Limb Transplantation Research Articles

Vascularised Composite Allotransplantation – A guide to optimal dissemination of scientific outputs

PurposeThe impact of academic research is not just important within the clinical domain but within society as a whole. Altmetric Attention Score (AAS) offers a means of assessing how scholarly outputs are interacted with online. Vascularised Composite Allotransplantation (VCA) is a modern but rapidly evolving topic which encompasses a broad range of complex and clinically significant surgical interventions. Primarily VCA is utilised in the reconstruction of complex, composite tissue defects, including limb and face transplantation. There is also a growing interest in the role of VCA as an early means of real-time immuno-monitoring, in sentinel skin flap transplant (SSF). Materials & methodsIn July 2024, a search was conducted using the Altmetric Explorer (AE) database using the search term ‘vascular-composite’ AND ‘allograft’ OR ‘allotransplant’. A simultaneous literature search was carried out using Web of Science (WoS) database utilising the same search terms with extraction of traditional citation-based metrics as well as relevant ‘meso’ and ‘micro’ subject headings. Corresponding citation-based metrics were extracted utilising SCImago. Data was compiled and analysed using a linear regression model with level of significance set at p < 0.05. ResultsThe Top 100 (T100) performing articles relating to VCA displayed a mean Altmetric Attention Score (AAS) of 3.31. All T100 papers were published in the English language. Sixty percent (n = 60) of T100 papers were published in Q1 Journals. News outlet mentions (r = 6.95), blog mentions (r = 6.20), and Twitter/X mentions (r = 0.52) demonstrated the greatest positive impact on AAS upon application of a linear regression model (p < 0.05). ConclusionAltmetric Scores offer a means of appraising the impact of research outputs in both academic and societal domains. Such modern metrics are useful in evolving topics such as VCA as AAS is not dependent on citation counts. Publishing of outputs in high quartile, open access journals with timely utilisation of news and social media outlets should be utilised by researchers aiming to maximise dissemination of research outputs in the field of VCA.

346.3: Hand and upper limb transplant – the UK experience.

346.3: Hand and upper limb transplant – the UK experience.

The role of the purposeful shared decision making model in vascularized composite allotransplantation.

For some patients who have lost the lower part of an arm, hand transplant offers the possibility of receiving a new limb with varying degrees of sensation and function. This procedure, Vascularized Composite Allotransplantation (VCA), is demanding for patients and their care community and comes with significant risks. As a high-stakes decision, patients interested in VCA are subject to extensive clinical evaluation and eligibility decision making. Patients and their care community must also decide if hand transplant (versus other approaches including rehabilitative therapies with or without prosthesis) is right for them. This decision making is often confusing and practically and emotionally fraught. It is complicated in four ways: by the numerous beneficial and harmful potential effects of hand transplant or other options, the number of people affected by VCA and the diverse or conflicting positions that they may hold, the practical demands and limitations of the patient's life situation, and the existential significance of limb loss and transplant for the patient's being. Patients need support in working through these treatment determining issues. Evaluation does not provide this support. Shared decision making (SDM) is a method of care that helps patients think, talk, and feel their way through to the right course of action for them. However, traditional models of SDM that focus on weighing possible beneficial and harmful effects of treatments are ill-equipped to tackle the heterogeneous issues of VCA. A recent model, Purposeful SDM extends the range of troubling issues that SDM can help support beyond opposing effects, to include conflicting positions, life situations, and existential being. In this paper we explore the pertinence of these issues in VCA, methods of SDM that each require of clinicians, the benefits of supporting patients with the breadth of issues in their unique problematic situations, implications for outcomes and practice, and extend the theory of the Purposeful SDM model itself based on the issues present in hand transplant decision making.

Depletion of donor dendritic cells ameliorates immunogenicity of both skin and hind limb transplants.

