Ischemia-reperfusion injury in vascularized composite allotransplantation

Machine Perfusion Enables 24-h Preservation of Vascularized Composite Allografts in a Swine Model of Allotransplantation

The current gold standard for preserving vascularized composite allografts (VCA) is 4°C static cold storage (SCS), albeit muscle vulnerability to ischemia can be described as early as after 2 h of SCS. Alternatively, machine perfusion (MP) is growing in the world of organ preservation. Herein, we investigated the outcomes of oxygenated acellular subnormothermic machine perfusion (SNMP) for 24-h VCA preservation before allotransplantation in a swine model. Six partial hindlimbs were procured on adult pigs and preserved ex vivo for 24 h with either SNMP (n = 3) or SCS (n = 3) before heterotopic allotransplantation. Recipient animals received immunosuppression and were followed up for 14 days. Clinical monitoring was carried out twice daily, and graft biopsies and blood samples were regularly collected. Two blinded pathologists assessed skin and muscle samples. Overall survival was higher in the SNMP group. Early euthanasia of 2 animals in the SCS group was linked to significant graft degeneration. Analyses of the grafts showed massive muscle degeneration in the SCS group and a normal aspect in the SNMP group 2 weeks after allotransplantation. Therefore, this 24-h SNMP protocol using a modified Steen solution generated better clinical and histological outcomes in allotransplantation when compared to time-matched SCS.

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.

First Composite Woman-to-Woman Facial Transplantation in Turkey: Challenges and Lessons to Be Learned

ABSTRACT

After the first face transplantation from woman to woman we performed in our clinic, it was aimed to eliminate the lack of knowledge about the subject in the literature by transferring our experiences and long-term results to the problems we had with the patient. A 20-year-old patient underwent partial osteomyocutaneous facial transplant (22nd facial transplant), which included 2 functional units of the face. The patient had no major problems in the early period and had a good aesthetic appearance. In the postoperative period, the patient ended her social isolation and adopted the transplanted face.In the late period, secondary surgical interventions, management of the problems caused by immunosuppression, and the patient's living in a remote location to our clinic were the difficulties encountered. Six revision surgeries were performed after the transplantation. Due to immunosuppression, opportunistic infections and metabolic problems required intermittent hospitalization. The patient died at the end of 56 months because of complications secondary to immunosuppression.A successful transplant involves the management of long-term problems rather than a successful tissue transfer in the early period. In today's conditions, long-term success can be achieved with a good patient compliance, as well as each team member should take an active role in the team at the transplantation centers. More case series are needed to adapt the standard treatment and follow-up protocols for solid organ transplantations for composite tissue allotransplantations. This will be possible by sharing the results and experiences transparently in the centers where face transplantation is performed worldwide.

Characterization of Novel P-Selectin Targeted Complement Inhibitors in Murine Models of Hindlimb Injury and Transplantation

The complement system has long been recognized as a potential druggable target for a variety of inflammatory conditions. Very few complement inhibitors have been approved for clinical use, but a great number are in clinical development, nearly all of which systemically inhibit complement. There are benefits of targeting complement inhibition to sites of activation/disease in terms of efficacy and safety, and here we describe P-selectin targeted complement inhibitors, with and without a dual function of directly blocking P-selectin-mediated cell-adhesion. The constructs are characterized in vitro and in murine models of hindlimb ischemia/reperfusion injury and hindlimb transplantation. Both constructs specifically targeted to reperfused hindlimb and provided protection in the hindlimb ischemia/reperfusion injury model. The P-selectin blocking construct was the more efficacious, which correlated with less myeloid cell infiltration, but with similarly reduced levels of complement deposition. The blocking construct also improved tissue perfusion and, unlike the nonblocking construct, inhibited coagulation, raising the possibility of differential application of each construct, such as in thrombotic vs. hemorrhagic conditions. Similar outcomes were obtained with the blocking construct following vascularized composite graft transplantation, and treatment also significantly increased graft survival. This is outcome may be particularly pertinent in the context of vascularized composite allograft transplantation, since reduced ischemia reperfusion injury is linked to a less rigorous alloimmune response that may translate to the requirement of a less aggressive immunosuppressive regime for this normally nonlife-threatening procedure. In summary, we describe a new generation of targeted complement inhibitor with multi-functionality that includes targeting to vascular injury, P-selectin blockade, complement inhibition and anti-thrombotic activity. The constructs described also bound to both mouse and human P-selectin which may facilitate potential translation.

