Differential effects of agarose and poly(lactic-co-glycolic acid) on dendritic cell maturation

Advances in agar-based composites: A comprehensive review

This review article explores the developments and applications in agar-based composites (ABCs), emphasizing various constituents such as metals, clay/ceramic, graphene, and polymers across diversified fields like wastewater treatment, drug delivery, food packaging, the energy sector, biomedical engineering, bioplastics, agriculture, and cosmetics. The focus is on agar as a sustainable and versatile biodegradable polysaccharide, highlighting research that has advanced the technology of ABCs. A bibliometric analysis is conducted using the Web of Science database, covering publications from January 2020 to March 2024, processed through VOSviewer Software Version 1.6.2. This analysis assesses evolving trends and scopes in the literature, visualizing co-words and themes that underscore the growing importance and potential of ABCs in various applications. This review paper contributes by showcasing the existing state-of-the-art knowledge and motivating further development in this promising field.

Defining the immunological compatibility of graphene oxide-loaded PLGA scaffolds for biomedical applications

Graphene oxide (GO), a carbon-based nanomaterial, presents significant potential across biomedical fields such as bioimaging, drug delivery, biosensors, and phototherapy. This study examines the effects of integrating GO into poly(lactic-co-glycolic acid) (PLGA) scaffolds on human immune cell function. Our results demonstrate that high concentrations of GO reduce the viability of peripheral blood mononuclear cells (PBMCs) following stimulation with anti-CD3 antibody. This reduction extends to T lymphocyte activation, evident from the diminished proliferative response to T cell receptor engagement and impaired differentiation into T helper subsets and regulatory T cells. Interestingly, although GO induces a minimal response in resting monocytes, but it significantly affects both the viability and the differentiation potential of monocytes induced to mature toward M1 pro-inflammatory and M2-like immunoregulatory macrophages. This study seeks to address a critical gap by investigating the in vitro immunomodulatory effects of PLGA scaffolds incorporating various concentrations of GO on primary immune cells, specifically PBMCs isolated from healthy donors. Our findings emphasize the need to optimize the GO to PLGA ratios and scaffold design to advance PLGA-GO-based biomedical applications. STATEMENT OF SIGNIFICANCE: Graphene oxide (GO) holds immense promise for biomedical applications due to its unique properties. However, concerns regarding its potential to trigger adverse immune responses remain. This study addresses this critical gap by investigating the in vitro immunomodulatory effects of PLGA scaffolds incorporating increasing GO concentrations on human peripheral blood mononuclear cells (PBMCs). By elucidating the impact on cell viability, T cell proliferation and differentiation, and the maturation/polarization of antigen-presenting cells, this work offers valuable insights for designing safe and immunologically compatible GO-based biomaterials for future clinical translation.

The role of dendritic cells in the immunomodulation to implanted biomaterials

Considering the substantial role played by dendritic cells (DCs) in the immune system to bridge innate and adaptive immunity, studies on DC-mediated immunity toward biomaterials principally center on their adjuvant effects in facilitating the adaptive immunity of codelivered antigens. However, the effect of the intrinsic properties of biomaterials on dendritic cells has not been clarified. Recently, researchers have begun to investigate and found that biomaterials that are nonadjuvant could also regulate the immune function of DCs and thus affect subsequent tissue regeneration. In the case of proteins adsorbed onto biomaterial surfaces, their intrinsic properties can direct their orientation and conformation, forming “biomaterial-associated molecular patterns (BAMPs)”. Thus, in this review, we focused on the intrinsic physiochemical properties of biomaterials in the absence of antigens that affect DC immune function and summarized the underlying signaling pathways. Moreover, we preliminarily clarified the specific composition of BAMPs and the interplay between some key molecules and DCs, such as heat shock proteins (HSPs) and high mobility group box 1 (HMGB1). This review provides a new direction for future biomaterial design, through which modulation of host immune responses is applicable to tissue engineering and immunotherapy.

Rational design of hydrogels for immunomodulation

The immune system protects organisms against endogenous and exogenous harm and plays a key role in tissue development, repair, and regeneration. Traditional immunomodulatory biologics exhibit limitations including degradation by enzymes, short half-life, and lack of targeting ability. Encapsulating or binding these biologics within biomaterials is an effective way to address these problems. Hydrogels are promising immunomodulatory materials because of their prominent biocompatibility, tuneability, and versatility. However, to take advantage of these opportunities and optimize material performance, it is important to more specifically elucidate, and leverage on, how hydrogels affect and control the immune response. Here, we summarize how key physical and chemical properties of hydrogels affect the immune response. We first provide an overview of underlying steps of the host immune response upon exposure to biomaterials. Then, we discuss recent advances in immunomodulatory strategies where hydrogels play a key role through a) physical properties including dimensionality, stiffness, porosity, and topography; b) chemical properties including wettability, electric property, and molecular presentation; and c) the delivery of bioactive molecules via chemical or physical cues. Thus, this review aims to build a conceptual and practical toolkit for the design of immune-instructive hydrogels capable of modulating the host immune response.

Bridging micro/nano-platform and airway allergy intervention

Allergic airway diseases, with incidence augmenting visibly as industrial development and environmental degradation, are characterized by sneezing, itching, wheezing, chest tightness, airway obstruction, and hyperresponsiveness. Current medical modalities attempt to combat these symptoms mostly by small molecule chemotherapeutants, such as corticosteroids, antihistamines, etc., via intranasal approach which is one of the most noninvasive, rapid-absorbed, and patient-friendly routes. Nevertheless, inherent defects for irritation to respiratory mucosa, drug inactivation and degradation, and rapid drug dispersal to off-target sites are inevitable. Lately, intratracheal micro/nano therapeutic systems are emerging as innovative alternatives for airway allergy interventions. This overview introduces several potential application directions of mic/nano-platform in the treatment of airway allergic diseases, including carriers, therapeutic agents, and immunomodulators. The improvement of the existing drug therapy of respiratory allergy management by micro/nano-platform is described in detail. The challenges of the micro/nano-platform nasal approach in the treatment of airway allergy are summarized and the development of micro/nano-platform is also prospected. Although still a burgeoning area, micro/nano therapeutic systems are gradually turning to be realistic orientations as crucial future alternative therapeutic options in allergic airway inflammation interventions.

Dendritic cells support a proliferative antigen-specific T-cell response in the presence of poly(lactic-co-glycolic acid)

Biomaterials are known to modulate immune cell functions, which subsequently determine the host inflammatory and immune responses. Poly(lactic-co-glycolic acid) or PLGA, a biodegradable and biocompatible biomaterial, induces a pro-inflammatory, mature phenotype in antigen presentation cells, namely dendritic cells (DCs) in vitro. In vivo, PLGA can boost the humoral immune response to a co-delivered model antigen, a phenomenon known as the PLGA-adjuvant effect. This study elucidates the link between PLGA's effect on the DC phenotype in vitro and its adjuvant effect in vivo using the CD11c-DTR mouse model. These mice undergo conditional ablation of DCs upon treatment with diphtheria toxin. To measure immune activation, the mice were first given ovalbumin (OVA)-reactive T cells from OT-II/OT-I mice. Later, the same mice received subcutaneous OVA-loaded PLGA scaffold implants. In response to the scaffold implants, OVA-reactive OT-II CD4+ T cells showed decreased proliferation in the absence of CD11c+ DCs, indicating an attenuation of the PLGA-adjuvant effect. Furthermore, PLGA may also influence the antigen cross-presentation function of DCs, as evident with the lowered OVA-reactive OT-I CD8+ T-cell response. Understanding the immunomodulatory ability of biomaterials in the context of DCs will aid in designing improved DC-based immunotherapies against infectious diseases and cancer.

Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

Modulation of immune-inflammatory responses through surface modifications of biomaterials to promote bone healing and regeneration

Control of inflammation is indispensable for optimal oral wound healing and tissue regeneration. Several biomaterials have been used to enhance the regenerative outcomes; however, the biomaterial implantation can ensure an immune-inflammatory response. The interface between the cells and the biomaterial surface plays a critical role in determining the success of soft and hard tissue regeneration. The initial inflammatory response upon biomaterial implantation helps in tissue repair and regeneration, however, persistant inflammation impairs the wound healing response. The cells interact with the biomaterials through extracellular matrix proteins leading to protein adsorption followed by recruitment, attachment, migration, and proliferation of several immune-inflammatory cells. Physical nanotopography of biomaterials, such as surface proteins, roughness, and porosity, is crucial for driving cellular attachment and migration. Similarly, modification of scaffold surface chemistry by adapting hydrophilicity, surface charge, surface coatings, can down-regulate the initiation of pro-inflammatory cascades. Besides, functionalization of scaffold surfaces with active biological molecules can down-regulate pro-inflammatory and pro-resorptive mediators' release as well as actively up-regulate anti-inflammatory markers. This review encompasses various strategies for the optimization of physical, chemical, and biological properties of biomaterial and the underlying mechanisms to modulate the immune-inflammatory response, thereby, promoting the tissue integration and subsequent soft and hard tissue regeneration potential of the administered biomaterial.

Novel Approaches for the Treatment of Pulmonary Tuberculosis

Tuberculosis (TB) is a contagious airborne disease caused by Mycobacterium tuberculosis, which primarily affects human lungs. The progression of drug-susceptible TB to drug-resistant strains, MDR-TB and XDR-TB, has become worldwide challenge in eliminating TB. The limitations of conventional TB treatment including frequent dosing and prolonged treatment, which results in patient’s noncompliance to the treatment because of treatment-related adverse effects. The non-invasive pulmonary drug administration provides the advantages of targeted-site delivery and avoids first-pass metabolism, which reduced the dose requirement and systemic adverse effects of the therapeutics. With the modification of the drugs with advanced carriers, the formulations may possess sustained released property, which helps in reducing the dosing frequency and enhanced patients’ compliances. The dry powder inhaler formulation is easy to handle and storage as it is relatively stable compared to liquids and suspension. This review mainly highlights the aerosolization properties of dry powder inhalable formulations with different anti-TB agents to understand and estimate the deposition manner of the drug in the lungs. Moreover, the safety profile of the novel dry powder inhaler formulations has been discussed. The results of the studies demonstrated that dry powder inhaler formulation has the potential in enhancing treatment efficacy.

Role of dendritic cells in the host response to biomaterials and their signaling pathways

Strategies to enhance, inhibit, or qualitatively modulate immune responses are important for diverse biomedical applications such as vaccine adjuvant, drug delivery, immunotherapy, cell transplant, tissue engineering, and regenerative medicine. However, the clinical efficiency of these biomaterial systems is affected by the limited understanding of their interaction with complex host microenvironments, for example, excessive foreign body reaction and immunotoxicity. Biomaterials and biomedical devices implanted in the body may induce a highly complicated and orchestrated series of host responses. As macrophages are among the first cells to infiltrate and respond to implanted biomaterials, the macrophage-mediated host response to biomaterials has been well studied. Dendritic cells (DCs) are the most potent antigen-presenting cells that activate naive T cells and bridge innate and adaptive immunity. The potential interaction of DCs with biomaterials appears to be critical for exerting the function of biomaterials and has become an important, developing area of investigation. Herein, we summarize the effects of the physicochemical properties of biomaterials on the immune function of DCs together with their receptors and signaling pathways. This review might provide a complete understanding of the interaction of DCs with biomaterials and serve as a reference for the design and selection of biomaterials with particular effects on targeted cells. STATEMENT OF SIGNIFICANCE: Biomaterials implanted in the body are increasingly applied in clinical practice. The performance of these implanted biomaterials is largely dependent on their interaction with the host immune system. As antigen-presenting cells, dendritic cells (DCs) directly interact with biomaterials through pattern recognition receptors (PRRs) recognizing "biomaterial-associated molecular patterns" and generate a battery of immune responses. In this review, the physicochemical properties of biomaterials that regulate the immune function of DCs together with their receptors and signaling pathways of biomaterial-DC interactions are summarized and discussed. We believe that knowledge of the interplay of DC and biomaterials may spur clinical translation by guiding the design and selection of biomaterials with particular effects on targeted cell for tissue engineering, vaccine delivery, and cancer therapy.

Aerosol immunization by alginate coated mycobacterium (BCG/MIP) particles provide enhanced immune response and protective efficacy than aerosol of plain mycobacterium against M.tb. H37Rv infection in mice

Background

With the aim of preparing a more effective, safe and economical vaccine for tuberculosis, inhalable live mycobacterium formulations were evaluated.

Methods

Alginate particles in the size range of 2–4 μm were prepared by encapsulating live Bacille Calmette–Guérin (BCG) and “Mycobacterium indicus pranii” (MIP). These particles were characterized for their size, stability and release profile. Mice were immunized with liquid aerosol or dry powder aerosol (DPA) alginate encapsulated mycobacterium particles and their in-vitro recall response and infection with mycobacterium H37Rv were investigated.

Results

It was found that the DPA of alginate encapsulated mycobacterium particles invoked superior immune response and provided higher protection in mice than the liquid aerosol. The BCG encapsulated in alginate particles (BEAP) and MIP encapsulated in alginate particles (MEAP) were engulfed by bone marrow dendritic cells (BMDCs) and co-localized with lysosome. The MEAP/BEAP activated BMDCs exhibited higher chemotaxis movement and had enhanced ability of antigen presentation to T cells.

The in-vitro recall response of BEAP/MEAP immunized mice when compared in terms of proliferation index and Interferon gamma (IFN-gamma) released by splenocytes and mediastinal lymph node cells was found to be higher than mice immunized by liquid aerosol of BCG/MIP. Finally, different groups of immunized mice were infected with M. tb H37Rv and after 16 weeks the Colony forming units (CFUs) in lung and spleen estimated. The bacilli burden in the BEAP/MEAP immunized mice was significantly less than the respective liquid aerosol immunized mice and the histopathology of BEAP/MEAP immunized mice lungs showed very little damage.

Conclusions

These inhale-able vaccines formulation of alginate coated live mycobacterium are more immunogenic as compared to the aerosol of bacilli and they provide better protection in mice when infected with H37Rv.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4157-2) contains supplementary material, which is available to authorized users.

