Dendritic cell derived exosomes loaded with immunoregulatory cargo reprogram local immune responses and inhibit degenerative bone disease in vivo

Advances in the application and research of biomaterials in promoting bone repair and regeneration through immune modulation

With the ongoing development of osteoimmunology, increasing evidence indicates that the local immune microenvironment plays a critical role in various stages of bone formation. Consequently, modulating the immune inflammatory response triggered by biomaterials to foster a more favorable immune microenvironment for bone regeneration has emerged as a novel strategy in bone tissue engineering. This review first examines the roles of various immune cells in bone tissue injury and repair. Then, the contributions of different biomaterials, including metals, bioceramics, and polymers, in promoting osteogenesis through immune regulation, as well as their future development directions, are discussed. Finally, various design strategies, such as modifying the physicochemical properties of biomaterials and integrating bioactive substances, to optimize material design and create an immune environment conducive to bone formation, are explored. In summary, this review comprehensively covers strategies and approaches for promoting bone tissue regeneration through immune modulation. It offers a thorough understanding of current research trends in biomaterial-based immune regulation, serving as a theoretical reference for the further development and clinical application of biomaterials in bone tissue engineering.

Nature's carriers: leveraging extracellular vesicles for targeted drug delivery

With the rapid development of drug delivery systems, extracellular vesicles (EVs) have emerged as promising stars for improving targeting abilities and realizing effective delivery. Numerous studies have shown when compared to conventional strategies in targeted drug delivery (TDD), EVs-based strategies have several distinguished advantages besides targeting, such as participating in cell-to-cell communications and immune response, showing high biocompatibility and stability, penetrating through biological barriers, etc. In this review, we mainly focus on the mass production of EVs including the challenges and strategies for scaling up EVs production in a cost-effective and reproducible manner, the loading and active targeting methods, and examples of EVs as vehicles for TDD in consideration of potential safety and regulatory issues associated. We also conclude and discuss the rigor and reproducibility of EVs production, the current research status of the application of EVs-based strategies to targeted drug delivery, clinical conversion prospects, and existing chances and challenges.

Microbial- and host immune cell-derived extracellular vesicles in the pathogenesis and therapy of periodontitis: A narrative review

Periodontitis is a chronic inflammatory disease caused by dysbiotic biofilms and destructive host immune responses. Extracellular vesicles (EVs) are circulating nanoparticles released by microbes and host cells involved in cell-to-cell communication, found in body biofluids, such as saliva and gingival crevicular fluid (GCF). EVs are mainly involved in cell-to-cell communication, and may hold promise for diagnostic and therapeutic purposes. Periodontal research has examined the potential involvement of bacterial- and host-cell-derived EVs in disease pathogenesis, diagnosis, and therapy, but data remains scarce on immune cell- or microbial-derived EVs. In this narrative review, we first provide an overview of the role of microbial and host-derived EVs on disease pathogenesis. Recent studies reveal that Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans-derived outer membrane vesicles (OMVs) can activate inflammatory cytokine release in host cells, while M1 macrophage EVs may contribute to bone loss. Additionally, we summarised current in vitro and pre-clinical research on the utilisation of immune cell and microbial-derived EVs as potential therapeutic tools in the context of periodontal treatment. Studies indicate that EVs from M2 macrophages and dendritic cells promote bone regeneration in animal models. While bacterial EVs remain underexplored for periodontal therapy, preliminary research suggests that P. gingivalis OMVs hold promise as vaccine candidates. Finally, we acknowledge the current limitations present in the field of translating immune cell derived EVs and microbial derived EVs in periodontology. It is concluded that microbial and host immune cell-derived EVs have a role in periodontitis pathogenesis and hence may be useful for studying disease pathophysiology, and as diagnostic and treatment monitoring biomarkers.

A perspective from the National Eye Institute Extracellular Vesicle Workshop: Gaps, needs, and opportunities for studies of extracellular vesicles in vision research

With an evolving understanding and new discoveries in extracellular vesicle (EV) biology and their implications in health and disease, the significant diagnostic and therapeutic potential of EVs for vision research has gained recognition. In 2021, the National Eye Institute (NEI) unveiled its Strategic Plan titled 'Vision for the Future (2021-2025),' which listed EV research as a priority within the domain of Regenerative Medicine, a pivotal area outlined in the Plan. In alignment with this prioritization, NEI organized a workshop inviting twenty experts from within and beyond the visual system. The workshop aimed to review current knowledge in EV research and explore gaps, needs and opportunities for EV research in the eye, including EV biology and applications of EVs in diagnosis, therapy and prognosis within the visual system. This perspective encapsulates the workshop's deliberations, highlighting the current landscape and potential implications of EV research in advancing eye health and addressing visual diseases.

Unraveling the role of long non-coding RNAs in therapeutic resistance in acute myeloid leukemia: New prospects & challenges

Acute Myeloid Leukemia (AML) is a fatal hematological disease characterized by the unchecked proliferation of immature myeloid blasts in different tissues developed by various mutations in hematopoiesis. Despite intense chemotherapeutic regimens, patients often experience poor outcomes, leading to substandard remission rates. In recent years, long non-coding RNAs (lncRNAs) have increasingly become important prognostic and therapeutic hotspots, due to their contributions to dysregulating many functional epigenetic, transcriptional, and post-translational mechanisms leading to alterations in cell expressions, resulting in increased chemoresistance and reduced apoptosis in leukemic cells. Through this review, I highlight and discuss the latest advances in understanding the major mechanisms through which lncRNAs confer therapy resistance in AML. In addition, I also provide perspective on the current strategies to target lncRNA expressions. A better knowledge of the critical role that lncRNAs play in controlling treatment outcomes in AML will help improve existing medications and devise new ones.

Microenvironment-responsive nanomedicines: a promising direction for tissue regeneration

Severe tissue defects present formidable challenges to human health, persisting as major contributors to mortality rates. The complex pathological microenvironment, particularly the disrupted immune landscape within these defects, poses substantial hurdles to existing tissue regeneration strategies. However, the emergence of nanobiotechnology has opened a new direction in immunomodulatory nanomedicine, providing encouraging prospects for tissue regeneration and restoration. This review aims to gather recent advances in immunomodulatory nanomedicine to foster tissue regeneration. We begin by elucidating the distinctive features of the local immune microenvironment within defective tissues and its crucial role in tissue regeneration. Subsequently, we explore the design and functional properties of immunomodulatory nanosystems. Finally, we address the challenges and prospects of clinical translation in nanomedicine development, aiming to propose a potent approach to enhance tissue regeneration through synergistic immune modulation and nanomedicine integration.

