Donor Recipient Chimeric Cells Induce Chimerism and Extend Survival of Vascularized Composite Allografts.

This study evaluated the efficacy of donor recipient chimeric cell (DRCC) therapy created by fusion of donor and recipient derived bone marrow cells (BMC) in chimerism and tolerance induction in a rat vascularized composite allograft (VCA) model. Twenty-four VCA (groin flaps) from MHC-mismatched ACI (RT1a) donors were transplanted to Lewis (RT1l) recipients. Rats were randomly divided into (n = 6/group): Group 1-untreated controls, Groups 2-7-day immunosuppression controls, Group 3-DRCC, and Group 4-DRCC with 7-day anti-αßTCR monoclonal antibody and cyclosporine A protocol. DRCC created by polyethylene glycol-mediated fusion of ACI and Lewis BMC were cultured and transplanted (2-4 × 106) to VCA recipients via intraosseous delivery route. Flow cytometry assessed peripheral blood chimerism while fluorescent microscopy and PCR tested the presence of DRCC in the recipient's blood, bone marrow (BM), and lymphoid organs at the study endpoint (VCA rejection). No complications were observed after DRCC intraosseous delivery. Group 4 presented the longest average VCA survival (79.3 ± 30.9 days) followed by Group 2 (53.3 ± 13.6 days), Group 3 (18 ± 7.5 days), and Group 1 (8.5 ± 1 days). The highest chimerism level was detected in Group 4 (57.9 ± 6.2%) at day 7 post-transplant. The chimerism declined at day 21 post-transplant and remained at 10% level during the entire follow-up period. Single dose of DRCC therapy induced long-term multilineage chimerism and extended VCA survival. DRCC introduces a novel concept of customized donor-recipient cell-based therapy supporting solid organ and VCA transplants.

Exosomes from donor-derived adipose mesenchymal stem cells prolong the survival of vascularized composite allografts.

Donor-derived adipose-derived mesenchymal stem cells (ADMSCs) dampen the alloimmune response and exosomes are reported to have biological activity similar to their parent cells. Here, we investigated the roles of exosomes from donor-derived ADMSCs (ADMSC-exo) in vascularized composite allotransplantation (VCA). Brown Norway-to-Lewis rat hindlimb transplantations were intravenously treated with either exosome from donor-derived ADMSCs or phosphate-buffered saline, combined with a short course of immunosuppression. We established that the treatment with ADMSC-exo prolongs the survival time of VCA grafts. Skin and muscle samples from ADMSC-exo-treated animals showed no histological signs of rejection, but samples from controls showed rejection of degree III. Comparing to the control group, a significant increase of donor cell chimerism, Tr1 and Treg, while a decrease of CD4+ T and Th1 cells were observed in the ADMSC-exo-treated group. Our findings imply that ADMSC-exo may be a valuable and safe treatment for extending VCA graft survival.

Biomarker and surrogate development in vascularised composite allograft transplantation: Current progress and future challenges.

Vascularised composite allograft (VCA) transplantation is now a feasible reconstructive option for patients who have suffered significant soft tissue injuries. However, despite numerous technical advances in the field over two decades, a number of challenges remain, not least the management of transplant rejection. Part of the difficulty faced by clinicians is the early recognition and prevention of acute rejection episodes. Whilst this is potentially easier in VCAs than solid organ transplants, due to their visible skin component, at present the only validated method for the diagnosis of acute rejection is histological examination of a tissue biopsy. The aim of this review article is to provide an evidence-based overview of progress in the field of VCA biomarker discovery, including immune cell subsets, immune cell effector pathways, and circulating markers of allograft damage, and to discuss future challenges in the field.

Combination of a CD26 Inhibitor, G-CSF, and Short-term Immunosuppressants Modulates Allotransplant Survival and Immunoregulation in a Rodent Hindlimb Allotransplant Model.

