Strategies to direct the enrichment, expansion, and recruitment of regulatory cells for the treatment of disease

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.

Reduction of NrF2 as coadjuvant during the development of persistent periapical lesions

BACKGROUND

Persistent periapical lesions (PPL) are the result of pulpar necrosis induced by bacterial infection resulting in bone degradation and culminating with the loss of dental piece. Pathological changes in the peripapice are associated with the presence of free radicals. The transcription factor Nrf2 is the main regulator of the endogenous antioxidant response against oxidative stress and has been implicated in the regulation of osteoclastogenesis.The aim is to determine the oxidative condition in samples from patients with Persistent Periapical Injuries as a detonating factor of tissue damage.

MATERIAL AND METHODS

An observational, descriptive, cross-sectional study was carried out in samples with PPL (cases) and samples by removal of third molars (controls) obtained in the clinic of the specialty in endodontics, University of Guadalajara. Samples were submitted to histological staining with Hematoxylin-Eosin, lipoperoxide analysis, Superoxide Dismutase (SOD), Glutathione-Peroxidase (GPx) and Catalase (CAT) activities were determined by immunoenzymatic assays and NrF2 by Western Blot analysis.

RESULTS

Samples from PPL patients histologically showed an increased presence of lymphocytes, plasma cells, and eosinophils, as well as a decrease in extracellular matrix proteins and fibroblast cells. There was a rise in lipid peroxidation, GPx and SOD activities, but an important decline (36%) in Catalase activity was observed (p<0.005); finally, NrF2-protein was diminished at 10.41%. All comparisons were between cases vs controls.

CONCLUSIONS

The alterations in antioxidants endogenous NrF2-controlled are related to osseous destruction in patients with PPL.

Immunomodulatory nanotherapeutic approaches for periodontal tissue regeneration

Periodontitis is an infection-induced inflammatory disease characterized by progressive destruction of tooth supporting tissues, which, if left untreated, can result in tooth loss. The destruction of periodontal tissues is primarily caused by an imbalance between the host immune protection and immune destruction mechanisms. The ultimate goal of periodontal therapy is to eliminate inflammation and promote the repair and regeneration of both hard and soft tissues, so as to restore the physiological structure and function of periodontium. Advancement in nanotechnologies has enabled the development of nanomaterials with immunomodulatory properties for regenerative dentistry. This review discusses the immune mechanisms of the major effector cells in the innate and adaptive immune systems, the physicochemical and biological properties of nanomaterials, and the research advancements in immunomodulatory nanotherapeutic approaches for the management of periodontitis and the regeneration of periodontal tissues. The current challenges, and prospects for future applications of nanomaterials are then discussed so that researchers at the intersections of osteoimmunology, regenerative dentistry and materiobiology will continue to advance the development of nanomaterials for improved periodontal tissue regeneration.

Drug-Eluting Endotracheal Tubes for Preventing Bacterial Inflammation in Subglottic Stenosis

OBJECTIVES/HYPOTHESIS

Subglottic stenosis (SGS) results from dysregulated extracellular matrix deposition by laryngotracheal fibroblasts causing scar tissue formation following intubation. Recent work has highlighted a relationship between this inflammatory state and imbalances in the upper airway microbiome. Herein, we engineer novel drug-eluting endotracheal (ET) tubes to deliver a model antimicrobial peptide Lasioglossin-III (Lasio) for the local modulation of the microbiome during intubation.

STUDY DESIGN

Controlled in vitro study.

METHODS

ET tubes were coated with a water-in-oil (w/o) emulsion of Lasio in poly(d,l-lactide-co-glycolide) (PLGA) by dipping thrice. Peptide release was quantified over 2 weeks via fluorometric peptide assays. The antibacterial activity was tested against airway microbes (Staphylococcus epidermidis, Streptococcus pneumoniae, and pooled human microbiome samples) by placing Lasio/PLGA-coated tubes and appropriate controls in 48 well plates with diluted bacteria. Bacterial inhibition and tube adhesion were tested by measuring optical density and colony formation after tube culture, respectively. Biocompatibility was tested against laryngotracheal fibroblasts and lung epithelial cells.

