Vascularized Composite Allotransplantation—An Emerging Concept for Burn Reconstruction:

Emerging strategies for tissue engineering in vascularized composite allotransplantation: A review

Vascularized composite allotransplantation (VCA), which can effectively improve quality of life, is a promising therapy for repair and reconstruction after face or body trauma. However, intractable issues are associated with VCA, such as the inevitable multiple immunogenicities of different tissues that cause severe rejection, the limited protocols available for clinical application, and the shortage of donor sources. The existing regimens used to extend the survival of patients receiving VCAs and suppress rejection are generally the lifelong application of immunosuppressive drugs, which have side effects. Consequently, studies aiming at tissue engineering methods for VCA have become a topic. In this review, we summarize the emerging therapeutic strategies for tissue engineering aimed to prolong the survival time of VCA grafts, delay the rejection and promote prevascularization and tissue regeneration to provide new ideas for future research on VCA treatment.

The 2020 Facial Transplantation Update: A 15-Year Compendium

Over the past 15 years, landmark achievements have established facial transplantation (FT) as a feasible reconstructive option for otherwise irreparable craniofacial defects. However, as the field matures and long-term outcomes begin to emerge, FT teams around the world are now facing new challenges. Data for this review were identified by searches of the PubMed/MEDLINE database from inception through August 2020. All English-language articles pertaining to FT were included. Significant advances in candidate selection, technology, operative technique, posttransplant care, and immunosuppressive management have contributed to the tremendous expansion of the field, culminating in the execution in the past 3 years of 2 facial re-transplantations, and most recently the world’s first successful combined face and double hand transplant in August 2020. Despite these achievements, the allograft donor pool remains limited, with long wait times, requiring surgical experimentation with cross-sex FT. Immunosuppressive management has improved, but significant adverse events continue to be reported. Most recently, the COVID-19 pandemic has placed an unprecedented strain on the healthcare system, with various implications for the practice of reconstructive transplantation. In this article, we provide the most comprehensive and up-to-date FT review, highlighting fundamental lessons learned and recent advancements, while looking toward the challenges ahead. Over the past 15 years, extensive multidisciplinary efforts have been instrumental to the establishment of FT as a feasible reconstructive option. As novel challenges are beginning to emerge, continued collaborative and multispecialty research efforts are needed to further this field.

Vascularized Composite Allotransplantation in Burn Reconstruction: Systematic Review and Meta-analysis

Vascularized composite allotransplantation has been successfully employed for burn reconstruction since 2003. However, its safety in this population has been questioned due to high levels of alloimmunization from burn care-related tissue exposures. To investigate this, a systematic review of vascularized composite allotransplantation employed for burn reconstruction was conducted, evaluating literature from January 2000 to September 2019. Articles containing vascularized composite allotransplantation, composite tissue allotransplantation, and burn reconstructive surgery were included; articles without published outcomes were excluded. Observational meta-analysis of pooled mortality and acute rejection episodes relative to allograft type (face vs extremity) and reconstruction type (burn vs non-burn) was performed. Twenty-four of the 63 identified articles met the criteria for inclusion, with 5 more articles added after secondary review. To date, 152 allotransplantations have been performed in 117 patients: 45 face transplants and 107 extremity transplants. Of these, 34 (22%) were performed for burn reconstruction in 25 patients (21%) with an overall higher 1-year mortality rate (12.0% vs 1.1%, P  = .030). Of these deaths, 75% received three or more simultaneous allografts. Additionally, more episodes of acute rejection occurred compared to non-burn patients (4.4 vs 2.4, P  = .035). Vascularized composite allotransplantation performed for burn reconstruction was found to be associated with a greater risk of 1-year mortality and nearly twice the number of episodes of acute rejection. Future studies should seek to identify unique risk factors of burn patients undergoing this operation and evaluate the relationship between antigenic burden and surgical outcomes.