Extracellular vesicles as therapeutic tools in regenerative dentistry

Dental and maxillofacial diseases are always accompanied by complicated hard and soft tissue defects, involving bone, teeth, blood vessels and nerves, which are difficult to repair and severely affect the life quality of patients. Recently, extracellular vesicles (EVs) secreted by all types of cells and extracted from body fluids have gained more attention as potential solutions for tissue regeneration due to their special physiological characteristics and intrinsic signaling molecules. Compared to stem cells, EVs present lower immunogenicity and tumorigenicity, cause fewer ethical problems, and have higher stability. Thus, EV therapy may have a broad clinical application in regenerative dentistry. Herein, we reviewed the currently available literature regarding the functional roles of EVs in oral and maxillofacial tissue regeneration, including in maxilla and mandible bone, periodontal tissues, temporomandibular joint cartilage, dental hard tissues, peripheral nerves and soft tissues. We also summarized the underlying mechanisms of actions of EVs and their delivery strategies for dental tissue regeneration. This review would provide helpful guidelines and valuable insights into the emerging potential of EVs in future research and clinical applications in regenerative dentistry.

The balance between helper T 17 and regulatory T cells in osteoimmunology and relevant research progress on bone tissue engineering

BACKGROUND

Bone regeneration is a well-regulated dynamic process, of which the prominent role of the immune system on bone homeostasis is more and more revealed by recent research. Before fully activation of the bone remodeling cells, the immune system needs to clean up the microenvironment in facilitating the bone repair initiation. Furthermore, this microenvironment must be maintained properly by various mechanisms over the entire bone regeneration process.

OBJECTIVE

This review aims to summarize the role of the T-helper 17/Regulatory T cell (Th17/Treg) balance in bone cell remodeling and discuss the relevant progress in bone tissue engineering.

RESULTS

The role of the immune response in the early stages of bone regeneration is crucial, especially the impact of the Th17/Treg balance on osteoclasts, mesenchymal stem cells (MSCs), and osteoblasts activity. By virtue of these knowledge advancements, innovative approaches in bone tissue engineering, such as nano-structures, hydrogel, and exosomes, are designed to influence the Th17/Treg balance and thereby augment bone repair and regeneration.

CONCLUSION

Targeting the Th17/Treg balance is a promising innovative strategy for developing new treatments to enhance bone regeneration, thus offering potential breakthroughs in bone injury clinics.

The role of exosomal molecular cargo in exosome biogenesis and disease diagnosis

Exosomes represent a type of extracellular vesicles derived from the endosomal pathway that transport diverse molecular cargoes such as proteins, lipids, and nucleic acids. These cargoes have emerged as crucial elements impacting disease diagnosis, treatment, and prognosis, and are integral to the process of exosome formation. This review delves into the essential molecular cargoes implicated in the phases of exosome production and release. Emphasis is placed on their significance as cancer biomarkers and potential therapeutic targets, accompanied by an exploration of the obstacles and feasible applications linked to these developments.

Amniotic fluid stem cell-derived extracellular vesicles educate type 2 conventional dendritic cells to rescue autoimmune disorders in a multiple sclerosis mouse model

Dendritic cells (DCs) are essential orchestrators of immune responses and represent potential targets for immunomodulation in autoimmune diseases. Human amniotic fluid secretome is abundant in immunoregulatory factors, with extracellular vesicles (EVs) being a significant component. However, the impact of these EVs on dendritic cells subsets remain unexplored. In this study, we investigated the interaction between highly purified dendritic cell subsets and EVs derived from amniotic fluid stem cell lines (HAFSC-EVs). Our results suggest that HAFSC-EVs are preferentially taken up by conventional dendritic cell type 2 (cDC2) through CD29 receptor-mediated internalization, resulting in a tolerogenic DC phenotype characterized by reduced expression and production of pro-inflammatory mediators. Furthermore, treatment of cDC2 cells with HAFSC-EVs in coculture systems resulted in a higher proportion of T cells expressing the regulatory T cell marker Foxp3 compared to vehicle-treated control cells. Moreover, transfer of HAFSC-EV-treated cDC2s into an EAE mouse model resulted in the suppression of autoimmune responses and clinical improvement. These results suggest that HAFSC-EVs may serve as a promising tool for reprogramming inflammatory cDC2s towards a tolerogenic phenotype and for controlling autoimmune responses in the central nervous system, representing a potential platform for the study of the effects of EVs in DC subsets.

The Therapeutic Potential of Human Umbilical Cord Mesenchymal Stromal Cells Derived Exosomes for Wound Healing: Harnessing Exosomes as a Cell-free Therapy

Wound healing is a complicated process that involves many different types of cells and signaling pathways. Mesenchymal stromal cells (MSCs) have shown great potential as a treatment to improve wound healing because they can modulate inflammation, promote the growth of new blood vessels, and stimulate the regeneration of tissue. Recent evidence indicates MSCs-derived extracellular vesicles known as exosomes may mediate many of the therapeutic effects of MSCs on wound healing. Exosomes contain bioactive molecules such as proteins, lipids, and RNAs that can be transferred to recipient cells to modulate cellular responses. This article reviews current evidence on the mechanisms and therapeutic effects of human umbilical cord MSCs (hUCMSCs)-derived exosomes on wound healing. In vitro and animal studies demonstrate that hUCMSC-derived exosomes promote fibroblast proliferation/migration, angiogenesis, and re-epithelialization while reducing inflammation and scar formation. These effects are mediated by exosomal transfer of cytokines, growth factors, and regulatory microRNAs that modulate signaling pathways involved in wound healing. Challenges remain in exosome isolation methods, optimizing targeting/retention, and translation to human studies. Nevertheless, hUCMSCs-derived exosomes show promise as a novel cell-free therapeutic approach to accelerate wound closure and improve healing outcomes. Further research is warranted to fully characterize hUCMSCs-exosomal mechanisms and explore their clinical potential for wound management.

Personalized Nanovaccines Enhance Lymph Node Accumulation and Reprogram the Tumor Microenvironment for Improved Photodynamic Immunotherapy

Tumor immunotherapy has emerged as an efficacious therapeutic approach that mobilizes the patient's immune system to achieve durable tumor suppression. Here, we design a photodynamic therapy-motivated nanovaccine (Dex-HDL/ALA-Fe3O4) co-delivering 5-aminolevulinic acid and Fe3O4 nanozyme that demonstrate a long-term durable immunotherapy strategy. After vaccination, the nanovaccine exhibits obvious tumor site accumulation, lymph node homing, and specific and memory antitumor immunity evocation. Upon laser irradiation, Dex-HDL/ALA-Fe3O4 effectively generates reactive oxygen species at the tumor site not only to induce the immunogenic cell death-cascade but also to trigger the on-demand release of full types of tumor antigens. Intriguingly, Fe3O4 nanozyme-catalyzed hydrogen peroxide generated oxygen for alleviating tumor hypoxia and modifying the inhibitory tumor microenvironment, thereby exhibiting remarkable potential as a sensitizer. The intravenous administration of nanovaccines in diverse preclinical cancer models has demonstrated remarkable tumor regression and inhibition of postoperative tumor recurrence and metastasis, thereby enabling personalized treatment strategies against highly heterogeneous tumors.

