Biodegradable microspheres alone do not stimulate murine macrophages in vitro, but prolong antigen presentation by macrophages in vitro and stimulate a solid immune response in mice

Polymeric nanoparticles for DNA vaccine-based cancer immunotherapy: a review

Cancer is one of the leading causes of death and mortality in the world. There is an essential need to develop new drugs or therapeutic approaches to manage treatment-resistant cancers. Cancer immunotherapy is a type of cancer treatment that uses the power of the body's immune system to prevent, control, and eliminate cancer. One of the materials used as a vaccine in immunotherapy is DNA. The application of polymeric nanoparticles as carriers for DNA vaccines could be an effective therapeutic approach to activate immune responses and increase antigen presentation efficiency. Various materials have been used as polymeric nanoparticles, including: chitosan, poly (lactic-co-glycolic acid), Polyethylenimine, dendrimers, polypeptides, and polyesters. Application of these polymer nanoparticles has several advantages, including increased vaccine delivery, enhanced antigen presentation, adjuvant effects, and more sustainable induction of the immune system. Besides many clinical trials and commercial products that were developed based on polymer nanoparticles, there is still a need for more comprehensive studies to increase the DNA vaccine efficiency in cancer immunotherapy using this type of carrier.

Modulating lung immune cells by pulmonary delivery of antigen-specific nanoparticles to treat autoimmune disease

Antigen-specific particles can treat autoimmunity, and pulmonary delivery may provide for easier delivery than intravenous or subcutaneous routes. The lung is a "hub" for autoimmunity where autoreactive T cells pass before arriving at disease sites. Here, we report that targeting lung antigen-presenting cells (APCs) via antigen-loaded poly(lactide-co-glycolide) particles modulates lung CD4+ T cells to tolerize murine experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Particles directly delivered to the lung via intratracheal administration demonstrated more substantial reduction in EAE severity when compared with particles delivered to the liver and spleen via intravenous administration. Intratracheally delivered particles were associated with lung APCs and decreased costimulatory molecule expression on the APCs, which inhibited CD4+ T cell proliferation and reduced their population in the central nervous system while increasing them in the lung. This study supports noninvasive pulmonary particle delivery, such as inhalable administration, to treat autoimmune disease.

Single-dose treatment for cutaneous leishmaniasis with an easily synthesized chalcone entrapped in polymeric microparticles

Cutaneous leishmaniasis (CL) is a major health problem in many countries and its current treatment involves multiple parenteral injections with toxic drugs and requires intensive health services. Previously, the efficacy of a single subcutaneous injection with a slow-release formulation consisting of poly(lactide-co-glycolide) (PLGA) microparticles loaded with an antileishmanial 3-nitro-2-hydroxy-4,6-dimethoxychalcone (CH8) was demonstrated in mice model. In the search for more easily synthesized active chalcone derivatives, and improved microparticle loading, CH8 analogues were synthesized and tested for antileishmanial activity in vitro and in vivo. The 3-nitro-2',4',6'-trimethoxychalcone (NAT22) analogue was chosen for its higher selectivity against intracellular amastigotes (selectivity index = 1489, as compared with 317 for CH8) and more efficient synthesis (89% yield, as compared with 18% for CH8). NAT22 was loaded into PLGA / polyvinylpyrrolidone (PVP) polymeric blend microspheres (NAT22-PLGAk) with average diameter of 1.9 μm. Although NAT22-PLGAk showed similar activity to free NAT22 in killing intracellular parasites in vitro (IC50 ~ 0.2 μm), in vivo studies in Leishmania amazonensis - infected mice demonstrated the significant superior efficacy of NAT22-PLGAk to reduce the parasite load. A single intralesional injection with NAT22-PLGAk was more effective than eight injections with free NAT22. Together, these results show that NAT22-PLGAk is a promising alternative for single-dose localized treatment of CL.

Biodegradable polymers for modern vaccine development

Most traditional vaccines are composed either of a whole pathogen or its parts; these vaccines, however, are not always effective and can even be harmful. As such, additional agents known as adjuvants are necessary to increase vaccine safety and efficacy. This review summarizes the potential of biodegradable materials, including synthetic and natural polymers, for vaccine delivery. These materials are highly biocompatible and have minimal toxicity, and most biomaterial-based vaccines delivering antigens or adjuvants have been shown to improve immune response, compared to formulations consisting of the antigen alone. Therefore, these materials can be applied in modern vaccine development.

A cell-free approach with a supporting biomaterial in the form of dispersed microspheres induces hyaline cartilage formation in a rabbit knee model

The objective of this study was to test a regenerative medicine strategy for the regeneration of articular cartilage. This approach combines microfracture of the subchondral bone with the implant at the site of the cartilage defect of a supporting biomaterial in the form of microspheres aimed at creating an adequate biomechanical environment for the differentiation of the mesenchymal stem cells that migrate from the bone marrow. The possible inflammatory response to these biomaterials was previously studied by means of the culture of RAW264.7 macrophages. The microspheres were implanted in a 3 mm-diameter defect in the trochlea of the femoral condyle of New Zealand rabbits, covering them with a poly(l-lactic acid) (PLLA) membrane manufactured by electrospinning. Experimental groups included a group where exclusively PLLA microspheres were implanted, another group where a mixture of 50/50 microspheres of PLLA (hydrophobic and rigid) and others of chitosan (a hydrogel) were used, and a third group used as a control where no material was used and only the membrane was covering the defect. The histological characteristics of the regenerated tissue have been evaluated 3 months after the operation. We found that during the regeneration process the microspheres, and the membrane covering them, are displaced by the neoformed tissue in the regeneration space toward the subchondral bone region, leaving room for the formation of a tissue with the characteristics of hyaline cartilage.

