Surgical angiogenesis with short-term immunosuppression maintains bone viability in rabbit allogenic knee joint transplantation

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.

Challenges and opportunities in vascularized composite allotransplantation of joints: a systematic literature review

Background

Joint allotransplantation (JA) within the field of vascularized composite allotransplantation (VCA) holds great potential for functional and non-prosthetic reconstruction of severely damaged joints. However, clinical use of JA remains limited due to the immune rejection associated with all forms of allotransplantation. In this study, we aim to provide a comprehensive overview of the current state of JA through a systematic review of clinical, animal, and immunological studies on this topic.

Methods

We conducted a systematic literature review in accordance with the PRISMA guidelines to identify relevant articles in PubMed, Cochrane Library, and Web of Science databases. The results were analyzed, and potential future prospects were discussed in detail.

Results

Our review included 14 articles describing relevant developments in JA. Currently, most JA-related research is being performed in small animal models, demonstrating graft survival and functional restoration with short-term immunosuppression. In human patients, only six knee allotransplantations have been performed to date, with all grafts ultimately failing and a maximum graft survival of 56 months.

Conclusion

Research on joint allotransplantation has been limited over the last 20 years due to the rarity of clinical applications, the complex nature of surgical procedures, and uncertain outcomes stemming from immune rejection. However, the key to overcoming these challenges lies in extending graft survival and minimizing immunosuppressive side effects. With the emergence of new immunosuppressive strategies, the feasibility and clinical potential of vascularized joint allotransplantation warrants further investigation.

Autogenous Arteriovenous Bundle Implantation Maintains Viability Without Increased Immune Response in Large Porcine Bone Allotransplants

BACKGROUND

Transplantation of living allogeneic bone segments may permit reconstruction of large defects, particularly if viability is maintained without immunosuppression. Development of a new autogenous osseous blood supply accomplishes this goal in rodent experimental models. This study evaluates potential systemic and local inflammatory responses to this angiogenesis in a large-animal model.

METHODS

Vascularized allogeneic tibia segments were transplanted orthotopically into matched tibial defects in Yucatan minipigs. Microvascular anastomoses of bone nutrient artery and vein were supplemented by intramedullary placement of an autogenous arteriovenous (AV) bundle in group 1. Group 2 served as a no-angiogenesis control. A 3-drug immunosuppression regimen was withdrawn after 2 weeks. During the 20-week survival period, periodic leukocyte counts and inflammatory cytokine levels were measured. Thereafter, osteocyte survival was quantified and transplant rejection graded by histologic examination and quantitative real-time polymerase chain reaction of immunologic markers.

RESULTS

Both groups developed an initial systemic response, which resolved after 4 to 6 weeks. No differences were seen in blood cytokine levels. Interleukin 2 expression was diminished in group 1 tibiae. As expected, nutrient pedicles had thrombosed without sustained immunosuppression, occluded by intimal hyperplasia. In group 1, angiogenesis from the autogenous AV bundle resulted in significantly less osteonecrosis (P = .04) and fibrosis (P = .02) than group 2 allotransplants.

CONCLUSIONS

Systemic immune responses to large-bone allotransplants were not increased by generation of an autogenous osseous blood supply within porcine tibial bone allotransplants. Implanted AV bundles diminished inflammation and fibrosis and improved bone viability when compared to no-angiogenesis controls.

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.

Neo-Angiogenesis, Transplant Viability, and Molecular Analyses of Vascularized Bone Allotransplantation Surgery in a Large Animal Model

Vascularized composite allotransplantation of bone is a possible alternative treatment for large osseous defects but requires life-long immunosuppression. Surgical induction of autogenous neo-angiogenic circulation maintains transplant viability without this requirement, providing encouraging results in small animal models [1-3]. A preliminary feasibility study in a swine tibia model demonstrated similar findings [4, 5]. This study in swine tibial allotransplantation tests its applicability in a pre-clinical large animal model. Previously, we have demonstrated bone vascularized composite allotransplantation (VCA) survival was not the result of induction of tolerance nor an incompetent immune system [1]. Fourteen tibia vascularized bone allotransplants were microsurgically transplanted orthotopically to reconstruct size-matched tibial defects in Yucatan miniature swine. Two weeks of immunosuppression was used to maintain allotransplant pedicle patency during angiogenesis from a simultaneously implanted autogenous arteriovenous bundle. The implanted arteriovenous bundle was patent in group 1 and ligated in group 2 (a neo-angiogenesis control). At twenty weeks, we quantified the neo-angiogenesis and correlated it with transplant viability, bone remodeling, and gene expression. All patent arteriovenous bundles maintained patency throughout the survival period. Micro-angiographic, osteocyte cell count and bone remodeling parameters were significantly higher than controls due to the formation of a neo-angiogenic autogenous circulation. Analysis of gene expression found maintained osteoblastic and osteoclastic activity as well as a significant increase in expression of endothelial growth factor-like 6 (EGFL-6) in the patent arteriovenous bundle group. Vascularized composite allotransplants of swine tibia maintained viability and actively remodeled over 20 weeks when short-term immunosuppression is combined with simultaneous autogenous neo-angiogenesis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:288-296, 2020.