RESULTS

We achieved a homogeneous coating of ET tubes with Lasio in a PLGA matrix that yields a prolonged, linear release over 1 week (typical timeframe before the ET tube is changed). We observed significant antibacterial activity against S. epidermidis, S. pneumoniae, and human microbiome samples, and prevention of bacterial adherence to the tube. Additionally, the released Lasio did not cause any cytotoxicity toward laryngotracheal fibroblasts or lung epithelial cells in vitro.

CONCLUSION

Overall, we demonstrate the design of an effective-eluting ET tube to modulate upper-airway bacterial infections during intubation which could be deployed to help prevent SGS.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2021.

Clinical and Immunological Efficacy of Mangosteen and Propolis Extracted Complex in Patients with Gingivitis: A Multi-Centered Randomized Controlled Clinical Trial

Background: Mangosteen and propolis extracts (MAEC) have been potential therapeutic agents known to exhibit powerful antioxidant and anti-inflammatory properties. The aim of the current study was to evaluate the clinical and immunological efficacy of MAEC as well as safety and patient-reported outcomes (PROMs) on gingivitis and incipient periodontitis. Methods: This study was performed on 104 patients diagnosed with gingivitis or incipient periodontitis. At baseline, the participants were randomly allocated to either the test group, with daily intake of a single capsule containing 194 mg of MAEC for eight weeks, or control group, with placebo. Clinical periodontal evaluation and immunological parameters from saliva and gingival sulcular fluid were assessed at baseline, four, and eight weeks. Individual PROMs were assessed by OHIP-14 questionnaires. Results: There was a significant difference of modified gingival index at four and eight weeks between the test and control groups. In the test group, crevicular interleukin (IL)-6 was reduced, and the salivary matrix metalloproteinase (MMP)-9 was increased after eight weeks. PROMs were improved up to four weeks compared to placebo. Conclusion: Oral administration of MAEC would have a potential to reduce gingival inflammation clinically and immunologically in the patients with gingivitis and incipient periodontitis.

Evidence revealing the role of T cell regulators (Tregs) in periodontal diseases: A review

Periodontitis is an inflammatory disease of the periodontium, which is a reflection of the overgrowth of oral commensals. This alteration in the oral microbiota initiates inflammation of the gingiva, which when left untreated, terminates with the resorption of the alveolar bone that may lead to a poor and hopeless prognosis. With upcoming trends in modulating the host's immunity, the role of regulatory T-cells has gained importance. These T-cells defend against inflammation and autoimmunity as they suppress both. However, in both the conditions, the regulatory cells are invariably reduced in number. Novel methods to enhance the function of Tregs have made their way in dentistry, as a promising approach to cure periodontitis. This article discusses various significant tests and trials of Tregs in the recent years.

Expression Levels of A Disintegrin-like Metalloproteinase with Thrombospondin Motifs-4 and -5 (ADAMTS-4 and ADAMTS-5) in Inflamed and Healthy Gingival Tissues

BACKGROUND

ADAMTS (A disintegrin-like metalloproteinase with thrombospondin motifs) is a group of 19 zinc-dependent metalloproteases known to function in many pathological and physiological processes, such as adhesion, cell fusion, signaling, proteolysis and ECM degradation.

OBJECTIVES

The aim of this study was to demonstrate the levels of ADAMTS-4 and -5 in gingival tissues with Stage III-Grade B generalized periodontitis (SIII-GB), Stage III-Grade C generalized periodontitis (SIII-GC) and healthy-control (C) groups.

METHODS

The clinical measurements were recorded for each patient. A total of 63 gingival biopsy specimens were obtained from the C (n:20), SIII-GB (n:23) and SIII-GC (n:20) groups. Polymerase chain reaction (Rt-PCR) and immunohistochemical (IHC) examinations were used to determine gene and protein levels.