Design of biodegradable nanoparticles to modulate phenotypes of antigen-presenting cells for antigen-specific treatment of autoimmune disease

Current therapeutic options for autoimmune diseases, such as multiple sclerosis (MS), often require lifelong treatment with immunosuppressive drugs, yet strategies for antigen-specific immunomodulation are emerging. Biodegradable particles loaded with disease-specific antigen, either alone or with immunomodulators, have been reported to ameliorate disease. Herein, we hypothesized that the carrier could impact polarization of the immune cells that associate with particles and the subsequent disease progression. Single injection of three polymeric carriers, 50:50 poly (DL-lactide-co-glycolide) (PLG) with two molecular weights (Low, High) and poly (DL-lactide) (PLA), loaded with the disease-specific antigen, proteolipid protein (PLP_139-151), were investigated for the ability to attenuate clinical scores in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. At a low particle dose, mice treated with PLA-based particles had significantly lower clinical scores at the chronic stage of the disease over 200 days post immunization, while neither PLG-based particles nor OVA control particles reduced the clinical scores. Compared to PLG-based particles, PLA-based particles were largely associated with Kupffer cells and liver sinusoidal endothelial cells, which had a reduced co-stimulatory molecule expression that correlated with a reduction of CD4⁺ T-cell populations in the central nervous system. Delivery of PLA-based particles encapsulated with higher levels of PLP_139-151 at a reduced dose were able to completely ameliorate EAE over 200 days along with inhibition of Th1 and Th17 polarization. Collectively, our study demonstrates that the carrier properties and antigen loading determine phenotypes of immune cells in the peripheral organs, influencing the amelioration of both acute and chronic stages of autoimmunity.

Modulating Immunological Responses of Electrospun Fibers for Tissue Engineering

The promise of tissue engineering is to improve or restore functions of impaired tissues or organs. However, one of the biggest challenges to its translation to clinical applications is the lack of tissue integration and functionality. The plethora of cellular and molecular events occurring following scaffold implantation is a major bottleneck. Recent studies confirmed that inflammation is a crucial component influencing tissue regeneration. Immuno-modulation or immune-engineering has been proposed as a potential solution to overcome this key challenge in regenerative medicine. In this review, strategies to modify scaffold physicochemical properties through the use of the electrospinning technique to modulate host response and improve scaffold integration will be discussed. Electrospinning, being highly versatile allows the fabrication of ECM-mimicking scaffolds and also offers the possibility to control scaffold properties for instance, tailoring of fiber properties, chemical conjugation or physical adsorption of non-immunogenic materials on the scaffold surface, encapsulating cells or anti-inflammatory molecules within the scaffold. Such electrospun scaffold-based immune-engineering strategies can significantly improve the resulting outcomes of tissue engineering scaffolds.

Nasal vaccination with poly(β-amino ester)-poly(d,l-lactide-co-glycolide) hybrid nanoparticles

Mucosal vaccination stimulates both mucosal and systemic immunity. However, mucosal applications of vaccine antigens in their free form generally result in poor systemic immune responses and need adjuvantation. In this study, bovine serum albumin loaded, new hybridised poly(β-amino ester)-poly(d,l-lactide-co-glycolide) nanoparticles were prepared by double emulsion-solvent evaporation method, characterised and evaluated in vivo as nasal vaccine carriers. Cationic spherical particles with a mean size of 240nm, good physical stability and high encapsulation efficiency were obtained. Protein structure was not affected throughout preparation and minimal toxicity was shown in Calu-3 and A549 cells. Nasal vaccination with these nanoparticles revealed markedly higher humoral immune responses compared with free antigen following intranasal and subcutaneous immunisation. Mucosal immune response was also stimulated and cytokine titres indicated that Th1 and Th2 pathways were successfully activated. This study shows that the formulated hybrid nanoparticles can be a promising carrier for nasal immunisation of poor antigenic proteins.

Adjuvanticity Regulation by Biodegradable Polymeric Nano/microparticle Size

Polymeric nano/microparticles as vaccine adjuvants have been researched in experimental and clinical studies. A more profound understanding of how the physicochemical properties regulate specific immune responses has become a vital requirement. Here we prepared poly(d,l-lactic-co-glycolic acid) (PLGA) nano/microparticles with uniform sizes (500 nm, 900 nm, 2.1 μm, and 4.9 μm), and the size effects on particle uptake, activation of macrophages, and antigen internalization were evaluated. Particle uptake kinetic studies demonstrated that 900 nm particles were the easiest to accumulate in cells. Moreover, they could induce macrophages to secrete NO and IL-1β and facilitate antigen internalization. Furthermore, 900 nm particles, mixed with antigen, could exhibit superior adjuvanticity in both humoral and cellular immune responses in vivo, including offering the highest antibody protection, promoting the maximum secretion levels of IFN-γ and IL-4 than particles with other sizes. Overall, 900 nm might be the optimum choice for PLGA particle-based vaccine adjuvants especially for recombinant antigens. Understanding the effect of particle size on the adjuvanticity based immune responses might have important enlightenments for rational vaccine design and applications.

