Clinical Vascularized Composite Allotransplantation Research Articles

Development of a Porcine VCA Model Using an External Iliac Vessel-Based Vertical Rectus Abdominus Myocutaneous Flap.

Vascularized composite allotransplantation (VCA) involves transplanting a functional and anatomically complete tissue graft, such as a hand or face, from a deceased donor to a recipient. Although clinical VCA has resulted in successful outcomes, high rates of acute rejection and increased requirements for immunosuppression have led to significant long-term complications. Of note, immunosuppressed graft recipients are predisposed to infections, organ dysfunction, and malignancies. The long-term success of VCA grafts requires the discovery and implementation of unique approaches that avoid these complications altogether. Here, we describe our surgical technique and initial experience with a reproducible heterotopic porcine VCA model for the preclinical assessment of approaches to improve graft outcomes. Six heterotopic porcine allogeneic vertical rectus abdominis myocutaneous flap transplants were performed using Sinclair donors and Yucatan recipients. Immunosuppressive therapy was not used. Each flap was based on the left external iliac vessel system. Animals were followed postoperatively for surgery-related complications. The six pigs underwent successful VCA and were euthanized at the end of the study. Each flap demonstrated complete survival following vessel anastomosis. For the allogeneic recipients, on average, minimal erythema and healthy flap color were observed from postoperative days 1 to 4. There were no surgery-related animal deaths or complications. We have developed a reproducible, technically feasible heterotopic porcine VCA model based on the left external iliac vessel system. Our results demonstrate this model's potential to improve VCA graft outcomes by exploring tolerance induction and rejection biomarker discovery in preclinical studies.

Military VCA in the World

The world’s first hand transplant was performed for a serviceman in 1964, following a blast injury. Despite a need for such effective reconstruction of military wounds, only eight further transplants have been performed for injured soldiers. This review analysed the specific factors that have informed the use of vascularized composite allotransplantation (VCA) in military patients. Nine servicemembers have received reconstructive transplants worldwide. Seven have received upper limb transplants, one a partial face transplant and one a penile transplant. These have been in Ecuador, the USA, Poland, India and Russia. Countries with clinical VCA programmes in military hospitals include Vietnam and China, whilst others have active pre-clinical VCA research programmes including the USA, the UK and Canada. Despite specific concerns in reconstructing military patients using VCA, outcomes have improved in the last decade and the field has evolved to include more complex tissue composites, across more international centres.

Evolution of the rat hind limb transplant as an experimental model of vascularized composite allotransplantation: Approaches and advantages.

As clinical experience with surgical techniques and immunosuppression in vascularized composite allotransplantation recipients has accumulated, vascularized composite allotransplantation for hand and face have become standard of care in some countries for select patients who have experienced catastrophic tissue loss. Experience to date suggests that clinical vascularized composite allotransplantation grafts undergo the same processes of allograft rejection as solid organ grafts. Nonetheless, there are some distinct differences, especially with respect to the immunologic influence of the skin and how the graft is affected by environmental and traumatic insults. Understanding the mechanisms around these similarities and differences has the potential to not only improve vascularized composite allotransplantation outcomes but also outcomes for all types of transplants and to contribute to our understanding of how complex systems of immunity and function work together. A distinct disadvantage in the study of upper extremity vascularized composite allotransplantation recipients is the low number of clinical transplants performed each year. As upper extremity transplantation is a quality of life rather than a lifesaving transplant, these numbers are not likely to increase significantly until the risks of systemic immunosuppression can be reduced. As such, experimental models of vascularized composite allotransplantation are essential to test hypotheses regarding unique characteristics of graft rejection and acceptance of vascularized composite allotransplantation allografts. Rat hind limb vascularized composite allotransplantation models have been widely used to address these questions and provide essential proof-of-concept findings which can then be extended to other experimental models, including mice and large animal models, as new concepts are translated to the clinic. Here, we review the large body of rat hind limb vascularized composite allotransplantation models in the literature, with a focus on the various surgical models that have been developed, contrasting the characteristics of the specific model and how they have been applied. We hope that this review will assist other researchers in choosing the most appropriate rat hind limb transplantation model for their scientific interests.

