation efficacy and viability. MMBIS must be developed, and appropriate models explored to address the highly complex multi-tissue structures and time-temperature changes of VCA. Combined with artificial intelligence (AI), MMBIS can serve to stratify allografts for improvement in transplantation outcomes.

Immunohistochemical Analysis of Lymphocyte Populations in Acute Skin Rejection: The University Health Network Addition to the Banff Classification

Acute rejection in vascularized composite allotransplantation has been identified using the Banff 2007 working classification. We propose an addition to this classification based on histological and immunological assessment within the skin and subcutaneous tissue.

Methods

Biopsies from vascularized composite transplant patients were obtained at scheduled visits and whenever skin changes occurred. Histology and immunohistochemistry were performed on all samples, looking at infiltrating cells.

Results

Observations were made specifically related to each component of the skin, including the epidermis, dermis, vessels, and subcutaneous tissue. Our findings led to the establishment of the University Health Network addition of skin rejection.

Conclusions

The high rate of rejection where the skin is involved requires novel techniques for early detection. The University Health Network skin rejection addition can serve as an adjunct to the Banff classification.

The MHC-characterized Miniature Swine: Lessons Learned From a 40-Year Experience in Transplantation

Over the last 40 y, a specialized herd of miniature swine has been intentionally bred to develop lines of animals homozygous for the swine major histocompatibility complex (MHC), which have facilitated transplantation studies across reproducible MHC and minor antigen mismatch barriers. These MHC-characterized miniature swine (Mc-MS) have been used for the study of novel surgical techniques, various approaches to tolerance induction of solid organ and vascularized composite allografts, as well as studies of the immunobiology of allografts and xenografts. Mc-MS possess characteristics that are highly advantageous to these studies, and their continued use will likely continue to play an important role in bridging "bench-to-cage-to bedside" therapies in the field of transplantation. In this review, we highlight the seminal contributions of the Mc-MS model to the field and analyze their role in the broader context of large animal models in transplantation research.

Early recognition of chronic rejection in a face allotransplant patient with alopecia

The features of chronic rejection (CR) in full-face vascularized composite allotransplantation (VCA) are not well-known. Herein, we report a full-face transplant patient that experienced two episodes of acute rejection (AR) and three episodes of AR/CR over the course of 6-years. The patient noticed a small, round patch of hair loss in his beard 9 months after the second AR episode, which occurred 21 months post-transplantation. Biopsy of the alopecic patch showed lichen-planopilaris-like features, which was suggestive of early CR. Despite an increase in immunosuppressive dosages, the alopecia progressed. Following the second and third AR/CR episodes, the alopecia became more pronounced, with the addition of hyperpigmentation as well as sclerosis and telangiectasia. The findings of multiple biopsies showed CR. Based on these findings we think that alopecia with lichen-planopilaris-like histopathological features similar to grade III AR features, particularly in hair follicles appears to be an early finding of CR in the presented patient. The findings further indicate that follicular involvement may be a significant feature of CR in VCA patients and that it can present prior to sclerosis, vasculopathy, or loss of adnexa. The present case is uniquely important because of the distinctive presentation of CR, with hair follicles clinically and histopathologically affected, leading to progressive and irreversible alopecia with lichen-planopilaris-like histopathology.

Penile allotransplantation: early outcomes from reported cases and survivorship considerations

Vascular composite allografts are at the forefront of medical and surgical innovation. With this new technique and the ability to transplant a face, hands, an abdominal wall, a uterus, or even a penis, patients can undergo operations that may drastically improve their quality of life. Although this process presents significant opportunities it is not always an easy road and requires significant upfront counseling and life-long immunosuppression. Often the recovery course is long, with functionality taking months to years to gain. Immunosuppression must be used to prevent rejection of the allograft although it has serious long-term side-effects. Only five patients have undergone penile allotransplantation but reported outcomes from these small numbers have nonetheless offered significant lessons with each patient. While the operation is still in its infancy, it is certain that shared experiences by surgical teams will yield improved outcomes in the future.

