Augmented humoral and cellular immune responses to hepatitis B DNA vaccine adsorbed onto cationic microparticles

Biomaterials and nanomaterials for sustained release vaccine delivery

Vaccines are considered one of the most significant medical advancements in human history, as they have prevented hundreds of millions of deaths since their discovery; however, modern travel permits disease spread at unprecedented rates, and vaccine shortcomings like thermal sensitivity and required booster shots have been made evident by the COVID-19 pandemic. Approaches to overcoming these issues appear promising via the integration of vaccine technology with biomaterials, which offer sustained-release properties and preserve proteins, prevent conformational changes, and enable storage at room temperature. Sustained release and thermal stabilization of therapeutic biomacromolecules is an emerging area that integrates material science, chemistry, immunology, nanotechnology, and pathology to investigate different biocompatible materials. Biomaterials, including natural sugar polymers, synthetic polyesters produced from biologically derived monomers, hydrogel blends, protein-polymer blends, and metal-organic frameworks, have emerged as early players in the field. This overview will focus on significant advances of sustained release biomaterial in the context of vaccines against infectious disease and the progress made towards thermally stable "single-shot" formulations. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Plasmid Biopharmaceuticals

Plasmids are currently an indispensable molecular tool in life science research and a central asset for the modern biotechnology industry, supporting its mission to produce pharmaceutical proteins, antibodies, vaccines, industrial enzymes, and molecular diagnostics, to name a few key products. Furthermore, plasmids have gradually stepped up in the past 20 years as useful biopharmaceuticals in the context of gene therapy and DNA vaccination interventions. This review provides a concise coverage of the scientific progress that has been made since the emergence of what are called today plasmid biopharmaceuticals. The most relevant topics are discussed to provide researchers with an updated overview of the field. A brief outline of the initial breakthroughs and innovations is followed by a discussion of the motivation behind the medical uses of plasmids in the context of therapeutic and prophylactic interventions. The molecular characteristics and rationale underlying the design of plasmid vectors as gene transfer agents are described and a description of the most important methods used to deliver plasmid biopharmaceuticals in vivo (gene gun, electroporation, cationic lipids and polymers, and micro- and nanoparticles) is provided. The major safety issues (integration and autoimmunity) surrounding the use of plasmid biopharmaceuticals is discussed next. Aspects related to the large-scale manufacturing are also covered, and reference is made to the plasmid products that have received marketing authorization as of today.

Engineering vaccines and niches for immune modulation

Controlled modulation of immune response, especially the balance between immunostimulatory and immunosuppressive responses, is critical for a variety of clinical applications, including immunotherapies against cancer and infectious diseases, treatment of autoimmune disorders, transplant surgeries, regenerative medicine, prosthetic implants, etc. Our ability to precisely modify both innate and adaptive immune responses could provide new therapeutic directions in a variety of diseases. In the context of vaccines and immunotherapies, the interplay between antigen-presenting cells (e.g. dendritic cells and macrophages), B cells, T helper and killer subtypes, and regulatory T- and B-cell responses is critical for generating effective immunity against cancer, infectious diseases and autoimmune diseases. In recent years, immunoengineering has emerged as a new field that uses quantitative engineering tools to understand molecular-, cellular- and system-level interactions of the immune system and to develop design-driven approaches to control and modulate immune responses. Biomaterials are an integral part of this engineering toolbox and can exploit the intrinsic biological and mechanical cues of the immune system to directly modulate and train immune cells and direct their response to a particular phenotype. A large body of literature exists on strategies to evade or suppress the immune response in implants, transplantation and regenerative medicine. This review specifically focuses on the use of biomaterials for immunostimulation and controlled modulation, especially in the context of vaccines and immunotherapies against cancer, infectious diseases and autoimmune disorders. Bioengineering smart systems that can simultaneously deliver multiple bioactive agents in a controlled manner or can work as a niche for in situ priming and modulation of the immune system could significantly enhance the efficacy of next-generation immunotherapeutics. In this review, we describe our perspective on the important design aspects for the development of biomaterials that can actively modulate immune responses by stimulating receptor complexes and cells, and delivering multiple immunomodulatory biomolecules.