Adipose-derived stromal cell therapy combined with a short course nonmyeloablative conditioning promotes long-term graft tolerance in vascularized composite allotransplantation.

The risks of chronic immunosuppression limit the utility of vascularized composite allotransplantation (VCA) as a reconstructive option in complex tissue defects. We evaluated a novel, clinically translatable, radiation-free conditioning protocol that combines anti-lymphocyte serum (ALS), tacrolimus, and cytotoxic T-lymphocyte-associated protein 4 immunoglobulin (CTLA4-Ig) with adipose-derived stromal cells (ASCs) to allow VCA survival without long-term systemic immunosuppression. Full-mismatched rat hind-limb-transplant recipients received tacrolimus (0.5mg/kg) for 14days and were assigned to 4 groups: controls (CTRL) received no conditioning; ASC-group received CTLA4-Ig (10mg/kg body weight i.p. postoperative day [POD] 2, 4, 7) and donor ASCs (1×106 iv, POD 2, 4, 7, 15, 28); the ASC-cyclophosphamide (CYP)-group received CTLA4-Ig, ASC plus cyclophosphamide (50mg/kg ip, POD 3); the ASC-ALS-group received CTLA4-Ig, ASCs plus ALS (500µL ip, POD 1, 5). Banff grade III or 120days were endpoints. ASCs suppressed alloresponse in vitro. Median rejection-free VCA survival was 28days in CTRL (n=7), 34 in ASC (n=6), and 27.5 in ASC-CYP (n=4). In contrast, ASC-ALS achieved significantly longer, rejection-free VCA survival in 6/7 animals (86%), with persistent mixed donor-cell chimerism, and elevated systemic and allograft skin Tregs , with no signs of acute cellular rejection. Taken together, a regimen comprised of short-course tacrolimus, repeated CTLA4-Ig and ASC administration, combined with ALS, promotes long-term VCA survival without chronic immunosuppression.

Immunological considerations and concerns as pertinent to whole eye transplantation.

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. 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. 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.

MMP3 Is a Non-invasive Biomarker of Rejection in Skin-Bearing Vascularized Composite Allotransplantation: A Multicenter Validation Study.

Background: There is unmet need for non-invasive immunomonitoring to improve diagnosis and treatment of acute rejection in vascularized composite allotransplantation (VCA). Circulating matrix metalloproteinase 3 (MMP3) was described as a candidate non-invasive biomarker to predict treatment response to acute rejection in clinical VCA. However, larger validation studies are yet to be reported to allow for more definitive conclusions.Methods: We retrospectively measured MMP3 levels using ELISA in a total of 140 longitudinal serum samples from six internal and three external face transplant recipients, as well as three internal and seven external upper extremity transplant recipients. The control groups comprised serum samples from 36 kidney transplant recipients, 14 healthy controls, and 38 patients with autoimmune skin disease. A linear mixed model was used to study the effect of rejection state (pre-transplant, no-rejection, non-severe rejection (NSR), and severe rejection) on MMP3 levels.Results: In VCA, MMP3 levels increased significantly (p < 0.001) between pre- and post-transplant no-rejection states. A further increase occurred during severe rejection (p < 0.001), while there was no difference in MMP3 levels between non-severe and no-rejection episodes. A threshold of 5-fold increase from pre-transplant levels could discriminate severe from NSR with 76% sensitivity and 81% specificity (AUC = 0.79, 95% CI = 0.65–0.92, p < 0.001). In kidney transplantation, the MMP3 levels were significantly (p < 0.001) elevated during antibody-mediated rejection but not during T-cell mediated rejection (TCMR) (p = 0.547). MMP3 levels in healthy controls and autoimmune skin disease patients were comparable with either pre-transplant or no-rejection/NSR episodes of VCA patients.Conclusion: The results of this study suggest that serum MMP3 protein is a promising marker for stratifying patients according to severity of rejection, complementary to biopsy findings.

Extracorporeal Perfusion in Vascularized Composite Allotransplantation: Current Concepts and Future Prospects.