In Situ Pre-Treatment of Vascularized Composite Allografts With a Targeted Complement Inhibitor Protects Against Brain Death and Ischemia Reperfusion Induced Injuries

Introduction

Donor brain death (BD) is an unavoidable component of vascularized composite allograft (VCA) transplantation and a key contributor to ischemia-reperfusion injury (IRI). Complement is activated and deposited within solid organ grafts as a consequence of BD and has been shown to exacerbate IRI, although the role of BD and complement in VCA and the role it plays in IRI and VCA rejection has not been studied.

Methods

BD was induced in Balb/c donors, and the VCA perfused prior to graft procurement with UW solution supplemented with or without CR2-Crry, a C3 convertase complement inhibitor that binds at sites of complement activation, such as that induced on the endothelium by induction of BD. Following perfusion, donor VCAs were cold stored for 6 hours before transplantation into C57BL/6 recipients. Donor VCAs from living donors (LD) were also procured and stored. Analyses included CR2-Crry graft binding, complement activation, toxicity, injury/inflammation, graft gene expression and survival.

Results

Compared to LD VCAs, BD donor VCAs had exacerbated IRI and rejected earlier. Following pretransplant in-situ perfusion of the donor graft, CR2-Crry bound within the graft and was retained post-transplantation. CR2-Crry treatment significantly reduced complement deposition, inflammation and IRI as compared to vehicle-treated BD donors. Treatment of BD donor VCAs with CR2-Crry led to an injury profile not dissimilar to that seen in recipients of LD VCAs.

Conclusion

Pre-coating a VCA with CR2-Crry in a clinically relevant treatment paradigm provides localized, and therefore minimally immunosuppressive, protection from the complement-mediated effects of BD induced exacerbated IRI.

Facial Transplantation

Facial transplantation represents a unique surgical solution for challenging facial injury patterns in which conservative reconstructive techniques fail to provide a satisfactory functional and aesthetic result. With advances in the field of vascularized composite allotransplantation over the past 15 years, more than 40 of these procedures have been performed worldwide with two recent reports of facial re-transplantation. In this article we discuss the multidisciplinary approach that is required for successful transplantation as well as the surgical techniques used and postoperative management. With ongoing research, recent technological innovation, and increased efforts to promote greater generalizability and transparency in this field, patients with these complex injuries will continue to see improvements in their treatment options, and thus quality of life.

Graft vasculopathy in upper extremity allotransplantation: Results of a retrospective high-resolution ultrasonographic study

Graft vasculopathy (GV) is the most severe pathologic change of chronic rejection in vascularized composite allotransplantation. Since 2012, the intimal media thickness (IMT) of radial and ulnar arteries was annually monitored by high-resolution ultrasonography in seven bilateral upper extremity transplant (UET) patients. We also investigated the IMT of seven matched healthy subjects (controls). No significant difference between IMT values of controls and UET patients was found. The median IMT values of recipient radial and ulnar arteries were 0.23 mm and 0.25 mm, respectively, while the median IMT values of grafted radial and ulnar arteries were 0.27 mm and 0.30 mm, respectively. There was a statistically significant difference in the IMT values of the grafted and recipient ulnar arteries (p = .043), but this difference was no longer significant when patient #2 was excluded. He showed a significant difference between recipient and grafted arteries and significantly higher IMT values (p = .001) of his grafted arteries compared with those of all transplanted patients. This patient developed GV leading to graft loss 11 years after the transplantation. In conclusion, this study showed a significant IMT increase in an UET recipient who developed GV.

