Local Injections of Tacrolimus-loaded Hydrogel Reduce Systemic Immunosuppression-related Toxicity in Vascularized Composite Allotransplantation

Drug delivery strategies for local immunomodulation in transplantation: Bridging the translational gap

Drug delivery strategies for local immunomodulation hold tremendous promise compared to current clinical gold-standard systemic immunosuppression as they could improve the benefit to risk ratio of life-saving or life-enhancing transplants. Such strategies have facilitated prolonged graft survival in animal models at lower drug doses while minimizing off-target effects. Despite the promising outcomes in preclinical animal studies, progression of these strategies to clinical trials has faced challenges. A comprehensive understanding of the translational barriers is a critical first step towards clinical validation of effective immunomodulatory drug delivery protocols proven for safety and tolerability in pre-clinical animal models. This review overviews the current state-of-the-art in local immunomodulatory strategies for transplantation and outlines the key challenges hindering their clinical translation.

Thermosensitive Hydrogels as Targeted and Controlled Drug Delivery Systems: Potential Applications in Transplantation

Drug delivery in transplantation plays a vital role in promoting graft survival, preventing rejection, managing complications, and contributing to positive patient outcomes. Targeted and controlled drug delivery can minimize systemic effects. Thermosensitive hydrogels, due to their unique sol-gel transition properties triggered by thermo-stimuli, have attracted significant research interest as a potential drug delivery system in transplantation. This review describes the current status, characteristics, and recent applications of thermosensitive hydrogels for drug delivery. Studies aimed at improving allotransplantation outcomes using thermosensitive hydrogels are then elaborated on. Finally, the challenges and opportunities associated with their use are discussed. Understanding the progress of research will serve as a guide for future improvements in their application as a means of targeted and controlled drug delivery in translational therapeutic applications for transplantation.

Nanotechnology-based Strategies for Molecular Imaging, Diagnosis, and Therapy of Organ Transplantation

Organ transplantation is the preferred paradigm for patients with end-stage organ failures. Despite unprecedented successes, complications such as immune rejection, ischemia-reperfusion injury, and graft dysfunction remain significant barriers to long-term recipient survival after transplantation. Conventional immunosuppressive drugs have limited efficacy because of significant drug toxicities, high systemic immune burden, and emergence of transplant infectious disease, leading to poor quality of life for patients. Nanoparticle-based drug delivery has emerged as a promising medical technology and offers several advantages by enhancing the delivery of drug payloads to their target sites, reducing systemic toxicity, and facilitating patient compliance over free drug administration. In addition, nanotechnology-based imaging approaches provide exciting diagnostic methods for monitoring molecular and cellular changes in transplanted organs, visualizing immune responses, and assessing the severity of rejection. These noninvasive technologies are expected to help enhance the posttransplantation patient survival through real time and early diagnosis of disease progression. Here, we present a comprehensive review of nanotechnology-assisted strategies in various aspects of organ transplantation, including organ protection before transplantation, mitigation of ischemia-reperfusion injury, counteraction of immune rejection, early detection of organ dysfunction posttransplantation, and molecular imaging and diagnosis of immune rejection.

A local drug delivery system prolongs graft survival by dampening T cell infiltration and neutrophil extracellular trap formation in vascularized composite allografts

Introduction

The standard treatment for preventing rejection in vascularized composite allotransplantation (VCA) currently relies on systemic immunosuppression, which exposes the host to well-known side effects. Locally administered immunosuppression strategies have shown promising results to bypass this hurdle. Nevertheless, their progress has been slow, partially attributed to a limited understanding of the essential mechanisms underlying graft rejection. Recent discoveries highlight the crucial involvement of innate immune components, such as neutrophil extracellular traps (NETs), in organ transplantation. Here we aimed to prolong graft survival through a tacrolimus-based drug delivery system and to understand the role of NETs in VCA graft rejection.

Methods

To prevent off-target toxicity and promote graft survival, we tested a locally administered tacrolimus-loaded on-demand drug delivery system (TGMS-TAC) in a multiple MHC-mismatched porcine VCA model. Off-target toxicity was assessed in tissue and blood. Graft rejection was evaluated macroscopically while the complement system, T cells, neutrophils and NETs were analyzed in graft tissues by immunofluorescence and/or western blot. Plasmatic levels of inflammatory cytokines were measured using a Luminex magnetic-bead porcine panel, and NETs were measured in plasma and tissue using DNA-MPO ELISA. Lastly, to evaluate the effect of tacrolimus on NET formation, NETs were induced in-vitro in porcine and human peripheral neutrophils following incubation with tacrolimus.