Anti-human Leukocyte Antigen Immune Sensitization Effects of Cryopreserved Allograft and Blood Transfusion

Vascularized composite allotransplantation (VCA) is the most advanced reconstructive technique available to patients who suffer devastating burns to the limbs or face. However, VCA requires donor-recipient matching. Burn patients have been reported to experience sensitization, or the development of anti-human leukocyte antigen antibodies, during resuscitation and wound coverage, potentially precluding them from future VCA. This study sought to investigate the contributions of both blood and allograft to sensitization in burn patients. Four groups were compared: burn patients who received blood products and allograft (group 1), burn patients who received blood products only (group 2), trauma patients who received blood products only (group 3), and healthy volunteer controls (group 4). The average calculated panel-reactive antibody (indicating sensitization) was higher in group 1 compared to group 4 (P = .035). Additionally, the incidence of severe sensitization was higher in group 1 relative to the other groups (P = .049). When comparing groups of patients who had no sensitization, mild sensitization, moderate sensitization, and severe sensitization, there were no significant differences in age, sex, blood products received, total body surface area burned, or allograft used between groups, though severely sensitized patients tended to have greater total body surface area involvement and received more units of packed red blood cells and allograft (P = .079, P = .196, and P = .072, respectively). We therefore conclude that while burn patients who received allograft and blood demonstrated a higher incidence of anti-human leukocyte antigen sensitization relative to healthy controls, this difference cannot solely be attributed to either allograft use or transfusion.

A chronic rejection model and potential biomarkers for vascularized composite allotransplantation

BACKGROUND

Chronic rejection remains the Achilles heel in vascularized composite allotransplantation. Animal models to specifically study chronic rejection in vascularized composite allotransplantation do not exist so far. However, there are established rat models to study chronic rejection in solid organ transplantation such as allogeneic transplantation between the rat strains Lewis and Fischer344. Thus, we initiated this study to investigate the applicability of hindlimb transplantation between these strains to imitate chronic rejection in vascularized composite allotransplantation and identify potential markers.

METHODS

Allogeneic hindlimb transplantation were performed between Lewis (recipient) and Fischer344 (donor) rats with either constant immunosuppression or a high dose immunosuppressive bolus only in case of acute skin rejections. Histology, immunohistochemistry, microarray and qPCR analysis were used to detect changes in skin and muscle at postoperative day 100.

RESULTS

We were able to demonstrate significant intimal proliferation, infiltration of CD68 and CD4 positive cells, up-regulation of inflammatory cytokines and initiation of muscular fibrosis in the chronic rejection group. Microarray analysis and subsequent qPCR identified CXC ligands 9-11 as potential markers of chronic rejection.

CONCLUSIONS

The Fischer344 to Lewis hindlimb transplantation model may represent a new option to study chronic rejection in vascularized composite allotransplantation in an experimental setting. CXC ligands 9-11 deserve further research to investigate their role as chronic rejection markers.

Local Immunosuppression for Vascularized Composite Allografts: Application of Topical FK506-TyroSpheres in a Nonhuman Primate Model

Transplantation of vascularized composite allografts (VCAs) provides a means of restoring complex anatomical and functional units following burns and other disfigurement otherwise not amenable to conventional autologous reconstructive surgery. While short- to intermediate-term VCA survival is largely dependent on patient compliance with medication, the myriad of side effects resulting from lifelong systemic immunosuppression continue to pose a significant challenge. Topical immunosuppression is therefore a logical and attractive alternative for VCA. Current formulations are limited though, by poor skin penetration but this may be mitigated by conjugation of immunosuppressive drugs to TyroSpheres for enhanced delivery. Therefore, we investigated the topical application of FK506-TyroSpheres (in the form of a gel dressing) in a clinically relevant nonhuman primate VCA model to determine if allograft survival could be prolonged at reduced levels of maintenance systemic immunosuppression. Six Major Histocompatibility Complex (MHC)-mismatched cynomolgus macaques (Macaca fascicularis) served as reciprocal donors and recipients of radial forearm fasciocutaneous flaps. Standard Bacitracin ointment and FK506-TyroSpheres were applied every other day to the VCAs of animals in groups 1 (controls, n = 2) and 2 (experimental, n = 4), respectively, before gradual taper of systemic FK506. Clinical features of VCA rejection still developed when systemic FK506 fell below 10 ng/ml despite application of FK506-TyroSpheres and prolonged VCA survival was not achieved. However, unwanted systemic FK506 absorption was avoided with TyroSphere technology. Further refinement to optimize local drug delivery profiles to achieve and maintain therapeutic delivery of FK506 with TyroSpheres is underway, leveraging significant experience in controlled drug delivery to mitigate acute rejection of VCAs.

