Composite tissue allotransplantation: opportunities and challenges

The contribution of the donor vascularised hand and face allograft in transplant rejection: An immunological perspective

Overcoming immunological rejection remains a barrier to the safe adoption of Vascularised Composite Allotransplantation (VCA). To mitigate this risk, clinical protocols have been derived from solid organ transplantation, targeting recipient immunomodulation, yet VCA is unique. Face and hand composite allografts are composed of multiple different tissues, each with their own immunological properties. Experimental work suggests that allografts carry variable numbers and populations of donor leukocytes in an organ specific manner. Ordinarily, these passenger leukocytes are transferred from the donor graft into the recipient circulation after transplantation. Whether alloantigen presentation manifests as acute allograft rejection or transplant tolerance is unknown. This review aims to characterise the immunological properties of the constituent parts of the donor face and hand, the potential fate of donor leukocytes and to consider theoretical graft specific interventions to mitigate early rejection.

Acute Rejection Rates in Vascularized Composite Allografts: A Systematic Review of Case Reports

INTRODUCTION

Vascularized Composite Allografts (VCA) are usually performed in a full major histocompatibility complex mismatch setting, with a risk of acute rejection depending on factors such as the type of immunosuppression therapy and the quality of graft preservation. In this systematic review, we present the different immunosuppression protocols used in VCA and point out relationships between acute rejection rates and possible factors that might influence it.

METHODS

This systematic review was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We systematically searched Medline (PubMed), Embase, and The Cochrane Library between November 2022 and February 2023, using following Mesh Terms: Transplant, Transplantation, Hand, Face, Uterus, Penis, Abdominal Wall, Larynx, and Composite Tissue Allografts. All VCA case reports and reviews describing multiple case reports were included.

RESULTS

We discovered 211 VCA cases reported. The preferred treatment was a combination of antithymocyte globulins, mycophenolate mofetil (MMF), tacrolimus, and steroids; and a combination of MMF, tacrolimus, and steroids for induction and maintenance treatment, respectively. Burn patients showed a higher acute rejection rate (P = 0.073) and were administered higher MMF doses (P = 0.020).

CONCLUSIONS

In contrast to previous statements, the field of VCA is not rapidly evolving, as it has encountered challenges in addressing immune-related concerns. This is highlighted by the absence of a standardized immunosuppression regimen. Consequently, more substantial data are required to draw more conclusive results regarding the immunogenicity of VCAs and the potential superiority of one immunosuppressive treatment over another. Future efforts should be made to report the VCA surgeries comprehensively, and muti-institutional long-term prospective follow-up studies should be performed to compare the number of acute rejections with influencing factors.

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

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

Immune modulation in transplant medicine: a comprehensive review of cell therapy applications and future directions

Balancing the immune response after solid organ transplantation (SOT) and vascularized composite allotransplantation (VCA) remains an ongoing clinical challenge. While immunosuppressants can effectively reduce acute rejection rates following transplant surgery, some patients still experience recurrent acute rejection episodes, which in turn may progress to chronic rejection. Furthermore, these immunosuppressive regimens are associated with an increased risk of malignancies and metabolic disorders. Despite significant advancements in the field, these IS related side effects persist as clinical hurdles, emphasizing the need for innovative therapeutic strategies to improve transplant survival and longevity. Cellular therapy, a novel therapeutic approach, has emerged as a potential pathway to promote immune tolerance while minimizing systemic side-effects of standard IS regiments. Various cell types, including chimeric antigen receptor T cells (CAR-T), mesenchymal stromal cells (MSCs), regulatory myeloid cells (RMCs) and regulatory T cells (Tregs), offer unique immunomodulatory properties that may help achieve improved outcomes in transplant patients. This review aims to elucidate the role of cellular therapies, particularly MSCs, T cells, Tregs, RMCs, macrophages, and dendritic cells in SOT and VCA. We explore the immunological features of each cell type, their capacity for immune regulation, and the prospective advantages and obstacles linked to their application in transplant patients. An in-depth outline of the current state of the technology may help SOT and VCA providers refine their perioperative treatment strategies while laying the foundation for further trials that investigate cellular therapeutics in transplantation surgery.