Heterotopic Transplantation of Allogeneic Vertical Rectus Abdominis Myocutaneous Flaps in Miniature Swine

BACKGROUND

Vascularized composite tissue allotransplantation (VCA) opens new possibilities for reconstruction of complex tissue defects, including upper extremity and facial transplantation. The main challenges in VCA transplantation are the side effects of long-term immunosuppression and chronic graft rejection. Translational preclinical animal models are crucial for VCA research to improve clinical outcomes and to study underlying immunologic mechanisms. Herein, we describe a novel, large animal, non-bone-bearing VCA model in inbred, swine leukocyte antigen-typed miniature swine.

METHODS

Transplantation of vertical rectus abdominis myocutaneous (VRAM) flaps was performed between fully swine leukocyte antigen-mismatched miniature swine. The flaps were transferred to the posterolateral aspect of the neck of recipients and anastomosed to the common carotid artery and internal jugular vein. Different immunosuppressive drug regimens were used. Clinical graft evaluation was performed daily, and punch biopsies were taken for histology.

RESULTS

Ten VRAM transplants were performed. The mean ischemia time was 89.4 min (SD ± 47), mean pedicle length 7.5 cm (SD ± 2), mean venous diameter 2.5 mm (SD ± 0.4), and mean arterial diameter 2.2 mm (SD ± 0.3). Follow-up demonstrated good correlation between clinical appearance and progression of graft rejection confirmed by histologic assessment. Complications were intraoperative cardiac arrest in one recipient and one flap loss due to venous compromise.

CONCLUSIONS

VRAM transplantation in miniature swine is an appropriate preclinical VCA model, with the advantage of good clinical and histologic correlation during the course of rejection, as well as easy access to the graft. The availability of inbred, haplotyped animals allows studies across different major histocompatibility complex barriers in a non-bone-bearing VCA.

Immunological considerations and concerns as pertinent to whole eye transplantation

PURPOSE OF REVIEW

The advent of clinical vascularized composite allotransplantation (VCA), offers hope for whole eye transplantation (WET) in patients with devastating vison loss that fails or defies current treatment options. Optic nerve regeneration and reintegration remain the overarching hurdles to WET. However, the realization of WET may indeed be limited by our lack of understanding of the singular immunological features of the eye as pertinent to graft survival and functional vision restoration in the setting of transplantation.

RECENT FINDINGS

Like other VCA, such as the hand or face, the eye includes multiple tissues with distinct embryonic lineage and differential antigenicity. The ultimate goal of vision restoration through WET requires optimal immune modulation of the graft for successful optic nerve regeneration. Our team is exploring barriers to our understanding of the immunology of the eye in the context of WET including the role of immune privilege and lymphatic drainage on rejection, as well as the effects ischemia, reperfusion injury and rejection on optic nerve regeneration.

SUMMARY

Elucidation of the unique immunological responses in the eye and adnexa after WET will provide foundational clues that will help inform therapies that prevent immune rejection without hindering optic nerve regeneration or reintegration.

Demonstration of technical feasibility and viability of whole eye transplantation in a rodent model

INTRODUCTION

Whole eye transplantation (WET) holds promise for vision restoration in devastating/disabling visual loss (congenital or traumatic) not amenable to surgical or neuroprosthetic treatment options. The eye includes multiple tissues with distinct embryonic lineage and differential antigenicity. Anatomically and immunologically, the eye is unique due to its avascular (cornea) and highly vascular (retina) components. Our goal was to establish technical feasibility, demonstrate graft viability, and evaluate histologic changes in ocular tissues/adnexae in a novel experimental model of WET that included globe, adnexal, optic nerve (ON), and periorbital soft tissues.

METHODS

Outbred Sprague-Dawley rats (n = 5) received heterotopic vascularized WET from donors. Each WET included the entire globe, adnexa, ON, and periorbital soft tissues supplied by the common carotid artery and external jugular vein. Viability and perfusion were confirmed by clinical examination, angiography and magnetic resonance imaging (MRI). Globe, adnexal, and periorbital tissues were analyzed for histopathologic changes, and the ON was examined for neuro-regeneration at study endpoint (30 days) or Banff Grade 3 rejection in the periorbital skin (whichever was earlier).