Results

Repeated intra-graft administrations of TGMS-TAC minimized systemic toxicity and prolonged graft survival. Nevertheless, signs of rejection were observed at endpoint. Systemically, there were no increases in cytokine levels, complement anaphylatoxins, T-cell subpopulations, or neutrophils during rejection. Yet, tissue analysis showed local infiltration of T cells and neutrophils, together with neutrophil extracellular traps (NETs) in rejected grafts. Interestingly, intra-graft administration of tacrolimus contributed to a reduction in both T-cellular infiltration and NETs. In fact, in-vitro NETosis assessment showed a 62-84% reduction in NETs after stimulated neutrophils were treated with tacrolimus.

Conclusion

Our data indicate that the proposed local delivery of immunosuppression avoids off-target toxicity while prolonging graft survival in a multiple MHC-mismatch VCA model. Furthermore, NETs are found to play a role in graft rejection and could therefore be a potential innovative therapeutic target.

Transcriptome profiling of immune rejection mechanisms in a porcine vascularized composite allotransplantation model

Background

Vascularized composite allotransplantation (VCA) offers the potential for a biological, functional reconstruction in individuals with limb loss or facial disfigurement. Yet, it faces substantial challenges due to heightened immune rejection rates compared to solid organ transplants. A deep understanding of the genetic and immunological drivers of VCA rejection is essential to improve VCA outcomes.

Methods

Heterotopic porcine hindlimb VCA models were established and followed until reaching the endpoint. Skin and muscle samples were obtained from VCA transplant recipient pigs for histological assessments and RNA sequencing analysis. The rejection groups included recipients with moderate pathological rejection, treated locally with tacrolimus encapsulated in triglycerol-monostearate gel (TGMS-TAC), as well as recipients with severe end-stage rejection presenting evident necrosis. Healthy donor tissue served as controls. Bioinformatics analysis, immunofluorescence, and electron microscopy were utilized to examine gene expression patterns and the expression of immune response markers.

Results

Our comprehensive analyses encompassed differentially expressed genes, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes pathways, spanning various composite tissues including skin and muscle, in comparison to the healthy control group. The analysis revealed a consistency and reproducibility in alignment with the pathological rejection grading. Genes and pathways associated with innate immunity, notably pattern recognition receptors (PRRs), damage-associated molecular patterns (DAMPs), and antigen processing and presentation pathways, exhibited upregulation in the VCA rejection groups compared to the healthy controls. Our investigation identified significant shifts in gene expression related to cytokines, chemokines, complement pathways, and diverse immune cell types, with CD8 T cells and macrophages notably enriched in the VCA rejection tissues. Mechanisms of cell death, such as apoptosis, necroptosis and ferroptosis were observed and coexisted in rejected tissues.

Conclusion

Our study provides insights into the genetic profile of tissue rejection in the porcine VCA model. We comprehensively analyze the molecular landscape of immune rejection mechanisms, from innate immunity activation to critical stages such as antigen recognition, cytotoxic rejection, and cell death. This research advances our understanding of graft rejection mechanisms and offers potential for improving diagnostic and therapeutic strategies to enhance the long-term success of VCA.

Tacrolimus-loaded Drug Delivery Systems in Vascularized Composite Allotransplantation: Lessons and Opportunities for Local Immunosuppression

Long-term systemic immunosuppression is needed for vascularized composite allotransplantation (VCA). The high rate of acute rejection episodes in the first posttransplant year, the development of chronic rejection, and the adverse effects that come along with this treatment, currently prevent a wider clinical application of VCA. Opportunistic infections and metabolic disturbances are among the most observed side effects in VCA recipients. To overcome these challenges, local immunosuppression using biomaterial-based drug delivery systems (DDS) have been developed. The aim of these systems is to provide high local concentrations of immunosuppressive drugs while reducing their systemic load. This review provides a summary of recently investigated local DDS with different mechanisms of action such as on-demand, ultrasound-sensitive, or continuous drug delivery. In preclinical models, ranging from rodent to porcine and nonhuman primate models, this approach has been shown to reduce systemic tacrolimus (TAC) load and adverse effects, while prolonging graft survival. Localized immunosuppression using biomaterial-based DDS represents an encouraging approach to enhance graft survival and reduce toxic side effects of immunosuppressive drugs in VCA patients. Preclinical models using TAC-releasing DDS have demonstrated high local immunosuppressive effects with a low systemic burden. However, to reduce acute rejection events in translational animal models or in the clinical reality, the use of additional low-dose systemic TAC treatment may be envisaged. Patients may benefit through efficient graft immunosuppression and survival with negligible systemic adverse effects, resulting in better compliance and quality of life.