Latent, Immunosuppressive Nature of Poly(lactic-co-glycolic acid) Microparticles

Use of biomaterials to spatiotemporally control the activation of immune cells is at the forefront of biomedical engineering research. As more biomaterial strategies are employed for immunomodulation, understanding the immunogenicity of biodegradable materials and their byproducts is paramount in tailoring systems for immune activation or suppression. Poly(D,L-lactic-co-glycolic acid) (PLGA), one of the most commonly studied polymers in tissue engineering and drug delivery, has been previously described on one hand as an immune adjuvant, and on the other as a nonactivating material. In this study, the effect of PLGA microparticles (MPs) on the maturation status of murine bone marrow-derived dendritic cells (DCs), the primary initiators of adaptive immunity, was investigated to decipher the immunomodulatory properties of this biomaterial. Treatment of bone marrow-derived DCs from C57BL/6 mice with PLGA MPs led to a time dependent decrease in the maturation level of these cells, as quantified by decreased expression of the positive stimulatory molecules MHCII, CD80, and CD86 as well as the ability to resist maturation following challenge with lipopolysaccharide (LPS). Moreover, this immunosuppression was dependent on the molecular weight of the PLGA used to fabricate the MPs, as higher molecular weight polymers required longer incubation to produce comparable dampening of maturation molecules. These phenomena were correlated to an increase in lactic acid both intracellularly and extracellularly during DC/PLGA MP coculture, which is postulated to be the primary agent behind the observed immune inhibition. This hypothesis is supported by our results demonstrating that resistance to LPS stimulation may be due to the ability of PLGA MP-derived lactic acid to inhibit the phosphorylation of TAK1 and therefore prevent NF-κB activation. This work is significant as it begins to elucidate how PLGA, a prominent biomaterial with broad applications ranging from tissue engineering to pharmaceutics, could modulate the local immune environment and offers insight on engineering PLGA to exploit its evolving immunogenicity.

Biomaterial strategies for generating therapeutic immune responses

Biomaterials employed to raise therapeutic immune responses have become a complex and active field. Historically, vaccines have been developed primarily to fight infectious diseases, but recent years have seen the development of immunologically active biomaterials towards an expanding list of non-infectious diseases and conditions including inflammation, autoimmunity, wounds, cancer, and others. This review structures its discussion of these approaches around a progression from single-target strategies to those that engage increasingly complex and multifactorial immune responses. First, the targeting of specific individual cytokines is discussed, both in terms of delivering the cytokines or blocking agents, and in terms of active immunotherapies that raise neutralizing immune responses against such single cytokine targets. Next, non-biological complex drugs such as randomized polyamino acid copolymers are discussed in terms of their ability to raise multiple different therapeutic immune responses, particularly in the context of autoimmunity. Last, biologically derived matrices and materials are discussed in terms of their ability to raise complex immune responses in the context of tissue repair. Collectively, these examples reflect the tremendous diversity of existing approaches and the breadth of opportunities that remain for generating therapeutic immune responses using biomaterials.

Solution blow spinning fibres: New immunologically inert substrates for the analysis of cell adhesion and motility

The control of cell behaviour through material geometry is appealing as it avoids the requirement for complex chemical surface modifications. Significant advances in new technologies have been made to the development of polymeric biomaterials with controlled geometry and physico-chemical properties. Solution blow spinning technique has the advantage of ease of use allowing the production of nano or microfibres and the direct fibre deposition on any surface in situ. Yet, in spite of these advantages, very little is known about the influence of such fibres on biological functions such as immune response and cell migration. In this work, we engineered polymeric fibres composed of either pure poly(lactic acid) (PLA) or blends of PLA and polyethylene glycol (PEG) by solution blow spinning and determined their impact on dendritic cells, highly specialised cells essential for immunity and tolerance. We also determined the influence of fibres on cell adhesion and motility. Cells readily interacted with fibres resulting in an intimate contact characterised by accumulation of actin filaments and focal adhesion components at sites of cell-fibre interactions. Moreover, cells were guided along the fibres and actin and focal adhesion components showed a highly dynamic behaviour at cell-fibre interface. Remarkably, fibres did not elicit any substantial increase of activation markers and inflammatory cytokines in dendritic cells, which remained in their immature (inactive) state. Taken together, these findings will be useful for developing new biomaterials for applications in tissue engineering and regenerative medicine.

Dendritic cells in host response to biologic scaffolds

Tissue regeneration and repair require a highly complex and orchestrated series of events that require inflammation, but can be compromised when inflammation is excessive or becomes chronic. Macrophages are one of the first cells to contact and respond to implanted materials, and mediate the inflammatory response. The series of events following macrophage association with biomaterials has been well-studied. Dendritic cells (DCs) also directly interact with biomaterials, are critical for specific immune responses, and can be activated in response to interactions with biomaterials. Yet, much less is known about the responses by DCs. This review discusses what we know about DC response to biomaterials, the underlying mechanisms involved, and how DCs can be influenced by the macrophage response to biomaterials. Lastly, I will discuss how biomaterials can be manipulated to enhance or suppress DC function to promote a specific desirable immune response - a major goal for implantable biologically active therapeutics.

Collagen scaffold microenvironments modulate cell lineage commitment for differentiation of bone marrow cells into regulatory dendritic cells

The microenvironment plays a pivotal role for cell survival and functional regulation, and directs the cell fate determination. The biological functions of DCs have been extensively investigated to date. However, the influences of the microenvironment on the differentiation of bone marrow cells (BMCs) into dendritic cells (DCs) are not well defined. Here, we established a 3D collagen scaffold microenvironment to investigate whether such 3D collagen scaffolds could provide a favourable niche for BMCs to differentiate into specialised DCs. We found that BMCs embedded in the 3D collagen scaffold differentiated into a distinct subset of DC, exhibiting high expression of CD11b and low expression of CD11c, co-stimulator (CD40, CD80, CD83, and CD86) and MHC-II molecules compared to those grown in 2D culture. DCs cultured in the 3D collagen scaffold possessed weak antigen uptake ability and inhibited T-cell proliferation in vitro; in addition, they exhibited potent immunoregulatory function to alleviate allo-delay type hypersensitivity when transferred in vivo. Thus, DCs differentiated in the 3D collagen scaffold were defined as regulatory DCs, indicating that collagen scaffold microenvironments probably play an important role in modulating the lineage commitment of DCs and therefore might be applied as a promising tool for generation of specialised DCs.

Effect of Different Titanium Surfaces on Maturation of Murine Bone Marrow-Derived Dendritic Cells

Dendritic cells (DCs) play a pivotal role in the host response to implanted biomaterials. Osseointegration of titanium (Ti) implant is an immunological and inflammatory-driven process. However, the role of DCs in this complex process is largely unknown. This study aimed to investigate the effect of different Ti surfaces on DC maturation, and evaluate its subsequent potential on osteogenic differentiation of preosteoblasts. Murine bone marrow-derived DCs were seeded on Ti disks with different surface treatments, including pretreatment (PT), sandblasted/acid-etched (SLA) and modified SLA (modSLA) surface. Compared with DCs cultured on PT and SLA surfaces, the cells seeded on modSLA surface demonstrated a more round morphology with lower expression of CD86 and MHC-II, the DC maturation markers. Those cells also secreted high levels of anti-inflammatory cytokine IL-10 and TGF-β. Notably, addition of conditioned medium (CM) from modSLA-induced DCs significantly increased the mRNA expression of Runx2 and ALP as well as ALP activity by murine preosteoblast MC3T3-E1 cells. Our data demonstrated that Ti disks with different surfaces lead to differential DCs responses. PT and SLA surfaces induce DCs mature, while DCs seeded on modSLA-Ti surface maintain an immature phenotype and exhibit a potential of promoting osteogenic differentiation of MC3T3-E1 cells.