Severe injuries of the face and limbs remain a major challenge in today's reconstructive surgery. Vascularized composite allotransplantation (VCA) has emerged as a promising approach to restore these defects. Yet, there are major obstacles preventing VCA from broad clinical application. Two key restrictions are (1) the graft's limited possible ischemia time, keeping the potential donor radius extremely small, and (2) the graft's immunogenicity, making extensive lifelong monitoring and immunosuppressive treatment mandatory. Machine perfusion systems have demonstrated clinical success addressing these issues in solid organ transplantation by extending possible ischemia times and decreasing immunogenicity. Despite many recent promising preclinical trials, machine perfusion has not yet been utilized in clinical VCA. This review presents latest perfusion strategies in clinical solid organ transplantation and experimental VCA in light of the specific requirements by the vascularized composite allograft's unique tissue composition. It discusses optimal settings for temperature, oxygenation, and flow types, as well as perfusion solutions and the most promising additives. Moreover, it highlights the implications for the utility of VCA as therapeutic measure in plastic surgery, if machine perfusion can be successfully introduced in a clinical setting.

Premise and promise of mesenchymal stem cell-based therapies in clinical vascularized composite allotransplantation.

Over the past decade, clinical vascularized composite allotransplantation (VCA) has enabled functional and quality of life restoration in a wide range of indications secondary to devastating tissue loss. However, the spectre of toxicity and long-term complications of chronic immunosuppression has curtailed the momentum of VCA. This study summarizes the literature evidence behind successful mesenchymal stem cell (MSC)-based cell therapies highlighting their multipronged immunomodulatory, restorative and regenerative characteristics with special emphasis towards VCA applications. Experimental and clinical studies in solid organs and VCA have confirmed that MSCs facilitate immunosuppression-free allograft survival or tolerance, stimulate peripheral nerve regeneration, attenuate ischaemia-reperfusion injury, and improve tissue healing after surgery. It has been hypothesized that MSC-induced long-term operational tolerance in experimental VCA is mediated by induction of mixed donor-specific chimerism and regulatory T-cell mechanisms. All these characteristics of MSCs could thus help expand the scope and clinical feasibility of VCA. Cellular therapies, especially those focusing on MSCs, are emerging in solid organ transplantation including VCA. Although some clinical trials have begun to assess the effects of MSCs in solid organ transplantation, much scientific domain remains uncharted, especially for VCA.

Vascularized composite allotransplantation: current standards and novel approaches to prevent acute rejection and chronic allograft deterioration.

The advent of more potent immunosuppressants led to the first successful human upper extremity transplantation in 1998. At this time, >100 upper extremity transplants, 30 face transplants, and a variety of other vascularized composite allotransplantation (VCA) procedures have been performed around the world. VCA recipients present unique challenges for transplantation. The incidence of acute rejection exceeds 80% in hand and face transplantation and is well documented, whereas reports about antibody-mediated rejection and chronic rejection remain scarce. Immunosuppression protocols commonly used at US centers are derived from solid organ transplantation protocols. Novel approaches to minimize rejections in VCA may include improved HLA matching and considerations toward cytomegalovirus infection status. New graft preservation techniques may decrease immunogenicity prior to transplant. Novel monitoring methods such as valid biomarkers, ultrasound biomicroscopy, and sentinel flaps may enable earlier diagnosis of rejection. Cell-based therapies are being explored to achieve immunosuppressive regimen minimization or even tolerance induction. The efficacy of local immunosuppression in clinical VCA remains controversial. In conclusion, although immunosuppressive strategies adapted from SOT have demonstrated good midterm results, focusing on the unique features of VCA grafts may enable additional, more specific treatment strategies in the future and improved long-term graft outcomes.

Lymphoid neogenesis in skin of human hand, nonhuman primate, and rat vascularized composite allografts.