Genital Chlamydia trachomatis: understanding the roles of innate and adaptive immunity in vaccine research

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted disease worldwide, and despite significant advances in chlamydial research, a prophylactic vaccine has yet to be developed. This Gram-negative obligate intracellular bacterium, which often causes asymptomatic infection, may cause pelvic inflammatory disease (PID), ectopic pregnancies, scarring of the fallopian tubes, miscarriage, and infertility when left untreated. In the genital tract, Chlamydia trachomatis infects primarily epithelial cells and requires Th1 immunity for optimal clearance. This review first focuses on the immune cells important in a chlamydial infection. Second, we summarize the research and challenges associated with developing a chlamydial vaccine that elicits a protective Th1-mediated immune response without inducing adverse immunopathologies.

Preclinical Development and In Vivo Efficacy of Ceftiofur-PLGA Microparticles

Drug delivery systems based on polymeric microparticles represent an interesting field of development for the treatment of several infectious diseases for humans and animals. In this work, we developed PLGA microparticles loaded with ceftiofur (PLGA-cef), a third- generation cephalosporin that is used exclusively used in animals. PLGA-cef was prepared by the double emulsion w/o/w method, and exhibited a diameter in the range of 1.5–2.2 μm, and a negative ζ potential in the range of -35 to -55 mV. The loading yield of PLGA-cef was ~7% and encapsulation efficiency was approximately 40%. The pharmacokinetic study demonstrated a sustained release profile of ceftiofur for 20 days. PLGA-cef administrated in a single dose was more effective than ceftiofur non-encapsulated in rats challenged with S. Typhimurium. The in vivo toxicological evaluation showed that PLGA-cef did not affect the blood biochemical, hematological and hemostasis parameters. Overall, the PLGA-cef showed slow in vivo release profile, high antibacterial efficacy, and low toxicity. The results obtained supports the safe application of PLGA-cef as sustained release platform in the veterinary industry.

Induction of long-lasting protective immunity against Toxoplasma gondii in BALB/c mice by recombinant surface antigen 1 protein encapsulated in poly (lactide-co-glycolide) microparticles

BACKGROUND

Current development efforts of subunit vaccines against Toxoplasma gondii, the etiological agent of toxoplasmosis, have been focused mainly on tachyzoite surface antigen 1 (SAG1). Since microparticles made from poly (lactide-co-glycolide) (PLG) polymers have been developed as safe, potent adjuvants or delivery systems, we aimed to encapsulate recombinant SAG1 (rSAG1) with the PLG polymers to prepare PLG-encapsulated rSAG1 (PLG-rSAG1) microparticles that would sustain rSAG1 release and generate long-lasting protective immunity against T. gondii in BALB/c mice.

METHODS

In the present study, rSAG1 was encapsulated into PLG microparticles by the double emulsion method. PLG-rSAG1 microparticles were then intraperitoneally injected twice at a 14-day interval into BALB/c mice. We examined the ability of PLG-rSAG1 microparticles to induce and prolong effective anti-Toxoplasma immune responses, in comparison with rSAG1 formulated with a Vet L-10 adjuvant (rSAG1 (Vet L-10)). Eight weeks after the last immunization, protective activities were also evaluated after a lethal subcutaneous challenge of 1 x 10(4) live T. gondii tachyzoites.

RESULTS

PLG-rSAG1 microparticles, 4.25~6.58 micrometers in diameter, showed 69%~81% entrapment efficiency. The amount of released rSAG1 protein from microparticles increased gradually over a 35-day period and the protein still retained native SAG1 antigenicity. Intraperitoneal vaccination of mice with the microparticles resulted in enhanced SAG1-specific IgG titers as well as lymphocyte proliferation and, more importantly, these enhanced activities were maintained for 10 weeks. In addition, eight weeks after the last immunization, maximum production of gamma interferon was detected in mice immunized with PLG-rSAG1 microparticles. Furthermore, 80% (8/10) of mice immunized with PLG-rSAG1 microparticles survived at least 28 days after a lethal subcutaneous tachyzoite challenge.

CONCLUSIONS

Encapsulation of rSAG1 into PLG microparticles preserves the native SAG1 antigenicity and sustains the release of rSAG1 from microparticles. PLG-rSAG1 microparticles can effectively induce not only significant long-lasting SAG1-specific humoral and cell-mediated immune responses but also high protection against T. gondii tachyzoite infection. Our study provides a valuable basis for developing long-lasting vaccines against T. gondii for future use in humans and animals.

Localized controlled release of stratifin reduces implantation-induced dermal fibrosis

Localized controlled release of anti-fibrogenic factors can potentially prevent tissue fibrosis surrounding biomedical prostheses, such as vascular stents and breast implants. We have previously demonstrated that therapeutic intervention with topically applied stratifin in a rabbit ear fibrotic model not only prevents dermal fibrosis but also promotes more normal tissue repair by regulating extracellular matrix deposition. In this work, the anti-fibrogenic effect of a controlled release form of stratifin was investigated in the prevention of fibrosis induced by dermal poly(lactic-co-glycolic acid) (PLGA) microsphere/poly(vinyl alcohol) (PVA) hydrogel implants. Pharmacodynamic effects were evaluated by histopathological examination of subcutaneous tissue surrounding implanted composites. Controlled release of stratifin from PLGA microsphere/PVA hydrogel implants significantly moderated dermal fibrosis and inflammation by reducing collagen deposition (30%), total tissue cellularity (48%) and infiltrated CD3(+) immune cells (81%) in the surrounding tissue compared with the stratifin-free implants. The controlled release of stratifin from implants markedly increased the level of matrix metalloproteinase-1 expression in the surrounding tissue, which resulted in less collagen deposition. These stratifin-eluting PLGA/PVA composites show promise as coatings to decrease the typical fibrosis exhibited around implanted biomedical prostheses, such as breast implants and vascular stents.