RESULTS

According to the results of all methods, ADAMTS-4 and -5 expressions existed in periodontitis and C groups (P> 0.05). Immunostaining for ADAMTS-4 was found to be higher in patients with periodontitis than for ADAMTS-5 (P>0.05). Gene expression levels for ADAMTS-4 and -5 seemed to be up-regulated in subjects diagnosed with periodontitis, but the results were not statistically significant (P>0.05). A positive correlation was observed between PPD and ADAMTS-4 mRNA in SIII-GC (p=0.035) and SIII-GB (p=0.015). A positive correlation was determined between ADAMTS-4 mRNA and ADAMTS-5 mRNA in SIII-GC (p=0.037) and SIII-GB (p=0.00).

CONCLUSION

ADAMTS expression may take part in both pathological and physiological processes in the periodontal tissues, and periodontal destruction may be the result of a complex interaction of several pathways with many participants, such as ADAMTS-4 and -5, thus facilitating the exaggeration of periodontal disease.

Current Trends in In Vitro Modeling to Mimic Cellular Crosstalk in Periodontal Tissue

Clinical evidence indicates that in physiological and therapeutic conditions a continuous remodeling of the tooth root cementum and the periodontal apparatus is required to maintain tissue strength, to prevent damage, and to secure teeth anchorage. Within the tooth's surrounding tissues, tooth root cementum and the periodontal ligament are the key regulators of a functional tissue homeostasis. While the root cementum anchors the periodontal fibers to the tooth root, the periodontal ligament itself is the key regulator of tissue resorption, the remodeling process, and mechanical signal transduction. Thus, a balanced crosstalk of both tissues is mandatory for maintaining the homeostasis of this complex system. However, the mechanobiological mechanisms that shape the remodeling process and the interaction between the tissues are largely unknown. In recent years, numerous 2D and 3D in vitro models have sought to mimic the physiological and pathophysiological conditions of periodontal tissue. They have been proposed to unravel the underlying nature of the cell-cell and the cell-extracellular matrix interactions. The present review provides an overview of recent in vitro models and relevant biomaterials used to enhance the understanding of periodontal crosstalk and aims to provide a scientific basis for advanced regenerative strategies.

Local promotion of B10 function alleviates experimental periodontitis bone loss through antagonizing RANKL-expressing neutrophils

BACKGROUND

Persistent host immune responses initiated by oral bacteria protect host against infection but may also elicit the process of sustained periodontal inflammation and subsequent alveolar bone loss. Interleukin-10 (IL-10), an anti-inflammatory cytokine, can downregulate pro-inflammatory cytokine and inhibit neutrophil migration in inflammation. IL-10-expressing regulatory B cells (B10) is termed by negatively regulating immune response through IL-10 and are mainly restricted in CD19⁺ CD1d^hi CD5⁺ B cells in mice. Our current study was aimed to explore the effect of locally transferred CD19⁺ CD1d^hi CD5⁺ B cells on inflammation and alveolar bone loss in an experimental periodontitis mouse model.

METHODS

Ligation plus P. gingivalis (Pg) infection was used to induce periodontitis in a mouse model. CD19⁺ CD1d^hi CD5⁺ B cells were sorted by flow cytometry and transferred into the gingivae immediately on the fifth day after ligation. All the mice were sacrificed on day 14 after ligation.

RESULTS

H&E staining showed that inflammatory cell infiltration was significantly reduced by the CD19⁺ CD1d^hi CD5⁺ B cells. Toluidine blue staining showed that the CD19⁺ CD1d^hi CD5⁺ B cells alleviated alveolar bone loss in the ligature/Pg-induced periodontitis in mice. Immunohistochemical staining showed Receptor Activator of NF-KappaB Ligand (RANKL), Interleukin-1β(IL-1β) and Interleukin-17 (IL-17) were decreased after the CD19⁺ CD1d^hi CD5⁺ B cell transfer. Immunofluorescent staining showed that IL-10 was increased while the number of Ly6G⁺ neutrophil and its RANKL production were decreased in gingival tissue.