Novel approach for enhancing skin allograft survival by bioadhesive nanoparticles loaded with rapamycin

Skin graft rejection is a significant challenge in skin allografts for skin defects, particularly in extensive burn injury patients when autografts are insufficient. Enhancing the survival duration of allogeneic skin grafts can improve the success rate of subsequent autologous skin grafting, thereby promoting the therapeutic efficacy for wound healing. Rapamycin (Rapa), a potent immunosuppressant with favorable efficacy in organ transplantation, is limited by its systemic administration-associated toxicity and side effects. Therefore, addressing the short survival time of allogeneic skin grafts and minimizing the toxicity related to systemic application of immunosuppressive agents is an urgent requirement. Here, we present a topical formulation based on bioadhesive poly (lactic acid)-hyperbranched polyglycerol nanoparticles (BNPs) with surface-modified encapsulation of Rapamycin (Rapa/BNPs), applied for local immunosuppression in a murine model of allogeneic skin grafts. Our Rapa/BNPs significantly prolong nanoparticle retention, reduce infiltration of T lymphocytes and macrophages, decrease the level of pro-inflammatory cytokines and ultimately extend skin allograft survival with little systemic toxicity compared to free Rapa or Rapamycin-loaded non-bioadhesive nanoparticles (Rapa/NNPs) administration. In conclusion, Rapa/BNPs effectively deliver local immunosuppression and demonstrate potential for enhancing skin allograft survival while minimizing localized inflammation, thus potentially increasing patient survival rates for various types of skin defects.

Emerging strategies for tissue engineering in vascularized composite allotransplantation: A review

Vascularized composite allotransplantation (VCA), which can effectively improve quality of life, is a promising therapy for repair and reconstruction after face or body trauma. However, intractable issues are associated with VCA, such as the inevitable multiple immunogenicities of different tissues that cause severe rejection, the limited protocols available for clinical application, and the shortage of donor sources. The existing regimens used to extend the survival of patients receiving VCAs and suppress rejection are generally the lifelong application of immunosuppressive drugs, which have side effects. Consequently, studies aiming at tissue engineering methods for VCA have become a topic. In this review, we summarize the emerging therapeutic strategies for tissue engineering aimed to prolong the survival time of VCA grafts, delay the rejection and promote prevascularization and tissue regeneration to provide new ideas for future research on VCA treatment.

Application possibilities of artificial intelligence in facial vascularized composite allotransplantation-a narrative review

Facial vascularized composite allotransplantation (FVCA) is an emerging field of reconstructive surgery that represents a dogmatic shift in the surgical treatment of patients with severe facial disfigurements. While conventional reconstructive strategies were previously considered the goldstandard for patients with devastating facial trauma, FVCA has demonstrated promising short- and long-term outcomes. Yet, there remain several obstacles that complicate the integration of FVCA procedures into the standard workflow for facial trauma patients. Artificial intelligence (AI) has been shown to provide targeted and resource-effective solutions for persisting clinical challenges in various specialties. However, there is a paucity of studies elucidating the combination of FVCA and AI to overcome such hurdles. Here, we delineate the application possibilities of AI in the field of FVCA and discuss the use of AI technology for FVCA outcome simulation, diagnosis and prediction of rejection episodes, and malignancy screening. This line of research may serve as a fundament for future studies linking these two revolutionary biotechnologies.