Immunoprotection of cellular transplants for autoimmune type 1 diabetes through local drug delivery

Type 1 diabetes mellitus (T1DM) is an autoimmune condition that results in the destruction of insulin-secreting β cells of the islets of Langerhans. Allogeneic islet transplantation could be a successful treatment for T1DM; however, it is limited by the need for effective, permanent immunosuppression to prevent graft rejection. Upon transplantation, islets are rejected through non-specific, alloantigen specific, and recurring autoimmune pathways. Immunosuppressive agents used for islet transplantation are generally successful in inhibiting alloantigen rejection, but they are suboptimal in hindering non-specific and autoimmune pathways. In this review, we summarize the challenges with cellular immunological rejection and therapeutics used for islet transplantation. We highlight agents that target these three immune rejection pathways and how to package them for controlled, local delivery via biomaterials. Exploring macro-, micro-, and nano-scale immunomodulatory biomaterial platforms, we summarize their advantages, challenges, and future directions. We hypothesize that understanding their key features will help identify effective platforms to prevent islet graft rejection. Outcomes can further be translated to other cellular therapies beyond T1DM.

Emerging strategies to bypass transplant rejection via biomaterial-assisted immunoengineering: Insights from islets and beyond

Novel transplantation techniques are currently under development to preserve the function of impaired tissues or organs. While current technologies can enhance the survival of recipients, they have remained elusive to date due to graft rejection by undesired in vivo immune responses despite systemic prescription of immunosuppressants. The need for life-long immunomodulation and serious adverse effects of current medicines, the development of novel biomaterial-based immunoengineering strategies has attracted much attention lately. Immunomodulatory 3D platforms can alter immune responses locally and/or prevent transplant rejection through the protection of the graft from the attack of immune system. These new approaches aim to overcome the complexity of the long-term administration of systemic immunosuppressants, including the risks of infection, cancer incidence, and systemic toxicity. In addition, they can decrease the effective dose of the delivered drugs via direct delivery at the transplantation site. In this review, we comprehensively address the immune rejection mechanisms, followed by recent developments in biomaterial-based immunoengineering strategies to prolong transplant survival. We also compare the efficacy and safety of these new platforms with conventional agents. Finally, challenges and barriers for the clinical translation of the biomaterial-based immunoengineering transplants and prospects are discussed.

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

Background

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

Methods

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

Results

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

Conclusion

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

Local delivery of FK506 to a nerve allograft is comparable to systemic delivery at suppressing allogeneic graft rejection

The objective of this study was to determine if locally delivered FK506 could prevent allogeneic nerve graft rejection long enough to allow axon regeneration to pass through the nerve graft. An 8mm mouse sciatic nerve gap injury repaired with a nerve allograft was used to assess the effectiveness of local FK506 immunosuppressive therapy. FK506-loaded poly(lactide-co-caprolactone) nerve conduits were used to provide sustained local FK506 delivery to nerve allografts. Continuous and temporary systemic FK506 therapy to nerve allografts, and autograft repair were used as control groups. Serial assessment of inflammatory cell and CD4+ cell infiltration into the nerve graft tissue was performed to characterize the immune response over time. Nerve regeneration and functional recovery was serially assessed by nerve histomorphometry, gastrocnemius muscle mass recovery, and the ladder rung skilled locomotion assay. At the end of the study, week 16, all the groups had similar levels of inflammatory cell infiltration. The local FK506 and continuous systemic FK506 groups had similar levels of CD4+ cell infiltration, however, it was significantly greater than the autograft control. In terms of nerve histmorphometry, the local FK506 and continunous systemic FK506 groups had similar amounts of myelinated axons, although they were significantly lower than the autograft and temporary systemic FK506 group. The autograft had significantly greater muscle mass recovery than all the other groups. In the ladder rung assay, the autograft, local FK506, and continuous systemic FK506 had similar levels of skilled locomotion performance, whereas the temporary systemic FK506 group had significanty better performance than all the other groups. The results of this study suggest that local delivery of FK506 can provide comparable immunosuppression and nerve regeneration outcomes as systemically delivered FK506.