CONCLUSIONS

These results indicated that locally transferred CD19⁺ CD1d^hi CD5⁺ B cells may alleviate alveolar bone loss through inhibiting pro-inflammatory cytokine expression and RANKL-expressing neutrophils in the periodontitis mouse model.

Toll-Like Receptor Signaling and Immune Regulatory Lymphocytes in Periodontal Disease

Periodontitis is known to be initiated by periodontal microbiota derived from biofilm formation. The microbial dysbiotic changes in the biofilm trigger the host immune and inflammatory responses that can be both beneficial for the protection of the host from infection, and detrimental to the host, causing tissue destruction. During this process, recognition of Pathogen-Associated Molecular Patterns (PAMPs) by the host Pattern Recognition Receptors (PRRs) such as Toll-like receptors (TLRs) play an essential role in the host–microbe interaction and the subsequent innate as well as adaptive responses. If persistent, the adverse interaction triggered by the host immune response to the microorganisms associated with periodontal biofilms is a direct cause of periodontal inflammation and bone loss. A large number of T and B lymphocytes are infiltrated in the diseased gingival tissues, which can secrete inflammatory mediators and activate the osteolytic pathways, promoting periodontal inflammation and bone resorption. On the other hand, there is evidence showing that immune regulatory T and B cells are present in the diseased tissue and can be induced for the enhancement of their anti-inflammatory effects. Changes and distribution of the T/B lymphocytes phenotype seem to be a key determinant of the periodontal disease outcome, as the functional activities of these cells not only shape up the overall immune response pattern, but may directly regulate the osteoimmunological balance. Therefore, interventional strategies targeting TLR signaling and immune regulatory T/B cells may be a promising approach to rebalance the immune response and alleviate bone loss in periodontal disease. In this review, we will examine the etiological role of TLR signaling and immune cell osteoclastogenic activity in the pathogenesis of periodontitis. More importantly, the protective effects of immune regulatory lymphocytes, particularly the activation and functional role of IL-10 expressing regulatory B cells, will be discussed.

Application of PLGA nano/microparticle delivery systems for immunomodulation and prevention of allotransplant rejection

INTRODUCTION

Allograft transplantation is an effective end-point therapy to replace the function of an impaired organ. The main problem associated with allotransplantation is the induction of immune responses that results in acute and chronic graft rejection. To modulate the response of the immune system, transplant recipients generally take high dose immunosuppressant drugs for life. These drugs are associated with serious side effects such as infection with opportunistic pathogens and the development of neoplasia.

AREAS COVERED

We reviewed the obstacles to successful transplantation and PLGA-based strategies to reduce immune-mediated allograft rejection.

EXPERT OPINION

Biomaterial-based approaches using micro- and nanoparticles such as poly (lactic-co-glycolic acid) (PLGA) can be used to achieve controlled release of drugs. This approach decreases the required effective dose of drugs and enables local delivery of these agents to specific tissues and cells, whilst decreasing systemic effects.

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.

Biomaterial-assisted scalable cell production for cell therapy

Cell therapy, the treatment of diseases using living cells, offers a promising clinical approach to treating refractory diseases. The global market for cell therapy is growing rapidly, and there is an increasing demand for automated methods that can produce large quantities of high quality therapeutic cells. Biomaterials can be used during cell production to establish a biomimetic microenvironment that promotes cell adhesion and proliferation while maintaining target cell genotype and phenotype. Here we review recent progress and emerging techniques in biomaterial-assisted cell production. The increasing use of auxiliary biomaterials and automated production methods provides an opportunity to improve quality control and increase production efficiency using standardized GMP-compliant procedures.