Oral Microbially-Induced Small Extracellular Vesicles Cross the Blood-Brain Barrier

Porphyromonas gingivalis (Pg) and its gingipain proteases contribute to Alzheimer's disease (AD) pathogenesis through yet unclear mechanisms. Cellular secretion of small extracellular vesicles or exosomes (EXO) increases with aging as part of the senescence-associated secretory phenotype (SASP). We have shown that EXO isolated from Pg-infected dendritic cells contain gingipains and other Pg antigens and transmit senescence to bystander gingival cells, inducing alveolar bone loss in mice in vivo. Here, EXO were isolated from the gingiva of mice and humans with/without periodontitis (PD) to determine their ability to penetrate the blood-brain barrier (BBB) in vitro and in vivo. PD was induced by Pg oral gavage for 6 weeks in C57B6 mice. EXO isolated from the gingiva or brain of donor Pg-infected (PD EXO) or control animals (Con EXO) were characterized by NTA, Western blot, and TEM. Gingival PD EXO or Con EXO were labeled and injected into the gingiva of uninfected WT mouse model. EXO biodistribution in brains was tracked by an in vivo imaging system (IVIS) and confocal microscopy. The effect of human PD EXO on BBB integrity and permeability was examined using TEER and FITC dextran assays in a human in vitro 3D model of the BBB. Pg antigens (RGP and Mfa-1) were detected in EXO derived from gingival and brain tissues of donor Pg-infected mice. Orally injected PD EXO from donor mice penetrated the brains of recipient uninfected mice and colocalized with hippocampal microglial cells. IL-1β and IL-6 were expressed in human PD EXO and not in Con EXO. Human PD EXO promoted BBB permeability and penetrated the BBB in vitro. This is the first demonstration that microbial-induced EXO in the oral cavity can disseminate, cross the BBB, and may contribute to AD pathogenesis.

Strategies for labelling of exogenous and endogenous extracellular vesicles and their application for in vitro and in vivo functional studies

This review presents a comprehensive overview of labelling strategies for endogenous and exogenous extracellular vesicles, that can be utilised both in vitro and in vivo. It covers a broad spectrum of approaches, including fluorescent and bioluminescent labelling, and provides an analysis of their applications, strengths, and limitations. Furthermore, this article presents techniques that use radioactive tracers and contrast agents with the ability to track EVs both spatially and temporally. Emphasis is also placed on endogenous labelling mechanisms, represented by Cre-lox and CRISPR-Cas systems, which are powerful and flexible tools for real-time EV monitoring or tracking their fate in target cells. By summarizing the latest developments across these diverse labelling techniques, this review provides researchers with a reference to select the most appropriate labelling method for their EV based research.

Interaction between immuno-stem dual lineages in jaw bone formation and injury repair

The jawbone, a unique structure in the human body, undergoes faster remodeling than other bones due to the presence of stem cells and its distinct immune microenvironment. Long-term exposure of jawbones to an oral environment rich in microbes results in a complex immune balance, as shown by the higher proportion of activated macrophage in the jaw. Stem cells derived from the jawbone have a higher propensity to differentiate into osteoblasts than those derived from other bones. The unique immune microenvironment of the jaw also promotes osteogenic differentiation of jaw stem cells. Here, we summarize the various types of stem cells and immune cells involved in jawbone reconstruction. We describe the mechanism relationship between immune cells and stem cells, including through the production of inflammatory bodies, secretion of cytokines, activation of signaling pathways, etc. In addition, we also comb out cellular interaction of immune cells and stem cells within the jaw under jaw development, homeostasis maintenance and pathological conditions. This review aims to eclucidate the uniqueness of jawbone in the context of stem cell within immune microenvironment, hopefully advancing clinical regeneration of the jawbone.

Understanding exosomes: Part 3-therapeutic + diagnostic potential in dentistry

Exosomes are the smallest subset of extracellular signaling vesicles secreted by most cells with the ability to communicate with other tissues and cell types over long distances. Their use in regenerative medicine has gained tremendous momentum recently due to their ability to be utilized as therapeutic options for a wide array of various diseases. Over 5000 publications are currently being published on this topic yearly, many of which in the dental space. This extensive review article is the first scoping review aimed at summarizing all therapeutic uses of exosomes in regenerative dentistry. A total of 944 articles were identified as using exosomes in the dental field for either their regenerative/therapeutic potential or for diagnostic purposes derived from the oral cavity. In total, 113 research articles were selected for their regenerative potential (102 in vitro, 60 in vivo, 50 studies included both). Therapeutic exosomes were most commonly derived from dental pulps, periodontal ligament cells, gingival fibroblasts, stem cells from exfoliated deciduous teeth, and the apical papilla which have all been shown to facilitate the regenerative potential of a number of tissues including bone, cementum, the periodontal ligament, nerves, aid in orthodontic tooth movement, and relieve temporomandibular joint disorders, among others. Results demonstrate that the use of exosomes led to positive outcomes in 100% of studies. In the bone field, exosomes were found to perform equally as well or better than rhBMP2 while significantly reducing inflammation. Periodontitis animal models were treated with simple gingival injections of exosomes and benefits were even observed when the exosomes were administered intravenously. Exosomes are much more stable than growth factors and were shown to be far more resistant against degradation by periodontal pathogens found routinely in a periodontitis environment. Comparative studies in the field of periodontal regeneration found better outcomes for exosomes even when compared to their native parent stem cells. In total 47 diagnostic studies revealed a role for salivary/crevicular fluid exosomes for the diagnosis of birth defects, cardiovascular disease, diabetes, gingival recession detection, gingivitis, irritable bowel syndrome, neurodegenerative disease, oral lichen planus, oral squamous cell carcinoma, oropharyngeal cancer detection, orthodontic root resorption, pancreatic cancer, periodontitis, peri-implantitis, Sjögren syndrome, and various systemic diseases. Hence, we characterize the exosomes as possessing "remarkable" potential, serving as a valuable tool for clinicians with significant advantages.

Non-bone-derived exosomes: a new perspective on regulators of bone homeostasis

Accumulating evidence indicates that exosomes help to regulate bone homeostasis. The roles of bone-derived exosomes have been well-described; however, recent studies have shown that some non-bone-derived exosomes have better bone targeting ability than bone-derived exosomes and that their performance as a drug delivery vehicle for regulating bone homeostasis may be better than that of bone-derived exosomes, and the sources of non-bone-derived exosomes are more extensive and can thus be better for clinical needs. Here, we sort non-bone-derived exosomes and describe their composition and biogenesis. Their roles and specific mechanisms in bone homeostasis and bone-related diseases are also discussed. Furthermore, we reveal obstacles to current research and future challenges in the practical application of exosomes, and we provide potential strategies for more effective application of exosomes for the regulation of bone homeostasis and the treatment of bone-related diseases. Video Abstract.

Emerging roles of exosomes in oral diseases progression

Oral diseases, such as periodontitis, salivary gland diseases, and oral cancers, significantly challenge health conditions due to their detrimental effects on patient's digestive functions, pronunciation, and esthetic demands. Delayed diagnosis and non-targeted treatment profoundly influence patients' prognosis and quality of life. The exploration of innovative approaches for early detection and precise treatment represents a promising frontier in oral medicine. Exosomes, which are characterized as nanometer-sized extracellular vesicles, are secreted by virtually all types of cells. As the research continues, the complex roles of these intracellular-derived extracellular vesicles in biological processes have gradually unfolded. Exosomes have attracted attention as valuable diagnostic and therapeutic tools for their ability to transfer abundant biological cargos and their intricate involvement in multiple cellular functions. In this review, we provide an overview of the recent applications of exosomes within the field of oral diseases, focusing on inflammation-related bone diseases and oral squamous cell carcinomas. We characterize the exosome alterations and demonstrate their potential applications as biomarkers for early diagnosis, highlighting their roles as indicators in multiple oral diseases. We also summarize the promising applications of exosomes in targeted therapy and proposed future directions for the use of exosomes in clinical treatment.