RESULTS

Gross examination confirmed transplant viability and corneal transparency. Average operative duration was 64.0 ± 5.8 min. Average ischemia time was 26.0 ± 4.2 min. MRI revealed loss of globe volume by 36.0 ± 2.8% after transplantation. Histopathology of globe and adnexal tissues showed unique and differential patterns of inflammatory cell infiltration. The ON revealed a neurodegeneration pattern.

CONCLUSION

The present study is the first in the literature to establish an experimental model of WET. This model holds significant potential in investigating mechanistic pathways, monitoring strategies or developing management approaches involving ocular viability, immune rejection, and ON regeneration after WET.

Advances in machine perfusion, organ preservation, and cryobiology: potential impact on vascularized composite allotransplantation

PURPOSE OF REVIEW

In this review, we discuss novel strategies that allow for extended preservation of vascularized composite allografts and their potential future clinical implications for the field of vascularized composite allotransplantation (VCA).

RECENT FINDINGS

The current gold standard in tissue preservation - static cold preservation on ice - is insufficient to preserve VCA grafts for more than a few hours. Advancements in the field of VCA regarding matching and allocation, desensitization, and potential tolerance induction are all within reasonable reach to achieve; these are, however, constrained by limited preservation time of VCA grafts. Although machine perfusion holds many advantages over static cold preservation, it currently does not elongate the preservation time. More extreme preservation techniques, such as cryopreservation approaches, are, however, specifically difficult to apply to composite tissues as the susceptibility to ischemia and cryoprotectant agents varies greatly by tissue type.

SUMMARY

In the current scope of extended preservation protocols, high subzero approaches of VCA grafts will be particularly critical enabling technologies for the implementation of tolerance protocols clinically. Ultimately, advances in both preservation techniques and tolerance induction have the potential to transform the field of VCA and eventually lead to broad applications in reconstructive transplantation.

Face Transplant: Status of Current Supporting Technology to Plan and Perform the Operation and Monitor the Graft in the Postoperative Period

Face transplant has rapidly advanced since the first operation in 2005, and to date, 40 partial or full-face transplants have been performed. The safety and efficacy of this operation are aided at all phases by supporting technologies. These include advanced imaging techniques to plan the operation, devices to monitor the flap in the immediate perioperative period, and noninvasive imaging and serum markers to monitor for acute and chronic rejection. Some of the technologies, such as those used in the immediate perioperative period, have extensive evidence supporting their use, whereas those to detect acute or chronic rejection remain investigational. The technologies of today will continue to evolve and make the operation safer with improved outcomes; however, the most significant barrier for face transplant continues to be immunologic rejection.

Ex-vivo flush of the limb allograft reduces inflammatory burden prior to transplantation

BACKGROUND

Passenger leucocytes and inflammatory debris transferred from the donor limb to the recipient can induce allorecognition, which activates the host immune response. This is the first study to evaluate whether the transfer of this inflammatory burden can be reduced via post-preservation flush prior to revascularisation, and whether this is influenced by ischaemia.

METHODS

Bilateral forelimbs from the same pig were procured and infused with preservation flush and stored on ice. Each limb from the same pig underwent a post-preservation intravascular flush with isotonic solution at either 2 or 6 h. Venous effluent underwent flow cytometry to phenotype leucocyte populations, with additional quantification of cytokines and cell-free DNA.

RESULTS

We identified large populations of viable leucocytes in the flush effluent (8.65 × 10⁸ ± 3.10 × 10⁸ cells at 2 h and 1.02 × 10⁹ ± 2.63 × 10⁸ at 6 h). This comprised T cells, B cells, NK cells and monocytes. Post-preservation flush yielded significant concentrations of pro-inflammatory cytokines including IL-6, IL-18, GM-CSF, IL-1β, IL1α and CXCL-8 and mitochondrial DNA. The regulatory cytokine, IL-10 was undetectable.

CONCLUSIONS

This study supports the finding that a post-preservation flush removes leucocytes and inflammatory components that are responsible for direct presentation. This study also gives an indication of how ischaemia impacts on the inflammatory burden transferred to the recipient upon reperfusion.