Advances in immunotherapy of type I diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease affecting 3 million individuals in the U.S. The pathogenesis of T1DM is driven by immune-mediated destruction of pancreatic β cells, the source of glucose regulator insulin. While T1DM can be successfully managed with insulin replacement therapy, approaches that can modify the underlying immuno-pathology of β cell destruction has been long sought after. Immunotherapy can attenuate T cell responses against β cell antigens. Given the detailed cellular and molecular definitions of T1DM immune responses, rational immunomodulation can be and have been developed in mouse models, and in some instances, tested in humans. The possibility of identifying individuals who are predisposed to T1DM through genotyping lend to the possibility of preventive vaccines. While much has been accomplished in delineating the mechanisms of immunotherapies, some of which are being tested in humans, long-term preservation of β cells and insulin independency has not been achieved. In this regard, the drug delivery field has much to offer in maximizing the benefits of immune modulators by optimizing spatiotemporal presentation of antigens and costimulatory signals. In this review, we attempt to capture the current state of T1DM immunotherapy by highlighting representative studies.

On-target and direct modulation of alloreactive T cells by a nanoparticle carrying MHC alloantigen, regulatory molecules and CD47 in a murine model of alloskin transplantation

Biomimetic nanoparticles have been reported as immune modulators in autoimmune diseases and allograft rejections by numerous researchers. However, most of the therapeutics carrying antigens, toxins or cytokines underlay the mechanism of antigen presentation by cellular uptake of NPs through pinocytosis and phagocytosis. Few researches focus on the direct and antigen-specific modulation on T cells by NPs and combined use of multiple regulatory molecules. Here, polylactic-co-glycolic acid nanoparticles (PLGA-NPs) were fabricated as scaffold to cocoupling H-2K^b-Ig dimer, anti-Fas mAb, PD-L1-Fc, TGF-β and CD47-Fc for the generation of alloantigen-presenting and tolerance-inducing NPs, termed killer NPs and followed by i.v. injection into a single MHC-mismatched murine model of alloskin transplantation. Three infusions prolonged alloskin graft survival for 45 days; depleted most of H-2K^b alloreactive CD8⁺ T cells in peripheral blood, spleen and local graft, in an antigen-specific manner. The killer NPs circulated throughout vasculature into various organs and local allograft, with a retention time up to 30 h. They made contacts with CD8⁺ T cells to facilitate vigorous apoptosis, inhibit the activation and proliferation of alloreactive CD8⁺ T cells and induce regulatory T cells in secondary lymphoid organs, with the greatly minimized uptake by phagocytes. More importantly, the impairment of host overall immune function and visible organ toxicity were not found. Our results provide the first experimental evidence for the direct and on-target modulation on alloreactive T cells by the biodegradable 200-nm killer NPs via co-presentation of alloantigen and multiple regulatory molecules, thus suggest a novel antigen-specific immune modulator for allograft rejections.

Modern Therapeutic Approaches for Noninfectious Ocular Diseases Involving Inflammation

Dry eye disease, age-related macular degeneration, and uveitis are ocular diseases that significantly affect the quality of life of millions of people each year. In these diseases, the action of chemokines, proinflammatory cytokines, and immune cells drives a local inflammatory response that results in ocular tissue damage. Multiple therapeutic strategies are developed to either address the symptoms or abate the underlying cause of these diseases. Herein, the challenges to deliver drugs to the relevant location in the eye for each of these diseases are reviewed along with current and innovative therapeutic approaches that attempt to restore homeostasis within the ocular microenvironment.

Treg-recruiting microspheres prevent inflammation in a murine model of dry eye disease