Acute cellular rejection remains a significant obstacle affecting successful outcomes of organ transplantation including vascularized composite tissue allografts (VCA). Donor antigen presenting cells (APCs), particularly dendritic cells (DCs), orchestrate early alloimmune responses by activating recipient effector T cells. Employing a targeted approach, we investigated the impact of donor-derived conventional DCs (cDCs) and APCs on the immunogenicity of skin and skin-containing VCA grafts, using mouse models of skin and hind limb transplantation. By post-transplantation day 6, skin grafts demonstrated severe rejections, characterized by predominance of recipient CD4 T cells. In contrast, hind limb grafts showed moderate rejection, primarily infiltrated by CD8 T cells. Notably, the skin component exhibited heightened immunogenicity when compared to the entire VCA, evidenced by increased frequencies of pan (CD11b-CD11c+), mature (CD11b-CD11c+MHCII+) and active (CD11b-CD11c+CD40+) DCs and cDC2 subset (CD11b+CD11c+ MHCII+) in the lymphoid tissues and the blood of skin transplant recipients. While donor depletion of cDC and APC reduced frequencies, maturation and activation of DCs in all analyzed tissues of skin transplant recipients, reduction in DC activities was only observed in the spleen of hind limb recipients. Donor cDC and APC depletion did not impact all lymphocyte compartments but significantly affected CD8 T cells and activated CD4 T in lymph nodes of skin recipients. Moreover, both donor APC and cDC depletion attenuated the Th17 immune response, evident by significantly reduced Th17 (CD4+IL-17+) cells in the spleen of skin recipients and reduced levels of IL-17E and lymphotoxin-α in the serum samples of both skin and hind limb recipients. In conclusion, our findings underscore the highly immunogenic nature of skin component in VCA. The depletion of donor APCs and cDCs mitigates the immunogenicity of skin grafts while exerting minimal impact on VCA.

Diplopia as the presenting symptom of a post‐transplant lymphoproliferative disorder in a bilateral inferior lim transplanted young adult

Aims/Purpose: To present a unique case of post‐transplant lymphoproliferative disorder (PTLD) after bilateral inferior limb transplantation, which is still controversial due to the absence of precedents in the literature and the unclear risk–benefit ratio.Methods: Case report.Results: A 22‐year‐old male presented to the emergency room complaining of double vision. He had a history of bilateral inferior limb amputation 8 years ago and received a bilateral lower limb transplantation 2 years later. He had normal graft function and was receiving cytomegalovirus prophylaxis. During neurological examinations left abducens nerve (CN VI) palsy was noted. Other cranial nerves affected produced facial hypoesthesia (CN V) and mild paresis (CN VII), hearing loss and tinnitus in left side (CN VIII) and soft palate asymmetry (CN X). He was otherwise neurologically intact, alert and orientated. MRI revealed a lesion located at the facial colliculus at the floor of 4th ventricle. In the context of immunosuppression, the differential diagnosis included abscess versus PTLD. Biopsy of the lesion was performed. Morphologically atypical lymphocytic cells suggestive of B lymphoma were identified. Monoclonal rearrangement for heavy chain Igen and immunoglobulins were identified with molecular biology techniques. The histology features were consistent with a diagnosis of CNS B lineage primary lymphoma. Two days later, bilateral supracondylar amputation was performed. Following the explant, immunosuppression was withdrawn. His underlying condition was finally diagnosed as PTLD, for which he started a chemotherapeutic regimen with radical intention (methotrexate and cytosine arabinoside). The patient recovered fully and up to date, 10 years later, is doing well.Conclusions: Due to its diverse aetiologias, a proper workup must be done of the patients presenting with diplopia to the emergency room. PLTD must be a condition to always be considered in patients with history of solid organ transplant; since the early diagnosis is crucial for a successful management of this often‐fatal condition.

Long-Term Survival and Functional Recovery of Cryopreserved Vascularized Groin Flap and Below-the-Knee Rat Limb Transplants.

Effective cryopreservation of large tissues, limbs, and organs has the potential to revolutionize medical post-trauma reconstruction options and organ preservation and transplantation procedures. To date, vitrification and directional freezing are the only viable methods for long-term organ or tissue preservation, but are of limited clinical relevance. This work aimed to develop a vitrification-based approach that will enable the long-term survival and functional recovery of large tissues and limbs following transplantation. The presented novel two-stage cooling process involves rapid specimen cooling to subzero temperatures, followed by gradual cooling to the vitrification solution (VS) and tissue glass transition temperature. Flap cooling and storage were only feasible at temperatures equal to or slightly lower than the VS Tg (i.e., -135°C). Vascularized rat groin flaps and below-the-knee (BTK) hind limb transplants cryopreserved using this approach exhibited long-term survival (>30 days) following transplantation to rats. BTK-limb recovery included hair regrowth, normal peripheral blood flow, and normal skin, fat, and muscle histology. Above all, BTK limbs were reinnervated, enabling rats to sense pain in the cryopreserved limb. These findings provide a strong foundation for the development of a long-term large-tissue, limb and organ preservation protocol for clinical use.