BACKGROUND: Recent studies have demonstrated that inhibition of CD26 potentiates stromal cell-derived factor-1α (SDF-1α), promotes tissue regeneration, and suppresses the rejection of organ transplants. This study investigated whether the combination of a CD26 inhibitor (CD26i) with granulocyte colony-stimulating factor (G-CSF) and short-term immunosuppressants modulates vascularized composite tissue allotransplant survival in a rodent orthotopic hindlimb allotransplant model. METHODS: The hindlimb allotransplantation from Brown-Norway to Lewis rats was divided into 4 groups. Group 1 (controls) did not receive any treatment. Group 2 was treated with short-term antilymphocyte serum (ALS) and cyclosporine-A (CsA). Group 3 was administrated CD26i and G-CSF. Group 4 received a combination of CD26i/G-CSF/ALS/CsA. Each subgroup comprised 10 rats. Peripheral blood and sampling of transplanted tissues were collected for immunological and histological analysis. RESULTS: The results revealed that allotransplant survival was found to be significantly prolonged in group 4 with CD26i/G-CSF/ALS/CsA treatment compared with those in the other groups. The interleukin-10 and transforming growth factor-ßl levels, the percentage of CD4+/CD25+/FoxP3+ T cells, as well as the levels of SDF-1α expressions were significantly increased in group 4 compared with those in the other groups. Group 4 revealed a statistical increase in the percentage of donor cells (RT1n) expression in the recipient peripheral blood, and the mixed lymphocyte reaction showed hyporesponsiveness of the T cells to donor alloantigens. CONCLUSION: The combination of CD26i/G-CSF and short-term immunosuppressants prolongs allotransplant survival by inducing immunoregulatory effects and enhancing the percentage of SDF-1α expression. This immunomodulatory approach has great potential as a strategy to increase vascularized composite allotransplantation survival.

Unraveling the Crucial Roles of FoxP3+ Regulatory T Cells in Vascularized Composite Allograft Tolerance Induction and Maintenance.

BACKGROUND: The role of regulatory T cells (Treg) in tolerance induction of vascularized composite allotransplantation (VCA) remains unclear. This study was designed to examine characteristics of Treg after VCA and their capacity to rescue allografts from rejection. METHODS: Osteomyocutaneous allografts were transplanted from Balb/c to C57BL/6 mice. All mice received costimulatory blockade and a short course of rapamycin. To elucidate the role of Treg for tolerance induction, Treg depletion was performed at postoperative day (POD) 0, 30, or 90. To assess capacity of Treg to rescue allografts from rejection, an injection of 2 × 106 Treg isolated from tolerant mice was applied. RESULTS: Eighty percent of VCA recipient mice using costimulatory blockade and rapamycin regimen developed tolerance. The tolerant recipients had a higher ratio of circulating Treg to effector T cells and elevated interleukin-10 at POD 30. A significantly higher rejection rate was observed when Treg were depleted at POD 30. But Treg depletion at POD 90 had no effect on tolerance. Treg from tolerant recipients showed stronger suppressive potential and the ability to rescue allografts from rejection. Furthermore, transplanted Treg-containing skin grafts from tolerant mice delayed rejection elicited by adoptively transferred effector T cells to Rag2-/- mice. CONCLUSIONS: Circulating Treg are crucial for inducing VCA tolerance in the early posttransplant phase, and allograft-residing Treg may maintain tolerance. Treg may, therefore, serve as a potential cellular therapeutic to improve VCA outcomes.

Pharmacokinetics and Biodistribution of Tacrolimus after Topical Administration: Implications for Vascularized Composite Allotransplantation.