Reconstruction of Extended Bone Defects Using Massive Allografts Combined with Surgical Angiogenesis: A Case Report

CASE

A 20-year-old patient presented with an extended composite knee defect with destruction of the medial femoral condyle, including the medial collateral ligament. Treatment included using an anterolateral thigh flap for soft-tissue reconstruction, tensor fasciae latae muscle for ligament repair, and a massive allogenic bone graft of the medial femoral condyle that was revascularized with an osteocutaneous composite free flap from the contralateral femur. At 17 months postoperatively, the outcome was evaluated with scores on several established scales and radiographic assessment.

CONCLUSION

The combination of vascularized soft-tissue reconstruction and osseous reconstruction using allogenic bone along with surgical angiogenesis proved to be effective. Complex extremity reconstruction should be discussed with interdisciplinary specialists.

Bone vascularized composite allotransplantation model in swine tibial defect: Evaluation of surgical angiogenesis and transplant viability

INTRODUCTION

In prior small animal studies, we maintained vascularized bone allotransplant viability without long-term immunotherapy. Instead, an autogenous neoangiogenic circulation is created from implanted vessels, sufficient to maintain bone viability with only 2 weeks immunosupression. Blood flow is maintained despite rejection of the allogeneic vascular pedicle thereafter. We have previously described a large animal (swine) pre-clinical model, reconstructing tibial defects with vascularized tibial allotransplants. In this manuscript, autologous angiogenesis is evaluated in this model and correlated with bone viability.

MATERIALS AND METHODS

Allogeneic tibial segments were transplanted across a major swine leukocyte antigen mismatch. Microvascular repair of the bone VCA pedicle was combined with intraosseous implantation of an autogenous arteriovenous (AV) bundle. The bundle was ligated in group 1 (n = 4), and allowed to perfuse in group 2 (n = 4). Three-drug immunotherapy was given for 2 weeks. At 16 weeks micro-CT angiography quantified neoangiogenic vessel volume. Bone viability, rejection grade, and bone healing were analyzed.

RESULTS

A substantial neoangiogenic circulation developed from the implanted AV-bundle in group 2, with vessel density superior to ligated AV-bundle controls (0.11 ± 0.05 vs. 0.01 ± 0.01, P = .029). Bone allotransplant viability was also significantly enhanced by neoangiogenesis (78.7 ± 4.4% vs. 27.7 ± 5.8%, P = .028) with higher bone healing scores (21.4 ± 2.9 vs. 12.5 ± 3.7, P = .029). Ligated control tibias demonstrated disorganized bone morphology and higher local inflammation (P = .143).

CONCLUSION

Implantation of autogenous AV bundles into vascularized bone allotransplants resulted in the rapid formation of a neoangiogenic autogenous blood supply in a swine tibia model that maintained bone viability, improved bone healing, and minimized rejection.

Surgical Angiogenesis in Porcine Tibial Allotransplantation: A New Large Animal Bone Vascularized Composite Allotransplantation Model

Segmental bone loss resulting from trauma, infection malignancy and congenital anomaly remains a major reconstructive challenge. Current therapeutic options have significant risk of failure and substantial morbidity. Use of bone vascularized composite allotransplantation (VCA) would offer both a close match of resected bone size and shape and the healing and remodeling potential of living bone. At present, life-long drug immunosuppression (IS) is required. Organ toxicity, opportunistic infection and neoplasm risks are of concern to treat such non-lethal indications. We have previously demonstrated that bone and joint VCA viability may be maintained in rats and rabbits without the need of long-term-immunosuppression by implantation of recipient derived vessels within the VCA. It generates an autogenous, neoangiogenic circulation with measurable flow and active bone remodeling, requiring only 2 weeks of IS. As small animals differ from man substantially in anatomy, bone physiology and immunology, we have developed a porcine bone VCA model to evaluate this technique before clinical application is undertaken. Miniature swine are currently widely used for allotransplantation research, given their immunologic, anatomic, physiologic and size similarities to man. Here, we describe a new porcine orthotopic tibial bone VCA model to test the role of autogenous surgical angiogenesis to maintain VCA viability. The model reconstructs segmental tibial bone defects using size- and shape-matched allogeneic tibial bone segments, transplanted across a major swine leukocyte antigen (SLA) mismatch in Yucatan miniature swine. Nutrient vessel repair and implantation of recipient derived autogenous vessels into the medullary canal of allogeneic tibial bone segments is performed in combination with simultaneous short-term IS. This permits a neoangiogenic autogenous circulation to develop from the implanted tissue, maintaining flow through the allogeneic nutrient vessels for a short time. Once established, the new autogenous circulation maintains bone viability following cessation of drug therapy and subsequent nutrient vessel thrombosis.