Emerging approaches to induce immune tolerance to therapeutic proteins

Immunogenicity affects the safety and efficacy of therapeutic proteins. This review is focused on approaches for inducing immunological tolerance to circumvent the immunogenicity of therapeutic proteins in the clinic. The few immune tolerance strategies that are used in the clinic tend to be inefficient and expensive and typically involve global immunosuppression, putting patients at risk of infections. The hallmark of a desirable immune tolerance regimen is the specific alleviation of immune responses to the therapeutic protein. In the past decade, proof-of-principle studies have demonstrated that emerging technologies, including nanoparticle-based delivery of immunomodulators, cellular targeting and depletion, cellular engineering, gene therapy, and gene editing, can be leveraged to promote tolerance to therapeutic proteins. We discuss the potential of these novel approaches and the barriers that need to be overcome for translation into the clinic.

Butyrate Inhibits Dendritic Cell Activation and Alleviates Periodontitis

Dendritic cells (DCs) can mediate inflammation-related bone resorption that is crucial in the development of periodontitis. Butyrate is a critical by-product of microbes with antibacterial and anti-inflammatory properties. Here, we found that butyrate inhibited the activation of lipopolysaccharide (LPS)-induced DCs and generation of inflammatory cytokines by DCs. Moreover, butyrate regulated glycolysis in LPS-induced DCs via the G-protein-coupled receptor/hypoxia-inducible factor-1α pathway. In addition, butyrate inhibited the maturation of CD11c+MHC-II+ DCs in vivo, suppressing local inflammatory infiltration and ultimately alleviating bone resorption in a periodontitis model. Our results imply that butyrate suppresses the activation of LPS-induced DCs by modulating their metabolism, highlighting its potential as a therapeutic agent for inflammatory diseases.

Roles of trained immunity in the pathogenesis of periodontitis

Periodontitis is a chronic, inflammatory, and destructive disease caused by the imbalance of host immune response and dental biofilm, and has strong epidemiological and pathogenesis correlations with systemic diseases. The immune response in periodontitis involves both innate and adaptive immunity, with numerous immune cells and inflammatory pathways participating in a complex network of interactions. In the past decade, the concept of "trained immunity" has emerged, which highlights the memory characteristics of innate immunity, thus opening up a new avenue of research. There is growing interest in exploring the role of trained immunity in chronic inflammatory and metabolic diseases such as atherosclerosis and diabetes mellitus. Evidence suggests that trained immunity may also regulate the onset and progression of periodontitis, serving as a bridge between periodontitis-related comorbidities. In this review, we summarize concepts related to trained immunity and its development. Furthermore, we present current evidence that endorses the notion of trained immunity in periodontitis and analyze possible roles it may assume regarding periodontitis-associated inflammatory reactions from a cellular perspective. Finally, we discuss various clinical therapeutic strategies for periodontitis and its associated comorbidities that target trained immunity. We hope that more researchers will pay attention to this emerging concept, thereby providing deeper insights into this novel field.

Influence of Vitamin D on Periodontal Inflammation: A Review

The active form of vitamin D is the hormonally active 1,25(OH)2D3 (Vit D) vitamin, which plays an important role in bone biology and host immunity. The vitamin D receptor (VDR) is a nuclear ligand-dependent transcription factor expressed by many cells. Ligation of VDR by VitD regulates a wide plethora of genes and physiologic functions through the formation of the complex Vit D-VDR signaling cascade. The influence of Vit D-VDR signaling in host immune response to microbial infection has been of interest to many researchers. This is particularly important in oral health and diseases, as oral mucosa is exposed to a complex microbiota, with certain species capable of causing disruption to immune homeostasis. In this review, we focus on the immune modulatory roles of Vit D in the bone degenerative oral disease, periodontitis.

Advances in the regulation of adipogenesis and lipid metabolism by exosomal ncRNAs and their role in related metabolic diseases

Exosomes are membrane-bound extracellular vesicles released following the fusion of multivesicular bodies (MVBs) with the cell membrane. Exosomes transport diverse molecules, including proteins, lipids, DNA and RNA, and regulate distant intercellular communication. Noncoding RNA (ncRNAs) carried by exosomes regulate cell-cell communication in tissues, including adipose tissue. This review summarizes the action mechanisms of ncRNAs carried by exosomes on adipocyte differentiation and modulation of adipogenesis by exosomal ncRNAs. This study aims to provide valuable insights for developing novel therapeutics.

Biomaterials for in situ cell therapy

Cell therapy has revolutionized the treatment of various diseases, such as cancers, genetic disorders, and autoimmune diseases. Currently, most cell therapy products rely on ex vivo cell engineering, which requires sophisticated manufacturing processes and poses safety concerns. The implementation of in situ cell therapy holds the potential to overcome the current limitations of cell therapy and provides a broad range of applications and clinical feasibility in the future. A variety of biomaterials have been developed to improve the function and target delivery to specific cell types due to their excellent biocompatibility, tunable properties, and other functionalities, which provide a reliable method to achieve in vivo modulation of cell reprogramming. In this article, we summarize recent advances in biomaterials for in situ cell therapy including T cells, macrophages, dendritic cells, and stem cells reprogramming leveraging lipid nanoparticles, polymers, inorganic materials, and other biomaterials. Finally, we discuss the current challenges and future perspectives of biomaterials for in situ cell therapy.

Drug delivery of extracellular vesicles: Preparation, delivery strategies and applications

Extracellular vesicles (EV) are cell-originated vesicles exhibited with characteristics similar to the parent cells. Several studies have suggested the therapeutic potential of EV since they played as an intercellular communicator and modulate disease microenvironment, and thus EV has been widely studied in cancer management and tissue regeneration. However, merely application of EV revealed limited therapeutic outcome in different disease scenario and co-administration of drugs may be necessary to exert proper therapeutic effect. The method of drug loading into EV and efficient delivery of the formulation is therefore important. In this review, the advantages of using EV as drug delivery system compared to traditional synthetic nanoparticles will be emphasized, followed by the method of preparing EV and drug loading. The pharmacokinetic characteristics of EV was discussed, together with the review of reported delivery strategies and related application of EV in different disease management.