AIM: The high doses of oral tacrolimus (TAC) (1,2) necessary to prevent acute rejection (AR) after vascularized composite allotransplantation (VCA) are associated with systemic adverse effects. The skin is the most antigenic tissue in VCA and the primary target of AR. However, the short-term use of topical TAC (Protopic®), as an off-label adjunct to oral TAC, to treat AR episodes pro re nata (PRN), has yielded inconsistent results. There is lack of data on the pharmacokinetics and tissue distribution of topical TAC in VCA, that hampers our understanding of the reasons for unreliable efficacy. Toward this goal, we evaluated the ability of topical TAC to achieve high local tissue concentrations at the site of application with low systemic concentrations. MATERIALS AND METHODS: We assessed the pharmacokinetics and tissue distribution of topical TAC (Protopic®, 0.03%) after single or repeated topical application in comparison to those after systemic delivery in rats. Animals received a single topical application of TAC ointment (Group 1) or an intravenous (IV) injection of TAC (Group 2) at a dose of 0.5 mg/kg. In another experiment, animals received daily topical application of TAC ointment (Group 3), or daily intraperitoneal (IP) injection of TAC (Group 4) at a dose of 0.5 mg/kg for 7 days. TAC concentrations in blood and tissues were analyzed by Liquid Chromatography-Mass Spectrometry (LC/MS-MS). RESULTS: Following single topical administration, TAC was absorbed slowly with a Tmax of 4 h and an absolute bioavailability of 11%. The concentrations of TAC in skin and muscle were several folds higher than whole blood concentrations. Systemic levels remained subtherapeutic (< 3 ng/ml) with repeated once daily applications. CONCLUSION: Topical application of TAC ointment (Protopic®, 0.03%) at a dose of 0.5 mg/kg/day provided high concentrations in the local tissues with low systemic exposure. Repeated topical administration of TAC is well tolerated with no local or systemic adverse effects. This study confirms the feasibility of topical application of TAC for site specific graft immunosuppression and enables future applications in VCA.

Toward Development of the Delayed Tolerance Induction Protocol for Vascularized Composite Allografts in Nonhuman Primates.

BACKGROUND: Transplantation of vascularized composite allografts is limited mainly by the need for life-long immunosuppression. The consequent side effects and looming specter of chronic rejection portend eventual allograft loss. Development of tolerogenic protocols is thus of utmost importance to the field of vascularized composite allograft transplantation. METHODS: With a modified delayed tolerance induction protocol, 10 cynomolgus macaques received hand (n = 2) or face vascularized composite allografts across both full and haploidentical major histocompatibility complex barriers before donor bone marrow transplantation at a later date. Protocol and for-cause allograft skin biopsies were performed for immunohistochemical analysis and analysis of donor-recipient leukocyte contribution; mixed chimerism in peripheral blood and in vitro immune responses were assessed serially. RESULTS: Before bone marrow transplantation, maintenance immunosuppression for 4 months led to lethal complications, including posttransplant lymphoproliferative disorder (in two of four recipients), which necessitated early study termination. Shortening the maintenance period to 2 months was clinically relevant and allowed all subsequent subjects (n = 6) to complete the delayed tolerance induction protocol. Acute rejection developed within the first 2 to 4 weeks after transplantation, with corresponding near-complete turnover of allograft leukocytes from donor to recipient origin, but donor-specific antibodies remained negative. After bone marrow transplantation, mixed chimerism failed to develop, although carboxyfluorescein succinimidyl ester mixed lymphocyte reaction demonstrated generalized unresponsiveness. However, the accrual of subsequent rejection episodes eventually culminated in graft vasculopathy and irreversible allograft loss. CONCLUSIONS: Despite the various advantages of the delayed tolerance induction protocol, it failed to reliably induce mixed chimerism and thus immunologic tolerance to vascularized composite allografts, given currently available immunosuppression treatment options. Ongoing work shows promise in overcoming these limitations.

Humoral Alloreactivity in VCA Recipients: Should We Learn From Our Experience?

Initially overlooked in favor of T cell-mediated rejection, the importance of the humoral alloimmune response has progressively emerged. As a result, antibody-mediated rejection is now widely recognized as the main cause of late allograft loss in most (if not all) types of solid-organ transplantation. Over the last 2 decades, vascularized composite allotransplantation (VCA) has appeared for replacing tissue defects in patients for whom no other satisfactory reconstructive options were available. Although it is now clear that VCA recipients can develop donor-specific antibodies, conclusions made in solid organ transplantation regarding antibody-mediated rejection may not systematically apply to VCA. Here, we propose to use the experience gained in organ transplantation to shed light on the path that shall be followed to evaluate and manage humoral alloreactivity in VCA recipients.