Current progress in gene delivery technology based on chemical methods and nano-carriers

Gene transfer methods are promising in the field of gene therapy. Current methods for gene transfer include three major groups: viral, physical and chemical methods. This review mainly summarizes development of several types of chemical methods for gene transfer in vitro and in vivo by means of nano-carriers like; calcium phosphates, lipids, and cationic polymers including chitosan, polyethylenimine, polyamidoamine dendrimers, and poly(lactide-co-glycolide). This review also briefly introduces applications of these chemical methods for gene delivery.

Calcium phosphate embedded PLGA nanoparticles: a promising gene delivery vector with high gene loading and transfection efficiency

In the purpose of increasing incorporation efficiency and improving the release kinetics of plasmid DNA (pDNA) from poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles, a facile method for the fabrication of calcium phosphate (CaPi) embedded PLGA nanoparticles (CaPi-pDNA-PLGA-NPs) was developed. The effect of several preparation factors on the particle size, incorporation efficiency, pDNA release and transfection efficiency in vitro was studied by Single Factor Screening Method. These preparation factors included the molecular weight (MW), hydrolysis degree (HD) of polyvinyl alcohol (PVA), sonication power and time, composition of organic phase, initial concentration of calcium phosphate and calcium (Ca) to phosphate ion (P) ratio (Ca/P ratio), etc. The CaPi-pDNA-PLGA-NPs made according to the optimal formulation were spherical in shape observed by transmission electron microscopy (TEM) with a mean particle size of 207±5 nm and an entrapment efficiency of 95.7±0.8%. Differential scanning calorimetry (DSC) suggested that there existed interaction between the DNA-calcium-phosphate (CaPi-pDNA) complexes and the polymeric matrices of PLGA. X-ray diffractometry (XRD) further proved the conclusion and indicated that the CaPi-pDNA was in weak crystallization form inside the nanoparticles. The Brunauer-Emmett-Teller (BET) surface area measurement demonstrated that the CaPi-pDNA-PLGA-NPs are mesoporous with specific surface area of 57.5m(2)/g and an average pore size of 96.5 Å. The transfection efficiency of the CaPi-pDNA-PLGA-NPs on human embryonic kidney 293 (HEK 293) cells in vitro was 22.4±1.2%, which was much higher than those of both the pDNA loaded PLGA nanoparticles (pDNA-PLGA-NPs) and the CaPi-pDNA embedded PLGA microparticles (CaPi-pDNA-PLGA-MPs). The CaPi-pDNA-PLGA-NPs are promising vectors for gene delivery.

Technologies for enhanced efficacy of DNA vaccines

Despite many years of research, human DNA vaccines have yet to fulfill their early promise. Over the past 15 years, multiple generations of DNA vaccines have been developed and tested in preclinical models for prophylactic and therapeutic applications in the areas of infectious disease and cancer, but have failed in the clinic. Thus, while DNA vaccines have achieved successful licensure for veterinary applications, their poor immunogenicity in humans when compared with traditional protein-based vaccines has hindered their progress. Many strategies have been attempted to improve DNA vaccine potency including use of more efficient promoters and codon optimization, addition of traditional or genetic adjuvants, electroporation, intradermal delivery and various prime-boost strategies. This review summarizes these advances in DNA vaccine technologies and attempts to answer the question of when DNA vaccines might eventually be licensed for human use.

Fundamentals of Vaccine Delivery in Infectious Diseases

Infectious diseases continue to be the major causes of illness, disability, and death. Moreover, in recent years, new infectious agents and diseases are being identified, and some diseases that were previously considered under control have reemerged. Furthermore, antimicrobial resistance has grown rapidly in a variety of hospital as well as community acquired infections. Thus, humanity still faces big challenges in the prevention and control of infectious diseases. Vaccination, generally considered to be the most effective method of preventing infectious diseases, works by presenting a foreign antigen to the immune system to evoke an immune response. The administered antigen can either be a live, but weakened, form of a pathogen (bacteria or virus), a killed or inactivated form of the pathogen, or a purified material such as a protein. However, no vaccine is completely safe; therefore, vaccine safety research and monitoring are necessary to minimize vaccine related harms. From the formulation point of view, the goal continues to be to improve the quality and global availability of vaccine delivery systems. This chapter provides an introduction to vaccine formulation, describes the delivery routes that are utilized, and discusses the factors that affect the safety and stability of a vaccine formulation.