Moderate LMWH Anticoagulation Improves Success Rate of Hind Limb Allotransplantation in Mice.

The mouse hind limb model represents a powerful research tool in vascularized composite tissue allotransplantation, but its applicability is limited due to poor graft survival (62%-83%). Vascular thrombosis and massive hemorrhage are the major causes for these drop-outs. We hypothesize that because of better anticoagulation effect and lower risk of thrombocytopenia, application of low molecular weight heparin (LMWH) will minimize vascular complications and enhance graft and animal survival. Fifty allogeneic hind limb transplantations were performed (C57BL/6 to DBA/2 mice) using five different anticoagulation protocols. Bleeding and thromboembolic events were recorded macroscopically by postoperative hemorrhage and livid discoloration of the graft, respectively. Graft perfusion and survival were monitored daily by capillary-refill-time of graft toes within 2-3 seconds. Vascular congestion and tissue necrosis were examined by histological evaluation of hematoxylin-eosin-stained tissue sections. All transplantations were technically successful. Increase in thromboembolic events and a concomitant decrease in bleeding events were observed with the decreasing concentration of heparin in the perfusion solution. Although treatment of donor and recipient with low dose of LMWH could not reduce thromboembolic events, moderate dose effectively reduced these events. Compared with the poor outcome of graft perfusion with heparin alone, additional treatment of donor and recipient with low dose of LMWH improved graft and animal survival by 18%. Interestingly, animals treated with moderate dose of LMWH demonstrated 100% graft and animal survival. Treatment of donor and recipient mice with a moderate dose of LMWH prevents vascular complications and improves the outcome of murine hind limb transplants.

Study on the preservation effects of the amputated forelimb by machine perfusion at physiological temperature

PurposeIschemia and hypoxia are the main factors limiting limb replantation and transplantation. Static cold storage (SCS), a common preservation method for tissues and organs, can only prolong limb ischemia time to 4 – 6 h. The normothermic machine perfusion (NMP) is a promising method for the preservation of tissues and organs, which can extend the preservation time in vitro by providing continuous oxygen and nutrients. This study aimed to evaluate the difference in the efficacy of the 2 limb preservation methods. MethodsThe 6 forelimbs from beagle dogs were divided into 2 groups. In the SCS group (n = 3), the limbs were preserved in a sterile refrigerator at 4 °C for 24 h, and in the NMP group (n = 3), the perfusate prepared with autologous blood was used for the oxygenated machine perfusion at physiological temperature for 24 h, and the solution was changed every 6 h. The effects of limb storage were evaluated by weight gain, perfusate biochemical analysis, enzyme-linked immunosorbent assay, and histological analysis. All statistical analyses and graphs were performed using GraphPad Prism 9.0 one-way or two-way analysis of variance. The p value of less than 0.05 was considered to indicate statistical significance. ResultsIn the NMP group, the weight gained percentage was 11.72% ± 4.06%; the hypoxia-inducible factor-1α contents showed no significant changes; the shape of muscle fibers was normal; the gap between muscle fibers slightly increased, showing the intercellular distance of (30.19 ± 2.83) μm; and the vascular α-smooth muscle actin (α-SMA) contents were lower than those in the normal blood vessels. The creatine kinase level in the perfusate of the NMP group increased from the beginning of perfusion, decreased after each perfusate change, and remained stable at the end of perfusion showing a peak level of 4097.6 U/L. The lactate dehydrogenase level of the NMP group increased near the end of perfusion and reached the peak level of 374.4 U/L. In the SCS group, the percentage of weight gain was 0.18% ± 0.10%, and the contents of hypoxia-inducible factor-1α increased gradually and reached the maximum level of (164.85 ± 20.75) pg/mL at the end of the experiment. The muscle fibers lost their normal shape and the gap between muscle fibers increased, showing an intercellular distance of (41.66 ± 5.38) μm. The contents of vascular α-SMA were much lower in the SCS group as compared to normal blood vessels. ConclusionsNMP caused lesser muscle damage and contained more vascular α-SMA as compared to SCS. This study demonstrated that NMP of the amputated limb with perfusate solution based on autologous blood could maintain the physiological activities of the limb for at least 24 h.