Mucosa and Rejection in Facial Vascularized Composite Allotransplantation: A Systematic Review.

BACKGROUND: Facial vascularized composite allotransplantation (fVCA) presents an established approach to restore form and function of patients with catastrophic facial defects. Skin is one of the target tissues of the rejection process, and due to its easy accessibility has become the gold standard in the diagnosis of rejection. Mucosal rejection frequently occurs; however, the added value of mucosal rejection assessment for patient management is unknown. METHODS: We conducted a systematic review of manuscripts listed in the MEDLINE/PubMed and GoogleScholar databases to identify articles that provide data on mucosal rejection following fVCA. For inclusion, papers had to be available as full-text and written in English. Non-VCA studies and animal studies were excluded. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. RESULTS: We included 17 articles that described changes in allotransplanted mucosa of fVCAs. These articles yielded data on 168 BANFF graded biopsies of corresponding skin and mucosa biopsies. Rejection grades were consistently higher in mucosal biopsies. Concordance between allograft skin and mucosa biopsy grades increased with an increasing skin-BANFF grade. Mucosa rejection grades were on average lower in the early stages of the posttransplant period (postoperative mo 12). CONCLUSIONS: The mucosa of facial allotransplants is one of the primary targets of rejection. The data indicates that higher-grade skin rejection does not occur in absence of mucosal rejection. Further investigations are needed to elucidate the exact role of mucosal biopsies for fVCA patient management.

The Significance of Vascular Alterations in Acute and Chronic Rejection for Vascularized Composite Allotransplantation.

Vascularized composite allotransplantation (VCA) has emerged as a useful reconstructive option for patients suffering from major tissue defects and functional deficits. While the technical feasibility has been optimized and more than 130 VCAs have been performed during the last two decades, hurdles such as acute and chronic allograft rejection, graft deterioration, and eventual functional impairment need to be addressed. Recently, chronic graft rejection and progressive failure have been linked to vascular alterations observed in the allografts. Graft vasculopathy (GV) may play a pivotal role in long-term graft deterioration. The understanding of the underlying pathophysiological processes and their initial triggers is of utmost importance in the prevention, attenuation, and therapy of GV. While there are reports on the etiology and development of GV in solid organ transplantation, there are limited data with respect to chronic rejection and GV in the realm of VCA. Nevertheless, recent reports from long-term VCA recipients suggest that GV could truly jeopardize allografts in the follow-up evaluation. Chronic rejection and GV include different entities and might have different pathways in distinct organs. Herein, we reviewed the current literature on vascular changes during both acute and chronic allograft rejection, with a focus on their clinical and translational significance for VCA.

Delivery of Rapamycin Using In Situ Forming Implants Promotes Immunoregulation and Vascularized Composite Allograft Survival.

Vascularized composite allotransplantation (VCA), such as hand and face transplantation, is emerging as a potential solution in patients that suffered severe injuries. However, adverse effects of chronic high-dose immunosuppression regimens strongly limit the access to these procedures. In this study, we developed an in situ forming implant (ISFI) loaded with rapamycin to promote VCA acceptance. We hypothesized that the sustained delivery of low-dose rapamycin in proximity to the graft may promote graft survival and induce an immunoregulatory microenvironment, boosting the expansion of T regulatory cells (Treg). In vitro and in vivo analysis of rapamycin-loaded ISFI (Rapa-ISFI) showed sustained drug release with subtherapeutic systemic levels and persistent tissue levels. A single injection of Rapa-ISFI in the groin on the same side as a transplanted limb significantly prolonged VCA survival. Moreover, treatment with Rapa-ISFI increased the levels of multilineage mixed chimerism and the frequency of Treg both in the circulation and VCA-skin. Our study shows that Rapa-ISFI therapy represents a promising approach for minimizing immunosuppression, decreasing toxicity and increasing patient compliance. Importantly, the use of such a delivery system may favor the reprogramming of allogeneic responses towards a regulatory function in VCA and, potentially, in other transplants and inflammatory conditions.