Chitosan-based systems for the delivery of vaccine antigens

This review discusses the current status of chitosan and its derivatives as adjuvants and delivery systems in vaccine delivery, and their future possibilities and challenges. After a brief introduction to adjuvants and delivery systems, chitosan will be described in detail in regard to vaccine formulation. Applications of chitosan and its derivatives will be reviewed and their proposed mechanisms in the enhancement of immune responses will be discussed.

Preparation, physiochemical characterization, and oral immunogenicity of Abeta(1-12), Abeta(29-40), and Abeta(1-42) loaded PLG microparticles formulations

Alzheimer's disease (AD) is caused by the deposition of beta-amyloid (Abeta) protein in brain. The current AD immunotherapy aims to prevent Abeta plaque deposition and enhance its degradation in the brain. In this work, the peptides B-cell epitope Abeta(1-12), T-cell epitope Abeta(29-40) and full-length Abeta(1-42) were loaded separately to the poly (D,L-lactide co-glycolide) (PLG) microparticles by using W/O/W double emulsion solvent evaporation method with entrapment efficacy of 70.46%, 60.93%, and 65.98%, respectively. The prepared Abeta PLG microparticles were smooth, spherical, individual, and nonporous in nature with diameters ranging from 2 to 12 microm. The cumulative in vitro release profiles of Abeta(1-12), Abeta(29-40), and Abeta(1-42) from PLG microparticles sustained for long periods and progressively reached to 73.89%, 69.29%, and 70.08% by week 15. In vitro degradation studies showed that the PLG microparticles maintained the surface integrity up to week 8 and eroded completely by week 16. Oral immunization of Abeta peptides loaded microparticles in mice elicited stronger immune response by inducing anti-Abeta antibodies for prolonged time (24 weeks). The physicochemical characterization and immunogenic potency of Abeta peptides incorporated PLG microparticles suggest that the microparticles formulation of Abeta can be a potential oral AD vaccine.

Multiepitope peptide-loaded virus-like particles as a vaccine against hepatitis B virus-related hepatocellular carcinoma

To develop a hepatitis B virus (HBV) therapeutic vaccine that can induce a broad but specific immune response and significant antitumor effects both in vivo and in vitro, we inserted HBV X protein (HBx)-derived epitopes HBx(52-60), HBx(92-100), and HBx(115-123); a novel subdominant cytolytic T lymphocyte (CTL) epitope HBx(140-148); and the universal T helper epitope pan human leukocyte antigen DR-binding epitope into HBV core protein to form multiepitope peptide-loaded virus-like particles (VLPs). CTL responses against epitope-loaded VLPs were elicited by priming with VLP-pulsed dendritic cells in both HLA-A*0201 transgenic (Tg) mice and peripheral blood lymphocytes from HLA-A2(+)/HBx(+) HBV-infected hepatocellular carcinoma (HCC) patients. The multiepitope peptide-loaded VLPs demonstrated significantly higher immunogenicity in Tg mice than any single responsive epitope. Significant antitumor effects were demonstrated both with primary cultured autologous HCC cells in vitro and tumor-bearing Tg mice in vivo in an HLA-A2-restricted and epitope-specific fashion.

CONCLUSION

The significant antitumor effects both in vivo and in vitro demonstrate the potential of multiepitope peptide-loaded VLPs as a vaccine against HCC.

Alginate coated chitosan nanoparticles are an effective subcutaneous adjuvant for hepatitis B surface antigen

We recently described a delivery system that is composed of a chitosan core to which the hepatitis B surface antigen (HBsAg) was adsorbed and subsequently coated with sodium alginate. In this present work, alginate coated chitosan nanoparticles were evaluated as a subcutaneous adjuvant for HBsAg. HBsAg loaded, alginate coated or uncoated chitosan nanoparticles, associated or not with CpGODN were subcutaneously administered to mice and several immunological parameters were evaluated. A high anti-HBsAg IgG titer (2271+/-120 mIU/ml), with the majority of antibodies being of Th2 type, was observed within group I, vaccinated with HBsAg loaded onto coated nanoparticles. However, regarding cellular immune response, no significant differences were observed for antigen-specific splenocyte proliferation or for the secretion of IFN-gamma and IL-4, when compared to the control group. The co-delivery of antigen-loaded nanoparticles in the presence of the immunopotentiator, CpG ODN 1826, resulted in an increase of anti-HBsAg IgG titers that was not statistically different from the first group; however, an increase of the IgG2a/IgG1 ratio from 0.1 to 1.0 and an increase (p<0.01) of the IFN-gamma production by the splenocytes stimulated with the HBV antigen was observed. The enhancement of the immune response observed with the antigen-loaded nanoparticles demonstrated that chitosan is a promising platform for parenteral HBsAg delivery and, when co-administered with the CpG ODN, resulted in a mixed Th1/Th2 type immune response.