Peripheral nerve repair is associated with augmented cross-tissue inflammation following vascularized composite allotransplantation.

Vascularized composite allotransplantation (VCA), with nerve repair/coaptation (NR) and tacrolimus (TAC) immunosuppressive therapy, is used to repair devastating traumatic injuries but is often complicated by inflammation spanning multiple tissues. We identified the parallel upregulation of transcriptional pathways involving chemokine signaling, T-cell receptor signaling, Th17, Th1, and Th2 pathways in skin and nerve tissue in complete VCA rejection compared to baseline in 7 human hand transplants and defined increasing complexity of protein-level dynamic networks involving chemokine, Th1, and Th17 pathways as a function of rejection severity in 5 of these patients. We next hypothesized that neural mechanisms may regulate the complex spatiotemporal evolution of rejection-associated inflammation post-VCA. For mechanistic and ethical reasons, protein-level inflammatory mediators in tissues from Lewis rats (8 per group) receiving either syngeneic (Lewis) or allogeneic (Brown-Norway) orthotopic hind limb transplants in combination with TAC, with and without sciatic NR, were compared to human hand transplant samples using computational methods. In cross-correlation analyses of these mediators, VCA tissues from human hand transplants (which included NR) were most similar to those from rats undergoing VCA + NR. Based on dynamic hypergraph analyses, NR following either syngeneic or allogeneic transplantation in rats was associated with greater trans-compartmental localization of early inflammatory mediators vs. no-NR, and impaired downregulation of mediators including IL-17A at later times. Thus, NR, while considered necessary for restoring graft function, may also result in dysregulated and mis-compartmentalized inflammation post-VCA and therefore necessitate mitigation strategies. Our novel computational pipeline may also yield translational, spatiotemporal insights in other contexts.

Mesenchymal stem cell therapy to promote functional recovery in a limb transplant model

Abstract Introduction: Battlefield trauma leads to limb amputations. We investigated whether Mesenchymal Stem Cell (MSC) therapy can improve nerve regeneration and functional outcome in limb transplantation (Tx). Methods: We performed orthotopic syngeneic hind-limb Tx in Lewis rats. Following Tx rats received syngeneic MSC (2×10 6; passage ≤6) or vehicle i.v. and locally via hydrogel. Limb sensory function (SF) and motor function (MF) were assessed weekly and at study endpoint (16 weeks) limb tissues were harvested for cell/molecular analysis. Results: SF in the tibial, peroneal/sural and saphenous nerve boundaries recovered as early as 5, 6 and 8 weeks, respectively. Total limb SF did not vary (P&amp;gt;0.05) between MSC and control groups; recovery was gradual at week 8 (Grade 1.4), week 12 (Grade 2.3) and week 16 (2.6) on a scale of Grade 0–3 (0, no function; 3, optimal function). A novel grading system was used to assess MF based on walking track footprints: Grade 0–4 (0, no footprint; 4, heel and 4–5 toe prints). MF was significantly (P&amp;lt;0.05) improved with MSC compared to controls at week 8 (Grade 1.33 Vs 0.5) and at week 16 (Grade 2.66 Vs 0.6). Ex vivoexpanded rat MSCs were CD29 +, CD31 −, CD34 −, CD44 +, CD45 low, CD90 +, MHC Class I +, Class II −and pluripotent. Neurofilament M (axonal marker), S100 and Krox20 (myelinating Schwann cells), Oct6 (Pre-myelinating Schwann cells) and GAP43 (regeneration marker) expressions were increased (P&amp;lt;0.05) and GFAP (non-myelinating Schwann cells) were reduced (P&amp;lt;0.05) in the distal portion of the sciatic nerve in MSC treated rats compared to controls. Conclusion: MSC administration following limb Tx appears to promote limb function recovery and is attributed to enhanced nerve regeneration/myelination/innervation. DoD –CDMRPL-19-0-DM190329 grant (PI, Salgar)

Implications of Vascularized Composite Allotransplantation in Plastic Surgery on Legal Medicine.