Noninvasive evaluation of intragraft immune responses in upper extremity transplantation

In vascularized composite allotransplantation (VCA), invasive tissue biopsies remain the gold standard in diagnosing rejection carrying significant morbidity. We aimed to show feasibility of tape-stripping for noninvasive immune monitoring in VCA. Tape-stripping was performed on allografts and native skin of upper extremity transplant recipients. Healthy nontransplanted individuals served as controls. The technique was also used in swine on naïve skin in nontransplanted animals, native skin of treated, transplanted swine, nonrejecting VCAs, and rejecting VCAs. Extracted protein was analyzed for differences in cytokine expression using Luminex technology. Significantly decreased levels of INFγ and IL-1Ra were seen between human allograft samples and native skin. In swine, rejecting grafts had increased IL-1Ra compared to naïve and native skin, decreased levels of GM-CSF compared to native skin, and decreased IL-10 compared to nonrejecting grafts. Unsupervised hierarchical clustering revealed rejecting grafts separated from the nonrejecting (P = 0.021). Variable importance in projection scores identified GM-CSF, IL-1Ra, and IL-2 as the most important profiles for group discrimination. Differences in cytokine expression are detectable in human VCA patient native skin and VCA graft skin using a noninvasive tape-stripping method. Swine studies suggest that differences in cytokines between rejecting and nonrejecting grafts are discernable.

Validation of Animal Models for Facial Transplantation Research

BACKGROUND

The development of consistent animal experimental models is important for continued research on specific biological and immunologic aspects of vascularized composite allografts. It is also important for the translation of immune regulation and tolerance induction strategies and treatment ideas from bench to bedside. The purpose of our study is to provide an outline of the use of animal models in simulated facial transplant surgery and to investigate the feasibility of animal model use.

METHODS

The animals underwent hemifacial flap transplant surgery. The flaps were placed on the external carotid artery and external jugular vein of the donor animal. Twenty-one procedures were performed in 4 different animals (6 rats, 5 rabbits, 6 dogs, 4 pigs). Two experienced plastic surgeons and 5 students performed allotransplant.

RESULTS

All 4 models were suitable for facial allotransplant with different anatomic characteristics. Average feasibility scores were 4.8 for pigs, 3.6 for rabbits, 3.2 for dogs, and 3.4 for rats. Evaluations concluded that pigs were the most practical and realistic models for facial allotransplant training. Other models achieved validation thresholds.

CONCLUSIONS

This study is the first comparative validation assessment of animal models used in facial allotransplant. It supports the use of pig models for surgical skills training. Pigs were the preferred simulation models, while rats, rabbits, and dogs were considered inferior models for transplant simulation.

Cryopreserved human skin allografts promote angiogenesis and dermal regeneration in a murine model

Cryopreserved human skin allografts (CHSAs) are used for the coverage of major burns when donor sites for autografts are insufficiently available and have clinically shown beneficial effects on chronic non-healing wounds. However, the biologic mechanisms behind the regenerative properties of CHSA remain elusive. Furthermore, the impact of cryopreservation on the immunogenicity of CHSA has not been thoroughly investigated and raised concerns with regard to their clinical application. To investigate the importance and fate of living cells, we compared cryopreserved CHSA with human acellular dermal matrix (ADM) grafts in which living cells had been removed by chemical processing. Both grafts were subcutaneously implanted into C57BL/6 mice and explanted after 1, 3, 7, and 28 days (n = 5 per group). A sham surgery where no graft was implanted served as a control. Transmission electron microscopy (TEM) and flow cytometry were used to characterise the ultrastructure and cells within CHSA before implantation. Immunofluorescent staining of tissue sections was used to determine the immune reaction against the implanted grafts, the rate of apoptotic cells, and vascularisation as well as collagen content of the overlaying murine dermis. Digital quantification of collagen fibre alignment on tissue sections was used to quantify the degree of fibrosis within the murine dermis. A substantial population of live human cells with intact organelles was identified in CHSA prior to implantation. Subcutaneous pockets with implanted xenografts or ADMs healed without clinically apparent rejection and with a similar cellular immune response. CHSA implantation largely preserved the cellularity of the overlying murine dermis, whereas ADM was associated with a significantly higher rate of cellular apoptosis, identified by cleaved caspase-3 staining, and a stronger dendritic cell infiltration of the murine dermis. CHSA was found to induce a local angiogenic response, leading to significantly more vascularisation of the murine dermis compared with ADM and sham surgery on day 7. By day 28, aggregate collagen-1 content within the murine dermis was greater following CHSA implantation compared with ADM. Collagen fibre alignment of the murine dermis, correlating with the degree of fibrosis, was significantly greater in the ADM group, whereas CHSA maintained the characteristic basket weave pattern of the native murine dermis. Our data indicate that CHSAs promote angiogenesis and collagen-1 production without eliciting a significant fibrotic response in a xenograft model. These findings may provide insight into the beneficial effects clinically observed after treatment of chronic wounds and burns with CHSA.