High loading efficiency and tunable release of plasmid DNA encapsulated in submicron particles fabricated from PLGA conjugated with poly-L-lysine

Poly(lactic-co-glycolic acid) (PLGA) particles have been widely explored as vehicles for delivery of plasmid DNA to mammalian cells both in vitro and in vivo. Achieving high incorporation efficiencies and control over release kinetics are significant challenges in encapsulating hydrophilic molecules such as DNA within submicron particles fabricated from PLGA. This study explored two modifications in the preparation of submicron particles to specifically address these challenges. Firstly, we compared homogenization and sonication as energy sources for emulsification. It was demonstrated that particles prepared with homogenization resulted in higher encapsulation efficiency and a linear release profile of DNA as compared to particles prepared with sonication, which exhibited lower encapsulation efficiency and a burst release. Also investigated was conjugation of poly-L-lysine to PLGA (PLGA-PLL) to create an electrostatically favorable interaction between the carrier material and the DNA. Particles fabricated with high weight percentages of PLGA-PLL/PLGA resulted in remarkably increased loading (>90%). Additionally, the release profile could be dictated by the quantity of PLGA-PLL incorporated into the particles. Particles incubated in vitro on COS-7 cells were able to transfect cells. These results demonstrated that DNA encapsulation and release were modulated by the method of fabrication.

A genetically engineered prime-boost vaccination strategy for oculonasal delivery with poly(D,L-lactic-co-glycolic acid) microparticles against infection of turkeys with avian Metapneumovirus

In this study we demonstrated the use of an oculonasally delivered poly(D,L-lactic-co-glycolic acid) microparticle (PLGA-MP)-based and genetically engineered vaccination strategy in the avian system. An avian Metapneumovirus (aMPV) fusion (F) protein-encoding plasmid vaccine and the corresponding recombinant protein vaccine were produced and bound to or encapsulated by PLGA-MP, respectively. The PLGA-MP as the controlled release system was shown in vitro to not induce any cytopathic effects and to efficiently deliver the F protein-based aMPV-vaccines to avian cells for further processing. Vaccination of turkeys was carried out by priming with an MP-bound F protein-encoding plasmid vaccine and a booster-vaccination with an MP-encapsulated recombinant F protein. Besides the prime-boost F-specific vaccinated birds, negative control birds inoculated with a mock-MP prime-boost regimen as well as non-vaccinated birds and live vaccinated positive control birds were included in the study. The MP-based immunization of turkeys via the oculonasal route induced systemic humoral immune reactions as well as local and systemic cellular immune reactions, and had no adverse effects on the upper respiratory tract. The F protein-specific prime-boost strategy induced partial protection. After challenge the F protein-specific MP-vaccinated birds showed less clinical signs and histopathological lesions than control birds of mock MP-vaccinated and non-vaccinated groups did. The vaccination improved viral clearance and induced accumulation of local and systemic CD4+ T cells when compared to the mock MP-vaccination. It also induced systemic aMPV-neutralizing antibodies. The comparison of mock- and F protein-specific MP-vaccinated birds to non-vaccinated control birds suggests that aMPV-specific effects as well as adjuvant effects mediated by MP may have contributed to the overall protective effect.

Preparation, characterization, cytotoxicity and transfection efficiency of poly(DL-lactide-co-glycolide) and poly(DL-lactic acid) cationic nanoparticles for controlled delivery of plasmid DNA

