Combined Anti-CD154/CTLA4Ig Costimulation Blockade-Based Therapy Induces Donor-Specific Tolerance to Vascularized Osteomyocutaneous Allografts

Reciprocal Donor-Recipient Strain Combinations Present Different Vascularized Composite Allotransplantation Outcomes in Rodent Models

BACKGROUND

Although vascularized composite allotransplantation (VCA) has been the focus of many animal studies, further research is needed to determine the potential for a generalized model and immunosuppression regimen that applies across different donor-recipient combinations. In this study, the authors evaluated the outcome of VCAs performed on reciprocal rodent donor-recipient combinations.

METHODS

VCA was performed in rats using Lewis and Brown Norway (BN) donor-recipient pairs, under the previously reported antilymphocyte serum/cyclosporine/adipose-derived stem cell regimen. Similarly, a published co-stimulatory blockade/rapamycin regimen was performed on the mouse VCA model between Balb/C and C57BL/6 strains.

RESULTS

To accommodate the active behaviors of BN recipients, the allograft had to be modified and inset to the neck instead of to the groin. The tolerogenic regimen did not provide the same benefits for BN rats as it did for Lewis recipients. Increasing antilymphocyte serum dose and extending the duration of cyclosporine administration from 10 to 21 days significantly prolonged allograft survival and induced donor-specific tolerance. In mice, the co-stimulatory blockade/rapamycin regimen produced inferior VCA outcomes in BALB/c recipients than in C57BL/6 recipients. In both rats and mice, the authors identified an association between the tolerance outcome and the peripheral chimerism measured on postoperative day 30.

CONCLUSIONS

Reciprocal donor-recipient combinations led to different responses toward the immunosuppression regimen and varied VCA outcomes. Sustained donor chimerism that remained in circulation for 1 month after surgery supported long-term VCA survival. Modification of the model and immunosuppression regimen accordingly is recommended.

CLINICAL RELEVANCE STATEMENT

Various donor-recipient combinations respond differently to the immunosuppression regimens. Maintaining donor chimerism for 30 days after surgery improves VCA survival. It is recommended to tailor the immunosuppression regimen based on the recipient's background to optimize outcomes.

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 (F4/80^hi+CD206^hi+MHCII^low), eosinophils (F4/80^lowSiglec-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.

IL-10 modified mRNA monotherapy prolongs survival after composite facial allografting through the induction of mixed chimerism

Vascularized composite allotransplantation has great potential in face transplantation by supporting functional restoration following tissue grafting. However, the need for lifelong administration of immunosuppressive drugs still limits its wide use. Modified mRNA (modRNA) technology provides an efficient and safe method to directly produce protein in vivo. Nevertheless, the use of IL-10 modRNA-based protein replacement, which exhibits anti-inflammatory properties, has not been shown to prolong composite facial allograft survival. In this study, IL-10 modRNA was demonstrated to produce functional IL-10 protein in vitro, which inhibited pro-inflammatory cytokines and in vivo formation of an anti-inflammatory environments. We found that without any immunosuppression, C57BL/6J mice with fully major histocompatibility complex (MHC)-mismatched facial allografts and local injection of IL-10 modRNA had a significantly prolonged survival rate. Decreased lymphocyte infiltration and pro-inflammatory T helper 1 subsets and increased anti-inflammatory regulatory T cells (Tregs) were seen in IL-10 modRNA-treated mice. Moreover, IL-10 modRNA induced multilineage chimerism, especially the development of donor Treg chimerism, which protected allografts from destruction because of recipient alloimmunity. These results support the use of monotherapy based on immunomodulatory IL-10 cytokines encoded by modRNA, which inhibit acute rejection and prolong allograft survival through the induction of donor Treg chimerism.

Tolerance Induction in Vascularized Composite Allotransplantation-A Brief Review of Preclinical Models

Pre-clinical studies are an obligatory tool to develop and translate novel therapeutic strategies into clinical practice. Acute and chronic rejection mediated by the recipient's immune system remains an important limiting factor for the (long-term) survival of vascularized composite allografts (VCA). Furthermore, high intensity immunosuppressive (IS) protocols are needed to mitigate the immediate and long-term effects of rejection. These IS regiments can have significant side-effects such as predisposing transplant recipients to infections, organ dysfunction and malignancies. To overcome these problems, tolerance induction has been proposed as one strategy to reduce the intensity of IS protocols and to thereby mitigate long-term effects of allograft rejection. In this review article, we provide an overview about animal models and strategies that have been used to induce tolerance. The induction of donor-specific tolerance was achieved in preclinical animal models and clinical translation may help improve short and long-term outcomes in VCAs in the future.