When a patient receives a transplant-be it classically an organ or bone marrow or, more recently, composite allotransplantations of the limb or face-it can result in artificial chimerism. Such chimerism raises considerations in forensic medicine, a field that relies on the collection and identification of biological samples from crime scenes. Beyond this chimerism, composite allotransplantations create further challenges. After screening the literature and press releases, we provide a brief history and summary of some of the technologies used in forensic identification, explaining their advantages and pitfalls in the light of transplantation and cautioning against misidentifying those who evade justice by taking advantage of such considerations. With face transplantation, patients can receive the skin, hair, salivary glands, teeth, and oral and nasal mucosa of their donors, components which hold great importance in forensic science. Modern technologies such as computer-assisted facial recognition, although gradually becoming more accurate over time, also face new challenges in this post-transplantation era as facial recognition software can be misled by surgical alterations of the face or face transplantation. With limb transplantation, there is an impact on fingerprint identification. Both surgical transplantation techniques and forensic technologies have seen incomprehensibly great innovation in the past century. Given the growing rate of successful composite transplantation in the USA and worldwide, it is now important for law enforcement agents to be aware of the new possibility of having two sets of genetic material, hair, saliva, fingerprints, or even facial recognition data for the same individual.

C-Reactive Protein Aggravates Acute Allograft Rejection via Subset-Specific Monocyte Activation Visualized in a VCA Model

Introduction: The impact of the innate immune response on acute and chronic allograft rejection is poorly understood. We have recently identified a molecular mechanism that leads to a conformational change within the structure of C-reactive protein (CRP), leading to activation of monocyte subsets and aggravation of the ischemia/reperfusion injury. Here, we visualized monocyte subsets in the early phase of allogeneic immune response and their differential regulation by CRP using intravital imaging in a hind limb VCA rat model. Materials and Methods: We performed allogeneic hind limb transplantations in the rat with and without the additional administration of human CRP to assess subset-specific infiltration and tissue distribution of recipient-derived monocytes at different time points postoperatively. We performed adoptive cell transfer with FACS-isolated GFP-labelled monocyte subsets from CD68-GFP Wistar rats for intravital visualization of cell adhesion and transmigration. Results: During acute allograft rejection, we identified a differential transmigration pattern of monocyte subsets by intravital imaging. We found non-classical monocytes to be pro-inflammatory and infiltrate the allograft primarily. CRP significantly increased activation and cytokine expression of this monocyte subset, thus accelerating clinical allograft rejection. Conclusion: Non-classical monocytes primarily infiltrate allogeneic tissue and contribute to acute rejection after allogeneic transplantation. Differential activation of these cells by CRP aggravates innate immune response and accelerates clinical allograft rejection, thus representing potential targets for immunomodulatory therapies.

Biomaterials-based immunomodulation enhances survival of murine vascularized composite allografts.

Vascularized composite allotransplantation (VCA) is a restorative option for patients suffering from severe tissue defects not amenable to conventional reconstruction. However, the toxicities associated with life-long multidrug immunosuppression to enable allograft survival and induce immune tolerance largely limit the broader application of VCA. Here, we investigate the potential of targeted immunomodulation using CTLA4-Ig combined with a biological porcine-derived extracellular matrix (ECM) scaffold that elicits a pro-regenerative Th2 response to promote allograft survival and regulate the inflammatory microenvironment in a stringent mouse orthotopic hind limb transplantation model (BALB/c to C57BL/6). The median allograft survival time (MST) increased significantly from 15.0 to 24.5 days (P = 0.0037; Mantel-Cox test) after adding ECM to the CTLA4-Ig regimen. Characterization of the immune infiltration shows a pro-regenerative phenotype prevails over those associated with inflammation and rejection including macrophages (F4/80hi+CD206hi+MHCIIlow), eosinophils (F4/80lowSiglec-F+), and T helper 2 (Th2) T cells (CD4+IL-4+). This was accompanied by an increased expression of genes associated with a Type 2 polarized immune state such as Il4, Ccl24, Arg1 and Ym1 within the graft. Furthermore, when ECM was applied along with a clinically relevant combination of CTLA4-Ig and Rapamycin, allograft survival was prolonged from 33.0 to 72.5 days (P = 0.0067; Mantel-Cox test). These studies implicate the clinical exploration of combined regimens involving local application of pro-regenerative, immunomodulatory biomaterials in surgical wound sites with targeted co-stimulatory blockade to reduce adverse effects of immunosuppression and enhance graft survival in VCA.