Is Skin the Most Allogenic Tissue in Vascularized Composite Allotransplantation and a Valid Monitor of the Deeper Tissues?

Since the 1960s, skin has been considered to be the most allogenic tissue in humans. This tenet has remained unquestioned in the reconstructive transplant arena, which has led to skin serving as the sole monitor for early rejection in vascularized composite allotransplantation. In this article, the authors question the validity of this belief. The authors' hypothesis is that skin is not always an accurate monitor of rejection in the deep tissues, thus questioning the positive and negative predictive value of the punch biopsy for suspected vascularized composite allotransplantation rejection. A search was carried out identifying vascularized composite allotransplantation publications where the allogenicity of transplanted skin was evaluated. Eighteen publications claimed skin was found to be the most allogenic tissue in humans, justifying its use as a superior monitor for rejection. Eight publications demonstrated skin to be a poor monitor of rejection deeper to the skin. Two vascularized composite allotransplantation animal studies reported skin rejecting simultaneously with the deeper tissues. Finally, three publications discussed a skin and kidney allograft, transplanted simultaneously, indicating skin allogenicity was equivalent to the that of the kidney allograft. Much of the literature in human vascularized composite allotransplantation claims skin to be an excellent monitor of the deep tissues. The conclusion from this study is that skin does not always function as a good monitor for what could be rejecting in the deep tissues. The authors believe continued research is necessary to focus on expanding novel monitoring techniques and technologies to accurately diagnose vascularized composite allotransplantation rejection without tissue destruction.

Graft vasculopathy of vascularized composite allografts in humans: a literature review and retrospective study.

Mechanisms of chronic rejection of vascularized composite allografts (VCA) remain poorly understood and likely present along a spectrum of highly varied clinicopathological findings. Across both animal and human VCA however, graft vasculopathy (GV) has been the most consistent pathological finding resulting clinically in irreversible allograft dysfunction and eventual loss. A literature review of all reported clinical VCA cases with documented GV up to December 2018 was thus performed to elucidate the possible mechanisms involved. Relevant data extracted include C4d deposition, donor-specific antibody (DSA) formation, extent of human leukocyte antigen (HLA) mismatch, pretransplant panel reactive antibody levels, induction and maintenance immunosuppression used, the number of preceding acute rejection episodes, and time to histological confirmation of GV. Approximately 6% (13 of 205) of all VCA patients reported to date developed GV at a mean of 6 years post-transplantation. 46% of these patients have either lost or had their VCAs removed. Neither C4d nor DSA alone was predictive of GV development; however, when both are present, VCA loss appears inevitable due to progressive GV. Of utmost concern, GV in VCA does not appear to be abrogated by currently available immunosuppressive treatment and is essentially irreversible by the time of diagnosis with allograft loss a likely eventuality.

The Urogenital Epithelium and Corporal Tissues Are the Primary Targets of Rejection in Penile Vascularized Composite Allotransplantation: A New Real-Time Tissue-Based Monitoring System.

BACKGROUND: Although significant surgical advances have been made in the form of microvascular surgery and autologous free tissue transfer, penile reconstruction still poses several difficult challenges. Although interest in penile vascularized composite allotransplantation has grown since the first attempted transplant in 2006, little is known regarding the kinetics of rejection and subsequent function of penile allografts. The penis contains multiple tissue types that are not qualified by the Banff 2007 vascularized composite allotransplantation classification system, including urogenital mucosal epithelium and erectile tissues. In this study, the authors investigate the propagation of rejection and the resultant function following rejection in rat and human penile tissues. METHODS: Rejected human and rat penile tissues were examined using an ex vivo real-time tissue-based derivative of the classic mixed lymphocyte reaction assay to determine the interactions occurring between en bloc penile tissues and peripheral blood mononuclear cells (autologous and allogeneic). Correlative in vivo heterotopic rat penile vascularized composite allotransplantation was used to correlate ex vivo findings. RESULTS: In both human and rat ex vivo systems and in vivo rat vascularized composite allotransplantation, the urethral mucosa was the first to undergo rejection-associated apoptosis. The urethral mucosa was the most immunogenic and led to the highest level of peripheral blood mononuclear cell proliferative generations in all systems, whereas the neural tissues of the penis remained immune privileged. CONCLUSION: These findings are the first to describe the kinetics of rejection in both human and rat penile vascularized composite allotransplantation and that the urethral mucosa is the most antigenic, suffering the highest level of rejection-associated apoptosis and peripheral blood mononuclear cell proliferative aggregation.