The intragraft vascularized bone marrow induces secondary donor-specific mystacial pad allograft tolerance

Introduction

Vascularized bone marrow (VBM) is essential in tolerance induction through chimerism. We hypothesized that the inclusion of VBM contributes to the induction of mystacial pad allotransplantation tolerance.

Method

In this study, 19 VBM, nine mystacial pad, and six sequential VBM and mystacial pad allografts were transplanted from Brown Norway (BN) rats to Lewis (LEW) rats to test our hypothesis. The VBM recipients were divided into antilymphocyte serum (ALS) monotherapy group (two doses of ALS on day 3 pretransplantation and day 1 posttransplantation), immunosuppressant group [a week of 2 mg/kg/day tacrolimus (Tac) and 3 weeks of 3 mg/kg/day rapamycin (RPM)], and combined therapy group. The mystacial pad recipients were divided into VBM and non-VBM transplantation groups, and both groups were treated with an immunosuppression regimen that consists of ALS, Tac, and RPM. For the recipients of sequential VBM and mystacial pad allotransplantations, additional Tac was given 1 week after mystacial pad transplantation. Allograft survival, donor-specific tolerance, and chimerism level were evaluated.

Results

With the administration of ALS and short-term Tac and RPM treatments, VBM recipients demonstrated long-term graft survival (>120 days) with persistent chimerism for 30 days. CD3+ T cells from tolerant rats showed donor-specific hyporesponsiveness and tolerance to donor skin grafts but not to third-party counterparts. Furthermore, mystacial pad graft recipients with VBM transplantation exhibited a higher allograft survival rate than those without VBM transplantation [median survival time (MST) >90 days vs. 70 days, p < 0.05].

Conclusion

This study demonstrated that VBM transplantation is an efficient strategy to induce and maintain donor-specific tolerance for an osseous-free allograft.

A systematic review of immunomodulatory strategies used in skin-containing preclinical vascularized composite allotransplant models

BACKGROUND

Acute rejection remains a vexing problem in vascularized composite allotransplantation (VCA). Available immunosuppressive regimens are successful at minimizing alloimmune response and allowing VCA in humans. However, repeated rejection episodes are common, and systemic side effects of the current standard regimen (Tacrolimus, MMF, Prednisone) are dose limiting. Novel immunomodulatory approaches to improve allograft acceptance and minimize systemic toxicity are continuously explored in preclinical models. We aimed to systematically summarize past and current approaches to help guide future research in this complex field.

METHODS

We conducted a systematic review of manuscripts listed in the MEDLINE and PubMed databases. For inclusion, articles had to primarily investigate the effect of a therapeutic approach on prolonging the survival of a skin-containing preclinical VCA model. Non-VCA studies, human trials, anatomical and feasibility studies, and articles written in a language other than English were excluded. We followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines.

RESULTS

The search retrieved 980 articles of which 112 articles were ultimately included. The majority of investigations used a rat model. An orthotopic hind limb VCA model was used in 53% of the studies. Cell and drug-based approaches were investigated 58 and 52 times, respectively. We provide a comprehensive review of immunomodulatory strategies used in VCA preclinical research over a timeframe of 44 years.

CONCLUSION

We identify a transition from anatomically non-specific to anatomical models mimicking clinical needs. As limb transplants have been most frequently performed, preclinical research focused on using the hind limb model. We also identify a transition from drug-based suppression therapies to cell-based immunomodulation strategies.

Preconditioned Mesenchymal Stromal Cells to Improve Allotransplantation Outcome

Mesenchymal stromal cells (MSCs) are tissue-derived progenitor cells with immunomodulatory as well as multilineage differentiation capacities, and have been widely applied as cellular therapeutics in different disease systems in both preclinical models and clinical studies. Although many studies have applied MSCs in different types of allotransplantation, the efficacy varies. It has been demonstrated that preconditioning MSCs prior to in vivo administration may enhance their efficacy. In the field of organ/tissue allotransplantation, many recent studies have shown that preconditioning of MSCs with (1) pretreatment with bioactive factors or reagents such as cytokines, or (2) specific gene transfection, could prolong allotransplant survival and improve allotransplant function. Herein, we review these preconditioning strategies and discuss potential directions for further improvement.