Dendritic cells in the host response to implanted materials

The role of dendritic cells (DCs) and their targeted manipulation in the body's response to implanted materials is an important and developing area of investigation, and a large component of the emerging field of biomaterials-based immune engineering. The key position of DCs in the immune system, serving to bridge innate and adaptive immunity, is facilitated by rich diversity in type and function and places DCs as a critical mediator to biomaterials of both synthetic and natural origins. This review presents current views regarding DC biology and summarizes recent findings in DC responses to implanted biomaterials. Based on these findings, there is promise that the directed programming of application-specific DC responses to biomaterials can become a reality, enabling and enhancing applications almost as diverse as the larger field of biomaterials itself.

Biodegradable nanoparticle delivery of inactivated swine influenza virus vaccine provides heterologous cell-mediated immune response in pigs

Swine influenza virus (SwIV) is one of the important zoonotic pathogens. Current flu vaccines have failed to provide cross-protection against evolving viruses in the field. Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable FDA approved polymer and widely used in drug and vaccine delivery. In this study, inactivated SwIV H1N2 antigens (KAg) encapsulated in PLGA nanoparticles (PLGA-KAg) were prepared, which were spherical in shape with 200 to 300nm diameter, and induced maturation of antigen presenting cells in vitro. Pigs vaccinated twice with PLGA-KAg via intranasal route showed increased antigen specific lymphocyte proliferation and enhanced the frequency of T-helper/memory and cytotoxic T cells (CTLs) in peripheral blood mononuclear cells (PBMCs). In PLGA-KAg vaccinated and heterologous SwIV H1N1 challenged pigs, clinical flu symptoms were absent, while the control pigs had fever for four days. Grossly and microscopically, reduced lung pathology and viral antigenic mass in the lung sections with clearance of infectious challenge virus in most of the PLGA-KAg vaccinated pig lung airways were observed. Immunologically, PLGA-KAg vaccine irrespective of not significantly boosting the mucosal antibody response, it augmented the frequency of IFN-γ secreting total T cells, T-helper and CTLs against both H1N2 and H1N1 SwIV. In summary, inactivated influenza virus delivered through PLGA-NPs reduced the clinical disease and induced cross-protective cell-mediated immune response in a pig model. Our data confirmed the utility of a pig model for intranasal particulate flu vaccine delivery platform to control flu in humans.

Entrapment of H1N1 Influenza Virus Derived Conserved Peptides in PLGA Nanoparticles Enhances T Cell Response and Vaccine Efficacy in Pigs

Pigs are believed to be one of the important sources of emerging human and swine influenza viruses (SwIV). Influenza virus conserved peptides have the potential to elicit cross-protective immune response, but without the help of potent adjuvant and delivery system they are poorly immunogenic. Biodegradable polylactic-co-glycolic acid (PLGA) nanoparticle (PLGA-NP) based vaccine delivery system enhances cross-presentation of antigens by the professional antigen presenting cells. In this study, Norovirus P particle containing SwIV M2e (extracellular domain of the matrix protein 2) chimera and highly conserved two each of H1N1 peptides of pandemic 2009 and classical human influenza viruses were entrapped in PLGA-NPs. Influenza antibody-free pigs were vaccinated with PLGA-NPs peptides cocktail vaccine twice with or without an adjuvant, Mycobacterium vaccae whole cell lysate, intranasally as mist. Vaccinated pigs were challenged with a virulent heterologous zoonotic SwIV H1N1, and one week later euthanized and the lung samples were analyzed for the specific immune response and viral load. Clinically, pigs vaccinated with PLGA-NP peptides vaccine had no fever and flu symptoms, and the replicating challenged SwIV was undetectable in the bronchoalveolar lavage fluid. Immunologically, PLGA-NP peptides vaccination (without adjuvant) significantly increased the frequency of antigen-specific IFNγ secreting CD4 and CD8 T cells response in the lung lymphocytes, despite not boosting the antibody response both at pre- and post-challenge. In summary, our data indicated that nanoparticle-mediated delivery of conserved H1N1 influenza peptides induced the virus specific T cell response in the lungs and reduced the challenged heterologous virus load in the airways of pigs.

Respiratory nanoparticle-based vaccines and challenges associated with animal models and translation

Vaccine development has had a huge impact on human health. However, there is a significant need to develop efficacious vaccines for several existing as well as emerging respiratory infectious diseases. Several challenges need to be overcome to develop efficacious vaccines with translational potential. This review focuses on two aspects to overcome some barriers - 1) the development of nanoparticle-based vaccines, and 2) the choice of suitable animal models for respiratory infectious diseases that will allow for translation. Nanoparticle-based vaccines, including subunit vaccines involving synthetic and/or natural polymeric adjuvants and carriers, as well as those based on virus-like particles offer several key advantages to help overcome the barriers to effective vaccine development. These include the ability to deliver combinations of antigens, target the vaccine formulation to specific immune cells, enable cross-protection against divergent strains, act as adjuvants or immunomodulators, allow for sustained release of antigen, enable single dose delivery, and potentially obviate the cold chain. While mouse models have provided several important insights into the mechanisms of infectious diseases, they are often a limiting step in translation of new vaccines to the clinic. An overview of different animal models involved in vaccine research for respiratory infections, with advantages and disadvantages of each model, is discussed. Taken together, advances in nanotechnology, combined with the right animal models for evaluating vaccine efficacy, has the potential to revolutionize vaccine development for respiratory infections.

Immunological principles regulating immunomodulation with biomaterials

The immune system has evolved to recognize and eliminate pathogens; this recognition relies on the identification of structural molecular patterns within unique tissue microenvironments. Therefore, bioengineers can harness these immunological cues to design materials that modulate innate and adaptive immunity in a controlled manner. This review acts as an immunology primer by focusing on the basic molecular and cellular immunology principles governing immunomodulation with biomaterials.