A Critical Update of the Assessment and Acute Management of Patients with Severe Burns

Significance: Burns are debilitating, life threatening, and difficult to assess and manage. Recent advances in assessment and management have occurred since a comprehensive review of the care of patients with severe burns was last published, which may influence research and clinical practice. Recent Advances: Recent advances have occurred in the understanding of burn pathophysiology, which has led to the identification of potential biomarkers of burn severity, such as protein C. There is new evidence about the potential superiority of natural colloids over crystalloids during fluid resuscitation, and new evidence about components of initial and perioperative management, including an improved understanding of pain following burns. Critical Issues: The limitations of the clinical examination highlight the need for imaging and biomarkers to assist in estimations of burn severity. Fluid resuscitation reduces mortality, although there is conjecture over the ideal method. The subsequent perioperative period is associated with significant morbidity and the evidence for preventing and treating pain, infection, and fluid overload while maximizing wound healing potential is described. Future Directions: Promising developments are ongoing in imaging technology, histopathology, biomarkers, and wound healing adjuncts such as hyperbaric oxygen therapy, topical negative pressure therapy, stem cell treatments, and skin substitutes. The greatest benefit from further research on management of patients with burns would most likely be derived from the elucidation of optimal fluid resuscitation protocols, pain management protocols, and surgical techniques from randomized controlled trials.

Optimizing the decellularization process of human maxillofacial muscles for facial reconstruction using a detergent-only approach

Trauma, congenital diseases, and cancer resection cause muscle deformities of the human facial muscle. Muscle defects are either treated with local or distal flaps if direct closure is not possible. However, such surgical interventions are limited by donor morbidity and limited tissue availability. Decellularized scaffolds provide alternative strategies for replacing and restoring missing facial muscle by creating scaffolds that mimic the native tissue. This study aimed to develop a protocol to decellularize human zygomaticus major muscle (ZMM) and masseter muscle (MM). Three protocols were assessed including a detergent-only treatment (DOT), detergent-enzymatic treatment (DET) protocol, and a third nondetergent nonenzymatic treatment protocol. Scaffolds were then characterized via histological, immunofluorescent, and quantitative techniques to assess which protocol provided optimal decellularization and maintenance of the extracellular matrix (ECM). The results demonstrated three cycles of DOT protocol consisting of 2% sodium dodecyl sulfate for 4 hr was optimal for decellularization for both ZMM and MM. After three cycles, DNA content was significantly reduced compared with native ZMM and MM (p < .05) with preservation of collagen and glycosaminoglycan content and ECM on histological analysis. DET and nondetergent nonenzymatic treatment protocols were unsuccessful in decellularizing the ZMM and MM with residual DNA content after four cycles and caused ECM disruption on histological analysis. All protocols did not impair the mechanical properties and supported human fibroblast growth. In conclusion, the DOT protocol is effective in producing human decellularized muscle scaffolds that maintain the ECM. Further investigation of detergent only decellurization techniques should be explored as a first step to create effective scaffolds for muscle tissue engineering.

Scar management in burn injuries using drug delivery and molecular signaling: Current treatments and future directions

In recent decades, there have been tremendous improvements in burn care that have allowed patients to survive severe burn injuries that were once fatal. However, a major limitation of burn care currently is the development of hypertrophic scars in approximately 70% of patients. This significantly decreases the quality of life for patients due to the physical and psychosocial symptoms associated with scarring. Current approaches to manage scarring include surgical techniques and non-surgical methods such as laser therapy, steroid injections, and compression therapy. These treatments are limited in their effectiveness and regularly fail to manage symptoms. As a result, the development of novel treatments that aim to improve outcomes and quality of life is imperative. Drug delivery that targets the molecular cascades of wound healing to attenuate or prevent hypertrophic scarring is a promising approach that has therapeutic potential. In this review, we discuss current treatments for scar management after burn injury, and how drug delivery targeting molecular signaling can lead to new therapeutic strategies.