Large Animal Models of Vascularized Composite Allotransplantation: A Review of Immune Strategies to Improve Allograft Outcomes

Over the past twenty years, significant technical strides have been made in the area of vascularized composite tissue allotransplantation (VCA). As in solid organ transplantation, the allogeneic immune response remains a significant barrier to long-term VCA survival and function. Strategies to overcome acute and chronic rejection, minimize immunosuppression and prolong VCA survival have important clinical implications. Historically, large animals have provided a valuable model for testing the clinical translatability of immune modulating approaches in transplantation, including tolerance induction, co-stimulation blockade, cellular therapies, and ex vivo perfusion. Recently, significant advancements have been made in these arenas utilizing large animal VCA models. In this comprehensive review, we highlight recent immune strategies undertaken to improve VCA outcomes with a focus on relevant preclinical large animal models.

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.

The intragraft vascularized bone marrow component plays a critical role in tolerance induction after reconstructive transplantation

The role of the vascularized bone marrow component as a continuous source of donor-derived hematopoietic stem cells that facilitate tolerance induction of vascularized composite allografts is not completely understood. In this study, vascularized composite tissue allograft transplantation outcomes between recipients receiving either conventional bone marrow transplantation (CBMT) or vascularized bone marrow (VBM) transplantation from Balb/c (H2d) to C57BL/6 (H2b) mice were compared. Either high- or low-dose CBMT (1.5 × 108 or 3 × 107 bone marrow cells, respectively) was applied. In addition, recipients were treated with costimulation blockade (1 mg anti-CD154 and 0.5 mg CTLA4Ig on postoperative days 0 and 2, respectively) and short-term rapamycin (3 mg/kg/day for the first posttransplant week and then every other day for another 3 weeks). Similar to high-dose conventional bone marrow transplantation, 5/6 animals in the vascularized bone marrow group demonstrated long-term allograft survival (>120 days). In contrast, significantly shorter median survival was noted in the low-dose CBMT group (~64 days). Consistently high chimerism levels were observed in the VBM transplantation group. Notably, low levels of circulating CD4+ and CD8+ T cells and a higher ratio of Treg to Teff cells were maintained in VBM transplantation and high-dose CBMT recipients (>30 days) but not in low-dose VBM transplant recipients. Donor-specific hyporesponsiveness was shown in tolerant recipients in vitro. Removal of the vascularized bone marrow component after secondary donor-specific skin transplantation did not affect either primary allograft or secondary skin graft survival.

The past the present and the future of face transplantation

PURPOSE OF REVIEW

Face transplantation represents vascularized composite allotransplantation (VCA) organ and became one of the most rewarding reconstructive options for severely disfigured patients. This review summarizes the past, current and future challenges of face transplantation, based on our experience and literature reports.

RECENT FINDINGS

In 2005, first partial face transplantation was reported by French team. In 2008, we have performed the US first near-total face transplantation. Currently, more than 40 face transplant cases were reported worldwide. Based on the outcomes of our three patients and the literature reports, face transplantation improved aesthetics, function and the quality of life of face transplant patients. However, there are still many challenges encountered including the side effects of immunosuppressive protocols, the psychological and social problems as well as the financial challenges which need to be address in the near future to maintain face transplantation in the armamentarium of reconstructive surgery.

SUMMARY

Currently, feasibility of face transplantation was confirmed; however, the life-long immunosuppressive protocols bearing serious side effects are still required to prevent face rejection. Thus, for the future of face and other VCA, novel approaches of cell-based therapies or engineered scaffolds should be developed to make face transplantation safer.

Costimulation Blockade in Vascularized Composite Allotransplantation

Vascular composite allotransplantation (VCA) is a field under research and has emerged as an alternative option for the repair of severe disfiguring defects that result from infections or traumatic amputation in a selected group of patients. VCA is performed in centers with appropriate expertise, experience and adequate resources to effectively manage the complexity and complications of this treatment. Lifelong immunosuppressive therapy, immunosuppression associated complications, and the effects of the host immune response in the graft are major concerns in VCA. VCA is considered a quality of life transplant and the risk-benefit ratio is dissimilar to life saving transplants. Belatacept seems a promising drug that prolongs patient and graft survival in kidney transplantation and it could also be an alternative approach to VCA immunosuppression. In this review, we are summarizing current literature about the role of costimulation blockade, with a focus on belatacept in VCA.