Tissue conservation for transplantation

Pathophysiological changes that occur during ischemia and subsequent reperfusion cause damage to tissues procured for transplantation and also affect long-term allograft function and survival. The proper preservation of organs before transplantation is a must to limit these injuries as much as possible. For decades, static cold storage has been the gold standard for organ preservation, with mechanical perfusion developing as a promising alternative only recently. The current literature points to the need of developing dedicated preservation protocols for every organ, which in combination with other interventions such as ischemic preconditioning and therapeutic additives offer the possibility of improving organ preservation and extending it to multiple times its current duration. This review strives to present an overview of the current body of knowledge with regard to the preservation of organs and tissues destined for transplantation.

Ischemia/reperfusion injury in vascularized tissue allotransplantation: tissue damage and clinical relevance

PURPOSE OF REVIEW

Ischemia and reperfusion injury (IRI) in vascularized tissue allotransplantation (VCA) remain largely undefined. Because VCA is comprised of different tissues, the sensitivity towards IRI may not be uniform. We, herein, attempt to address mechanistic aspects of IRI in VCA and provide a summary on potential technologies and targets for amelioration or treatment of IRI in this novel field.

RECENT FINDINGS

IRI results in a loosened architecture of musculature, hypertrophic, centrally located cell nuclei as well as a high degree of neovascularization. Mitochondria in muscle tissue show a high degree of degeneration after prolonged ischemia whereas the ultrastructure remains normal after short cold ischemia time (CIT). Muscle cell necrosis accompanied by a diffuse inflammatory infiltrate and vasculopathy of small vessels is observed after 30 h of CIT. Nerves revealed a high degree of separation and vacuolization of myelin lamellae because of Wallerian degeneration. Approaches to minimize IRI include use of novel preservation solutions, administration of antioxidative and anti-inflammatory molecules/drugs as well as the implementation of machine perfusion in the setting of VCA.

SUMMARY

Hand and face transplantations are logistically challenging procedures. Optimal planning and a highly congruent and motivated team are key to keep ischemia times to a minimum. In addition to pharmacological approaches, machine perfusion seems promising to help circumvent logistic problems and expand the donor pool in VCA.

Immunological and inflammatory mapping of vascularized composite allograft rejection processes in a rat model

BACKGROUND

Hand and face vascularized composite allotransplantation (VCA) is an evolving and challenging field with great opportunities. During VCA, massive surgical damage is inflicted on both donor and recipient tissues, which may contribute to the high VCA rejection rates. To segregate between the damage-induced and rejection phase of post-VCA responses, we compared responses occurring up to 5 days following syngeneic versus allogeneic vascularized groin flap transplantations, culminating in transplant acceptance or rejection, respectively.

METHODS

The immune response elicited upon transplantation of a syngeneic versus allogeneic vascularized groin flap was compared at Post-operative days 2 or 5 by histology, immunohistochemistry and by broad-scope gene and protein analyses using quantitative real-time PCR and Multiplex respectively.

RESULTS

Immune cell infiltration began at the donor-recipient interface and paralleled expression of a large group of wound healing-associated genes in both allografts and syngrafts. By day 5 post-transplantation, cell infiltration spread over the entire allograft but remained confined to the wound site in the syngraft. This shift correlated with upregulation of IL-18, INFg, CXCL9, 10 and 11, CCL2, CCL5, CX3CL1 and IL-10 in the allograft only, suggesting their role in the induction of the anti-alloantigen adaptive immune response.

CONCLUSIONS

High resemblance between the cues governing VCA and solid organ rejection was observed. Despite this high resemblance we describe also, for the first time, a damage induced inflammatory component in VCA rejection as immune cell infiltration into the graft initiated at the surgical damage site spreading to the entire allograft only at late stage rejection. We speculate that the highly inflammatory setting created by the unique surgical damage during VCA may enhance acute allograft rejection.