Biodegradable PLGA85/15 nanoparticles as a delivery vehicle for Chlamydia trachomatis recombinant MOMP-187 peptide

Development of a Chlamydia trachomatis vaccine has been a formidable task partly because of an ineffective delivery system. Our laboratory has generated a recombinant peptide of C. trachomatis major outer membrane protein (MOMP) (rMOMP-187) and demonstrated that it induced at 20 μg ml(-1) maximal interleukin (IL)-6 and IL-12p40 Th1 cytokines in mouse J774 macrophages. In a continuous pursuit of a C. trachomatis effective vaccine-delivery system, we encapsulated rMOMP-187 in poly(d,l-lactic-co-glycolic acid) (PLGA, 85:15 PLA/PGA ratio) to serve as a nanovaccine candidate. Physiochemical characterizations were assessed by Fourier transform-infrared spectroscopy, atomic force microscopy, Zetasizer, Zeta potential, transmission electron microcopy and differential scanning calorimetry. The encapsulated rMOMP-187 was small (∼200 nm) with an apparently smooth uniform oval structure, thermally stable (54 °C), negatively charged ( - 27.00 mV) and exhibited minimal toxicity at concentrations <250 μg ml (-1) to eukaryotic cells (>95% viable cells) over a 24-72 h period. We achieved a high encapsulation efficiency of rMOMP-187 (∼98%) in PLGA, a loading peptide capacity of 2.7% and a slow release of the encapsulated peptide. Stimulation of J774 macrophages with a concentration as low as 1 μg ml (-1) of encapsulated rMOMP-187 evoked high production levels of the Th1 cytokines IL-6 (874 pg ml(-1)) and IL-12p40 (674 pg ml(-1)) as well as nitric oxide (8 μM) at 24 h post-stimulation, and in a dose-response and time-kinetics manner. Our data indicate the successful encapsulation and characterization of rMOMP-187 in PLGA and, more importantly, that PLGA enhanced the capacity of the peptide to induce Th1 cytokines and NO in vitro. These findings make this nanovaccine an attractive candidate in pursuit of an efficacious vaccine against C. trachomatis.

Use of lectin-functionalized particles for oral immunotherapy

Immunotherapy, in recent times, has found its application in a variety of immunologically mediated diseases. Oral immunotherapy may not only increase patient compliance but may, in particular, also induce both systemic as well as mucosal immune responses, due to mucosal application of active agents. To improve the bioavailability and to trigger strong immunological responses, recent research projects focused on the encapsulation of drugs and antigens into polymer particles. These particles protect the loaded antigen from the harsh conditions in the GI tract. Furthermore, modification of the surface of particles by the use of lectins, such as Aleuria aurantia lectin, wheatgerm agglutinin or Ulex europaeus-I, enhances the binding to epithelial cells, in particular to membranous cells, of the mucosa-associated lymphoid tissue. Membranous cell-specific targeting leads to an improved transepithelial transport of the particle carriers. Thus, enhanced uptake and presentation of the encapsulated antigen by antigen-presenting cells favor strong systemic, but also local, mucosal immune responses.

Polyelectrolyte LbL microcapsules versus PLGA microparticles for immunization with a protein antigen

The transition from organism-based traditional vaccines to the use of safer subunit vaccines has implemented the use of adjuvants to enhance immunogenicity. This study compares the potential of two types of polymeric microparticles as delivery systems for the model antigen ovalbumin. The delivery systems encompassed polyelectrolyte microcapsules, assembled via Layer-by-Layer technology, and PLGA microparticles fabricated by spray-drying. Mice were immunized subcutaneously either by a single injection or by two injections separated by four weeks with an equivalent dose of the OVA-loaded particles. Both particulate formulations mediated high, long-term IgG(1) responses whereas the IgG(2c) titers remained low. Additionally, Th1 and Th2 phenotype immune responses against OVA were assessed by quantifying the production of cytokines in CD4+ T-cells derived from the spleens of immunized mice at 6 months after the first injection. Immunization with particulate formulations led to significantly increased IL-2, IL-4, IL-10 and IFN-γ production by splenic CD4+ T-cells compared to control animals. LbL microcapsules and PLGA microparticles generated strong immune responses in vivo, characterized by a mixed Th1/Th2 type response with predominance of Th2 immunity. Both particulate formulations elicited a comparable type of immune response and appear to be promising for antigen delivery.

A fibroblast/macrophage co-culture model to evaluate the biocompatibility of an electrospun Dextran/PLGA scaffold and its potential to induce inflammatory responses

Fibroblasts and macrophages are the two major types of cells responding to implanted biomaterials. They play crucial roles in inflammatory responses, host-material interactions and tissue remodeling. However, the synergistic interactions of these two cell types with biomaterials are not fully understood. In this investigation, an in vitro fibroblast/macrophage co-culture system was utilized to examine the biocompatibility and the potential to induce inflammatory responses of an electrospun Dextran/PLGA scaffold. The scaffold did not affect the morphologies, attachments, proliferations and viabilities of both the fibroblasts and macrophages, cultured separately or together. Moreover, it only activated a small subset of the macrophages implicating a low potential to induce either severe acute or chronic inflammatory response. Additionally, fibroblasts played a role in prolonging macrophage activation in the presence of the scaffolds. Using antibody arrays, IL-10, SDF-1, MIP-1 gamma and RANTES were found to be up-regulated when the cells were incubated with the scaffolds. The results of subdermal implantation of the Dextran/PLGA scaffolds confirmed its biocompatibility and low inflammatory potential.