Efficacy of single-agent immunosuppressive regimens in a murine model of vascularized composite allotransplantation

We herein investigate the safety and efficacy of single-agent anti-rejection regimens in a mouse vascularized composite allotransplantation (VCA) model. Orthotopic hind-limb transplantations (Balb/c → C57BL/6) were performed using 6- to 8-week-old mice. A thirty-day regimen of either rapamycin, tacrolimus (both 1, 3, 5 mg/kg/day) or cyclosporine (25, 35, 50 mg/kg/day) was used. Primary endpoints were animal and graft survival, and secondary chimerism and regulatory T-cell levels. For rapamycin and tacrolimus given at 1, 3, and 5 mg/kg/day, median graft survival time (MST) was 23 days (18-28 days), 30 days (23-30 days), and 30 d (30-30 days) and 14 days (13-18 days), 30 days (16-30 days), and 30 days (30-30 days), respectively. For cyclosporine dosed at 25 and 35 mg/kg/day, MST was 15 days (12-18 days) and 21 days (14-27 days). Toxicity from CsA 50 mg/kg led to 100% mortality. Mixed chimerism levels were higher in rapamycin-treated animals than in tacrolimus-treated recipients (P = 0.029). Tacrolimus was superior in preventing leukocyte recruitment to the allograft. In murine VCA, no standardized immunosuppressive regimen exists, limiting comparability of outcomes and survival. Our data demonstrate that rapamycin and tacrolimus maintenance treatment at 5 mg/kg/day both yielded allograft survival (<grade 3 rejection) in all animals. Rapamycin displayed less toxicity and maintained mixed chimerism but was not as potent in controlling leukocyte recruitment compared with tacrolimus.

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 (0.5 mg/kg) for 14 days and were assigned to 4 groups: controls (CTRL) received no conditioning; ASC-group received CTLA4-Ig (10 mg/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 (50 mg/kg ip, POD 3); the ASC-ALS-group received CTLA4-Ig, ASCs plus ALS (500 µL ip, POD 1, 5). Banff grade III or 120 days were endpoints. ASCs suppressed alloresponse in vitro. Median rejection-free VCA survival was 28 days 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 T_regs , 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.

Vascularized composite allotransplantation combined with costimulation blockade induces mixed chimerism and reveals intrinsic tolerogenic potential

Vascularized composite allotransplantation (VCA) has become a valid therapeutic option to restore form and function after devastating tissue loss. However, the need for high-dose multidrug immunosuppression to maintain allograft survival is still hampering more widespread application of VCA. In this study, we investigated the immunoregulatory potential of costimulation blockade (CoB; CTLA4-Ig and anti-CD154 mAb) combined with nonmyeoablative total body irradiation (TBI) to promote allograft survival of VCA in a fully MHC-mismatched mouse model of orthotopic hind limb transplantation. Compared with untreated controls (median survival time [MST] 8 days) and CTLA4-Ig treatment alone (MST 17 days), CoB treatment increased graft survival (MST 82 days), and the addition of nonmyeloablative TBI led to indefinite graft survival (MST > 210 days). Our analysis suggests that VCA-derived BM induced mixed chimerism in animals treated with CoB and TBI + CoB, promoting gradual deletion of alloreactive T cells as the underlying mechanism of long-term allograft survival. Acceptance of donor-matched secondary skin grafts, decreased ex vivo T cell responsiveness, and increased graft-infiltrating Tregs further indicated donor-specific tolerance induced by TBI + CoB. In summary, our data suggest that vascularized BM-containing VCAs are immunologically favorable grafts promoting chimerism induction and long-term allograft survival in the context of CoB.

ECDI-fixed donor splenocytes prolong skin allograft survival by promoting M2 macrophage polarization and inducing regulatory T cells