Phenotype and polarization of autologous T cells by biomaterial-treated dendritic cells

Given the central role of dendritic cells (DCs) in directing T-cell phenotypes, the ability of biomaterial-treated DCs to dictate autologous T-cell phenotype was investigated. In this study, we demonstrate that differentially biomaterial-treated DCs differentially directed autologous T-cell phenotype and polarization, depending on the biomaterial used to pretreat the DCs. Immature DCs (iDCs) were derived from human peripheral blood monocytes and treated with biomaterial films of alginate, agarose, chitosan, hyaluronic acid, or 75:25 poly(lactic-co-glycolic acid) (PLGA), followed by co-culture of these biomaterial-treated DCs and autologous T cells. When autologous T cells were co-cultured with DCs treated with biomaterial film/antigen (ovalbumin, OVA) combinations, different biomaterial films induced differential levels of T-cell marker (CD4, CD8, CD25, CD69) expression, as well as differential cytokine profiles [interferon (IFN)-γ, interleukin (IL)-12p70, IL-10, IL-4] in the polarization of T helper (Th) types. Dendritic cells treated with agarose films/OVA induced CD4+CD25+FoxP3+ (T regulatory cells) expression, comparable to untreated iDCs, on autologous T cells in the DC-T co-culture system. Furthermore, in this co-culture, agarose treatment induced release of IL-12p70 and IL-10 at higher levels as compared with DC treatment with other biomaterial films/OVA, suggesting Th1 and Th2 polarization, respectively. Dendritic cells treated with PLGA film/OVA treatment induced release of IFN-γ at higher levels compared with that observed for co-cultures with iDCs or DCs treated with all other biomaterial films. These results indicate that DC treatment with different biomaterial films has potential as a tool for immunomodulation by directing autologous T-cell responses.

Adjuvanted poly(lactic-co-glycolic) acid nanoparticle-entrapped inactivated porcine reproductive and respiratory syndrome virus vaccine elicits cross-protective immune response in pigs

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), is an economically devastating disease, causing daily losses of approximately $3 million to the US pork industry. Current vaccines have failed to completely prevent PRRS outbreaks. Recently, we have shown that poly(lactic-co-glycolic) acid (PLGA) nanoparticle-entrapped inactivated PRRSV vaccine (NP-KAg) induces a cross-protective immune response in pigs. To further improve its cross-protective efficacy, the NP-KAg vaccine formulation was slightly modified, and pigs were coadministered the vaccine twice intranasally with a potent adjuvant: Mycobacterium tuberculosis whole-cell lysate. In vaccinated virulent heterologous PRRSV-challenged pigs, the immune correlates in the blood were as follows: 1) enhanced PRRSV-specific antibody response with enhanced avidity of both immunoglobulin (Ig)-G and IgA isotypes, associated with augmented virus-neutralizing antibody titers; 2) comparable and increased levels of virus-specific IgG₁ and IgG₂ antibody subtypes and production of high levels of both T-helper (Th)-1 and Th2 cytokines, indicative of a balanced Th1–Th2 response; 3) suppressed immunosuppressive cytokine response; 4) increased frequency of interferon-γ⁺ lymphocyte subsets and expanded population of antigen-presenting cells; and most importantly 5) complete clearance of detectable replicating challenged heterologous PRRSV and close to threefold reduction in viral ribonucleic acid load detected in the blood. In conclusion, intranasal delivery of adjuvanted NP-KAg vaccine formulation to growing pigs elicited a broadly cross-protective immune response, showing the potential of this innovative vaccination strategy to prevent PRRS outbreaks in pigs. A similar approach to control other respiratory diseases in food animals and humans appears to be feasible.

The nanomaterial-dependent modulation of dendritic cells and its potential influence on therapeutic immunosuppression in lupus

Targeting dendritic cells with nanoparticles is an attractive modality for instigating immunity or inducing immunosuppression. An important aspect of successful delivery of antigen and immune modulators to these cells is the efficacy of nanoparticle internalization, which can dictate the strength and robustness of immune responses; optimizing particulate uptake is thus key. We compared the internalization of two nanoparticulate platforms: a vesicular "nanogel" platform with a lipid exterior, and the widely-used solid biodegradable poly(lactic-co-glycolic acid) (PLGA) system. We found that nanogels were more effectively internalized by dendritic cells in vitro, as demonstrated by fluorescent tracer measurements. Additionally, the magnitude of dendritic cell immunosuppression achieved by nanogels loaded with mycophenolic acid, an immunosuppressant, was greater than similarly drug-loaded PLGA. Although both types of particles could mitigate the production of inflammatory cytokines and the up-regulation of stimulatory surface markers, nanogels yielded greater reductions. These in vitro measurements correlated with in vivo efficacy, where immunosuppressive therapy with nanogels extended the survival of lupus-prone NZB/W F1 mice whereas PLGA particles did not. Our results highlight the importance of material on nanoparticle uptake by dendritic cells, which impacts the quality of therapeutic immunosuppression.

Efficient ex vivo induction of T cells with potent anti-tumor activity by protein antigen encapsulated in nanoparticles

Protein antigen (Ag)-based immunotherapies have the advantage to induce T cells with a potentially broad repertoire of specificities. However, soluble protein Ag is generally poorly cross-presented in MHC class I molecules and not efficient in inducing robust cytotoxic CD8(+) T cell responses. In the present study, we have applied poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NP) which strongly improve protein Ag presentation by dendritic cells (DC) in the absence of additional Toll-like receptor ligands or targeting devices. Protein Ag-loaded DC were used as antigen presenting cells to stimulate T cells in vitro and subsequently analyzed in vivo for their anti-tumor effect via adoptive transfer, a treatment strategy widely studied in clinical trials as a therapy against various malignancies. In a direct comparison with soluble protein Ag, we show that DC presentation of protein encapsulated in plain PLGA-NP results in efficient activation of CD4(+) and CD8(+) T cells as reflected by high numbers of activated CD69(+) and CD25(+), interferon (IFN)-γ and interleukin (IL)-2-producing T cells. Adoptive transfer of PLGA-NP-activated CD8(+) T cells in tumor-bearing mice displayed good in vivo expansion capacity, potent Ag-specific cytotoxicity and IFN-γ cytokine production, resulting in curing mice with established tumors. We conclude that delivery of protein Ag through encapsulation in plain PLGA-NP is a very efficient and simple procedure to stimulate potent anti-tumor T cells.

Bone tissue engineering: recent advances and challenges

The worldwide incidence of bone disorders and conditions has trended steeply upward and is expected to double by 2020, especially in populations where aging is coupled with increased obesity and poor physical activity. Engineered bone tissue has been viewed as a potential alternative to the conventional use of bone grafts, due to their limitless supply and no disease transmission. However, bone tissue engineering practices have not proceeded to clinical practice due to several limitations or challenges. Bone tissue engineering aims to induce new functional bone regeneration via the synergistic combination of biomaterials, cells, and factor therapy. In this review, we discuss the fundamentals of bone tissue engineering, highlighting the current state of this field. Further, we review the recent advances of biomaterial and cell-based research, as well as approaches used to enhance bone regeneration. Specifically, we discuss widely investigated biomaterial scaffolds, micro- and nano-structural properties of these scaffolds, and the incorporation of biomimetic properties and/or growth factors. In addition, we examine various cellular approaches, including the use of mesenchymal stem cells (MSCs), embryonic stem cells (ESCs), adult stem cells, induced pluripotent stem cells (iPSCs), and platelet-rich plasma (PRP), and their clinical application strengths and limitations. We conclude by overviewing the challenges that face the bone tissue engineering field, such as the lack of sufficient vascularization at the defect site, and the research aimed at functional bone tissue engineering. These challenges will drive future research in the field.