Effect of zein on biodegradable inserts for the delivery of tetracycline within periodontal pockets

Treatment with antibiotics within the periodontal pocket against bacterial infections represents a useful and adjunctive tool to conventional therapy for healing and teeth preservation. With this function in view, an implantable, tetracycline delivery device for the treatment of periodontal disease was developed. The aim of this study was to develop biodegradable, tetracycline-loaded microparticles made of two polymers: PLGA and zein which were compressed into monolithic devices. In this polymer delivery system, the encapsulation efficiency, release characteristics, drug–polymer interaction, and antibacterial activity of loaded drug were investigated. The interaction of tetracycline with the corn protein zein was studied by nuclear magnetic resonance (NMR), Fourier transform infrared, and X-ray diffraction. The hydrophobic interaction of tetracycline with zein in the formulations was deduced from the NMR studies, whereas X-ray diffraction studies showed a new crystalline state of the drug in the presence of the protein. Zein was not denatured by preparation of inserts. Sustained release of tetracycline was obtained, and the proportion of zein in the inserts had a great impact on the drug release. Finally, an effective tetracycline release from inserts against Staphylococcus aureus was achieved over 30 days. In conclusion, the PLGA:zein delivery system described in this study was found to be effective in controlled delivery of tetracycline, and hence may be suitable for intra-pocket delivery of antimicrobial agents in the treatment of periodontitis.

Intravital microscopy imaging of macrophage localization to immunogenic particles and co-localized tissue oxygen saturation

Well-designed biomaterial polymer particle-based vaccines will optimally promote immune cell antigen-presenting behavior while minimizing adverse inflammatory responses to the particles and encapsulated drugs or adjuvants. It is important in the design of particle-based vaccines to consider possible harmful effects of immune response on tissue at the vaccination site. Intravital microscopy with rodent dorsal skin window chambers enables in vivo serial observations in the same animal, and such models which have been used to study angiogenesis and macrophage response to implanted biomaterials may also be useful for the development of particle-based vaccines. To our knowledge there have been no reports where intravital microscopy has documented real-time immune cell localization and potentially harmful co-localized tissue effects. In this proof-of-principle study we used fluorescence and spectral imaging intravital microscopy of mouse window chambers to measure macrophage localization and co-localized tissue microvessel hemoglobin saturation changes in response to an immunogenic stimulus from polymer particles loaded with lipopolysaccharide (LPS) serving as a model vaccine/adjuvant system. We observed greater and faster macrophage localization to stronger inflammatory stimuli from LPS-loaded particle doses, a trend of decreased microvessel oxygenation with increased macrophage accumulation and, in an extreme case, complete microvessel collapse accompanied by tissue necrosis. Our technique may be useful for optimizing design of particle-based vaccines and may give insight into the use of hemoglobin saturation as a biomarker of tissue inflammation for clinical investigations of particle-based vaccines.

Advances in the design and delivery of peptide subunit vaccines with a focus on toll-like receptor agonists

Considerable success has been made with many peptide antigen formulations, and peptide-based vaccines are emerging as the next generation of prophylactic and remedial immunotherapy. However, finding an optimal platform balancing all of the requirements for an effective, specific and safe immune response remains a major challenge for many infectious and chronic diseases. This review outlines how peptide immunogenicity is influenced by the way in which peptides are presented to the immune system, underscoring the need for multifunctional delivery systems that couple antigen and adjuvant into a single construct. Particular attention is given to the ability of Toll-like receptor agonists to act as adjuvants. A survey of recent approaches to developing peptide antigen delivery systems is given, many of which incorporate Toll-like receptor agonists into the design.

Comparison of chitosan nanoparticles and chitosan hydrogels for vaccine delivery

In this work the potential of chitosan nanoparticles (CNP) and thermosensitive chitosan hydrogels as particulate and sustained release vaccine delivery systems was investigated. CNP and chitosan hydrogels were prepared, loaded with the model protein antigen ovalbumin (OVA) and characterised. The immunostimulatory capacity of these vaccine delivery systems was assessed in-vitro and in-vivo. Particle sizing measurements and SEM images showed that optimised OVA-loaded CNP had a size of approximately 200 nm, a polydispersity index &lt; 0.2, and a positive zeta-potential of approximately 18 mV. The amount of OVA adsorbed onto CNP was high with an adsorption efficacy of greater than 96%. Raman spectroscopy indicated conformational changes of OVA when adsorbed onto the surface of CNP. Uptake of the dispersions and immunological activation of murine dendritic cells in-vitro could be demonstrated. Investigation of the release of fluorescently-labelled OVA (FITC-OVA) from CNP and chitosan hydrogels in-vitro showed that approximately 50% of the total protein was released from CNP within a period of ten days; release of antigen from chitosan gel occurred in a more sustained manner, with &lt; 10% of total protein being released after 10 days. The slow release from gel formulations may be explained by the strong interactions of the protein with chitosan. While OVA-loaded CNP showed no significant immunogenicity, formulations of OVA in chitosan gel were able to stimulate both cell-mediated and humoral immunity in-vivo.

Assays on the influence of biomaterials on allogeneic rejection in tissue engineering

In tissue engineering, innate responses to biomaterial scaffolds will affect rejection of allogeneic cells. Biomaterials directly influence innate and adaptive immune cell adhesion, reactive oxygen intermediate production, cytokine secretion, nuclear factor-kappa B nuclear translocation, gene expression, and cell surface markers, all of which are likely to affect allogeneic rejection responses. A major goal in tissue engineering is to induce transplant tolerance, potentially by manipulating the biomaterial component. This review describes methods of measuring responses of macrophages, dendritic cells, and T cells stimulated in vitro and in vivo and addresses key factors in assay development. Such tests include mixed leukocyte reactions, enzyme-linked immunosorbent spot assays, trans-vivo delayed-type hypersensitivity assays, and measurement of dendritic cell subsets and anti-donor antibodies; we propose extending these studies to tissue engineering.