Rejection is a common complication of allogeneic tissue transplantation. Fixation of splenocytes (SP) with 1-ethyl-3-(3'-dimethylaminopropyl)-carbodiimide (ECDI) induces immune tolerance in recipients post-transplantation; however, the mechanism underlying this effect remains unclear. Here, we determined the mechanisms of ECDI-fixed donor SP (ECDI-SP) in inducing tolerance in skin allograft transplantation. C57BL/6-recipient mice that received Balb/c full-thickness skin transplants with two infusions of donor-derived ECDI-SP, along with rapamycin showed superior skin allograft survival and lower inflammatory cell infiltration than mice that received rapamycin-only treatment. In ECDI-SP-treated mice, the levels of anti-inflammatory cytokines such as interleukin (IL)-10 in sera were markedly increased, whereas the expression of inflammatory cytokines was significantly suppressed. Splenic macrophages were significantly polarized to the alternative activated macrophage (M2) phenotype, with expansion of CD4+Foxp3+ regulatory T cells (Tregs) in the spleen and draining lymph nodes. Allostimulatory activity of ECDI-SP in vitro and donor-specific ex vivo hyporesponsiveness were observed. C57BL/6 macrophages engulfed allogeneic Balb/c-derived ECDI-SP, polarized to the M2 phenotype, with pronounced cAMP response element-binding (CREB) protein phosphorylation. By facilitating increased IL-10 expression, ECDI-SP induced M2 polarization and Treg production, inhibiting effector T-cell proliferation. Thus, ECDI-SP modulates macrophage M2 polarization by increasing CREB phosphorylation and promoting Treg production to suppress allogeneic skin graft rejection.

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 (T_reg). 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 T_reg 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.

Mechanisms of rejection in vascular composite allotransplantation

PURPOSE OF REVIEW

For patients with devastating injuries in whom standard reconstruction is not an option, vascularized composite allotransplantation (VCA) has become a viable means of restoring form and function. However, immunological rejection continues to be a problem in VCA and has not yet been fully characterized. As the field is relatively new, much of the data on rejection and immunosuppression have been extrapolated from that of solid organ transplantation. In this review, we cover the basic mechanisms of rejection as they relate specifically to VCA with analysis of recent literature and future directions.

RECENT FINDINGS

Recent clinical studies have supported previously postulated T-cell-mediated mechanism of acute rejection and have also made strides in differentiating rejection from inflammation from other skin conditions and with different treatment regimens. Antibody-mediated rejection has been described in recent cases as well as treatment of presensitized patients receiving VCAs. With more long-term grafts, chronic changes, including vasculopathy, are being reported.

SUMMARY

Clinically observed types of rejection in VCA include mainly cell-mediated, antibody-mediated and chronic rejection. Advances in diagnosis and treatment of rejection have been made, but there is still much to be learned about VCA-specific rejection.

Complement factor and T-cell interactions during alloimmune inflammation in transplantation

Complement factor and T-cell signaling during an effective alloimmune response plays a key role in transplant-associated injury, which leads to the progression of chronic rejection (CR). During an alloimmune response, activated complement factors (C3a and C5a) bind to their corresponding receptors (C3aR and C5aR) on a number of lymphocytes, including T-regulatory cells (Tregs), and these cell-molecular interactions have been vital to modulate an effective immune response to/from Th1-effector cell and Treg activities, which result in massive inflammation, microvascular impairments, and fibrotic remodeling. Involvement of the complement-mediated cell signaling during transplantation signifies a crucial role of complement components as a key therapeutic switch to regulate ongoing inflammatory state, and further to avoid the progression of CR of the transplanted organ. This review highlights the role of complement-T cell interactions, and how these interactions shunt the effector immune response during alloimmune inflammation in transplantation, which could be a novel therapeutic tool to protect a transplanted organ and avoid progression of CR.

Blimp-1 prolongs allograft survival without regimen via influencing T cell development in favor of regulatory T cells while suppressing Th1

BACKGROUND

B lymphocyte-induced maturation protein 1 (Blimp-1) transcription factor is expressed in multiple cell lineages and in particular, T cells. However, the role of Blimp-1 in T cell-mediated allograft tolerance is still unknown.

METHODS

This study is the first to investigate transplanted skin allograft survival using transgenic (Tg) mice with T cell overexpression of Blimp-1.

RESULTS

Without any immunosuppression, fully MHC-mismatched skin allografts on Tg(+) mice had a significantly prolonged survival rate and partial tolerance at 90 days. Allograft lymphocytic infiltration was decreased in Tg(+) mice and a dampened donor-stimulated alloimmune response was seen. An absolute cell number ratio of inflammatory Th1 and Th17 cells against anti-inflammatory regulatory T (Treg) and IL-10-producing T cells, as well as cytolytic proteins, were significantly decreased in lymphoid organs and allograft. Blimp-1 transgenic T cells displayed an increased Treg differentiation capability and enhanced suppression of T cell proliferation. Overexpression of Blimp-1 in T cells promoted the formation of an anti-inflammatory cell-cytokine composition, both systemically and locally via transcription factor modulation such as T-bet downregulation and FoxP3 upregulation.