Exceeding the Limits of Static Cold Storage in Limb Transplantation Using Subnormothermic Machine Perfusion.

For 50 years, static cold storage (SCS) has been the gold standard for solid organ preservation in transplantation. Although logistically convenient, this preservation method presents important constraints in terms of duration and cold ischemia-induced lesions. We aimed to develop a machine perfusion (MP) protocol for recovery of vascularized composite allografts (VCA) after static cold preservation and determine its effects in a rat limb transplantation model. Partial hindlimbs were procured from Lewis rats and subjected to SCS in Histidine-Tryptophan-Ketoglutarate solution for 0, 12, 18, 24, and 48 hours. They were then either transplanted (Txp), subjected to subnormothermic machine perfusion (SNMP) for 3 hours with a modified Steen solution, or to SNMP + Txp. Perfusion parameters were assessed for blood gas and electrolytes measurement, and flow rate and arterial pressures were monitored continuously. Histology was assessed at the end of perfusion. For select SCS durations, graft survival and clinical outcomes after transplantation were compared between groups at 21 days. Transplantation of limbs preserved for 0, 12, 18, and 24-hour SCS resulted in similar survival rates at postoperative day 21. Grafts cold-stored for 48 hours presented delayed graft failure (p = 0.0032). SNMP of limbs after 12-hour SCS recovered the vascular resistance, potassium, and lactate levels to values similar to limbs that were not subjected to SCS. However, 18-hour SCS grafts developed significant edema during SNMP recovery. Transplantation of grafts that had undergone a mixed preservation method (12-hour SCS + SNMP + Txp) resulted in better clinical outcomes based on skin clinical scores at day 21 post-transplantation when compared to the SCS + Txp group (p = 0.01613). To date, VCA MP is still limited to animal models and no protocols are yet developed for graft recovery. Our study suggests that ex vivo SNMP could help increase the preservation duration and limit cold ischemia-induced injury in VCA transplantation.

The Future of Microsurgery: Vascularized Composite Allotransplantation and Engineering Vascularized Tissue

BackgroundMicrosurgical techniques have revolutionized the field of reconstructive surgery and are the mainstay for complex soft tissue reconstruction. However, their limitations have promoted the development of viable alternatives. This article seeks to explore technologies that have the potential of revolutionizing microsurgical reconstruction as it is currently known, reflect on current and future vascularized composite allotransplantation (VCA) practices, as well as describe the basic science within emerging technologies and their potential translational applications. MethodsA literature review was performed of the technologies that may represent the future of microsurgery: vascularized tissue engineering (VCA) and flap-specific tissue engineering. ResultsVCA has shown great promise and has already been employed in the clinical setting (especially in face and limb transplantation). Immunosuppression, logistics, cost, and regulatory pathways remain barriers to overcome to make it freely available. Vascularized and flap-specific tissue engineering remain a laboratory reality but have the potential to supersede VCA. The capability of creating an off-the-shelf free flap matching the required tissue, size, and shape is a significant advantage. However, these technologies are still at the early stage and require significant advancement before they can be translated into the clinical setting. ConclusionVCA, vascularized tissue engineering, and flap-specific bioengineering represent possible avenues for the evolution of current microsurgical techniques. The next decade will elucidate which of these three strategies will evolve into a tangible translational option and hopefully bring a paradigm shift of reconstructive surgery.

317.5: Novel Biologic Therapies to Promote Functional Recovery in Limb Transplantation

317.5: Novel Biologic Therapies to Promote Functional Recovery in Limb Transplantation

427.1: Donor Dendritic Cell Depletion Allows Novel Insights Into the Alloimmune Response Following Murine Composite Tissue and Skin Transplantation