Engineered Human Dendritic Cell Exosomes as Effective Delivery System for Immune Modulation

Exosomes (exos) contain molecular cargo of therapeutic and diagnostic value for cancers and other inflammatory diseases, but their therapeutic potential for periodontitis (PD) remains unclear. Dendritic cells (DCs) are the directors of immune response and have been extensively used in immune therapy. We previously reported in a mouse model of PD that custom murine DC-derived exo subtypes could reprogram the immune response toward a bone-sparing or bone-loss phenotype, depending on immune profile. Further advancement of this technology requires the testing of human DC-based exos with human target cells. Our main objective in this study is to test the hypothesis that human monocyte-derived dendritic cell (MoDC)-derived exos constitute a well-tolerated and effective immune therapeutic approach to modulate human target DC and T cell immune responses in vitro. MoDC subtypes were generated with TGFb/IL-10 (regulatory (reg) MoDCs, CD86lowHLA-DRlowPDL1high), E. coli LPS (stimulatory (stim) MoDCs, CD86highHLA-DRhighPDL1low) and buffer (immature (i) MoDCs, CD86lowHLA-DRmedPDL1low). Exosomes were isolated from different MoDC subtypes and characterized. Once released from the secreting cell into the surrounding environment, exosomes protect their prepackaged molecular cargo and deliver it to bystander cells. This modulates the functions of these cells, depending on the cargo content. RegMoDCexos were internalized by recipient MoDCs and induced upregulation of PDL1 and downregulation of costimulatory molecules CD86, HLADR, and CD80, while stimMoDCexos had the opposite influence. RegMoDCexos induced CD25+Foxp3+ Tregs, which expressed CTLA4 and PD1 but not IL-17A. In contrast, T cells treated with stimMoDCexos induced IL-17A+ Th17 T cells, which were negative for immunoregulatory CTLA4 and PD1. T cells and DCs treated with iMoDCexos were immune 'neutral', equivalent to controls. In conclusion, human DC exos present an effective delivery system to modulate human DC and T cell immune responses in vitro. Thus, MoDC exos may present a viable immunotherapeutic agent for modulating immune response in the gingival tissue to inhibit bone loss in periodontal disease.

Bone marrow mesenchymal stem cell-derived exosomes loaded with miR-26a through the novel immunomodulatory peptide DP7-C can promote osteogenesis

PURPOSE

As small bioactive molecules, exosomes can deliver osteogenesis-related miRNAs to target cells and promote osteogenesis. This study aimed to investigate miR-26a as a therapeutic cargo to be loaded into bone marrow stromal cell exosomes through a novel immunomodulatory peptide (DP7-C).

METHODS

After transfecting BMSCs with DP7-C as a transfection agent, exosomes were extracted by ultracentrifugation from the culture supernatant of miR-26a-modified BMSCs. We then characterized and identified the engineered exosomes. The effect of the engineered exosomes on osteogenesis was then evaluated in vitro and in vivo, including transwell, wound healing, modified alizarin red staining, western blot, real-time quantitative PCR, and experimental periodontitis assays. Bioinformatics and data analyses were conducted to investigate the role of miR-26a in bone regeneration.

RESULTS

The DP7-C/miR-26a complex successfully transfected miR-26a into BMSCs and stimulated them to release more than 300 times the amount of exosomes overexpressing miR-26a compared with the Exo^NC group. Furthermore, exosomes loaded with miR-26a could enhance proliferation, migration, and osteogenic differentiation of BMSCs in vitro compared with the Exo^NC and blank groups. In vivo, the Exo^miR-26a group inhibited the destruction of periodontitis compared with the Exo^NC and blank groups, as revealed by HE staining. Micro-CT indicated that treatment of Exo^miR-26a increased the percent bone volume and the bone mineral density compared with those of the Exo^NC (P < 0.05) and blank groups (P < 0.001). Target gene analysis indicated that the osteogenic effect of miR-26a is related to the mTOR pathway.

CONCLUSION

miR-26a can be encapsulated into exosomes through DP7-C. Exosomes loaded with miR-26a can promote osteogenesis and inhibit bone loss in experimental periodontitis and serve as the foundation for a novel treatment strategy.

Extracellular vesicles as next generation immunotherapeutics

Extracellular vesicles (EVs) function as a mode of intercellular communication and molecular transfer to elicit diverse biological/functional response. Accumulating evidence has highlighted that EVs from immune, tumour, stromal cells and even bacteria and parasites mediate the communication of various immune cell types to dynamically regulate host immune response. EVs have an innate capacity to evade recognition, transport and transfer functional components to target cells, with subsequent removal by the immune system, where the immunological activities of EVs impact immunoregulation including modulation of antigen presentation and cross-dressing, immune activation, immune suppression, and immune surveillance, impacting the tumour immune microenvironment. In this review, we outline the recent progress of EVs in immunorecognition and therapeutic intervention in cancer, including vaccine and targeted drug delivery and summarise their utility towards clinical translation. We highlight the strategies where EVs (natural and engineered) are being employed as a therapeutic approach for immunogenicity, tumoricidal function, and vaccine development, termed immuno-EVs. With seminal studies providing significant progress in the sequential development of engineered EVs as therapeutic anti-tumour platforms, we now require direct assessment to tune and improve the efficacy of resulting immune responses - essential in their translation into the clinic. We believe such a review could strengthen our understanding of the progress in EV immunobiology and facilitate advances in engineering EVs for the development of novel EV-based immunotherapeutics as a platform for cancer treatment.

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.

Extracellular Vesicles as reconfigurable therapeutics for eye diseases: Promises and hurdles

A large number of people worldwide suffer from visual impairment. However, most available therapies rely on impeding the development of a particular eye disorder. Therefore, there is an increasing demand for effective alternative treatments, specifically regenerative therapies. Extracellular vesicles, including exosomes, ectosomes, or microvesicles, are released by cells and play a potential role in regeneration. Following an introduction to EV biogenesis and isolation methods, this integrative review provides an overview of our current knowledge about EVs as a communication paradigm in the eye. Then, we focused on the therapeutic applications of EVs derived from conditioned medium, biological fluid, or tissue and highlighted some recent developments in strategies to boost the innate therapeutic potential of EVs by loading various kinds of drugs or being engineered at the level of producing cells or EVs. Challenges faced in the development of safe and effective translation of EV-based therapy into clinical settings for eye diseases are also discussed to pave the road toward reaching feasible regenerative therapies required for eye-related complications.

Biomimetic synthesis and optimization of extracellular vesicles for bone regeneration

Critical-size bone defect repair is in high demand but is difficult to treat. Modern therapies, such as autograft and cell-based treatments, face limitations, including potential immunological rejection and tumorigenesis. Therefore, extracellular vesicle (EV)-based strategies have been proposed as a novel approach for tissue regeneration owing to EVs' complex composition of lipids, proteins, and nucleic acids, as well as their low immunogenicity and congenital cell-targeting features. Despite these remarkable features of EVs, biomimetic synthesis and optimization of natural EVs can lead to enhanced bioactivity, increased cellular uptake, and specific cell targeting, aiming to achieve optimal therapeutic efficacy. To maximize their function, these nanoparticles can be integrated into bone graft biomaterials for superior bone regeneration. Herein, we summarize the role of naturally occurring EVs from distinct cell types in bone regeneration, the current strategies for optimizing biomimetic synthetic EVs in bone regeneration, and discuss the recent advances in applying bone graft biomaterials for the delivery of EVs to bone defect repair. We focused on distinct strategies for optimizing EVs with different functions and the most recent research on achieving time-controlled release of nanoparticles from EV-loaded biomaterials. Furthermore, we thoroughly discuss several current challenges and proposed solutions, aiming to provide insight into current progress, inspiration for future development directions, and incentives for clinical application in this field.