Supercooling: A Promising Technique for Prolonged Organ Preservation in Solid Organ Transplantation, and Early Perspectives in Vascularized Composite Allografts

Ex-vivo preservation of transplanted organs is undergoing spectacular advances. Machine perfusion is now used in common practice for abdominal and thoracic organ transportation and preservation, and early results are in favor of substantially improved outcomes. It is based on decreasing ischemia-reperfusion phenomena by providing physiological or sub-physiological conditions until transplantation. Alternatively, supercooling techniques involving static preservation at negative temperatures while avoiding ice formation have shown encouraging results in solid organs. Here, the rationale is to decrease the organ's metabolism and need for oxygen and nutrients, allowing for extended preservation durations. The aim of this work is to review all advances of supercooling in transplantation, browsing the literature for each organ. A specific objective was also to study the initial evidence, the prospects, and potential applications of supercooling preservation in Vascularized Composite Allotransplantation (VCA). This complex entity needs a substantial effort to improve long-term outcomes, marked by chronic rejection. Improving preservation techniques is critical to ensure the favorable evolution of VCAs, and supercooling techniques could greatly participate in these advances.

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

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

Cellular activation pathways and interaction networks in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an evolving field of reconstructive surgery that has revolutionized the treatment of patients with devastating injuries, including those with limb losses or facial disfigurement. The transplanted units are typically comprised of different tissue types, including skin, mucosa, blood and lymphatic vasculature, muscle, and bone. It is widely accepted that the antigenicity of some VCA components, such as skin, is particularly potent in eliciting a strong recipient rejection response following transplantation. The fine line between tolerance and rejection of the graft is orchestrated by different cell types, including both donor and recipient-derived lymphocytes, macrophages, and other immune and donor-derived tissue cells (e.g., endothelium). Here, we delineate the role of different cell and tissue types during VCA rejection. Rejection of VCA grafts and the necessity of life-long multidrug immunosuppression remains one of the major challenges in this field. This review sheds light on recent developments in decoding the cellular signature of graft rejection in VCA and how these may, ultimately, influence the clinical management of VCA patients by way of novel therapies that target specific cellular processes.

A Patient-Centered Website (Within Reach) to Foster Informed Decision-making About Upper Extremity Vascularized Composite Allotransplantation: Development and Usability Study

BACKGROUND

Upper extremity (UE) vascularized composite allotransplantation (VCA; hand transplantation) is a reconstructive treatment option for patients with UE loss. Approximately 37 UE VCAs have been performed in the United States to date; thus, little is known about long-term psychosocial outcomes and whether the benefits outweigh the risks. To make an informed treatment decision, patients must understand the procedure, risks, and potential benefits of UE VCA. However, few educational resources are publicly available providing unbiased, comprehensive information about UE VCA.

OBJECTIVE

This paper described the development of a neutral, and accessible, educational website supporting informed decision-making about UE VCA as a treatment option for individuals with UE amputations.

METHODS

Website content development was informed by 9 focus groups conducted with individuals with UE amputations at 3 study sites. After initial website development, we conducted usability testing to identify ways to improve navigability, design, content, comprehension, and cultural sensitivity. Participants were administered the After-Scenario Questionnaire to assess user performance after completing navigational tasks, System Usability Scale to measure the perceived usability of the website, and Net Promoter Score to measure user satisfaction. Quantitative data were analyzed using descriptive statistics. Qualitative data were analyzed using rapid thematic analysis.

RESULTS

A total of 44 individuals with UE amputations participated in focus groups (n=37, 84%) and usability testing (n=14, 32%). Most participants in the focus groups and usability testing were male (24/37, 65% and 11/14, 79%, respectively) and White (27/37, 73% and 9/14, 64%, respectively), had unilateral limb loss (22/37, 59% and 12/14, 86%, respectively), and had mean ages of 48 (SD 9.2) and 50 (SD 12.0) years, respectively. Focus group results are organized into accessibility, website design, website development, website tone and values, sitemap, terminology, images and videos, and tables and graphics. Usability testing revealed that participants had a positive impression of the website. The mean After-Scenario Questionnaire score of 1.3 to 2.3 across task scenarios indicated high satisfaction with website usability, the mean System Usability Scale score of 88.9 indicated user satisfaction with website usability, and the mean Net Promoter Score of 9.6 indicated that users were enthusiastic and would likely refer individuals to the website.

