Optimizing PLG nanoparticle-peptide delivery platforms for transplantation tolerance using an allogeneic skin transplant model

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.

Negative Vaccination Strategies for Promotion of Transplant Tolerance

Organ transplantation requires the use of immunosuppressive medications that lack antigen specificity, have many adverse side effects, and fail to induce immunological tolerance to the graft. The safe induction of tolerance to allogeneic tissue without compromising host responses to infection or enhancing the risk of malignant disease is a major goal in transplantation. One promising approach to achieve this goal is based on the concept of "negative vaccination." Vaccination (or actively acquired immunity) involves the presentation of both a foreign antigen and immunostimulatory adjuvant to the immune system to induce antigen-specific immunity. By contrast, negative vaccination, in the context of transplantation, involves the delivery of donor antigen before or after transplantation, together with a "negative adjuvant" to selectively inhibit the alloimmune response. This review will explore established and emerging negative vaccination strategies for promotion of organ or pancreatic islet transplant tolerance. These include donor regulatory myeloid cell infusion, which has progressed to early-phase clinical trials, apoptotic donor cell infusion that has advanced to nonhuman primate models, and novel nanoparticle antigen-delivery systems.

Biomaterial-enhanced treg cell immunotherapy: A promising approach for transplant medicine and autoimmune disease treatment

Regulatory T cells (Tregs) are crucial for preserving tolerance in the body, rendering Treg immunotherapy a promising treatment option for both organ transplants and autoimmune diseases. Presently, organ transplant recipients must undergo lifelong immunosuppression to prevent allograft rejection, while autoimmune disorders lack definitive cures. In the last years, there has been notable advancement in comprehending the biology of both antigen-specific and polyclonal Tregs. Clinical trials involving Tregs have demonstrated their safety and effectiveness. To maximize the efficacy of Treg immunotherapy, it is essential for these cells to migrate to specific target tissues, maintain stability within local organs, bolster their suppressive capabilities, and ensure their intended function's longevity. In pursuit of these goals, the utilization of biomaterials emerges as an attractive supportive strategy for Treg immunotherapy in addressing these challenges. As a result, the prospect of employing biomaterial-enhanced Treg immunotherapy holds tremendous promise as a treatment option for organ transplant recipients and individuals grappling with autoimmune diseases in the near future. This paper introduces strategies based on biomaterial-assisted Treg immunotherapy to enhance transplant medicine and autoimmune treatments.

Novel Approaches to Immunomodulation for Solid Organ Transplantation

Despite significant advances in the field of transplantation in the past two decades, current clinically available therapeutic options for immunomodulation remain fairly limited. The advent of calcineurin inhibitor-based immunosuppression has led to significant success in improving short-term graft survival; however, improvements in long-term graft survival have stalled. Solid organ transplantation provides a unique opportunity for immunomodulation of both the donor organ prior to implantation and the recipient post transplantation. Furthermore, therapies beyond targeting the adaptive immune system have the potential to ameliorate ischemic injury to the allograft and halt its aging process, augment its repair, and promote recipient immune tolerance. Other recent advances include expanding the donor pool by reducing organ discard, and bioengineering and genetically modifying organs from other species to generate transplantable organs. Therapies discussed here will likely be most impactful if individualized on the basis of specific donor and recipient considerations.

A new paradigm in transplant immunology: At the crossroad of synthetic biology and biomaterials

Solid organ transplant (SOT) recipients require meticulously tailored immunosuppressive regimens to minimize graft loss and mortality. Traditional approaches focus on inhibiting effector T cells, while the intricate and dynamic immune responses mediated by other components remain unsolved. Emerging advances in synthetic biology and material science have provided novel treatment modalities with increased diversity and precision to the transplantation community. This review investigates the active interface between these two fields, highlights how living and non-living structures can be engineered and integrated for immunomodulation, and discusses their potential application in addressing the challenges in SOT clinical practice.

Nanomedicine and nanoparticle-based delivery systems in plastic and reconstructive surgery

BACKGROUND

Nanotechnology and nanomedicine are rising novel fields in plastic and reconstructive surgery (PRS). The use of nanomaterials often goes with regenerative medicine. Due to their nanoscale, these materials stimulate repair at the cellular and molecular levels. Nanomaterials may be placed as components of nanocomposite polymers allowing enhancement of overall biochemical and biomechanical properties with improved scaffold properties, cellular attachment, and tissue regeneration. They may also be formulated as nanoparticle-based delivery systems for controlled release of signal factors or antimicrobials, for example. However, more studies on nanoparticle-based delivery systems still need to be done in this field. Nanomaterials are also used as frameworks for nerves, tendons, and other soft tissues.