Microbially-Induced Exosomes from Dendritic Cells Promote Paracrine Immune Senescence: Novel Mechanism of Bone Degenerative Disease in Mice

As the aging population grows, chronic age-related bone degenerative diseases become more prevalent and severe. One such disease, periodontitis (PD), rises to 70.1% prevalence in Americans 65 years and older. PD has been linked to increased risk of other age-related diseases with more serious mortality and morbidity profiles such as Alzheimer's disease and cardiovascular disease, but the cellular and biological mechanisms remain unclear. Recent in vitro studies from our group indicate that murine dendritic cells (DCs) and T cells are vulnerable to immune senescence. This occurs through a distinct process involving invasion of DCs by dysbiotic pathogen Porphyromonas gingivalis (Pg) activating the senescence associated secretory phenotype (SASP). Exosomes of the Pg-induced SASP transmit senescence to normal bystander DC and T cells, ablating antigen presentation. The biological significance of these findings in vivo and the mechanisms involved were examined in the present study using young (4-5mo) or old (22-24mo) mice subjected to ligature-induced PD, with or without dysbiotic oral pathogen and injection of Pg-induced DC exosomes. Senescence profiling of gingiva and draining lymph nodes (LN) corroborates role of advanced age and PD in elevation of senescence biomarkers beta galactosidase (SA-β-Gal), p16 INK4A p21Waf1/Clip1, IL6, TNFα, and IL1β, with attendant increase in alveolar bone loss, reversed by senolytic agent rapamycin. Immunophenotyping of gingiva and LN revealed that myeloid CD11c+ DCs and T cells are particularly vulnerable to senescence in vivo under these conditions. Moreover, Pg-induced DC exosomes were the most potent inducers of alveolar bone loss and immune senescence, and capable of overcoming senescence resistance of LN T cells in young mice. We conclude that immune senescence, compounded by advanced age, and accelerated by oral dysbiosis and its induced SASP exosomes, plays a pivotal role in the pathophysiology of experimental periodontitis.

Small Extracellular Vesicles as a New Class of Medicines

Extracellular vesicles (EVs) are nanovesicles that are naturally released from cells in a lipid bilayer-bound form. A subset population with a size of 200 nm, small EVs (sEVs), is enticing in many ways. Initially perceived as mere waste receptacles, sEVs have revealed other biological functions, such as cell-to-cell signal transduction and communication. Besides their notable biological functions, sEVs have profound advantages as future drug modalities: (i) excellent biocompatibility, (ii) high stability, and (iii) the potential to carry undruggable macromolecules as cargo. Indeed, many biopharmaceutical companies are utilizing sEVs, not only as diagnostic biomarkers but as therapeutic drugs. However, as all inchoate fields are challenging, there are limitations and hindrances in the clinical translation of sEV therapeutics. In this review, we summarize different types of sEV therapeutics, future improvements, and current strategies in large-scale production.

The potential therapeutic role of extracellular vesicles in critical-size bone defects: Spring of cell-free regenerative medicine is coming

In recent years, the incidence of critical-size bone defects has significantly increased. Critical-size bone defects seriously affect patients' motor functions and quality of life and increase the need for additional clinical treatments. Bone tissue engineering (BTE) has made great progress in repairing critical-size bone defects. As one of the main components of bone tissue engineering, stem cell-based therapy is considered a potential effective strategy to regenerate bone tissues. However, there are some disadvantages including phenotypic changes, immune rejection, potential tumorigenicity, low homing efficiency and cell survival rate that restrict its wider clinical applications. Evidence has shown that the positive biological effects of stem cells on tissue repair are largely mediated through paracrine action by nanostructured extracellular vesicles (EVs), which may overcome the limitations of traditional stem cell-based treatments. In addition to stem cell-derived extracellular vesicles, the potential therapeutic roles of nonstem cell-derived extracellular vesicles in critical-size bone defect repair have also attracted attention from scholars in recent years. Currently, the development of extracellular vesicles-mediated cell-free regenerative medicine is still in the preliminary stage, and the specific mechanisms remain elusive. Herein, the authors first review the research progress and possible mechanisms of extracellular vesicles combined with bone tissue engineering scaffolds to promote bone regeneration via bioactive molecules. Engineering modified extracellular vesicles is an emerging component of bone tissue engineering and its main progression and clinical applications will be discussed. Finally, future perspectives and challenges of developing extracellular vesicle-based regenerative medicine will be given. This review may provide a theoretical basis for the future development of extracellular vesicle-based biomedicine and provide clinical references for promoting the repair of critical-size bone defects.

The role of extracellular vesicles in periodontitis: pathogenesis, diagnosis, and therapy

Periodontitis is a prevalent disease and one of the leading causes of tooth loss. Biofilms are initiating factor of periodontitis, which can destroy periodontal tissue by producing virulence factors. The overactivated host immune response is the primary cause of periodontitis. The clinical examination of periodontal tissues and the patient's medical history are the mainstays of periodontitis diagnosis. However, there is a lack of molecular biomarkers that can be used to identify and predict periodontitis activity precisely. Non-surgical and surgical treatments are currently available for periodontitis, although both have drawbacks. In clinical practice, achieving the ideal therapeutic effect remains a challenge. Studies have revealed that bacteria produce extracellular vesicles (EVs) to export virulence proteins to host cells. Meanwhile, periodontal tissue cells and immune cells produce EVs that have pro- or anti-inflammatory effects. Accordingly, EVs play a critical role in the pathogenesis of periodontitis. Recent studies have also presented that the content and composition of EVs in saliva and gingival crevicular fluid (GCF) can serve as possible periodontitis diagnostic indicators. In addition, studies have indicated that stem cell EVs may encourage periodontal regeneration. In this article, we mainly review the role of EVs in the pathogenesis of periodontitis and discuss their diagnostic and therapeutic potential.

Extracellular Vesicles Derived from Allergen Immunotherapy-Treated Mice Suppressed IL-5 Production from Group 2 Innate Lymphoid Cells

Allergen immunotherapy (AIT), such as subcutaneous immunotherapy (SCIT), is a treatment targeting the causes of allergic diseases. The roles of extracellular vesicles (EVs), bilayer lipid membrane blebs released from all types of cells, in AIT have not been clarified. To examine the roles of EVs in SCIT, it was analyzed whether (1) EVs are phenotypically changed by treatment with SCIT, and (2) EVs derived from SCIT treatment suppress the function of group 2 innate lymphoid cells (ILC2s), which are major cells contributing to type 2 allergic inflammation. As a result, (1) expression of CD9, a canonical EV marker, was highly up-regulated by SCIT in a murine model of asthma; and (2) IL-5 production from ILC2s in vitro was significantly decreased by the addition of serum EVs derived from SCIT-treated but not non-SCIT-treated mice. In conclusion, it was indicated that EVs were transformed by SCIT, changing to a suppressive phenotype of type 2 allergic inflammation.