Dry eye disease (DED) is a common ocular disorder affecting millions of individuals worldwide. The pathology of DED involves the infiltration of CD4+ lymphocytes, leading to tear film instability and destructive inflammation. In the healthy steady state, a population of immunosuppressive T-cells called regulatory T-cells (Treg) regulates proliferation of immune cells that would otherwise lead to a disruption of immunological homeostasis. For this reason, it has been suggested that Tregs could restore the immunological imbalance in DED. To this end, one possible approach would be to recruit the body's own, endogenous Tregs in order to enrich them at the site of inflammation and tissue destruction. Previously, we have demonstrated a reduction of inflammation and disease symptoms in models of periodontitis corresponding to recruitment of endogenous Tregs, which was accomplished by local placement of controlled release systems that sustain a gradient of the chemokine CCL22, referred to here as Treg-recruiting microspheres. Given that DED is characterized by a pro-inflammatory environment resulting in local tissue destruction, we hypothesized that the controlled release of CCL22 could also recruit Tregs to the ocular surface potentially mediating inflammation and symptoms of DED. Indeed, data suggest that Treg-recruiting microspheres are capable of overcoming the immunological imbalance of Tregs and CD4+ IFN-γ+ cells in the lacrimal gland. Administration of Treg-recruiting microspheres effectively mitigated the symptoms of DED as measured through a number of outcomes such as tear clearance, goblet cells density and corneal epithelial integrity, suggesting that recruitment of endogenous Treg can mitigate inflammation associated with DED.

Promoting tissue regeneration by modulating the immune system

The immune system plays a central role in tissue repair and regeneration. Indeed, the immune response to tissue injury is crucial in determining the speed and the outcome of the healing process, including the extent of scarring and the restoration of organ function. Therefore, controlling immune components via biomaterials and drug delivery systems is becoming an attractive approach in regenerative medicine, since therapies based on stem cells and growth factors have not yet proven to be broadly effective in the clinic. To integrate the immune system into regenerative strategies, one of the first challenges is to understand the precise functions of the different immune components during the tissue healing process. While remarkable progress has been made, the immune mechanisms involved are still elusive, and there is indication for both negative and positive roles depending on the tissue type or organ and life stage. It is well recognized that the innate immune response comprising danger signals, neutrophils and macrophages modulates tissue healing. In addition, it is becoming evident that the adaptive immune response, in particular T cell subset activities, plays a critical role. In this review, we first present an overview of the basic immune mechanisms involved in tissue repair and regeneration. Then, we highlight various approaches based on biomaterials and drug delivery systems that aim at modulating these mechanisms to limit fibrosis and promote regeneration. We propose that the next generation of regenerative therapies may evolve from typical biomaterial-, stem cell-, or growth factor-centric approaches to an immune-centric approach.

STATEMENT OF SIGNIFICANCE

Most regenerative strategies have not yet proven to be safe or reasonably efficient in the clinic. In addition to stem cells and growth factors, the immune system plays a crucial role in the tissue healing process. Here, we propose that controlling the immune-mediated mechanisms of tissue repair and regeneration may support existing regenerative strategies or could be an alternative to using stem cells and growth factors. The first part of this review we highlight key immune mechanisms involved in the tissue healing process and marks them as potential target for designing regenerative strategies. In the second part, we discuss various approaches using biomaterials and drug delivery systems that aim at modulating the components of the immune system to promote tissue regeneration.

Matrix Metalloproteinases as Regulators of Periodontal Inflammation

Periodontitis are infectious diseases characterized by immune-mediated destruction of periodontal supporting tissues and tooth loss. Matrix metalloproteinases (MMPs) are key proteases involved in destructive periodontal diseases. The study and interest in MMP has been fuelled by emerging evidence demonstrating the broad spectrum of molecules that can be cleaved by them and the myriad of biological processes that they can potentially regulate. The huge complexity of MMP functions within the 'protease web' is crucial for many physiologic and pathologic processes, including immunity, inflammation, bone resorption, and wound healing. Evidence points out that MMPs assemble in activation cascades and besides their classical extracellular matrix substrates, they cleave several signalling molecules-such as cytokines, chemokines, and growth factors, among others-regulating their biological functions and/or bioavailability during periodontal diseases. In this review, we provide an overview of emerging evidence of MMPs as regulators of periodontal inflammation.