MAIN BODY

In this mini-review, we focus on nanoparticle-based delivery systems and nanoparticles targeting cells for response and regeneration in PRS. Specifically, we investigate their roles in various tissue regeneration, skin and wound healing, and infection control. Cell surface-targeted, controlled-release, and inorganic nanoparticle formulations with inherent biological properties have enabled enhanced wound healing, tumor visualization/imaging, tissue viability, and decreased infection, and graft/transplantation rejection through immunosuppression.

CONCLUSIONS

Nanomedicine is also now being applied with electronics, theranostics, and advanced bioengineering technologies. Overall, it is a promising field that can improve patient clinical outcomes in PRS.

Membrane-coated nanoparticles for direct recognition by T cells

The direct modulation of T cell responses is an emerging therapeutic strategy with the potential to modulate undesired immune responses including, autoimmune disease, and allogeneic cells transplantation. We have previously demonstrated that poly(lactide-co-glycolide) particles were able to modulate T cell responses indirectly through antigen-presenting cells (APCs). In this report, we investigated the design of nanoparticles that can directly interact and modulate T cells by coating the membranes from APCs onto nanoparticles to form membrane-coated nanoparticles (MCNPs). Proteins within the membranes of the APCs, such as Major Histocompatibility Complex class II and co-stimulatory factors, were effectively transferred to the MCNP. Using alloreactive T cell models, MCNP derived from allogeneic dendritic cells were able to stimulate proliferation, which was not observed with membranes from syngeneic dendritic cells and influenced cytokine secretion. Furthermore, we investigated the engineering of the membranes either on the dendritic cells or postfabrication of MCNP. Engineered membranes could be to promote antigen-specific responses, to differentially activate T cells, or to directly induce apoptosis. Collectively, MCNPs represent a tunable platform that can directly interact with and modulate T cell responses.

Biomaterial Strategies for Selective Immune Tolerance: Advances and Gaps

Autoimmunity and allergies affect a large number of people across the globe. Current approaches to these diseases target cell types and pathways that drive disease, but these approaches are not cures and cannot differentiate between healthy cells and disease-causing cells. New immunotherapies that induce potent and selective antigen-specific tolerance is a transformative goal of emerging treatments for autoimmunity and serious allergies. These approaches offer the potential of halting-or even reversing-disease, without immunosuppressive side effects. However, translating successful induction of tolerance to patients is unsuccessful. Biomaterials offer strategies to direct and maximize immunological mechanisms of tolerance through unique capabilities such as codelivery of small molecules or signaling molecules, controlling signal density in key immune tissues, and targeting. While a growing body of work in this area demonstrates success in preclinical animal models, these therapies are only recently being evaluated in human trials. This review will highlight the most recent advances in the use of materials to achieve antigen-specific tolerance and provide commentary on the current state of the clinical development of these technologies.

Engineering the lymph node environment promotes antigen-specific efficacy in type 1 diabetes and islet transplantation

Antigen-specific tolerance is a key goal of experimental immunotherapies for autoimmune disease and allograft rejection. This outcome could selectively inhibit detrimental inflammatory immune responses without compromising functional protective immunity. A major challenge facing antigen-specific immunotherapies is ineffective control over immune signal targeting and integration, limiting efficacy and causing systemic non-specific suppression. Here we use intra-lymph node injection of diffusion-limited degradable microparticles that encapsulate self-antigens with the immunomodulatory small molecule, rapamycin. We show this strategy potently inhibits disease during pre-clinical type 1 diabetes and allogenic islet transplantation. Antigen and rapamycin are required for maximal efficacy, and tolerance is accompanied by expansion of antigen-specific regulatory T cells in treated and untreated lymph nodes. The antigen-specific tolerance in type 1 diabetes is systemic but avoids non-specific immune suppression. Further, microparticle treatment results in the development of tolerogenic structural microdomains in lymph nodes. Finally, these local structural and functional changes in lymph nodes promote memory markers among antigen-specific regulatory T cells, and tolerance that is durable. This work supports intra-lymph node injection of tolerogenic microparticles as a powerful platform to promote antigen-dependent efficacy in type 1 diabetes and allogenic islet transplantation.

Nanotechnology in Kidney and Islet Transplantation: An Ongoing, Promising Field

Organ transplantation has evolved rapidly in recent years as a reliable option for patients with end-stage organ failure. However, organ shortage, surgical risks, acute and chronic rejection reactions and long-term immunosuppressive drug applications and their inevitable side effects remain extremely challenging problems. The application of nanotechnology in medicine has proven highly successful and has unique advantages for diagnosing and treating diseases compared to conventional methods. The combination of nanotechnology and transplantation brings a new direction of thinking to transplantation medicine. In this article, we provide an overview of the application and progress of nanotechnology in kidney and islet transplantation, including nanotechnology for renal pre-transplantation preservation, artificial biological islets, organ imaging and drug delivery.