Biodegradable nanoparticle-entrapped vaccine induces cross-protective immune response against a virulent heterologous respiratory viral infection in pigs

Biodegradable nanoparticle-based vaccine development research is unexplored in large animals and humans. In this study, we illustrated the efficacy of nanoparticle-entrapped UV-killed virus vaccine against an economically important respiratory viral disease of pigs called porcine reproductive and respiratory syndrome virus (PRRSV). We entrapped PLGA [poly (lactide-co-glycolides)] nanoparticles with killed PRRSV antigens (Nano-KAg) and detected its phagocytosis by pig alveolar macrophages. Single doses of Nano-KAg vaccine administered intranasally to pigs upregulated innate and PRRSV specific adaptive responses. In a virulent heterologous PRRSV challenge study, Nano-KAg vaccine significantly reduced the lung pathology and viremia, and the viral load in the lungs. Immunologically, enhanced innate and adaptive immune cell population and associated cytokines with decreased secretion of immunosuppressive mediators were observed at both mucosal sites and blood. In summary, we demonstrated the benefits of intranasal delivery of nanoparticle-based viral vaccine in eliciting cross-protective immune response in pigs, a potential large animal model.

Nanovectorized radiotherapy: a new strategy to induce anti-tumor immunity

Recent experimental findings show that activation of the host immune system is required for the success of chemo- and radiotherapy. However, clinically apparent tumors have already developed multiple mechanisms to escape anti-tumor immunity. The fact that tumors are able to induce a state of tolerance and immunosuppression is a major obstacle in immunotherapy. Hence, there is an overwhelming need to develop new strategies that overcome this state of immune tolerance and induce an anti-tumor immune response both at primary and metastatic sites. Nanovectorized radiotherapy that combines ionizing radiation and nanodevices, is one strategy that could boost the quality and magnitude of an immune response in a predictable and designable fashion. The potential benefits of this emerging treatment may be based on the unique combination of immunostimulatory properties of nanoparticles with the ability of ionizing radiation to induce immunogenic tumor cell death. In this review, we will discuss available data and propose that the nanovectorized radiotherapy could be a powerful new strategy to induce anti-tumor immunity required for positive patient outcome.

Differential functional effects of biomaterials on dendritic cell maturation

The immunological outcome of dendritic cell (DC) treatment with different biomaterials was assessed to demonstrate the range of DC phenotypes induced by biomaterials commonly used in combination products. Immature DCs (iDCs) were derived from human peripheral blood monocytes, and treated with different biomaterial films of alginate, agarose, chitosan, hyaluronic acid (HA), or 75:25 poly(lactic-co-glycolic acid) (PLGA) and a comprehensive battery of phenotypic functional outcomes was assessed. Different levels of functional changes in DC phenotype were observed depending on the type of biomaterial films used to treat the DCs. Treatment of DCs with PLGA or chitosan films supported DC maturation, with higher levels of DC allostimulatory capacity, pro-inflammatory cytokine release, and expression of CD80, CD86, CD83, HLA-DQ and CD44 compared with iDCs, and lower endocytic ability compared with iDCs. Alginate film induced pro-inflammatory cytokine release from DCs at levels higher than from iDCs. Dendritic cells treated with HA film expressed lower levels of CD40, CD80, CD86 and HLA-DR compared with iDCs. They also exhibited lower endocytic ability and CD44 expression than iDCs, possibly due to an insolubilized (cross-linked) form of high molecular weight HA. Interestingly, treatment of DCs with agarose film maintained the DC functional phenotype at levels similar to iDCs except for CD44 expression, which was lower than that of iDCs. Taken together, these results can provide selection criteria for biomaterials to be used in immunomodulating applications and can inform potential outcomes of biomaterials within combination products on associated immune responses as desired by the application.

Recent advances in polymeric microspheres for parenteral drug delivery--part 2

INTRODUCTION

Currently marketed microsphere products are manufactured with the use of organic solvents which have a negative impact on the environment and stability of biological molecules. With recent advances in fabrication technologies, solvent free methods have demonstrated potential for the preparation of microspheres.

AREAS COVERED

New technical advances recently achieved in solvent based microsphere manufacturing processes have allowed for major improvement in product quality and properties. Novel solvent free fabrication methods combined with newly functionalized biodegradable polymers have been explored for their application in the preparation of microspheres containing biological molecules.

EXPERT OPINION

Novel fabrication methods for microspheres have been recently reported but technical challenges and development risks remain high for scale up from bench to industrial commercialization. While the applications of microspheres for delivery of proteins, genes and vaccines have shown promise for clinical use, the approval of newly functionalized polymers as carriers may still face scrutiny on safety and biocompatibility, which can be key factors in securing the regulatory approval of the product.

Application of collagen hydrogel/sponge scaffold facilitates periodontal wound healing in class II furcation defects in beagle dogs

BACKGROUND AND OBJECTIVE

A three-dimensional scaffold may play an important role in periodontal tissue engineering. We prepared bio-safe collagen hydrogel, which exhibits properties similar to those of native extracellular matrix. The aim of this study was to examine the effect of implantation of collagen hydrogel/sponge scaffold on periodontal wound healing in class II furcation defects in dogs.

MATERIAL AND METHODS

The collagen hydrogel/sponge scaffold was prepared by injecting collagen hydrogel, cross-linked to the ascorbate-copper ion system, into a collagen sponge. Class II furcation defects (of 5 mm depth and 3 mm width) were surgically created in beagle dogs. The exposed root surface was planed and demineralized with EDTA. In the experimental group, the defect was filled with collagen hydrogel/sponge scaffold. In the control group, no implantation was performed. Histometric parameters were evaluated 2 and 4 wk after surgery.

RESULTS

At 2 wk, the collagen hydrogel/sponge scaffold displayed high biocompatibility and biodegradability with numerous cells infiltrating the scaffold. In the experimental group, reconstruction of alveolar bone and cementum was frequently observed 4 wk after surgery. Periodontal ligament tissue was also re-established between alveolar bone and cementum. Volumes of new bone, new cementum and new periodontal ligament were significantly greater in the experimental group than in the control group. In addition, epithelial down-growth was suppressed by application of collagen hydrogel.

CONCLUSION

The collagen hydrogel/sponge scaffold possessed high tissue compatibility and degradability. Implantation of the scaffold facilitated periodontal wound healing in class II furcation defects in beagle dogs.

Predicting biomaterial property-dendritic cell phenotype relationships from the multivariate analysis of responses to polymethacrylates

Dendritic cells (DCs) play a critical role in orchestrating the host responses to a wide variety of foreign antigens and are essential in maintaining immune tolerance. Distinct biomaterials have been shown to differentially affect the phenotype of DCs, which suggested that biomaterials may be used to modulate immune response toward the biologic component in combination products. The elucidation of biomaterial property-DC phenotype relationships is expected to inform rational design of immuno-modulatory biomaterials. In this study, DC response to a set of 12 polymethacrylates (pMAs) was assessed in terms of surface marker expression and cytokine profile. Principal component analysis (PCA) determined that surface carbon correlated with enhanced DC maturation, while surface oxygen was associated with an immature DC phenotype. Partial square linear regression, a multivariate modeling approach, was implemented and successfully predicted biomaterial-induced DC phenotype in terms of surface marker expression from biomaterial properties with R(prediction)(2) = 0.76. Furthermore, prediction of DC phenotype was effective based on only theoretical chemical composition of the bulk polymers with R(prediction)(2) = 0.80. These results demonstrated that immune cell response can be predicted from biomaterial properties, and computational models will expedite future biomaterial design and selection.