The mechanisms of skin rejection in vascularized composite allotransplantation (VCA) remain incompletely understood. The formation of tertiary lymphoid organs (TLO) in hand transplantation has been recently described. We assess this phenomenon in experimental and clinical VCA rejection. Skin biopsies of human (n=187), nonhuman primate (n=11), and rat (n=15) VCAs were analyzed for presence of TLO. A comprehensive immunohistochemical assessment (characterization of the cell infiltrate, expression of adhesion molecules) including staining for peripheral node addressin (PNAd) was performed and correlated with rejection and time post-transplantation. TLO were identified in human, nonhuman primate, and rat skin samples. Expression of PNAd was increased in the endothelium of vessels upon rejection in human skin (P=0.003) and correlated with B- and T-lymphocyte numbers and LFA-1 expression. PNAd expression was observed at all time-points after transplantation and increased significantly after year 5. In nonhuman primate skin, PNAd expression was found during inflammatory conditions early and late after transplantation. In rat skin, PNAd expression was strongly associated with acute rejection and time post-transplantation. Lymphoid neogenesis and TLO formation can be uniformly found in experimental and human VCA. PNAd expression in vascular endothelium correlates with skin rejection and T- and B-cell infiltration.

Large Animal Models for Vascularized Composite Allotransplantation

Large animal models have served as the foundation for clinical trials in all solid organ transplantation. Likewise, pre-clinical studies in vascularized composite allotransplantation (VCA) have provided a foundation for initial human applications in VCA. The growth of clinical VCA correspondingly benefits from large animal studies investigating the unique immunobiology, improved immunosuppressive regimens, and the potential induction of immunologic tolerance. VCA studies in large animal models of nonhuman primates, swine, and canines have and continue to build knowledge towards improved clinical outcomes.

Above-Elbow (Supracondylar) Arm Transplantation

Vascularized composite allotransplantation, also known as "Reconstructive Transplantation" is becoming more commonplace worldwide. Hand and upper extremity transplantation make up the majority of clinical vascularized composite allotransplantation cases performed so far. As success with reconstructive transplantation becomes more common, more challenging examples of limb loss are being addressed, including above-elbow, or "supracondylar" upper extremity transplants. Although very few of these cases have been performed worldwide, the authors' experience includes the only 2 cases performed in the United States at the time of this report. This article will discuss indications, challenges, surgical technique, expected outcomes, and alternative technologies for treatment of limb loss above the elbow.

Perioperative risk factors for vascularized composite allotransplantation: A systematic review and proposal of identity‐defining VCA

Vascularized composite allotransplantation (VCA) is a new dimension in reconstructive surgery. Generally, these procedures are offered for quality of life and functional indications rather than life-saving indications. Controversy exists, therefore, over the indications and risk/benefit ratios of VCA. Transplantation failure is a basic measurable risk of VCA. In this report we attempt to analyze perioperative factors associated with failures. Such factors are generally independent of technical performance and can be assessed to better define regulations applied to VCA. Ninety-one VCA procedures were identified, and 18 (19.8%) of them failed. Significant (P < 0.05) failure rates were associated with idiosyncratic cases (100%), cases performed without psychological screening (56.3%), cases performed without competent social support systems (44%), and cases done in developing countries (52.4%). A substantial but not significant failure rate was observed in cases performed without institutional review (36.4%). These findings suggest that institutional, professional, social, and ethical standards applied to VCA should require clarification of perioperative risk managements for any clinical VCA program, because such managements can be critical factors in determining outcome. The special character of these transplantation procedures suggest the concept of identity-defining vascularized composite allotransplantation (IVCA), for which psychological screening and third-party supervision is recommended.

Immunology of Vascularized Composite Allografts

Immunology of Vascularized Composite Allografts

Tolerance Induction Strategies in Vascularized Composite Allotransplantation: Mixed Chimerism and Novel Developments

Since the start of the clinical vascularized composite allotransplantation (VCA) era over a decade ago this field has witnessed significant developments in both basic and translational research. Transplant tolerance, defined as rejection-free acceptance of transplanted organs or tissues without long-term immunosuppression, holds the potential to revolutionize the field of VCA by removing the need for life-long immunosuppression. While tolerance of organ and vascularized composite transplants may be induced in small animal models by a variety of protocols, only mixed-chimerism-based protocols have successfully bridged the gap to preclinical study and to clinical trial in solid organ transplantation to date. In this paper we review the mixed-chimerism approach to tolerance induction, with specific reference to the field of VCA transplantation, and provide an overview of some novel cellular therapies as potential adjuvants to mixed chimerism in the development of tolerance induction protocols for clinical vascularized composite allotransplantation.