Vascularized composite allograft rejection is delayed by infusion of IFN-γ-conditioned BMSCs through upregulating PD-L1.

Mesenchymal stromal cells (MSCs) have been applied in prevention from allograft rejection based on their immunomodulatory effects. However, conflicting results have been presented among recent studies, for which one possibility being acknowledged is that the exact effect is determined by the microenvironment when MSCs are applied in vivo. Using a hind limb composite tissue allograft model, we investigate the influence of IFN-γ-preconditioning on the immunomodulatory effects of MSCs and the subsequent allograft survival. Firstly, different doses of IFN-γ were respectively used to incubate with bone marrow-derived MSCs (BMSCs). We found that IFN-γ altered the expression of PD-L1, a major suppressor gene in the immune system during allograft rejection, in a strictly dose-dependent manner in BMSCs. Ten nanograms per milliliter IFN-γ-incubated BMSCs significantly stimulated PD-L1 expression and suppressed T cell proliferation and differentiation, while 50 ng/mL IFN-γ-incubated BMSCs sharply reduced PD-L1 expression. Moreover, we observed that, in contrast to the naive BMSC transplantation group, BMSCs pre-conditioned with 10 ng/mL IFN-γ (BMSCs-IFN-γ) significantly delayed the allograft rejection in vivo. In vitro mixed lymphocyte reaction (MLR) indicated that BMSCs-IFN-γ inhibited T lymphocyte proliferation and activation via PD-L1. Moreover, BMSCs-IFN-γ did not influence the proliferation and activation of T lymphocytes when PD-L1 protein was neutralized by the PD-L1 antibody. These data collectively reveal a role of recipient ongoing immune microenviroment in BMSC-based immunesuppressive therapy. Graphical abstract ᅟ.

Graft-implanted, enzyme responsive, tacrolimus-eluting hydrogel enables long-term survival of orthotopic porcine limb vascularized composite allografts: A proof of concept study.

BACKGROUND: Currently, patients receiving vascularized composite allotransplantation (VCA) grafts must take long-term systemic immunosuppressive therapy to prevent immunologic rejection. The morbidity and mortality associated with these medications is the single greatest barrier to more patients being able to receive these life-enhancing transplants. In contrast to solid organs, VCA, exemplified by hand or face transplants, allow visual diagnosis of clinical acute rejection (AR), directed biopsy and targeted graft therapies. Local immunosuppression in VCA could reduce systemic drug exposure and limit adverse effects. This proof of concept study evaluated, in a large animal forelimb VCA model, the efficacy and tolerability of a novel graft-implanted enzyme-responsive, tacrolimus (TAC)-eluting hydrogel platform, in achieving long-term graft survival. METHODS: Orthotopic forelimb VCA were performed in single haplotype mismatched mini-swine. Controls (n = 2) received no treatment. Two groups received TAC hydrogel: high dose (n = 4, 91 mg TAC) and low dose (n = 4, 49 mg TAC). The goal was to find a dose that was tolerable and resulted in long-term graft survival. Limbs were evaluated for clinical and histopathological signs of AR. TAC levels were measured in serial blood and skin tissue samples. Tolerability of the dose was evaluated by monitoring animal feeding behavior and weight. RESULTS: Control limbs underwent Banff Grade IV AR by post-operative day six. Low dose TAC hydrogel treatment resulted in long-term graft survival time to onset of Grade IV AR ranging from 56 days to 93 days. High dose TAC hydrogel also resulted in long-term graft survival (24 to 42 days), but was not well tolerated. CONCLUSION: Graft-implanted TAC-loaded hydrogel delays the onset of Grade IV AR of mismatched porcine forelimb VCA grafts, resulting in long term graft survival and demonstrates dose-dependent tolerability.