Recipient-derived angiogenesis with short term immunosuppression increases bone remodeling in bone vascularized composite allotransplantation: A pilot study in a swine tibial defect model

Current vascularized composite allotransplantation (VCA) transplantation protocols rely upon life-long immune modulation to maintain tissue perfusion. Alternatively, bone-only VCA viability may be maintained in small animal models using surgical angiogenesis from implanted autogenous vessels to develop a neoangiogenic bone circulation that will not be rejected. This study tests the method's efficacy in a large animal model as a bridge to clinical practice, quantifying the remodeling and mechanical properties of porcine tibial VCAs. A segmental tibial defect was reconstructed in Yucatan miniature swine by transplantation of a matched tibia segment from an immunologically mismatched donor. Microsurgical repair of nutrient vessels was performed in all pigs, with simultaneous intramedullary placement of an autogenous arteriovenous (AV) bundle in Group 2. Group 1 served as a no-angiogenesis control. All received 2 weeks of immunosuppression. After 16 weeks, micro-CT and histomorphometric analyses were used to evaluate healing and remodeling. Axial compression and nanoindentation studies evaluated bone mechanical properties. Micro-CT analysis demonstrated significantly more new bone formation and bone remodeling at the distal allotransplant/recipient junction and on the endosteal surfaces of Group 2 tibias (p = 0.03). Elastic modulus and hardness were not adversely affected by angiogenesis. The combination of 2 weeks of immunosuppression and autogenous AV-bundle implantation within a microsurgically transplanted tibial allotransplant permitted long-term allotransplant survival over the study period of 16 weeks in this large animal model. Angiogenesis increased bone formation and remodeling without adverse mechanical effects. The method may allow future composite-tissue allotransplantation of bone without the risks associated with long-term immunosuppression. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1242-1249, 2017.

Vascularized bone transplant chimerism mediated by vascular endothelial growth factor

BACKGROUND

Vascular endothelial growth factor (VEGF) induces angiogenesis and osteogenesis in bone allotransplants. We aim to determine whether bone remodeling in VEGF-treated bone allotransplants results from repopulation with circulation-derived autogenous cells or survival of allogenic transplant-derived cells.

METHODS

Vascularized femoral bone transplants were transplanted from female Dark Agouti rats (DA;RT1(a) ) to male Piebald Viral Glaxo (PVG;RT1(c) ). Arteriovenous bundle implantation and short-term immunosuppression were used to maintain cellular viability. VEGF was encapsulated in biodegradable microspheres and delivered intramedullary in the experimental group (n = 22). In the control group (n = 22), no VEGF was delivered. Rats were sacrificed at 4 or 18 weeks. Laser capture microdissection of bone remodeling areas was performed at the inner and outer cortex. Sex-mismatched genes were quantified with reverse transcription-polymerase chain reaction to determine the amount of male cells to total cells, defined as the relative expression ratio (rER).

RESULTS

At 4 weeks, rER was significantly higher at the inner cortex in VEGF-treated transplants as compared to untreated transplants (0.622 ± 0.225 vs. 0.362 ± 0.081, P = 0.043). At 4 weeks, the outer cortex in the control group had a significantly higher rER (P = 0.038), whereas in the VEGF group, the inner cortex had a higher rER (P = 0.015). Over time, in the outer cortex the rER significantly increased to 0.634 ± 0.106 at 18 weeks in VEGF-treated rats (P = 0.049). At 18 weeks, the rER was >0.5 at all cortical areas in both groups.

CONCLUSIONS

These in vivo findings suggest a chemotactic effect of intramedullary applied VEGF on recipient-derived bone and could imply that more rapid angiogenesis of vascularized allotransplants can be established with microencapsulated VEGF.