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.

Polymer nanotherapeutics to correct autoimmunity

The immune system maintains homeostasis and protects the body from pathogens, mutated cells, and other harmful substances. When immune homeostasis is disrupted, excessive autoimmunity will lead to diseases. To inhibit the unexpected immune responses and reduce the impact of treatment on immunoprotective functions, polymer nanotherapeutics, such as nanomedicines, nanovaccines, and nanodecoys, were developed as part of an advanced strategy for precise immunomodulation. Nanomedicines transport cytotoxic drugs to target sites to reduce the occurrence of side effects and increase the stability and bioactivity of various immunomodulating agents, especially nucleic acids and cytokines. In addition, polymer nanomaterials carrying autoantigens used as nanovaccines can induce antigen-specific immune tolerance without interfering with protective immune responses. The precise immunomodulatory function of nanovaccines has broad prospects for the treatment of immune related-diseases. Besides, nanodecoys, which are designed to protect the body from various pathogenic substances by intravenous administration, are a simple and relatively noninvasive treatment. Herein, we have discussed and predicted the application of polymer nanotherapeutics in the correction of autoimmunity, including treating autoimmune diseases, controlling hypersensitivity, and avoiding transplant rejection.

The ancillary effects of nanoparticles and their implications for nanomedicine

Nanoparticles are often engineered as a scaffolding system to combine targeting, imaging and/or therapeutic moieties into a unitary agent. However, mostly overlooked, the nanomaterial itself interacts with biological systems exclusive of application-specific particle functionalization. This nanoparticle biointerface has been found to elicit specific biological effects, which we term 'ancillary effects'. In this Review, we describe the current state of knowledge of nanobiology gleaned from existing studies of ancillary effects with the objectives to describe the potential of nanoparticles to modulate biological effects independently of any engineered function; evaluate how these effects might be relevant for nanomedicine design and functional considerations, particularly how they might be useful to inform clinical decision-making; identify potential clinical harm that arises from adverse nanoparticle interactions with biology; and, finally, highlight the current lack of knowledge in this area as both a barrier and an incentive to the further development of nanomedicine.

Biomaterial-based approaches to engineering immune tolerance

The development of biomaterial-based therapeutics to induce immune tolerance holds great promise for the treatment of autoimmune diseases, allergy, and graft rejection in transplantation. Historical approaches to treat these immunological challenges have primarily relied on systemic delivery of broadly-acting immunosuppressive agents that confer undesirable, off-target effects. The evolution and expansion of biomaterial platforms has proven to be a powerful tool in engineering immunotherapeutics and enabled a great diversity of novel and targeted approaches in engineering immune tolerance, with the potential to eliminate side effects associated with systemic, non-specific immunosuppressive approaches. In this review, we summarize the technological advances within three broad biomaterials-based strategies to engineering immune tolerance: nonspecific tolerogenic agent delivery, antigen-specific tolerogenic therapy, and the emergent area of tolerogenic cell therapy.

Integration of Islet/Beta-Cell Transplants with Host Tissue Using Biomaterial Platforms

Cell-based therapies are emerging for type I diabetes mellitus (T1D), an autoimmune disease characterized by the destruction of insulin-producing pancreatic β-cells, as a means to provide long-term restoration of glycemic control. Biomaterial scaffolds provide an opportunity to enhance the manufacturing and transplantation of islets or stem cell-derived β-cells. In contrast to encapsulation strategies that prevent host contact with the graft, recent approaches aim to integrate the transplant with the host to facilitate glucose sensing and insulin distribution, while also needing to modulate the immune response. Scaffolds can provide a supportive niche for cells either during the manufacturing process or following transplantation at extrahepatic sites. Scaffolds are being functionalized to deliver oxygen, angiogenic, anti-inflammatory, or trophic factors, and may facilitate cotransplantation of cells that can enhance engraftment or modulate immune responses. This local engineering of the transplant environment can complement systemic approaches for maximizing β-cell function or modulating immune responses leading to rejection. This review discusses the various scaffold platforms and design parameters that have been identified for the manufacture of human pluripotent stem cell-derived β-cells, and the transplantation of islets/β-cells to maintain normal blood glucose levels.