Cellular Senescence and Periodontitis: Mechanisms and Therapeutics

Periodontitis is a chronic inflammatory disease which increases in prevalence and severity in the older population. Aging is a leading risk factor for periodontitis, which exacerbates alveolar bone loss and results in tooth loss in the elderly. However, the mechanism by which aging affects periodontitis is not well understood. There is considerable evidence to suggest that targeting cellular senescence could slow down the fundamental aging process, and thus alleviate a series of age-related pathological conditions, likely including alveolar bone loss. Recently, it has been discovered that the senescent cells accumulate in the alveolar bone and promote a senescence-associated secretory phenotype (SASP). Senescent cells interacting with bacteria, together with secreted SASP components altering the local microenvironment and inducing paracrine effects in neighboring cells, exacerbate the chronic inflammation in periodontal tissue and lead to more alveolar bone loss. This review will probe into mechanisms underlying excessive alveolar bone loss in periodontitis with aging and discuss potential therapeutics for the treatment of alveolar bone loss targeting cellular senescence and the SASP. Inspecting the relationship between cellular senescence and periodontitis will lead to new avenues of research in this field and contribute to developing potential translatable clinical interventions to mitigate or even reverse the harmful effects of aging on oral health.

Extracellular Vesicles: The Next Generation Theranostic Nanomedicine for Inflammatory Bowel Disease

The recent rapid development in the field of extracellular vesicles (EVs) based nanotechnology has provided unprecedented opportunities for nanomedicine platforms. As natural nanocarriers, EVs such as exosomes, exosome-like nanoparticles and outer membrane vesicles (OMVs), have unique structure/composition/morphology characteristics, and show excellent physical and chemical/biochemical properties, making them a new generation of theranostic nanomedicine. Here, we reviewed the characteristics of EVs from the perspective of their formation and biological function in inflammatory bowel disease (IBD). Moreover, EVs can crucially participate in the interaction and communication of intestinal epithelial cells (IECs)-immune cells-gut microbiota to regulate immune response, intestinal inflammation and intestinal homeostasis. Interestingly, based on current representative examples in the field of exosomes and exosome-like nanoparticles for IBD treatment, it is shown that plant, milk, and cells-derived exosomes and exosome-like nanoparticles can exert a therapeutic effect through their components, such as proteins, nucleic acid, and lipids. Moreover, several drug loading methods and target modification of exosomes are used to improve their therapeutic capability. We also discussed the application of exosomes and exosome-like nanoparticles in the treatment of IBD. In this review, we aim to better and more clearly clarify the underlying mechanisms of the EVs in the pathogenesis of IBD, and provide directions of exosomes and exosome-like nanoparticles mediated for IBD treatment.

Current perspectives on clinical use of exosomes as novel biomarkers for cancer diagnosis

Exosomes are a heterogeneous subset of extracellular vesicles (EVs) that biogenesis from endosomes. Besides, exosomes contain a variety of molecular cargoes including proteins, lipids and nucleic acids, which play a key role in the mechanism of exosome formation. Meanwhile, exosomes are involved with physiological and pathological conditions. The molecular profile of exosomes reflects the type and pathophysiological status of the originating cells so could potentially be exploited for diagnostic of cancer. This review aims to describe important molecular cargoes involved in exosome biogenesis. In addition, we highlight exogenous factors, especially autophagy, hypoxia and pharmacology, that regulate the release of exosomes and their corresponding cargoes. Particularly, we also emphasize exosome molecular cargoes as potential biomarkers in liquid biopsy for diagnosis of cancer.

Extracellular Vesicles for Immunomodulation in Tissue Regeneration

A large number of people suffer from tissue injury and defect worldwide, which constitutes a critical challenge for regenerative medicine. During the complicated process of tissue repair and regeneration, immune response that involves many kinds of immune cells often concurrently exists and plays a significant role, thus providing a promising target for the development of therapeutic strategies. As a critical player in cell-cell communication, extracellular vesicles (EVs) are a cluster of nano-sized vesicles of different categories, which have been reported to possess favorable immunoregulatory potential, and participate in the process of tissue repair and regeneration. Furthermore, EVs can be engineered with genetic or chemical strategies for optimized performance as therapeutic mediators. Here, we provide an outline on the biology of EVs as well as the role of EVs in immune regulation, focusing on exosomes, microvesicles, and apoptotic vesicles. We further summarize the applications of EV-based therapies for tissue regeneration, with particular emphasis on the modulation of immune system. Also, we have discussed the construction strategies of engineered EVs and the immunomodulatory capability of engineered EVs as well as their therapeutic potential in tissue repair. This review will highlight the outstanding potential of EV-based therapeutic strategies for tissue repair and regeneration.

Advances of exosomes in periodontitis treatment

Periodontitis is an inflammatory disease initiated by dysbiosis of the local microbial community. Periodontitis can result in destruction of tooth-supporting tissue; however, overactivation of the host immune response is the main reason for alveolar bone loss. Periodontal tissue cells, immune cells, and even further activated osteoclasts and neutrophils play pro-inflammatory or anti-inflammatory roles. Traditional therapies for periodontitis are effective in reducing the microbial quantities and improving the clinical symptoms of periodontitis. However, these methods are non-selective, and it is still challenging to achieve an ideal treatment effect in clinics using the currently available treatments and approaches. Exosomes have shown promising potential in various preclinical and clinical studies, including in the diagnosis and treatment of periodontitis. Exos can be secreted by almost all types of cells, containing specific substances of cells: RNA, free fatty acids, proteins, surface receptors and cytokines. Exos act as local and systemic intercellular communication medium, play significant roles in various biological functions, and regulate physiological and pathological processes in numerous diseases. Exos-based periodontitis diagnosis and treatment strategies have been reported to obtain the potential to overcome the drawbacks of traditional therapies. This review focuses on the accumulating evidence from the last 5 years, indicating the therapeutic potential of the Exos in preclinical and clinical studies of periodontitis. Recent advances on Exos-based periodontitis diagnosis and treatment strategies, existing challenges, and prospect are summarized as guidance to improve the effectiveness of Exos on periodontitis in clinics.

Immune cells-derived exosomes function as a double-edged sword: role in disease progression and their therapeutic applications

Exosomes, ranging in size from 30 to 150 nm as identified initially via electron microscopy in 1946, are one of the extracellular vesicles (EVs) produced by many cells and have been the subject of many studies; initially, they were considered as cell wastes with the belief that cells produced exosomes to maintain homeostasis. Nowadays, it has been found that EVs secreted by different cells play a vital role in cellular communication and are usually secreted in both physiological and pathological conditions. Due to the presence of different markers and ligands on the surface of exosomes, they have paracrine, endocrine and autocrine effects in some cases. Immune cells, like other cells, can secrete exosomes that interact with surrounding cells via these vesicles. Immune system cells-derived exosomes (IEXs) induce different responses, such as increasing and decreasing the transcription of various genes and regulating cytokine production. This review deliberate the function of innate and acquired immune cells derived exosomes, their role in the pathogenesis of immune diseases, and their therapeutic appliances.