CONCLUSIONS

The findings suggest that our educational website, Within Reach, provides neutral, patient-centered information and may be a useful resource about UE VCA for individuals with UE amputations, their families, and health care professionals. Health care professionals may inform UE VCA candidates about Within Reach to supplement current VCA education processes. Within Reach serves as a resource about treatment options for patients preparing for scheduled or recovering from traumatic UE amputations. Future research should assess whether Within Reach improves knowledge about UE VCA and enhances informed decision-making about UE VCA as a treatment option.

Regulatory T Cells: Liquid and Living Precision Medicine for the Future of VCA

Transplant rejection remains a challenge especially in the field of vascularized composite allotransplantation (VCA). To blunt the alloreactive immune response' stable levels of maintenance immunosupression are required. However' the need for lifelong immunosuppression poses the risk of severe side effects, such as increased risk of infection, metabolic complications, and malignancies. To balance therapeutic efficacy and medication side effects, immunotolerance promoting immune cells (especially regulatory T cells [Treg]) have become of great scientific interest. This approach leverages immune system mechanisms that usually ensure immunotolerance toward self-antigens and prevent autoimmunopathies. Treg can be bioengineered to express a chimeric antigen receptor or a T-cell receptor. Such bioengineered Treg can target specific antigens and thereby reduce unwanted off-target effects. Treg have demonstrated beneficial clinical effects in solid organ transplantation and promising in vivo data in VCAs. In this review, we summarize the functional, phenotypic, and immunometabolic characteristics of Treg and outline recent advancements and current developments regarding Treg in the field of VCA and solid organ transplantation.

Video Messaging to Increase Vascularized Composite Allograft Donation Willingness in United States Military Veterans

Expansion of vascularized composite allograft (VCA) transplantation depends on the public's willingness to donate VCA organs, including face, extremities, and genitourinary organs. This study evaluated the effectiveness of video messaging on VCA donation willingness in US military veterans, a key stakeholder in VCA transplantation.

Methods

Participants (n = 556) were randomized to 1 of 3 VCA video messaging interventions (informational, testimonial, or blended), a general (non-VCA) organ donation video message, or a control (nondonation) video message. Questionnaires were completed at pre- and postintervention and at 3-wk follow-up.

Results

Veterans exposed to any VCA video messaging were more likely to express VCA donation willingness (69%, n = 203/296) than those exposed to general donation messaging (53%, n = 47 of 89; P = 0.006) or No Donation Messaging (37%, n = 36 of 97; P < 0.001). A significantly higher proportion of participants who received Blended VCA Messaging were willing to be VCA donors, compared with the Informational VCA Messaging group (79% versus 61%, P = 0.006). Each VCA messaging video resulted in a significant pre- to postintervention increase in the proportion of participants willing to donate their own face, hands, and legs (P < 0.03).

Conclusions

Brief educational videos focused on VCA transplantation can have a demonstrable and verifiable impact on rates of VCA donation willingness in veterans.

Tacrolimus before CTLA4Ig and rapamycin promotes vascularized composite allograft survival in MGH miniature swine

BACKGROUND

We evaluated the outcome of vertical rectus abdominus myocutaneous flap (VRAM) allotransplantation in a mini-pig model, using a combined co-stimulation blockade (Co-SB) and mechanistic target of rapamycin inhibition (mTORi)-based regimen, with or without preceding calcineurin inhibition (CNI).

MATERIALS AND METHODS

VRAM allotransplants were performed between SLA-mismatched MGH miniature swine. Group A (n = 2) was treated continuously with the mTOR inhibitor rapamycin from day -1 in combination with the Co-SB agent cytotoxic T lymphocyte antigen 4-Ig (CTLA4-Ig) from post-operative day (POD) 0. In group B (n = 3), animals received tacrolimus daily from POD 0 to POD 13, followed by rapamycin daily from POD 7 and CTLA4-Ig weekly from POD 7-28. Graft rejection was determined by Banff criteria and host cellular and humoral immunity monitored.