Background: Cell-based therapies in vascularized composite tissue allotransplantation (VCA) have demonstrated promising results with the potential to modify life-long conventional immunosuppression. Dendritic cells (DCs) promote pro-inflammatory, alloimmune responses. Of particular interest is the role of DCs as antigen-presenting cells and potential tolerogenic effects as immature DCs. Material and Methods: Diphteria Toxin Receptor (DTR) transgenic or wild-type (WT) donor mice were used to deplete subsets of DCs or APCs respectively in a fully histoincompatible murine hind limb and skin transplant models; prior to procurement, all donors were either treated with diphteria toxin (DT; at -15 hours) or with clodronate (CL; 8 days prior to Tx). DBA/2J mice served as recipients. Study endpoint was on POD 6. Alloimmune response was assessed sequentially; graft survival, intragraft structural and inflammatory changes were tested serially. Results: The total number of dendritic cells (CD11b- CD11c+ DC) had markedly increased in recipients of skin WT grafts compared to recipients of VCA WT grafts (p<0.0001). The treatment with CL or DT significantly reduced the numbers of maturated and activated DC in the spleen, blood, and LN of mice receiving a skin graft, whereas numbers of CD11b-CD11c+MHCII+ and CD11b-CD11c+CD40+ DC were exclusively reduced in the spleen of VCA recipients after donor pretreatment with DT. cDC 1 subtypes were significantly higher in VCA WT vs. skin WT recipients (p<0.001). Donor pretreatment with DT decreased cDC1 counts only in recipients of VCA grafts (p<0.001).Luminex analysis revealed significantly higher TNF-alpha serum levels in the VCA WT vs. skin WT group (p<0.01). TNF-beta serum levels were significantly decreased in VCA depletion groups vs VCA WT group (p<0.001). Clinical signs of acute rejection among the VCA groups revealed higher rejection grades in the WT compared to the DC depletion group according to the BANFF criteria (grade III vs. grade II). Additional injection of immature DCs did not show any difference in allograft survival (p=ns).Conclusion: This is to our knowledge the first systematic study delineating the role of mature and immature DCs tested across and skin transplants. Those data may help explaining split-tolerance phenomenon in VCA while providing a basic concept for the utilization of mature and immature DCs in modifying alloimmune responses in VCA transplants.

422.2: Investigating Galectin-3 as a Novel Therapeutic Target To Block Inflammation and Reduce Ischemia Reperfusion Injury During Vascular Composite Allograft Transplantation

Introduction: Vascularized Composite Allograft (VCA) transplantation is a treatment option for complex injuries that leave patients with structural and functional deficits that cannot be adequately reconstructed. During transplantation, grafts are subjected to hypoxic/ischemic injury during procurement, storage, and reperfusion. Skin and muscle containing VCA are highly susceptible to ischemia reperfusion injury. Galectin-3 is an endogenous β-galactoside binding lectin known to play a role in driving inflammatory responses in response to hypoxic/ischemic stress. Blocking galectin-3 using known inhibitors including modified citrus pectin (MCP) has been shown in animal models to reduce inflammation and fibrosis. We hypothesized that galectin-3 significantly contributes to VCA IRI and that blocking galectin-3 can serve as a novel therapeutic approach to prevent or reduce IRI. We aimed to determine the role of galectin-3 in VCA ischemia reperfusion injury and the effect of blocking galectin-3 using MCP in syngeneic VCA models. Method: Male Brown Norway rats underwent syngeneic hind limb transplantation following 0, 6 or 24 hours of cold ischemia time. A group of rats receiving hind limbs subjected to 24 hours of static cold storage were treated with MCP (1% w/v) in the drinking water starting one week prior to transplantation. Recipient serum and donor VCA tissues were collected at end-of-study 6 days post transplantation. Sera and tissues collected from naive Brown Norway rats were included as controls. Sera levels of galectin-3 were determined by sandwich ELISA (Novus Biologics, Inc). Galectin-3 expression in the muscle was determined by Western Blotting. The degree of inflammation in the muscle tissue was determined by H&E. Results: Sera galectin-3 levels averaged 0.854±0.557ng/ml in naïve BN rats (n=7), 4.232±2.134ng/ml in recipients of grafts transplanted immediately without static cold storage (n=3), 12.86±1.292ng/ml in recipients of grafts subjected to 6 hours cold storage without MCP treatment (n=3),20.10±3.185ng/ml in recipients of grafts subjected to 24 hours cold storage without MCP treatment (n=6), and 12.77±2.098ng/ml in recipients of grafts subjected to 24 hours cold storage with MCP treatment (n=9) (Figure 1A). Galectin-3 expression in the VCA muscle increased according to the extent of cold ischemia. MCP treatment decreased muscle galectin-3 expression (Figure 1B) and inflammation in the muscle (Figure 2) post transplantation.Conclusion: Galectin-3 levels significantly increased in recipient sera and donor muscle within a week in rats transplanted with donor VCA grafts subjected to prolonged ischemia. Blocking galectin-3 using MCP can reduce the amount of galectin-3 in circulation and muscle tissue post transplantation and may decrease inflammation associated with VCA IRI. Galectin-3 may serve as a novel therapeutic target to reduce inflammation associated with ischemic injury and improve VCA outcomes. DOD CDMRP RTRP W81XWH1910163 RT180168.