Chronic rejection of human face allografts.

Face vascularized composite allografts (FVCAs) have helped patients with severe facial disfigurement, with acute rejection now largely controlled through iatrogenic immunosuppression. However, little is known regarding the incidence and mechanism(s) of more long-term pathologic alterations in FVCAs that may affect function and graft durability. Protocol surveillance biopsy specimens for up to an 8-year interval in 7 patients who received FVCAs at our institution revealed histopathologic evidence of chronic rejection. Clinical manifestations included features of premature aging, mottled leukoderma accentuating suture lines, telangiectasia, and dryness of nasal mucosa. Pathologic changes consisted of epidermal thinning accompanied by discrete foci of lymphocyte-mediated cytotoxicity, hyperkeratosis, follicular plugging, vascular ectasia, and sclerosis beneath the epidermal layer associated with collagen type I deposition. Genomic interrogation and immunohistochemistry of sclerotic zones revealed upregulation of the AP-1 pathway components, JunB and c-Fos, previously implicated in overproduction of type I dermal collagen in the setting of systemic sclerosis. We conclude that some patients develop chronic rejection in FVCAs with striking similarities to alterations seen in certain autoimmune cutaneous disorders (lupus erythematosus and scleroderma/chronic sclerodermoid graft-versus-host disease). Identification of relevant pathways and genes, such as JunB and c-Fos, may provide new targets for preventative therapies for chronic immune-mediated changes in vascularized composite allografts.

Relative antigenicity of components in vascularized composite allotransplants: An experimental study of microRNAs expression in rat hind limb transplantation model.

BACKGROUND: Skin is considered to be the most antigenic component of all vascularized composite allotransplantation tissues. However, no studies have used methods other than histological assessment to analyze the relative antigenicity of various components. In this study, we analyzed gene expression to investigate the relative antigenicity of each component in the transplanted limb. METHODS: Seven Brown Norway rats and 31 Lewis rats were assigned to two groups: an allograft group and a syngeneic (control) group. Brown Norway rats were used as the allogeneic donors, and Lewis rats were used as the syngeneic donors and recipients. About 13 recipients in the allograft group and 12 recipients in the control group were analyzed. Histological assessment was performed in 5 of the recipients in each group, and microRNA expression was analyzed in the remaining recipients, except for 1 recipient in the syngeneic group. RESULTS: In the allograft group, the relative microRNA-146a expression was significantly higher in skin (2.34 ± 0.44) than in muscle (1.25 ± 0.22; p = .034) and bone (1; p = .0081). In the allograft group, microRNA-155 expression was significantly higher in skin (1.91 ± 0.18) than in bone (1; p = .010). Histological assessment showed that some skin tissue in the allograft group showed evidence of severe acute rejection. CONCLUSIONS: The microRNA-146a and microRNA-155 seemed to reflect the relative antigenicity during acute rejection of transplanted limbs. Skin seemed to be more antigenic than muscle and bone in both the histological assessment and gene expression analysis.

Abdominal Wall Transplant Surgery.

The evolution and success of intestinal and multi-visceral transplantation over the past 20 years have raised the issue of difficult or even impossible abdominal closure, a topic rarely encountered in other fields of transplantation. Different techniques have been proposed to address this topic. The choice depends on the transplant team's expertise and/or the availability of a plastic surgery service. Abdominal wall transplant is a type of composite tissue allograft that can be utilized to reconstitute the abdominal domains of patients who undergo intestinal transplant, and the results are encouraging. It is an effective option to achieve primary abdominal closure after intestinal transplant. In its full-thickness form, it may be useful for monitoring rejection or viability of visceral organs. Our aim is to review the role of abdominal wall transplant in achieving tension-free closure of the abdomen.