Immune response to controlled release of immunomodulating peptides in a murine experimental autoimmune encephalomyelitis (EAE) model

The effects of controlled release on immune response to an immunomodulating peptide were evaluated in a murine experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS). The peptide, Ac-PLP-BPI-NH(2)-2 (Ac-HSLGKWLGHPDKF-(AcpGAcpGAcp)(2)-ITDGEATDSG-NH(2); Ac = acetyl, Acp = epsilon aminocaproic acid) was designed to suppress T-cell activation in response to PLP(139-151), an antigenic peptide in MS. Poly-lactide-co-glycolide (PLGA) microparticles containing Ac-PLP-BPI-NH(2)-2 (8+/-4 microm, 1.4+/-0.2% (w/w)) were prepared by a powder-in oil-in water emulsion-solvent evaporation method, sterilized and administered subcutaneously (s.c.) to SJL/J (H-2(s)) mice in which EAE had been induced by immunization with PLP(139-151). Treatment groups received Ac-PLP-BPI-NH(2)-2: (i) in solution by repeated i.v. or s.c. injection, (ii) in solution co-administered with blank PLGA microparticles, (iii) in solution co-administered with Ac-PLP-BPI-NH(2)-2 loaded microparticles, and (iv) as Ac-PLP-BPI-NH(2)-2 loaded microparticles. Administration of Ac-PLP-BPI-NH(2)-2 as an s.c. solution produced clinical scores and maintenance of body weight comparable to i.v. solution, but with reduced overall survival, presumably due to anaphylaxis. Administration as s.c. microparticles provided a somewhat less effective reduction in symptoms but with no toxicity during treatment. Thus, the results suggest that s.c. administration of Ac-PLP-BPI-NH(2)-2 microparticles can provide pharmacological efficacy and reduction in dosing frequency without increased toxicity.

Mechanistic study of the adjuvant effect of biodegradable nanoparticles in mucosal vaccination

For oral vaccination, incorporation of antigens into nanoparticles has been shown to protect the antigen from degradation, but may also increase its uptake through the intestinal epithelium via M-cells. The aim of this study was to understand the mechanisms by which oral administration of antigen-loaded nanoparticles induces an immune response and to analyze the effect of the nanoparticle composition on these mechanisms. Nanoparticles made from chitosan (CS) and its N-trimethylated derivative, TMC, loaded with a model antigen ovalbumin (OVA) were prepared by ionic gelation with tripolyphosphate. Intraduodenal vaccination with OVA-loaded nanoparticles led to significantly higher antibody responses than immunization with OVA alone. TMC nanoparticles induced anti-OVA antibodies after only a priming dose. To explain these results, the interaction of nanoparticles with the intestinal epithelium was explored, in vitro, using a follicle associated epithelium model and visualized, ex vivo, using confocal laser scanning microscopy. The transport of FITC-OVA-loaded TMC nanoparticles by Caco-2 cells or follicle associated epithelium model was higher than FITC-OVA-loaded CS or PLGA nanoparticles. The association of nanoparticles with human monocyte derived dendritic cells and their effect on their maturation were determined with flow cytometry. TMC nanoparticles but not CS or PLGA nanoparticles had intrinsic adjuvant effect on DCs. In conclusion, depending on their composition, nanoparticles can increase the M-cell dependent uptake and enhance the association of the antigen with DC. In this respect, TMC nanoparticles are a promising strategy for oral vaccination.

Targeted delivery with peptidomimetic conjugated self-assembled nanoparticles

Peptides produce specific nanostructures, making them useful for targeting in biological systems but they have low bioavailability, potential immunogenicity and poor metabolic stability. Peptidomimetic self-assembled NPs can possess biological recognition motifs as well as providing desired engineering properties. Inorganic NPs, coated with self-assembled macromers for stability and anti-fouling, and conjugated with target-specific ligands, are advancing imaging from the anatomy-based level to the molecular level. Ligand conjugated NPs are attractive for cell-selective tumor drug delivery, since this process has high transport capacity as well as ligand dependent cell specificity. Peptidomimetic NPs can provide stronger interaction with surface receptors on tumor cells, resulting in higher uptake and reduced drug resistance. Self-assembled NPs conjugated with peptidomimetic antigens are ideal for sustained presentation of vaccine antigens to dendritic cells and subsequent activation of T cell mediated adaptive immune response. Self-assembled NPs are a viable alternative to encapsulation for sustained delivery of proteins in tissue engineering. Cell penetrating peptides conjugated to NPs are used as intracellular delivery vectors for gene expression and as transfection agents for plasmid delivery. In this work, synthesis, characterization, properties, immunogenicity, and medical applications of peptidomimetic NPs in imaging, tumor delivery, vaccination, tissue engineering, and intracellular delivery are reviewed.