RESULTS

In group A, allografts developed grade-I acute rejection by POD 2 and POD 7, and reached grade-IV by POD 17 and POD 20, respectively. By contrast, in group B, two allografts demonstrated grade-I rejection on POD 30 and grade-IV on POD 74, while the third exhibited grade-I rejection starting on POD 50, though this animal had to be euthanized on POD 58 due to Pneumocystis jirovecii infection. Time-to-event incidence of grade-I rejection was significantly lower in group A compared to group B. During the first 3 weeks post-transplant, no significant differences in anti-donor immunity were observed between the groups.

CONCLUSION

A short course of CNI, followed by combined Co-SB and mTORi significantly delays acute rejection of VRAM allografts in SLA-mismatched miniature swine.

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

BACKGROUND

Vascularized composite tissue allotransplantation (VCA) to replace limbs or faces damaged beyond repair is now possible. The resulting clear benefit to quality of life is a compelling reason to attempt this complex procedure. Unfortunately, the high doses of immunosuppressive drugs required to protect this type of allograft result in significant morbidity and mortality giving rise to ethical concerns about performing this surgery in patients with non-life-threatening conditions. Here we tested whether we could suppress anti-graft immune activity by using a safe β2 -adrenergic receptor (AR) agonist, terbutaline, to mimic the natural immune suppression generated by nervous system-induced signalling through AR.

METHODS

A heterotopic hind limb transplantation model was used with C57BL/6 (H-2b) as recipients and BALB/c (H-2d) mice as donors. To test the modulation of the immune response, graft survival was investigated after daily intraperitoneal injection of β2 -AR agonist with and without tacrolimus. Analyses of immune compositions and quantification of pro-inflammatory cytokines were performed to gauge functional immunomodulation. The contributions to allograft survival of β2 -AR signalling in donor and recipient tissue were investigated with β2 -AR-/- strains.

RESULTS

Treatment with the β2 -AR agonist delayed VCA rejection, even with a subtherapeutic dose of tacrolimus. β2 -AR agonist decreased T-cell infiltration into the transplanted grafts and decreased memory T-cell populations in recipient's circulation. In addition, decreased levels of inflammatory cytokines (IFN-γ, IL-6, TNF-α, CXCL-1/10 and CCL3/4/5/7) were detected following β2 -AR agonist treatment, and there was a decreased expression of ICAM-1 and vascular cell adhesion molecule-1 in donor stromal cells.

CONCLUSIONS

β2 -AR agonist can be used safely to mimic the natural suppression of immune responses, which occurs during adrenergic stress-signalling and thereby can be used in combination regimens to reduce the dose needed of toxic immunosuppressive drugs such as tacrolimus. This strategy can be further evaluated for feasibility in the clinic.

Genetic modification of limbs using ex vivo machine perfusion

Genetic engineering is a promising tool to repair genetic disorders, improve graft function or to reduce immune responses towards the allografts. Ex vivo organ perfusion systems have the potential to mitigate ischemic-reperfusion injury, prolong preservation time or even rescue organ function. We aim to combine both technologies to develop a modular platform allowing the genetic modification of vascularized composite (VC) allografts. Rat hind limbs were perfused ex vivo under subnormothermic conditions with lentiviral vectors. Specific perfusion conditions such as controlled pressure, temperature and flow rates were optimized to support the genetic modification of the limbs. Genetic modification was detected in vascular, muscular and dermal limb tissues. Remarkably, skin follicular and interfollicular keratinocytes as well as endothelial cells (ECs) showed stable transgene expression. Furthermore, levels of injury markers such as lactate, myoglobin and lactate dehydrogenase (LDH) as well as histological analyses showed that ex vivo limb perfusion with lentiviral vectors did not cause tissue damage and limb cytokine secretion signatures were not significantly affected. The use of ex vivo VC perfusion in combination with lentiviral vectors allows an efficient and stable genetic modification of limbs representing a robust platform to genetically engineer limbs towards increasing graft survival after transplantation.