Bone Cell Exosomes and Emerging Strategies in Bone Engineering

Bone tissue remodeling is a highly regulated process balancing bone formation and resorption through complex cellular crosstalk between resident bone and microenvironment cells. This cellular communication is mediated by direct cell and cell–matrix contact, autocrine, endocrine, and paracrine receptor mediated mechanisms such as local soluble signaling molecules and extracellular vesicles including nanometer sized exosomes. An impairment in this balanced process leads to development of pathological conditions. Bone tissue engineering is an emerging interdisciplinary field with potential to address bone defects and disorders by synthesizing three-dimensional bone substitutes embedded with cells for clinical implantation. However, current cell-based therapeutic approaches have faced hurdles due to safety and ethical concerns, challenging their clinical translation. Recent studies on exosome-regulated bone homeostasis and regeneration have gained interest as prospective cell free therapy in conjugation with tissue engineered bone grafts. However, exosome research is still in its nascent stages of bone tissue engineering. In this review, we specifically describe the role of exosomes secreted by cells within bone microenvironment such as osteoblasts, osteocytes, osteoclasts, mesenchymal stem cell cells, immune cells, endothelial cells, and even tumor cells during bone homeostasis and crosstalk. We also review exosome-based osteoinductive functionalization strategies for various bone-based biomaterials such as ceramics, polymers, and metals in bone tissue engineering. We further highlight biomaterials as carrier agents for exosome delivery to bone defect sites and, finally, the influence of various biomaterials in modulation of cell exosome secretome.

Exosomes for Regulation of Immune Responses and Immunotherapy

Exosomes are membrane-enveloped nanosized (30–150 nm) extracellular vesicles of endosomal origin produced by almost all cell types and encompass a multitude of functioning biomolecules. Exosomes have been considered crucial players of cell-to-cell communication in physiological and pathological conditions. Accumulating evidence suggests that exosomes can modulate the immune system by delivering a plethora of signals that can either stimulate or suppress immune responses, which have potential applications as immunotherapies for cancer and autoimmune diseases. Here, we discuss the current knowledge about the active biomolecular components of exosomes that contribute to exosomal function in modulating different immune cells and also how these immune cell-derived exosomes play critical roles in immune responses. We further discuss the translational potential of engineered exosomes as immunotherapeutic agents with their advantages over conventional nanocarriers for drug delivery and ongoing clinical trials.

M. de Rosales R. PET Imaging of Small Extracellular Vesicles via [89Zr]Zr(oxinate)4 Direct Radiolabeling

Exosomes or small extracellular vesicles (sEVs) are increasingly gaining attention for their potential as drug delivery systems and biomarkers of disease. Therefore, it is important to understand their in vivo biodistribution using imaging techniques that allow tracking over time and at the whole-body level. Positron emission tomography (PET) allows short- and long-term whole-body tracking of radiolabeled compounds in both animals and humans and with excellent quantification properties compared to other nuclear imaging techniques. In this report, we explored the use of [89Zr]Zr(oxinate)4 (a cell and liposome radiotracer) for direct and intraluminal radiolabeling of several types of sEVs, achieving high radiolabeling yields. The radiosynthesis and radiolabeling protocols were optimized for sEV labeling, avoiding sEV damage, as demonstrated using several characterizations (cryoEM, nanoparticle tracking analysis, dot blot, and flow cytometry) and in vitro techniques. Using pancreatic cancer sEVs (PANC1) in a healthy mouse model, we showed that it is possible to track 89Zr-labeled sEVs in vivo using PET imaging for at least up to 24 h. We also report differential biodistribution of intact sEVs compared to intentionally heat-damaged sEVs, with significantly reduced spleen uptake for the latter. Therefore, we conclude that 89Zr-labeled sEVs using this method can reliably be used for in vivo PET tracking and thus allow efficient exploration of their potential as drug delivery systems.

A Tale of Two Fimbriae: How Invasion of Dendritic Cells by Porphyromonas gingivalis Disrupts DC Maturation and Depolarizes the T-Cell-Mediated Immune Response

Porphyromonas gingivalis (P. gingivalis) is a unique pathogen implicated in severe forms of periodontitis (PD), a disease that affects around 50% of the US population. P. gingivalis is equipped with a plethora of virulence factors that it uses to exploit its environment and survive. These include distinct fimbrial adhesins that enable it to bind to other microbes, colonize inflamed tissues, acquire nutrients, and invade cells of the stroma and immune system. Most notable for this review is its ability to invade dendritic cells (DCs), which bridge the innate and adaptive immune systems. This invasion process is tightly linked to the bridging functions of resultant DCs, in that it can disable (or stimulate) the maturation function of DCs and cytokines that are secreted. Maturation molecules (e.g., MHCII, CD80/CD86, CD40) and inflammatory cytokines (e.g., IL-1b, TNFa, IL-6) are essential signals for antigen presentation and for proliferation of effector T-cells such as Th17 cells. In this regard, the ability of P. gingivalis to coordinately regulate its expression of major (fimA) and minor (mfa-1) fimbriae under different environmental influences becomes highly relevant. This review will, therefore, focus on the immunoregulatory role of P. gingivalis fimbriae in the invasion of DCs, intracellular signaling, and functional outcomes such as alveolar bone loss and immune senescence.

Dendritic cells a critical link to alveolar bone loss and systemic disease risk in periodontitis: Immunotherapeutic implications

Extensive research in humans and animal models has begun to unravel the complex mechanisms that drive the immunopathogenesis of periodontitis. Neutrophils mount an early and rapid response to the subgingival oral microbiome, producing destructive enzymes to kill microbes. Chemokines and cytokines are released that attract macrophages, dendritic cells, and T cells to the site. Dendritic cells, the focus of this review, are professional antigen-presenting cells on the front line of immune surveillance. Dendritic cells consist of multiple subsets that reside in the epithelium, connective tissues, and major organs. Our work in humans and mice established that myeloid dendritic cells are mobilized in periodontitis. This occurs in lymphoid and nonlymphoid oral tissues, in the bloodstream, and in response to Porphyromonas gingivalis. Moreover, the dendritic cells mature in situ in gingival lamina propria, forming immune conjugates with cluster of differentiation (CD) 4+ T cells, called oral lymphoid foci. At such foci, the decisions are made as to whether to promote bone destructive T helper 17 or bone-sparing regulatory T cell responses. Interestingly, dendritic cells lack potent enzymes and reactive oxygen species needed to kill and degrade endocytosed microbes. The keystone pathogen P. gingivalis exploits this vulnerability by invading dendritic cells in the tissues and peripheral blood using its distinct fimbrial adhesins. This promotes pathogen dissemination and inflammatory disease at distant sites, such as atherosclerotic plaques. Interestingly, our recent studies indicate that such P. gingivalis-infected dendritic cells release nanosized extracellular vesicles called exosomes, in higher numbers than uninfected dendritic cells do. Secreted exosomes and inflammasome-related cytokines are a key feature of the senescence-associated secretory phenotype. Exosomes communicate in paracrine with neighboring stromal cells and immune cells to promote and amplify cellular senescence. We have shown that dendritic cell-derived exosomes can be custom tailored to target and reprogram specific immune cells responsible for inflammatory bone loss in mice. The long-term goal of these immunotherapeutic approaches, ongoing in our laboratory and others, is to promote human health and longevity.