Targeted Complement Inhibition Protects Vascularized Composite Allografts From Acute Graft Injury and Prolongs Graft Survival When Combined With Subtherapeutic Cyclosporine A Therapy

BACKGROUND

Recipients of vascularized composite allografts require aggressive and lifelong immunosuppression, and because the surgery is usually performed in nonlife-threatening situations, the development of strategies to minimize immunosuppression is especially pertinent for this procedure. We investigated how complement affects acute graft injury, alloimmunity, and immunosuppressive therapy.

METHODS

Vascularized composite allografts were transplanted from Balb/C to C57BL/6 mice that were complement deficient (C3 or double C3a Receptor (R)/C5aR), or treated with a targeted complement inhibitor (CR2-Crry). Allografts were analyzed for acute inflammation and injury, subacute T cell response, and survival in the absence and presence of cyclosporine A (CsA) therapy.

RESULTS

Allografts in C3-deficient or CR2-Crry-treated recipients were protected from skin and muscle ischemia-reperfusion injury (IRI). C3aR/C5aR-deficient recipients were more modestly protected. IgM and C3d colocalized within allografts from wild type and C3aR/C5aR-deficient recipients indicating IgM-mediated complement activation, and C3d deposition was almost absent in allografts from C3-deficient and CR2-Crry-treated recipients. Inflammatory cell infiltration and P-selectin expression was also significantly reduced in C3-deficient and CR2-Crry-treated recipients. Acute treatment with CR2-Crry or with 3 mg/kg per day CsA modestly, but significantly increased median allograft survival from 5.8 to 7.4 and 7.2 days, respectively. However, combined acute CR2-Crry treatment and CsA therapy increased mean graft survival to 17.2 days. Protection was associated with significantly reduced T cell infiltration of allografts and Tc1 cells in recipient spleens.

CONCLUSIONS

Complement-mediated IRI augments graft allogenicity, and appropriate complement inhibition ameliorates IRI, decreases alloimmune priming and allows more immune-sparing CsA dosing.

Hand transplants and the mandate for tolerance

PURPOSE OF REVIEW

The field of vascularized composite allograft (VCA) to achieve its full potential will require induction of tolerance. This review will introduce a new method of potential inducing tolerance in hand transplantation.

RECENT FINDINGS

Hand transplantation is never a life-extending transplant. This fact resulted in considerable debate both for and against the use of immunosuppression for nonlife-extending transplants. There is considerable debate about the ethics of hand transplantation. There is now consensus that nonlife-extending transplants are acceptable in properly selected patients. However, ideally, hand transplants should not receive life-long immunosuppression. Therefore, attempts to achieve drug-free tolerance through nonlife-endangering therapies are warranted. To this end, we propose implementation of tolerizing therapy long after periinflammation has subsided and drug minimization has proven successful. Evidence that short-term treatment with low doses of IL-2 or a long-lived IL-2 immunoglobulin (Ig) can tilt the balance of immunity from tissue destructive to tolerance come from preclinical demonstrations in mouse and nonhuman primate models of autoimmunity and/or transplantation and even more recent clinical trials.

SUMMARY

We believe that with the proper use of low-dose IL-2 given at an opportune time in the inflammatory process of transplant that reduce immunosuppression and even tolerance can be induced in hand transplantation. We propose that tolerance can be inducted after a long period of conventional treatment to avoid 'tolerance-hindering' adverse inflammation that occurs in the posttransplant period. With abatement of posttransplant inflammation and with time, we will institute low-dose IL-2-based therapy to support the proliferation, viability and functional phenotype of regulatory T cells.

Current status of vascularized composite tissue allotransplantation

Vascularized composite tissue allotransplantation (VCA) offers treatment options of complex functional deficiencies that cannot be repaired with conventional reconstructive methods. VCAs consist of blocks of functional units comprising different tissue types such as skin, bone, muscle, nerves, blood vessels, tendons, ligaments and others, and are thus substantially different from the composition of organ transplants. The field of VCA has made fascinating progresses in the recent past. Among other VCAs, numerous successful hand, face and limb transplants have been performed in the world. At the same time, specific questions in regard to innate and adaptive immunity, consequences of ischemia/reperfusion injury, immunosuppression, preservation, and regenerative capacity remain. In spite of this, the field is poised to make significant advances in the near future.