Preservation solutions for attenuation of ischemia-reperfusion injury in vascularized composite allotransplantation

Vascularized composite allotransplantation represents the final level of the reconstructive ladder, offering treatment options for severe tissue loss and functional deficiencies. Vascularized composite allotransplantation is particularly susceptible to ischemia–reperfusion injury and requires preservation techniques when subjected to extended storage times prior to transplantation. While static cold storage functions to reduce ischemic damage and is widely employed in clinical settings, there exists no consensus on the ideal preservation solution for vascularized composite allotransplantation. This review aims to highlight current clinical and experimental advances in preservation solution development and their critical role in attenuating ischemia–reperfusion injury in the context of vascularized composite allotransplantation.

Limitations and limits and of vascularized composite allotransplantations: can we reach the holy grail?

PURPOSE OF REVIEW

In recent times, vascularized composite allotransplantation (VCA) have been gaining more attention and applications. Currently, VCA are at the highest level of the reconstruction pyramid, and thus the effects expected after them are intended to outweigh what the 'classical' reconstructive surgery can offer us, including even the most advanced microsurgical techniques.

RECENT FINDINGS

Over 40 patients have received a partial or full-face transplant. Others have received penis, uterus, larynx, abdominal wall, and lower extremity transplants. Each type of VCA has its own problems and limitations. However, resolving the limits defined by immunosuppression and improved donor selection would revolutionize all of them.

SUMMARY

Defining the limits and limitations of given procedures will not only allow for better preparation of transplant teams but will also help in determining the direction of future research.

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.

Mesenchymal stem cells transfected with sFgl2 inhibit the acute rejection of heart transplantation in mice by regulating macrophage activation

Background

Mesenchymal stem cells (MSCs) have become a promising candidate for cell-based immune therapy for acute rejection (AR) after heart transplantation due to possessing immunomodulatory properties. In this study, we evaluated the efficacy of soluble fibronectin-like protein 2 (sFgl2) overexpressing mesenchymal stem cells (sFgl2-MSCs) in inhibiting AR of heart transplantation in mice by regulating immune tolerance through inducing M2 phenotype macrophage polarization.

Methods and results

The sFgl2, a novel immunomodulatory factor secreted by regulatory T cells, was transfected into MSCs to enhance their immunosuppressive functions. After being co-cultured for 72 h, the sFgl2-MSCs inhibited M1 polarization whereas promoted M2 of polarization macrophages through STAT1 and NF-κB pathways in vitro. Besides, the sFgl2-MSCs significantly enhanced the migration and phagocytosis ability of macrophages stimulated with interferon-γ (IFN-γ) and lipopolysaccharide (LPS). Further, the application potential of sFgl2-MSCs in AR treatment was demonstrated by heterotopic cardiac transplantation in mice. The tissue damage and macrophage infiltration were evaluated by H&E and immunohistochemistry staining, and the secretion of inflammatory cytokines was analyzed by ELISA. The results showed that sFgl2-MSCs injected intravenously were able to locate in the graft, promote the M2 polarization of macrophages in vivo, regulate the local and systemic immune response, significantly protect tissues from damaging, and finally prolonged the survival time of mice heart grafts.

Conclusion

sFgl2-MSCs ameliorate AR of heart transplantation by regulating macrophages, which provides a new idea for the development of anti-AR treatment methods after heart transplantation.

Vascularized composite allotransplantation versus solid organ transplantation: innate-adaptive immune interphase

PURPOSE OF REVIEW

Vascularized composite allotransplantation (VCA), a life-enhancing treatment for patients with complex tissue defects, trauma or illness, expounds upon the foundation of solid organ transplantation (SOT), the gold standard in end-stage organ failure. As innate and adaptive immunity remain the fundamental concern, this review highlights divergent immunobiology responses in VCA and SOT recipients.