Encapsulation of antigen in poly(D,L-lactide-co-glycolide) microspheres protects from harmful effects of γ-irradiation as assessed in mice

During the last two decades, synthetic polymers such as poly(lactide-co-glycolide) (PLGA) have been investigated for the development of nano- or microparticles as adjuvants or antigen vehicles. To enable transfer of this technology to human settings, the issue of sterilisation is of central importance. Since most polymers are heat-sensitive, sterilisation of polymeric microspheres for parenteral administration is assured either by costly and laborious aseptical preparation or the more preferred γ-irradiation. Many studies have investigated the effect of γ-irradiation on various physiochemical properties of the microspheres, but investigations on immunological effects are rare. We prepared poly(lactide-co-glycolide) (PLGA) microspheres containing ovalbumin (OVA) and tested the effect of γ-irradiation on the various immunological properties in mice. For reference, OVA was γ-irradiated and tested equivalently. The ability of encapsulated or non-encapsulated OVA to trigger activation of dendritic cells (DCs) was not affected by irradiation. However, while γ-irradiation of free OVA strongly influenced the antigen presentation, encapsulated OVA was not affected by irradiation. γ-Irradiation of OVA also reduced the immunogenicity in mice with regard to OVA-specific IgG1 production. In contrast, the antibody and the T-cell responses in mice immunised with PLGA-encapsulated OVA were similar irrespective of the γ-irradiation status. Hence, encapsulation of antigen into PLGA microspheres protects antigen from the potential detrimental effect of γ-irradiation leading to inactivation or altered immunogenicity. Sterilisation by γ-irradiation therefore enables a cost-effective production of PLGA-based antigen-delivery systems as compared to the more laborious and expensive aseptical production of such vaccines.

Immune responses to implants - a review of the implications for the design of immunomodulatory biomaterials

A key for long-term survival and function of biomaterials is that they do not elicit a detrimental immune response. As biomaterials can have profound impacts on the host immune response the concept emerged to design biomaterials that are able to trigger desired immunological outcomes and thus support the healing process. However, engineering such biomaterials requires an in-depth understanding of the host inflammatory and wound healing response to implanted materials. One focus of this review is to outline the up-to-date knowledge on immune responses to biomaterials. Understanding the complex interactions of host response and material implants reveals the need for and also the potential of "immunomodulating" biomaterials. Based on this knowledge, we discuss strategies of triggering appropriate immune responses by functional biomaterials and highlight recent approaches of biomaterials that mimic the physiological extracellular matrix and modify cellular immune responses.

Dendritic cell responses to surface properties of clinical titanium surfaces

Dendritic cells (DCs) play pivotal roles in responding to foreign entities during the innate immune response and in initiating effective adaptive immunity as well as maintaining immune tolerance. The sensitivity of DCs to foreign stimuli also makes them useful cells to assess the inflammatory response to biomaterials. Elucidating material property-DC phenotype relationships using a well-defined biomaterial system is expected to provide criteria for immunomodulatory biomaterial design. Clinical titanium (Ti) substrates, including pretreatment (PT), sand blasted and acid etched (SLA), and modified SLA (modSLA), with different roughnesses and surface energies were used to treat DCs and resulted in differential DC responses. PT and SLA induced a mature DC (mDC) phenotype, while modSLA promoted a non-inflammatory environment by supporting an immature DC (iDC) phenotype, based on surface marker expression, cytokine production profiles and cell morphology. Principal component analysis (PCA) confirmed these experimental results, and also indicated that the non-stimulating property of modSLA covaried with certain surface properties, such as high surface hydrophilicity, percent oxygen and percent Ti of the substrates. In addition to previous research that demonstrated superior osteogenic properties of modSLA compared with PT and SLA, the results reported herein indicates that modSLA may further benefit implant osteointegration by reducing local inflammation and its associated osteoclastogenesis.

Adhesive substrates modulate the activation and stimulatory capacity of non-obese diabetic mouse-derived dendritic cells

It is known that adsorbed adhesive proteins on implanted biomaterials modulate inflammatory responses; however, modulation of dendritic cell (DC) responses upon interaction with adhesive proteins has only begun to be characterized. DCs are specialized antigen-presenting cells that modulate both innate and adaptive immune responses. Previously we have shown that the activation and stimulatory capacity of DCs derived from C57BL6/j mice is differentially modulated by adhesive substrates. Here we extend our investigation of adhesive substrate modulation of DC responses to consider the case where the DCs had maturational defects associated with diabetes. Understanding the adhesive responses of DCs in diabetics is potentially important for immunotherapy and tissue engineering applications. In this work we use the non-obese diabetic (NOD) mouse, an established animal model for type 1 diabetes, to generate DCs (NOD-DCs). We demonstrate that NOD-DCs cultured on different adhesive substrates (collagen, fibrinogen, fibronectin, laminin, vitronectin, albumin and serum) respond with substrate-dependent modulation of the surface expression of the stimulatory molecule MHC-II and the co-stimulatory molecules CD80 and CD86 and production of the cytokines IL-12p40 and IL-10. Furthermore, the capacity of NOD-DCs to stimulate CD4(+) T-cell proliferation and cytokine production (IL-4 and IFN-γ) showed substrate-dependent modulation. Specifically, NOD-DCs cultured on vitronectin induced the highest IL-12p40 production, whereas collagen induced the highest IL-10 production. Dendritic cells cultured on collagen, fibrinogen and serum-coated substrates stimulated the highest CD4(+) T-cell proliferation. It was further determined that DCs cultured on vitronectin induced the highest percent population of IL-4-producing T-cells and DCs cultured on a fibronectin-coated substrate induced the highest expression of IFN-γ in T-cells. Pearson's correlation analysis revealed high correlations between T-cell proliferation and DC expression level of CD80 and T-cell production of IL-4 and DC production of IL-10. This demonstration of substrate-based control of NOD-DC activatory and stimulatory capacity, distinct from non-diabetic B6-DC responses, establishes the field of adhesive modulation of immune cell responses and informs the rational design of biomaterials for patients with type 1 diabetes.

Macrophage and dendritic cell phenotypic diversity in the context of biomaterials

Macrophages (Mϕ) and dendritic cells (DCs) are critical antigen presenting cells that play pivotal roles in host responses to biomaterial implants. Although Mϕs have been widely studied for their roles in the inflammatory responses against biomaterials, the roles that DCs play in the host responses toward implanted materials have only recently been explored. DCs are of significant research interest because of the emergence of a large number of combination products that cross-traditional medical device boundaries. These products combine biomaterials with biologics, including cells, nucleic acids, and/or proteins. The biomaterial component may evoke an inflammatory response, primarily mediated by neutrophils and Mϕs, whereas the biologic component may elicit an immunogenic immune response, initiated by DCs involving lymphocyte activation. Control of Mϕ phenotypic balance from proinflammatory M1 to reparative M2 is a goal of investigators to optimize the host response to biomaterials. Similarly, control of DC phenotype from proinflammatory to toleragenic is of interest in vaccine delivery and tissue engineering/transplantation situations, respectively. This review discusses the interconnection between innate and adaptive immunity, the comparative and contrasting phenotypes and roles of Mϕs and DCs in immunity, their responses to biomaterials and the strategies to modulate their phenotype for applications in tissue engineering and vaccine delivery. Furthermore, the collaboration between and unique roles of DCs and Mϕs needs to be addressed in future studies to gain a more complete picture of host responses toward combination products.