The objective of this study was to investigate the effect of formulation parameters (i.e. polymer molecular weight and homogenization speed) on various physicochemical and biological properties of cationic nanoparticles. Cationic nanoparticles were prepared using different molecular weights of poly(DL-lactide-co-glycolide) (PLGA) and poly(DL-lactic acid) (PLA) by double emulsion solvent evaporation at two different homogenization speeds, and were characterized in terms of size, surface charge, morphology, loading efficiency, plasmid release, plasmid integrity, cytotoxicity, and transfection efficiency. Cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used to provide positive charge on the surface of nanoparticles. Reporter plasmid gWIZ Beta-gal was loaded on the surface of nanoparticles by incubation. Use of higher homogenization speed and lower molecular weight polymer led to a decrease in mean particle size, increase in zeta potential, increase in plasmid loading efficiency, and a decrease in burst release. The nanoparticles displayed good morphology as evident from scanning electron micrographs. In vitro cytotoxicity study by MTT assay showed a low toxicity. Structural integrity of the pDNA released from nanoparticles was maintained. Transfecting human embryonic kidney (HEK293) cells with nanoparticles prepared from low molecular weight PLGA and PLA resulted in an increased expression of beta-galactosidase as compared to those prepared from high molecular weight polymer. Our results demonstrate that the PLGA and PLA cationic nanoparticles can be used to achieve prolonged release of pDNA, and the plasmid release rate and transfection efficiency are dependent on the formulation variables.

Microparticle-based technologies for vaccines

Microparticles have been effectively used for many years as delivery systems for drugs and therapeutic proteins. Their application to the delivery of vaccines is not as extensive, but is growing. Utility has been demonstrated for the delivery of various types of vaccines (e.g., recombinant proteins, plasmid DNA, and peptides) and other vaccine components (e.g., immune potentiators). With respect to delivery of immune potentiators, synergistic effects are often observed whereby much more potent immune responses are induced with a combination than with either component alone. Hence, the prospects for broad application of microparticle-based delivery systems for vaccines are excellent.

Novel chitosan derivative nanoparticles enhance the immunogenicity of a DNA vaccine encoding hepatitis B virus core antigen in mice

BACKGROUND

Chitosan has been shown to possess useful properties such as non-toxicity, high biocompatibility and non-antigenicity that offer advantages for vaccine delivery systems. In this study, we prepared novel chitosan derivative nanoparticles as DNA vaccine carriers and the potential and mechanism of the DNA-nanoparticle complexes in inducing augmented immune responses were explored.

METHODS

The pVAX(HBc)DNA-nanoparticle complexes as vaccine delivery systems were studied in several aspects: the protection against DNase I degradation was measured by an in vitro inhibition assay; the sustained expression of the plasmid in vivo was determined by RT-PCR; the elevated uptake efficiency by phagocytes was observed with confocal microscopy; the biocompatibility was evaluated by cytotoxicity and histology assay; the complexes were administrated to C57BL/6 mice and the humoral and cellular immune responses were evaluated by ELISA, IFN-gamma production and cytolytic T lymphocyte (CTL)-specific lysis assay.

RESULTS

The remaining relative activity of DNase I after inhibition varied from 32.3% to 77.6%. The complexes were observed with higher uptake efficiency by phagocytes than naked DNA. Three types of nanoparticles did not induce significant cytotoxicity at concentrations<or=400 microg/ml. No specific histological alteration related to the injection of the complexes was observed. The formulations of DNA-nanoparticle complexes significantly enhanced the immunogenicity in several parameters: elevated antibody production, higher level of IFN-gamma secretion, and augmented specific cell lysis.

CONCLUSIONS

This study demonstrated the potential of the novel chitosan derivative nanoparticles for safe and effective DNA vaccine delivery.

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.

Enhanced immunogenicity of microencapsulated multiepitope DNA vaccine encoding T and B cell epitopes of foot-and-mouth disease virus in mice

The role of poly(D,L-lactic-co-glycolic acid, PLGA) microparticles on enhancing immune responses of multiepitope DNA vaccines was investigated in vitro and in vivo. pcDNA-SG encoding T and B cell epitopes of foot-and-mouth disease virus (FMDV) was encapsulated into PLGA microparticles. PLGA microparticles could protect themselves from nuclease degradation in vitro. PLGA-pcDNA-SG microparticles could be uptaken by cells and expressed His-tagged SG immunogen in vitro and in vivo. A prolonged expression and presentation of SG immunogen were observed by confocal laser scanning microscopy in the lymphocytes from the mice incubated with PLGA-pcDNA-SG microparticles, compared with the mice immunized with naked pcDNA-SG. PLGA-pcDNA-SG microparticles displayed a significant stronger immunogenicity than naked DNA vaccines with a higher titer of virus-specific antibody, elevated IFN-gamma production and enhanced lymphocyte proliferation. PLGA-DNA microparticle could elicit augmented humoral and cellular responses with reduced amounts and times of immunization.