Evaluation of the transverse aortic constriction model in ICR and C57BL/6J mice

Transverse aortic constriction (TAC) is a frequently used model to investigate pressure overload-induced progressive heart failure (HF); however, there is considerable phenotypic variation among different mouse strains and even sub-strains. Moreover, less is known about the TAC model in ICR mice. Therefore, to determine the suitability of the ICR strain for TAC-induced HF research, we compared the effects of TAC on ICR and C57BL/6J mice at one, two and four weeks post-TAC via echocardiography, organ index, morphology, and histology. At the end of the study, behavior and gene expression patterns were assessed, and overall survival was monitored. Compared to the sham-operated mice, ICR and C57BL/6J mice displayed hypertrophic phenotypes with a significant increase in ventricle wall thickness, heart weight and ratio, and cross-sectional area of cardiomyocytes after a 2-week TAC exposure. In addition, ICR mice developed reduced systolic function and severe lung congestion 4 weeks post-TAC, whereas C57BL/6J did not. Besides, ICR mice demonstrated comparable survival, similar gene expression alteration but severer fibrotic remodeling and poor behavioral performance compared to the C57BL/6J mice. Our data demonstrated that ICR was quite sensitive to TAC-induced heart failure and can be an ideal research tool to investigate mechanisms and drug intervention for pressure overload-induced HF.

Emerging local immunomodulatory strategies to circumvent systemic immunosuppression in cell transplantation

INTRODUCTION

Cell transplantation is a promising curative therapeutic strategy whereby impaired organ functions can be restored without the need for whole organ transplantation. A key challenge in allotransplantation is the requirement for life-long systemic immunosuppression to prevent rejection, which is associated with serious adverse effects such as increased risk of opportunistic infections and the development of neoplasms. This challenge underscores the urgent need for novel strategies to prevent graft rejection while abrogating toxicity-associated adverse events.

AREAS COVERED

We review recent advances in immunoengineering strategies for localized immunomodulation that aim to support allograft function and provide immune tolerance in a safe and effective manner.

EXPERT OPINION

Immunoengineering strategies are tailored approaches for achieving immunomodulation of the transplant microenvironment. Biomaterials can be adapted for localized and controlled release of immunomodulatory agents, decreasing the effective dose threshold and frequency of administration. The future of transplant rejection management lies in the shift from systemic to local immunomodulation with suppression of effector and activation of regulatory T cells, to promote immune tolerance.

Bionic Prostheses: The Emerging Alternative to Vascularised Composite Allotransplantation of the Limb

Twenty years have surpassed since the first vascularised composite allotransplantation (VCA) of the upper limb. This is an opportunity to reflect on the position of VCA as the gold standard in limb reconstruction. The paucity of recipients, tentative clinical outcomes, and insufficient scientific progress question whether VCA will remain a viable treatment option for the growing numbers of amputees. Bionic technology is advancing at a rapid pace. The prospect of widely available, affordable, safely applied prostheses with long-standing functional benefit is appealing. Progress in the field stems from the contributions made by engineering, electronic, computing and material science research groups. This review will address the ongoing reservations surrounding VCA whilst acknowledging the future impact of bionic technology as a realistic alternative for limb reconstruction.

Implantable Immunosuppressant Delivery to Prevent Rejection in Transplantation

An innovative immunosuppressant with a minimally invasive delivery system has emerged in the biomedical field. The application of biodegradable and biocompatible polymer forms, such as hydrogels, scaffolds, microspheres, and nanoparticles, in transplant recipients to control the release of immunosuppressants can minimize the risk of developing unfavorable conditions. In this review, we summarized several studies that have used implantable immunosuppressant delivery to release therapeutic agents to prolong allograft survival. We also compared their applications, efficacy, efficiency, and safety/side effects with conventional therapeutic-agent administration. Finally, challenges and the future prospective were discussed. Collectively, this review will help relevant readers understand the different approaches to prevent transplant rejection in a new era of therapeutic agent delivery.