The role of integrins in the recognition and response of dendritic cells to biomaterials

Biomaterials have the potential to be utilized as immunostimulatory or immunosuppressive delivery agents for biologics. It is hypothesized that this is directed by the ability of a biomaterial to drive dendritic cells (DC) in situ toward an immunostimulatory or an immunosuppressive phenotype, respectively. However, the specific pattern recognition receptors (PRRs) that DCs use to recognize and respond to biomaterials are unknown. From among the many receptors that DCs use to recognize and respond to foreign entities, herein the focus is on integrins. A biomaterial that induces DC maturation, namely poly(lactic-co-glycolic) acid (PLGA), supported increased human monocyte-derived DC adhesion and up-regulation of integrin receptor gene expression, measured via RT-PCR, as compared to culture on tissue culture polystyrene (TCPS). This was not observed for a biomaterial that does not support DC maturation. Through antibody-blocking techniques, the adhesion to both TCPS and PLGA was found to be β(2) integrin dependent and β(1) independent. Significantly, inhibiting β(2)-mediated adhesion to biomaterials via blocking antibodies also lowered the level of maturation of DCs (CD86 expression). β(2) integrins (but not β(1)) were found localized in biomaterial-adherent DC podosomes and also were found in direct contact with the PLGA surface. Therefore, it appeared that β(2) integrin-mediated adhesion is involved in determining the state of DC maturation on the PLGA surface. DC adhesion to biomaterials may be engaged or avoided to manipulate an immune response to biological component delivered with a biomaterial carrier.

Collagen type I hydrogel allows migration, proliferation, and osteogenic differentiation of rat bone marrow stromal cells

Hydrogels are potentially useful for many purposes in regenerative medicine including drug and growth factor delivery, as single scaffold for bone repair or as a filler of pores of another biomaterial in which host mesenchymal progenitor cells can migrate in and differentiate into matrix-producing osteoblasts. Collagen type I is of special interest as it is a very important and abundant natural matrix component. The purpose of this study was to investigate whether rat bone marrow stromal cells (rBMSCs) are able to adhere to, to survive, to proliferate and to migrate in collagen type I hydrogels and whether they can adopt an osteoblastic fate. rBMSCs were obtained from rat femora and plated on collagen type I hydrogels. Before harvest by day 7, 14, and 21, hydrogels were fluorescently labeled, cryo-cut and analyzed by fluorescent-based and laser scanning confocal microscopy to determine cell proliferation, migration, and viability. Osteogenic differentiation was determined by alkaline phosphatase activity. Collagen type I hydrogels allowed the attachment of rBMSCs to the hydrogel, their proliferation, and migration towards the inner part of the gel. rBMSCs started to differentiate into osteoblasts as determined by an increase in alkaline phosphatase activity after two weeks in culture. This study therefore suggests that collagen type I hydrogels could be useful for musculoskeletal regenerative therapies.

Validation of a high-throughput methodology to assess the effects of biomaterials on dendritic cell phenotype

A variety of combination products composed of biomaterials and biologics have been developed for tissue regeneration or vaccine delivery. The host immune response to the immunogenic biological components in such products may be modulated by the biomaterial component. Distinct biomaterials have been shown to differentially affect the maturation of dendritic cells (DCs). DCs are professional antigen-presenting cells (APCs) that bridge innate and adaptive immunity and play a central role in inducing immunity or initiating immune tolerance. However, the biomaterials systems used to study DC response thus far have been insufficient to draw a clear conclusion as to which biomaterial properties are the key to controlling DC phenotype. In this study, we developed a 96-well filter plate-based high-throughput (HTP) methodology to assess DC maturation upon biomaterial treatment. Equivalent biomaterial effects on DC phenotype were measured using the conventional flow cytometric and filter-plate method, which validated the HTP methodology. This methodology will be used to screen a large number of biomaterials simultaneously and to draw correlations between material properties and DC phenotype, thereby providing biomaterial design criteria and immunomodulatory strategies for both tissue engineering and vaccine delivery applications.

Biomaterial adjuvant effect is attenuated by anti-inflammatory drug delivery or material selection

Biomaterials have been shown to differentially support dendritic cell (DC) maturation, a prerequisite for an adjuvant effect. Treatment of DCs with poly(D,L-lactic-co-glycolic acid) (PLGA) films resulted in DC maturation but agarose films did not. In these studies, the biomaterial adjuvant effect was attenuated by material selection (PLGA or agarose scaffolds) or local delivery of an anti-inflammatory/immunosuppressive glucocorticoid, dexamethasone (DX), from PLGA scaffolds. Porous scaffolds (SCs) of PLGA or agarose were produced to deliver equivalent amounts of model antigen, ovalbumin (OVA). Alternatively, PLGA SCs with incorporated OVA were produced with or without DX. These SCs were implanted individually, subcutaneously, and dorsally in C57BL/6 mice. Blood was collected from mice at specific times over a 12-week duration for measurement of antibody production against OVA. Scaffolds were explanted at 12 weeks for histological examination of foreign body response. Scaffolds of PLGA, but not of agarose, were found to elicit higher antibody production against co-delivered OVA, than negative controls. Short-term delivery of DX from PLGA SCs delivering OVA temporarily delayed onset of anti-OVA antibody production. More sustained release of DX at an effective dose and with an appropriate time course is expected to extend the effect of DX on the biomaterial adjuvant effect. The immunomodulatory ability of biomaterials to affect the immune response to co-delivered antigen is demonstrated wherein this immunomodulatory ability correlates with the observed in vitro differential effects of biomaterials on DC maturation.

The role of multiple toll-like receptor signalling cascades on interactions between biomedical polymers and dendritic cells

Biomaterials are used in several health-related applications ranging from tissue regeneration to antigen-delivery systems. Yet, biomaterials often cause inflammatory reactions suggesting that they profoundly alter the homeostasis of host immune cells such as dendritic cells (DCs). Thus, there is a major need to understand how biomaterials affect the function of these cells. In this study, we have analysed the influence of chemically and physically diverse biomaterials on DCs using several murine knockouts. DCs can sense biomedical polymers through a mechanism, which involves multiple TLR/MyD88-dependent signalling pathways, in particular TLR2, TLR4 and TLR6. TLR-biomaterial interactions induce the expression of activation markers and pro-inflammatory cytokines and are sufficient to confer on DCs the ability to activate antigen-specific T cells. This happens through a direct biomaterial-DC interaction although, for degradable biomaterials, soluble polymer molecules can also alter DC function. Finally, the engagement of TLRs by biomaterials profoundly alters DC adhesive properties. Our findings could be useful for designing structure-function studies aimed at developing more bioinert materials. Moreover, they could also be exploited to generate biomaterials for studying the molecular mechanisms of TLR signalling and DC activation aiming at fine-tuning desired and pre-determined immune responses.