Pulsatile release of biomolecules from polydimethylsiloxane (PDMS) chips with hydrolytically degradable seals

We demonstrate, for the first time, a robust novel polydimethylsiloxane (PDMS) chip that can provide controlled pulsatile release of DNA based molecules, proteins and oligonucleotides without external stimuli or triggers. The PDMS chip with arrays of wells was constructed by replica molding. Poly(lactic acid-co-glycolic acid) (PLGA) polymer films of varying composition and thickness were used as seals to the wells. The composition, molecular weight and thickness of the PLGA films were all parameters used to control the degradation rate of the seals and therefore the release profiles. Degradation of the films followed the PLGA composition order of 50:50 PLGA>75:25 PLGA>85:15 PLGA at all time-points beyond week 1. Scanning electron microscopy images showed that films were initially smooth, became porous and ruptured as the osmotic pressure pushed the degrading PLGA film outwards. Pulsatile release of DNA was controlled by the composition and thickness of the PLGA used to seal the well. Transfection experiments in a model Human Embryonic Kidney 293 (HEK293) cell line showed that plasmid DNA loaded in the wells was functional after pulsatile release in comparison to control plasmid DNA at all time-points. Thicker films degraded faster than thinner films and could be used to fine-tune the release of DNA over day length periods. Finally the PDMS chip was shown to provide repeated sequential release of CpG oligonucleotides and a model antigen, Ovalbumin (OVA), indicating significant potential for this device for vaccinations or applications that require defined complex release patterns of a variety of chemicals, drugs and biomolecules.

Phagocytic activity of alveolar macrophages toward polystyrene latex microspheres and PLGA microspheres loaded with anti-tuberculosis agent

Phagocytosis of alveolar macrophages (Mphis) toward poly(lactic-co-glycolic acid) (PLGA) microspheres (MS) loaded with the anti-tuberculosis agent rifampicin (RFP-PLGA MS) has been shown to be effective for the treatment of tuberculosis. The phagocytosis should be evaluated in terms of that toward reference MS. We chose polystyrene latex (PSL) MS as a reference. In this study, phagocytic activity of cell line NR8383, derived from rat alveolar Mphi, toward PSL MS with various diameters was examined by incubating the cells for 4h at 37 degrees C with various numbers of PSL MS per Mphi cell (MS/Mphi=0.1-10). The results were then compared with those of the phagocytosis toward RFP-PLGA MS. We determined the phagocytic activity by counting the population of Mphi cells that had phagocytosed MS (N) and the number of particles phagocytosed (n) in microscopic fields. Both N and n for PSL and RFP-PLGA MS increased in general with an increase in MS/Mphi, but both of these values for PSL MS were smaller than those for RFP-PLGA MS. Phagocytosis of the particles were dependent on the particle size; i.e., of the PSL MS the 6-mum ones were taken up by Mphi the most, and the RFP-PLGA MS 3 microm in diameter seemed to be phagocytosed the most efficiently, although we were not able to determine exactly the phagocytosis of 6- and 10-microm RFP-PLGA MS. From the changes in N and n values with MS/Mphi, the phagocytosis of RFP-PLGA MS was likely to enhance the phagocytic activity of Mphi cells, but this effect did not seem to be significant for PSL MS.

The preservation of phenotype and functionality of dendritic cells upon phagocytosis of polyelectrolyte-coated PLGA microparticles

Biodegradable microparticles (MP) represent a promising and efficient delivery system for parenteral vaccination. Recently, MP have also been explored as tool for the ex vivo antigen loading of professional antigen-presenting cells such as dendritic cells (DC) to be used as cellular vaccines. The purpose of this study was to investigate various polycationic coatings on poly(lactide-co-glycolide) (PLGA) MP, with regard to their effect on phenotypic and functional maturation of monocyte-derived DC (MoDC) that had previously been loaded with the MP in vitro. The preparation and concomitant coating of the PLGA was performed by means of a solvent extraction/evaporation method using a recently developed microextrusion-based technique. The polyelectrolytes tested for MP coating encompassed aminodextran, chitosan, poly(ethylene imine) (PEI), poly(L-lysine) and protamine. Uncoated and differently coated PLGA MP were fed to immature MoDC, which ingested efficiently the different MP types irrespective of their surface coating. The MP-loaded immature MoDC were then matured with the help of a cytokine/PGE-2 maturation cocktail. Here, the presence of the ingested MP did not affect the MoDC maturation in terms of expression of the surface markers CD80, CD83, CD86, HLA-DR and MMR, irrespective of the MP surface coating. Importantly, none of the PLGA MP types alone induced significant maturation of MoDC in the absence of the maturation cocktail. MP-loaded and subsequently matured MoDC expressed high levels of the chemokine receptor CCR7, whose functional activity was evidenced by the migration of MoDC towards CCL21, irrespective of the presence of ingested MP. Further, MP-loaded and subsequently matured MoDC also secreted comparable amounts of IL-10 and IL-12p70, irrespective of the presence of ingested MP except for PEI-coated PLGA MP, which enhanced significantly the secretion of IL-12p70 in mature MoDC. In conclusion, phenotypic and functional maturation of MoDC by means of a maturation cocktail remained unchanged irrespective of the presence of previously ingested differently coated PLGA MP. This offers interesting perspectives for using these particulate systems together with entrapped antigens for ex vivo loading of MoDC in view of cellular immunotherapy.

Uptake of inhalable microparticles affects defence responses of macrophages infected with Mycobacterium tuberculosis H37Ra

OBJECTIVES

To investigate whether inhalable microparticles containing two anti-tuberculosis agents, isoniazid and rifampicin, evoke host-defence strategies in macrophages in addition to targeting the incorporated drugs.

METHODS

Microparticles were prepared by spray-drying a homogeneous solution of drugs and poly(lactic acid) (PLA; apparent viscosity 1.1 cP). Four parts PLA and three parts rifampicin were dissolved in dichloromethane. One part isoniazid was dissolved in methanol. The two solutions were mixed in the ratio 22 : 3 at which none of the solutes precipitated. These were administered as 'nose-only' inhalations to mice or exposed to cultured J774 mouse macrophages. Targeting to lung macrophages was investigated by transmission electron microscopy. Reactive oxygen species (ROS) were estimated by a cytochrome c assay and flow cytometry. Reactive nitrogen intermediates (RNI) were assayed using Griess reagent. Cytokines in culture supernatants were estimated by ELISA.