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.

Local delivery strategies to restore immune homeostasis in the context of inflammation

Immune homeostasis is maintained by a precise balance between effector immune cells and regulatory immune cells. Chronic deviations from immune homeostasis, driven by a greater ratio of effector to regulatory cues, can promote the development and propagation of inflammatory diseases/conditions (i.e., autoimmune diseases, transplant rejection, etc.). Current methods to treat chronic inflammation rely upon systemic administration of non-specific small molecules, resulting in broad immunosuppression with unwanted side effects. Consequently, recent studies have developed more localized and specific immunomodulatory approaches to treat inflammation through the use of local biomaterial-based delivery systems. In particular, this review focuses on (1) local biomaterial-based delivery systems, (2) common materials used for polymeric-delivery systems and (3) emerging immunomodulatory trends used to treat inflammation with increased specificity.

Presence of Donor Lymph Nodes Within Vascularized Composite Allotransplantation Ameliorates VEGF-C-mediated Lymphangiogenesis and Delays the Onset of Acute Rejection

BACKGROUND

The lymphatic system plays an active role in modulating inflammation in autoimmune diseases and organ rejection. In this work, we hypothesized that the transfer of donor lymph node (LN) might be used to promote lymphangiogenesis and influence rejection in vascularized composite allotransplantation (VCA).

METHODS

Hindlimb transplantations were performed in which (1) recipient rats received VCA containing donor LN (D:LN+), (2) recipient rats received VCA depleted of all donor LN (D:LN-), and (3) D:LN+ transplantations were followed by lymphangiogenesis inhibition using a vascular endothelial growth factor receptor-3 (VEGFR3) blocker.

RESULTS

Our data show that graft rejection started significantly later in D:LN+ transplanted rats as compared to the D:LN- group. Moreover, we observed a higher level of VEGF-C and a quicker and more efficient lymphangiogenesis in the D:LN+ group as compared to the D:LN- group. The presence of donor LN within the graft was associated with reduced immunoactivation in the draining LN and increased frequency of circulating and skin-resident donor T regulatory cells. Blocking of the VEGF-C pathway using a VEGFR3 blocker disrupts the lymphangiogenesis process, accelerates rejection onset, and interferes with donor T-cell migration.

CONCLUSIONS

This study demonstrates that VCA LNs play a pivotal role in the regulation of graft rejection and underlines the potential of specifically targeting the LN component of a VCA to control graft rejection.

Long-term Outcomes After Facial Allotransplantation: Systematic Review of the Literature

BACKGROUND

Facial vascularized composite allotransplantation (fVCA) represents a reconstructive approach that enables superior improvements in functional and esthetic restoration compared with conventional craniomaxillofacial reconstruction. Outcome reports of fVCA are usually limited to short-term follow-up or single-center experiences. We merge scientific literature on reported long-term outcome data to better define the risks and benefits of fVCA.

METHODS

We conducted a systematic review of PubMed/MEDLINE databases in accordance with PRISMA guidelines. English full-text articles providing data on at least 1 unique fVCA patient, with ≥3 years follow-up, were included.

RESULTS

The search yielded 1812 articles, of which 28 were ultimately included. We retrieved data on 23 fVCA patients with mean follow-up of 5.3 years. More than half of the patients showed improved quality of life, eating, speech, and motor and sensory function following fVCA. On average, the patients had 1 acute cell-mediated rejection and infectious episode per year. The incidence rates of acute rejection and infectious complications were high within first-year posttransplant but declined thereafter. Sixty-five percent of the patients developed at least 1 neoplastic or metabolic complication after transplantation. Chronic vascular rejection was confirmed in 2 patients, leading to allograft loss after 8 and 9 years. Two patient deaths occurred 3.5 and 10.5 years after transplant due to suicide and lung cancer, respectively.

CONCLUSIONS

Allograft functionality and improvements in quality of life suggest a positive risk-benefit ratio for fVCA. Recurrent acute rejection episodes, chronic rejection, immunosuppression-related complications, and heterogeneity in outcome reporting present ongoing challenges in this field.

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.