Tacrolimus-Eluting Disk within the Allograft Enables Vascularized Composite Allograft Survival with Site-Specific Immunosuppression without Systemic Toxicity.

Widespread clinical application of vascularized composite allotransplantation (VCA) has been limited by the need for lifelong systemic immunosuppression to prevent rejection. Our goal was to develop a site-specific immunosuppressive strategy that promotes VCA allograft survival and minimizes the risk of systemic side effects. Tacrolimus loaded polycaprolactone (TAC-PCL) disks were prepared and tested for their efficacy in sustaining VCA allograft survival via site-specific immunosuppression. Brown Norway-to-Lewis rat hind limb transplantations were performed; animals received one TAC disk either in the transplanted (DTx) or in the contralateral non-transplanted (DnonTx) limbs. In another group, animals received DTx and lymphadenectomy on Tx side. Blood and allograft levels of TAC were measured using LC-MS/MS. Systemic toxicity was evaluated. Animals that received DTx achieved long-term allograft survival (> 200days) without signs of metabolic and infectious complications. In these animals, TAC blood levels were low but stable between 2 to 5ng/mL for nearly 100days. High concentrations of TAC were achieved in the allografts and the draining lymph nodes (DLN). Animals that underwent lymphadenectomy rejected their allograft by 175days. Animals that received DnonTx rejected their allografts by day 70. Controlled delivery of TAC directly within the allograft (with a single TAC disk) effectively inhibits rejection and prolongs VCA allograft survival, while mitigating the complications of systemic immunosuppression. There was a survival benefit of delivering TAC within the allograft as compared to a remote site. We believe this approach of local drug delivery has significant implications for drug administration in transplantation.

Manipulating adrenergic stress receptor signalling to enhance immunosuppression and prolong survival of vascularized composite tissue transplants.

BackgroundVascularized composite tissue allotransplantation (VCA) to replace limbs or faces damaged beyond repair is now possible. The resulting clear benefit to quality of life is a compelling reason to attempt this complex procedure. Unfortunately, the high doses of immunosuppressive drugs required to protect this type of allograft result in significant morbidity and mortality giving rise to ethical concerns about performing this surgery in patients with non‐life‐threatening conditions. Here we tested whether we could suppress anti‐graft immune activity by using a safe β2‐adrenergic receptor (AR) agonist, terbutaline, to mimic the natural immune suppression generated by nervous system‐induced signalling through AR.MethodsA heterotopic hind limb transplantation model was used with C57BL/6 (H‐2b) as recipients and BALB/c (H‐2d) mice as donors. To test the modulation of the immune response, graft survival was investigated after daily intraperitoneal injection of β2‐AR agonist with and without tacrolimus. Analyses of immune compositions and quantification of pro‐inflammatory cytokines were performed to gauge functional immunomodulation. The contributions to allograft survival of β2‐AR signalling in donor and recipient tissue were investigated with β2‐AR−/− strains.ResultsTreatment with the β2‐AR agonist delayed VCA rejection, even with a subtherapeutic dose of tacrolimus. β2‐AR agonist decreased T‐cell infiltration into the transplanted grafts and decreased memory T‐cell populations in recipient's circulation. In addition, decreased levels of inflammatory cytokines (IFN‐γ, IL‐6, TNF‐α, CXCL‐1/10 and CCL3/4/5/7) were detected following β2‐AR agonist treatment, and there was a decreased expression of ICAM‐1 and vascular cell adhesion molecule‐1 in donor stromal cells.Conclusionsβ2‐AR agonist can be used safely to mimic the natural suppression of immune responses, which occurs during adrenergic stress‐signalling and thereby can be used in combination regimens to reduce the dose needed of toxic immunosuppressive drugs such as tacrolimus. This strategy can be further evaluated for feasibility in the clinic.