Immune Tolerance for Autoimmune Disease and Cell Transplantation

The undesired destruction of healthy cells, either endogenous or transplanted, by the immune system results in the loss of tissue function or limits strategies to restore tissue function. Current therapies typically involve nonspecific immunosuppression that may prevent the appropriate response to an antigen, thereby decreasing humoral immunity and increasing the risks of patient susceptibility to opportunistic infections, viral reactivation, and neoplasia. The induction of antigen-specific immunological tolerance to block undesired immune responses to self- or allogeneic antigens, while maintaining the integrity of the remaining immune system, has the potential to transform the current treatment of autoimmune disease and serve as a key enabling technology for therapies based on cell transplantation.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Characterization of the Protective Role of Regulatory T Cells in Experimental Periapical Lesion Development and Their Chemoattraction Manipulation as a Therapeutic Tool

INTRODUCTION

The pathogenesis of periapical lesions is determined by the balance between host proinflammatory immune response and counteracting anti-inflammatory and reparative responses, which include regulatory T cells (Tregs) as potential immunoregulatory agents. In this study, we investigated (in a cause-and-effect manner) the involvement of CCL22-CCR4 axis in Treg migration to the periapical area and the role of Tregs in the determination of outcomes in periapical lesions.

METHODS

Periapical lesions were induced in C57Bl/6 (wild-type) and CCR4KO mice (pulp exposure and bacterial inoculation) and treated with anti-glucocorticoid-induced TNF receptor family regulated gene to inhibit Treg function or alternatively with CCL22-releasing, polylactic-glycolic acid particles to induce site-specific migration of Tregs. After treatment, lesions were analyzed for Treg influx and phenotype, overall periapical bone loss, and inflammatory/immunologic and wound healing marker expression (analyzed by real-time polymerase chain reaction array).

RESULTS

Treg inhibition by anti-glucocorticoid-induced TNF receptor family regulated gene or CCR4 depletion results in a significant increase in periapical lesion severity, associated with upregulation of proinflammatory, T-helper 1, T-helper 17, and tissue destruction markers in parallel with decreased Treg and healing marker expression. The local release of CCL22 in the root canal system resulted in the promotion of Treg migration in a CCR4-dependent manner, leading to the arrest of periapical lesion progression, associated with downregulation of proinflammatory, T-helper 1, T-helper 17, and tissue destruction markers in parallel with increased Treg and healing marker expression.

CONCLUSIONS

Because the natural and CCL22-induced Treg migration switches active lesion into inactivity phenotype, Treg chemoattractant may be a promising strategy for the clinical management of periapical lesions.

The scope and sequence of growth factor delivery for vascularized bone tissue regeneration

Bone regeneration is a complex process, that in vivo, requires the highly coordinated presentation of biochemical cues to promote the various stages of angiogenesis and osteogenesis. Taking inspiration from the natural healing process, a wide variety of growth factors are currently being released within next generation tissue engineered scaffolds (in a variety of ways) in order to heal non-union fractures and bone defects. This review will focus on the delivery of multiple growth factors to the bone regeneration niche, specifically 1) dual growth factor delivery signaling and crosstalk, 2) the importance of growth factor timing and temporal separation, and 3) the engineering of delivery systems that allow for temporal control over presentation of soluble growth factors. Alternative methods for growth factor presentation, including the use of gene therapy and platelet-rich plasma scaffolds, are also discussed.

Micro and nanoparticle drug delivery systems for preventing allotransplant rejection

Despite decades of advances in transplant immunology, tissue damage caused by acute allograft rejection remains the primary cause of morbidity and mortality in the transplant recipient. Moreover, the long-term sequelae of lifelong immunosuppression leaves patients at risk for developing a host of other deleterious conditions. Controlled drug delivery using micro- and nanoparticles (MNPs) is an effective way to deliver higher local doses of a given drug to specific tissues and cells while mitigating systemic effects. Herein, we review several descriptions of MNP immunotherapies aimed at prolonging allograft survival. We also discuss developments in the field of biomimetic drug delivery that use MNP constructs to induce and recruit our bodies' own suppressive immune cells. Finally, we comment on the regulatory pathway associated with these drug delivery systems. Collectively, it is our hope the studies described in this review will help to usher in a new era of immunotherapy in organ transplantation.