RECENT FINDINGS

Host innate immune activation drives peritransplant tissue ischemia-reperfusion injury (IRI). Despite the direct relationship between ischemia-reperfusion (IR)-stress and cell-mediated acute rejection, the mechanism of how IRI may affect VCA loss needs investigation. With skin grafts being highly immunogenic, the incidence of cell-mediated rejection is higher in VCA than SOT; whereas ex-vivo perfusion may exert cytoprotection against IRI in VCA and SOT. New treatment concepts, such as topical immunosuppression or cell-based tolerogenic therapies, may avoid systemic immunosuppression in VCA. Although antibody-mediated rejection is relatively rare in VCA and its disease seems to be distinct from that in SOT, little is known as to whether and how IRI may influence humoral immune rejection cascade in VCA or SOT.

SUMMARY

Further understanding of the innate-adaptive immune crosstalk should contribute to much needed development of novel therapies to improve VCA outcomes, based on strategies established in SOT.

The many shades of macrophages in regulating transplant outcome

The shift of emphasis from short-term to long-term graft outcomes has led to renewed interests in how the innate immune cells regulate transplant survival, an area that is traditionally dominated by T cells in the adaptive system. This shift is driven largely by the limited efficacy of current immunosuppression protocols which primarily target T cells in preventing chronic graft loss, as well as by the rapid advance of basic sciences in the realm of innate immunity. In fact, the innate immune cells have emerged as key players in the allograft response in various models, contributing to both graft rejection and graft acceptance. Here, we focus on the macrophages, highlighting their diversity, plasticity and emerging features in transplant models, as well as recent developments in our studies of diverse subsets of macrophages. We also discuss challenges, unsolved questions, and emerging approaches in therapeutically modulating macrophages in further improvement of transplant outcomes.

Targeted Migration of Human Adipose-Derived Stem Cells to Secondary Lymphoid Organs Enhances Their Immunomodulatory Effect and Prolongs the Survival of Allografted Vascularized Composites

The targeted delivery of therapeutic agents to secondary lymphoid organs (SLOs), which are the niches for immune initiation, provides an unprecedented opportunity for immune intolerance induction. The alloimmune rejection postvascularized composite allotransplantation (VCA) is mediated by T lymphocytes. Human adipose-derived stem cells (hASCs) possess the superiority of convenient availability and potent immunoregulatory property, but their therapeutic results in the VCA are unambiguous thus far. Chemokine receptor 7 (CCR7) can specifically guide immune cells migrating into SLOs. There, the genes of CCR7-GFP or GFP alone were introduced into hASCs by lentivirus. hASCs/CCR7 maintained the multidifferentiation and immunoregulatory abilities, but it gained the migration capacity elicited by secondary lymphoid organ chemokine (SCL) (CCR7 ligand) in vitro. Noteworthily, intravenously infused hASCs/CCR7 targetedly relocated in the T-cell aggression area in SLOs. In a rat VCA model, hASCs/GFP transfusion had a rare effect on the allografted vascularized composite. However, hASCs/CCR7 infusion potently prolonged the grafts' survival time. The ameliorated pathologic exhibition and the regulated inflammatory cytokines in the peripheral blood were also observed. The altered axis of Th1/Th2 and Tregs/Th17 in SLOs may underlie the downregulated rejection response. Moreover, the proteomic examination of splenic T lymphocytes also confirmed that hASCs/CCR7 decreased the proteins related to cytokinesis, lymphocyte proliferation, differentiation, and apoptotic process. In conclusion, our present study demonstrated that targeted migration of hASCs/CCR7 to SLOs highly intensifies their in vivo immunomodulatory effect in the VCA model for the first time. We believe this SLO-targeting strategy may improve the clinical therapeutic efficacy of hASC for allogeneic and autogenic immune disease. Stem Cells 2019;37:1581-1594.