The impact of locally-delivered tacrolimus-releasing microspheres and polyethylene glycol-based islet surface modification on xenogeneic islet survival

Pancreatic islet replacement therapy is an advanced choice for severe cases of type I diabetes. Nevertheless, extensive host immune response toward islet grafts remains a huge challenge for long-term graft function, and a lack of islet donors further increases the difficulties associated with upscaling this therapy. Mounting evidence suggests local delivery of immunosuppressive agents provides a feasible means of enhancing graft-protection. Among many immunosuppressants, tacrolimus (FK506) is one of the most potent interleukin-2 (IL-2)-mediated T-cell proliferation blockers. Here, we reported the effect of locally-delivered FK506-releasing PLGA microspheres (FK506-M) combined with polyethylene glycol (PEG)-based islet surface modification on xenogeneic islet survival in C57BL/6 mouse model. FK506-M was prepared using an emulsion method to a particle size of 10-40 μm and released FK506 over 40 days in vitro. Around 80% of the initial dose of FK506-M stably localized near transplanted islets, as observed under a bioimaging instrument and by immunofluorescence staining of islet grafts. Interestingly, FK506-M at very low-doses (equivalent to 150 to 2400 ng FK506 per recipient) was found to inhibit the infiltration of immune cells into grafts and reduce serum IL-1β levels, thereby improving graft survival times dose-dependently. The PEGylation of islets alone was not enough to protect islets from early rejection. However, combined treatment with FK506-M additively prolonged xenograft survival. In conclusion, this study describes a safe, effective approach for translating a systemic exposure-free local drug delivery into clinical trials of islet transplantation.

Local FK506 drug delivery enhances nerve regeneration through fresh, unprocessed peripheral nerve allografts

OBJECTIVE

Nerve allografts offer many advantages in the reconstruction of peripheral nerve gaps: they retain their native microstructure, contain pro-regenerative Schwann cells, are widely available, and avoid donor site morbidity. Unfortunately, clinical use of nerve allografts is limited by the need for systemic immunosuppression and its adverse effects. To eliminate the toxicity of the systemic immunosuppressant FK506, we developed a local FK506 drug delivery system (DDS) to provide drug release over 28 days. The study objective was to investigate if the local FK506 DDS enhances nerve regeneration in a rodent model of nerve gap defect reconstruction with immunologically-disparate nerve allografts.

METHODS

In male Lewis rats, a common peroneal nerve gap defect was reconstructed with either a 20 mm nerve isograft from a donor Lewis rat or a 20 mm fresh, unprocessed nerve allograft from an immunologically incompatible donor ACI rat. After 4 weeks of survival, nerve regeneration was evaluated using retrograde neuronal labelling, quantitative histomorphometry, and serum cytokine profile.

RESULTS

Treatment with both systemic FK506 and the local FK506 DDS significantly improved motor and sensory neuronal regeneration, as well as histomorphometric indices including myelinated axon number. Rats with nerve allografts treated with either systemic or local FK506 had significantly reduced serum concentrations of the pro-inflammatory cytokine IL-12 compared to untreated vehicle control rats with nerve allografts. Serum FK506 levels were undetectable in rats with local FK506 DDS.

INTERPRETATION

The local FK506 DDS improved motor and sensory nerve regeneration through fresh nerve allografts to a level equal to that of either systemic FK506 or nerve isografting. This treatment may be clinically translatable in peripheral nerve reconstruction or vascularized composite allotransplantation.

Local immunosuppression in vascularized composite allotransplantation (VCA): A systematic review

BACKGROUND

Local immunosuppression in vascularized composite allotransplantation (VCA) aims to minimize immunosuppressant-related toxic and malignant side effects. Promising allograft survival data have been published by multiple workgroups. In this systematic review, we examine preclinical animal studies that investigated local immunosuppression in VCA.

MATERIAL AND METHODS

We conducted a systematic review of manuscripts listed in the MEDLINE and PubMed database concerning preclinical VCA models. Papers included had to be available as full-text and written in English. Non-VCA studies, human trials, and studies using cell-based therapy strategies were excluded. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Literature research retrieved 980 articles. Ten studies published between 2010 and 2019 met the inclusion and exclusion criteria. Seven out of ten articles demonstrated a significant prolongation of allograft survival by using local immunosuppression. Five articles employed tacrolimus (TAC) as the main immunosuppressive agent. Seven studies performed hind-limb VCA in a rat model.

CONCLUSION

The easily accessible location of skin containing VCAs makes it an ideal candidate for local immunosuppression. Published preclinical data are very promising in terms of improved allograft survival and reduced systemic toxicity.