RESULTS

Treatment with inhalable microparticles targeted lung macrophages in vivo and induced intense Golgi activity in the vicinity of microparticle-containing phagosomes. Microparticles induced a respiratory burst involving NADPH oxidase and enhanced NO production by infected macrophages. Microparticle-induced NADPH oxidase activation required optimal calcium ions. Microparticles efficiently induced tumour necrosis factor-alpha (TNF-alpha) secretion by macrophages recovered from infected mice.

CONCLUSIONS

Microparticle phagocytosis induces responses in infected murine macrophages that are indicative of activation of innate bactericidal mechanisms, and are inimical to bacterial survival. It is likely that such responses augment straightforward drug action on the bacterium and contribute to the unexpectedly high efficacy of microparticles in experimental tuberculosis.

Engagement of CD14 mediates the inflammatory potential of monosodium urate crystals

Phagocyte ingestion of monosodium urate (MSU) crystals can induce proinflammatory responses and trigger acute gouty inflammation. Alternatively, the uptake of MSU crystals by mature macrophages can be noninflammatory and promote resolution of gouty inflammation. Macrophage activation by extracellular MSU crystals involves apparent recognition and ingestion mediated by TLR2 and TLR4, with subsequent intracellular recognition linked to caspase-1 activation and IL-1beta processing driven by the NACHT-LRR-PYD-containing protein-3 inflammasome. In this study, we examined the potential role in gouty inflammation of CD14, a phagocyte-expressed pattern recognition receptor that functionally interacts with both TLR2 and TLR4. MSU crystals, but not latex beads, directly bound recombinant soluble (s) CD14 in vitro. CD14(-/-) bone marrow-derived macrophages (BMDMs) demonstrated unimpaired phagocytosis of MSU crystals but reduced p38 phosphorylation and approximately 90% less IL-1beta and CXCL1 release. Attenuated MSU crystal-induced IL-1beta release in CD14(-/-) BMDMs was mediated by decreased pro-IL-1beta protein expression and additionally by decreased caspase-1 activation and IL-1beta processing consistent with diminished NACHT-LRR-PYD-containing protein-3 inflammasome activation. Coating of MSU crystals with sCD14, but not sTLR2 or sTLR4, restored IL-1beta and CXCL1 production in CD14(-/-) BMDMs in vitro. Gain of function of CD14 directly enhanced TLR4-mediated signaling in response to MSU crystals in transfected Chinese hamster ovary cells in vitro. Last, MSU crystal-induced leukocyte influx at 6 h was reduced by approximately 75%, and local induction of IL-1beta decreased by >80% in CD14(-/-) mouse s.c. air pouches in vivo. We conclude that engagement of CD14 is a central determinant of the inflammatory potential of MSU crystals.

Formulation and delivery issues for monoclonal antibody therapeutics

Antibodies can have exquisite specificity of target recognition and thus generate highly selective outcomes following their systemic administration. While antibodies can have high specificity, the doses required to treat patients, particularly for a chronic condition, are typically large. Fortunately, advances in production and purification capacities have allowed for the exceptionally large amounts of highly purified monoclonal antibodies to be produced. Additionally, genetic engineering of antibodies has provided a stable of antibody-like proteins that can be easier to prepare. Together, these advances have made antibody-based therapies one of the most commonly pursued pharmaceuticals in biotechnology pipelines. With this success, however, has come a series of technical challenges in the formulation of antibody-based materials to maintain sufficient stability in a variety of configurations and sometimes at particularly high concentrations. This review focuses on issues related to identifying and verifying stable antibody-based formulations.

Prophylactic anti-tumor effects in a B cell lymphoma model with DNA vaccines delivered on polyethylenimine (PEI) functionalized PLGA microparticles

Idiotypic sequences, specific to the hypervariable regions of immunoglobulins expressed by malignant B cells offer a therapeutic target in B cell lymphoma. Efficient approaches have been described to clone a single chain fragment of the tumor immunoglobulin (Ig) comprising of heavy and light Ig chains (sFv) fused with proinflammatory chemokines. Tumor associated, poorly immunogenic self antigens encoded by plasmid DNA (pDNA) have been rendered immunogenic by chemokine fusion, thereby targeting to antigen presenting cells (APCs) which differentially express chemokine receptors. Here we present an injectable (parenteral) approach using synthetic polymer based cationic microparticle formulations for enhancing the potency of such chemokine/self antigen expressing plasmid construct. Branched and linear polyethyleneimine (PEI) were conjugated on poly (D, L lactide-co-glycolide) (PLGA) microparticles using carbodiimide chemistry followed by efficient loading of plasmid DNA. In addition to imparting significant buffering ability to these cationic microparticles, flow cytometry studies indicate that these DNA loaded microparticles significantly up regulate CD80 and MHC class II markers in phagocytic RAW264.7 cells, indicating intrinsic adjuvant effects. Intradermal injections in Balb/c mice with these formulations induced significant protection upon tumor challenge with 2.5 times the minimal lethal dose. Long term survival rates were significant (p < 0.05) in comparison with saline injected controls or blank microparticles. Further studies indicated that intramuscular delivery might provide better protection compared to intradermal injections and perform similar to gene gun mediated administration. We conclude, based on these promising in vivo results, that such surface-functionalized microparticles offer an attractive strategy to improve the potency of self antigen-based cancer DNA vaccines.