Nanotechnology Applications in Transplantation Medicine

A recent technological advance that shows promise for applications in health care, including transplantation medicine, is the implementation of nanoparticles. Nanoparticles can be composed of a variety of organic or inorganic materials and confer many advantages over conventional treatments available, such as low toxicity, low-effective dosage required, and a high degree of manipulability. Although also used for imaging and diagnostics, nanoparticles' utility as a drug or genetic delivery system is of particular interest in transplantation medicine. Currently, researchers are exploring options to integrate nanoparticles into both diagnostics and therapy for both grafts ex-situ before transplantation and for patients following transplantation. These studies have demonstrated that nanoparticles can mitigate damage to organs and patients through a large variety of mechanisms-ranging from the induction of cellular genetic changes to the enhancement of immunosuppressive drug delivery. Specifically, with the advent of machine perfusion preservation ex vivo, treatment of the graft became a very attractive approach and nanoparticles have great potential. However, before nanoparticles can be translated into clinical use, their short-term and long-term toxicity must be thoroughly characterized, especially with regards to their interactions with other biological molecules present in the human body.

Nanoparticle Platforms for Antigen-Specific Immune Tolerance

Innovative approaches in nanoparticle design have facilitated the creation of new formulations of nanoparticles that are capable of selectively calibrating the immune response. These nanomaterials may be engineered to interact with specific cellular and molecular targets. Recent advancements in nanoparticle synthesis have enabled surface functionalization of particles that mimic the diversity of ligands on the cell surface. Platforms synthesized using these design principles, called "biomimetic" nanoparticles, have achieved increasingly sophisticated targeting specificity and cellular trafficking capabilities. This holds great promise for next generation therapies that seek to achieve immune tolerance. In this review, we discuss the importance of physical design parameters including size, shape, and biomimetic surface functionalization, on the biodistribution, safety and efficacy of biologic nanoparticles. We will also explore potential applications for immune tolerance for organ or stem cell transplantation.

Design and Optimization of PLGA Particles to Deliver Immunomodulatory Drugs for the Prevention of Skin Allograft Rejection

Background: Recent advancements in therapeutic strategies have attracted considerable attention to control the acute organs and tissues rejection, which is the main cause of mortality in transplant recipients. The long-term usage of immunosuppressive drugs compromises the body immunity against simple infections and decrease the patients' quality of life. Tolerance of allograft in recipients without harming the rest of host immune system is the basic idea to develop the therapeutic approaches after induction of donor-specific transplant. Methods: Controlled and targeted delivery system by using biomimetic micro and nanoparticles as carriers is an effective strategy to deplete the immune cells in response to allograft in an antigen-specific manner. Polylactic-co-glycolic acid (PLGA) is a biocompatible and biodegradable polymer, which has frequently being used as drug delivery vehicle. Results: This review focuses on the biomedical applications of PLGA based biomimetic micro and nano-sized particles in drug delivery systems to prolong the survival of alloskin graft. Conclusion: We will discuss the mediating factors for rejection of alloskin graft, selective depletion of immune cells, controlled release mechanism, physiochemical properties, size-based body distribution of PLGA particles and their effect on overall host immune system.

Cargo-less nanoparticles program innate immune cell responses to toll-like receptor activation

Developing biomaterials to control the responsiveness of innate immune cells represents a clinically relevant approach to treat diseases with an underlying inflammatory basis, such as sepsis. Sepsis can involve activation of Toll-like receptor (TLR) signaling, which activates numerous inflammatory pathways. The breadth of this inflammation has limited the efficacy of pharmacological interventions that target a single molecular pathway. Here, we developed cargo-less particles as a single-agent, multi-target platform to elicit broad anti-inflammatory action against innate immune cells challenged by multiple TLR agonists. The particles, prepared from poly(lactic-co-glycolic acid) (PLGA) and poly(lactic acid) (PLA), displayed potent molecular weight-, polymer composition-, and charge-dependent immunomodulatory properties, including downregulation of TLR-induced costimulatory molecule expression and cytokine secretion. Particles prepared using the anionic surfactant poly(ethylene-alt-maleic acid) (PEMA) significantly blunted the responses of antigen presenting cells to TLR4 (lipopolysaccharide) and TLR9 (CpG-ODN) agonists, demonstrating broad inhibitory activity to both extracellular and intracellular TLR ligands. Interestingly, particles prepared using poly(vinyl alcohol) (PVA), a neutrally-charged surfactant, only marginally inhibited inflammatory cytokine secretions. The biochemical pathways modulated by particles were investigated using TRanscriptional Activity CEll aRrays (TRACER), which implicated IRF1, STAT1, and AP-1 in the mechanism of action for PLA-PEMA particles. Using an LPS-induced endotoxemia mouse model, administration of PLA-PEMA particles prior to or following a lethal challenge resulted in significantly improved mean survival. Cargo-less particles affect multiple biological pathways involved in the development of inflammatory responses by innate immune cells and represent a potentially promising therapeutic strategy to treat severe inflammation.