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.

Evaluation of PLGA microspheres with triple regimen on long-term survival of vascularized composite allograft - an experimental study

Systemic immunosuppression is indispensable for vascularized composite allotransplantation (VCA). Daily administration of standard triple therapy regimen of tacrolimus (FK506), mycophenolate mofetil (MMF), and steroid has severe side effects and reduces the compliance of VCA recipients. To overcome these hurdles, FK506/MMF/prednisolone (PDNN) was loaded into PLGA microspheres (PGLA MS). A single injection of FK506/MMF/PDNN-PLGA MS significantly prolonged the survival time of allograft in a rat hind limb transplantation model with a median survival time (MST) of more than 150 days compared to 34.5 days in the group treated orally with FK506/MMF/PDNN and 11 days in the nontreatment allograft and MS control groups. Analysis of showed that FK506/MMF/PDNN-PLGA MS could maintain relatively higher plasma and tissue drug concentrations for a long time. Moreover, histopathology and flow cytometry of circulating mononuclear cells revealed significantly prolonged immunosuppression by the FK506/MMF/PDNN-PLGA MS compared with the orally given FK506/MMF/PDNN. In conclusion, a single injection of FK506/MMF/PDNN-PLGA MS may provide a new approach for long-term prevention of immune rejection in VCA.

Biomaterials for topical and transdermal drug delivery in reconstructive transplantation

Lifelong systemic immunosuppression remains the biggest challenge in vascularized composite allotransplantation (VCA) due to the adverse effects it causes. Since VCA is a life-enhancing procedure as compared with solid organ transplant which is life-saving; one needs to weigh the benefits and risks carefully. Thus, there is a huge unmet clinical need to design biomaterial-based vehicles that can deliver drugs more efficiently, topically and locally to eliminate adverse effects of systemic immune suppression. This review discusses several biomaterial-based systems that have been carefully designed, conceived and attempted to make VCA a more patient compliant approach. Variety of promising preclinical studies has shown the feasibility of the approaches, and clinical trials are required to bridge the gap. Several challenges for the future and new approaches have been discussed.

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.

Local release of tacrolimus from hydrogel-based drug delivery system is controlled by inflammatory enzymes in vivo and can be monitored non-invasively using in vivo imaging

BACKGROUND

Local drug delivery systems that adjust the release of immunosuppressive drug in response to the nature and intensity of inflammation represent a promising approach to reduce systemic immunosuppression and its side effects in allotransplantation. Here we aimed to demonstrate that release of tacrolimus from triglycerol monostearate hydrogel is inflammation-dependent in vivo. We further report that by loading the hydrogel with a near-infrared dye, it is possible to monitor drug release non-invasively in an in vivo model of vascularized composite allotransplantation.

MATERIALS AND METHODS

Inflammation was induced by local challenge with lipopolysaccharides in naïve rats 7 days after injection of tacrolimus-loaded hydrogel in the hind limb. Tacrolimus levels in blood and tissues were measured at selected time points. A near-infrared dye was encapsulated in the hydrogel together with tacrolimus in order to monitor hydrogel deposits and drug release in vitro and in vivo in a model of vascularized composite allotransplantation.

RESULTS

Injection of lipopolysaccharides led to increased blood and skin tacrolimus levels (p = 0.0076, day 7 vs. day 12 in blood, and p = 0.0007 in treated limbs, 48 h after injection compared to controls). Moreover, lipopolysaccharides-injected animals had higher tacrolimus levels in treated limbs compared to contralateral limbs (p = 0.0003 for skin and p = 0.0053 for muscle). Imaging of hydrogel deposits and tacrolimus release was achieved by encapsulating near-infrared dye in the hydrogel for 160 days. The correlation of tacrolimus and near-infrared dye release from hydrogel was R2 = 0.6297 and R2 = 0.5619 in blood and grafts of transplanted animals respectively and R2 = 0.6066 in vitro.

CONCLUSIONS

Here we demonstrate the inflammation-responsiveness of a tacrolimus-loaded hydrogel in vivo. Moreover, we show that encapsulating a near-infrared dye in the hydrogel provides a reliable correlation of tacrolimus and dye release from the hydrogel, and an accessible non-invasive method for monitoring drug release from hydrogel deposits.