DISCUSSION

As such, allograft survival was made possible due to Th1 suppression and Treg amplification with the creation of an 'allograft protective microenvironment'.

Evolution of an evidence-based supermicrosurgery simulation training curriculum: A systematic review

BACKGROUND

Supermicrosurgery (SM) involves operating on vessels with calibers from 0.3-0.8 mm. SM requires skills beyond those of conventional microsurgery. Current microsurgery courses do not prepare a junior surgeon for such a challenge. Several models have been developed to assist in the early learning curve, but their true purpose, benefit, and validation have not been addressed. This systematic literature review summarizes the existing SM simulation models, and their likely impact on microsurgery training for small-caliber vessel-based procedures is assessed.

METHODS

An electronic literature search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. From the literature search, 90 potential articles from MEDLINE and 300 articles from other databases were identified and screened. Twenty-five studies were screened against the inclusion criteria by two independent reviewers for a final critical analysis.

RESULTS

Thirty-six articles were included in the reviewing process, and 15 SM simulation training models were identified. The simulation models were classified as nonbiological or biological and as ex vivo or in vivo. None of these models demonstrated validity. However, critical analysis of the full-text articles established the clinical correlation of each model along with the specific skill demonstrated. A novel ladder-based curriculum was established. Further, an expert's questionnaire generated a Likert scale and the clinical impact of each SM simulation training model.

CONCLUSION

This is the first review to highlight the clinical relevance of SM models and the need for validation. Currently, a variety of training models in SM appear to enable the acquisition of specific skills, and the clinical impact of a selection is recognized in a proposed SM simulation training curriculum.

Split Tolerance in a Murine Model of Heterotopic En Bloc Chest Wall Transplantation

Background

Congenital and acquired chest wall deformities represent a significant challenge to functional reconstruction and may impact feasibility of heart transplantation for patients with end-stage organ failure. In the recent past, the concept of replacing like-with-like tissue by using vascularized composite allografts (VCA) has been enthusiastically employed for reconstruction of complex tissue defects.

Methods

In this study, we introduce a novel murine model for en bloc chest wall, heart, and thymus transplantation and thereby the use of complex tissue allografts for reconstruction of both chest wall defects and also end-stage organ failure. Additionally, this model allows us to study the features of combined vascularized bone marrow (VBM), thymus, and heart transplantation on allograft survival and function. Heterotopic chest wall, thymus, and heart transplants were performed in untreated syngeneic and allogeneic combinations and in allogeneic combinations treated with costimulation blockade (CTLA4-Ig and MR-1).

Results

Indefinite (ie, 150 d, N = 3) graft survival was observed in syngeneic controls. In untreated recipients of allogeneic grafts, the skin component was rejected after 10 (±1) days, whereas rejection of the heart occurred after 13 (± 1) days (N = 3). Costimulation blockade treatment prolonged survival of the heart and chest wall component (130 d, N = 3) as well as the VBM niche as evidenced by donor-specific chimerism (average: 2.35 ± 1.44%), whereas interestingly, the skin component was rejected after 13 (±1) days.

Conclusion

Thus, this novel microsurgical model of VCA combined with solid organ transplantation is technically feasible and results in split tolerance when treated with costimulatory blockade.

Longitudinal immunological characterization of the first presensitized recipient of a face transplant

Rejection affects greater than 80% of face transplants, yet no diagnostic criteria for antibody-mediated rejection (AMR) following face transplantation have been established. Given that different treatment strategies are required to address AMR and T cell-mediated rejection (TCMR), there is a critical need to delineate the features that can differentiate these two alloimmune responses. Here, we report the longitudinal immunological examination of what we believe to be the first and only highly sensitized recipient of a crossmatch-positive face transplant up to 4 years following transplantation. We conducted gene expression profiling on allograft biopsies collected during suspected AMR and TCMR episodes as well as during 5 nonrejection time points. Our data suggest that there are distinctive molecular features in AMR, characterized by overexpression of endothelial-associated genes, including ICAM1, VCAM1, and SELE. Although our findings are limited to a single patient, these findings highlight the potential importance of developing and implementing molecular markers to differentiate AMR from TCMR to guide clinical management. Furthermore, our case illustrates that molecular assessment of allograft biopsies offers the potential for new insights into the mechanisms underlying rejection. Finally, our medium-term outcomes demonstrate that face transplantation in a highly sensitized patient with a positive preoperative crossmatch is feasible and manageable.