Immune responses and protection obtained by oral immunization with rotavirus VP4 and VP7 DNA vaccines encapsulated in microparticles

The mRNA Vaccine Revolution: COVID-19 Has Launched the Future of Vaccinology

During the COVID-19 pandemic, mRNA (mRNA) vaccines emerged as leading vaccine candidates in a record time. Nonreplicating mRNA (NRM) and self-amplifying mRNA (SAM) technologies have been developed into high-performing and clinically viable vaccines against a range of infectious agents, notably SARS-CoV-2. mRNA vaccines demonstrate efficient in vivo delivery, long-lasting stability, and nonexistent risk of infection. The stability and translational efficiency of in vitro transcription (IVT)-mRNA can be further increased by modulating its structural elements. In this review, we present a comprehensive overview of the recent advances, key applications, and future challenges in the field of mRNA-based vaccinology.

Vaccinomics Approach for Multi-Epitope Vaccine Design against Group A Rotavirus Using VP4 and VP7 Proteins

Rotavirus A is the most common cause of Acute Gastroenteritis globally among children <5 years of age. Due to a segmented genome, there is a high frequency of genetic reassortment and interspecies transmission which has resulted in the emergence of novel genotypes. There are concerns that monovalent (Rotarix: GlaxoSmithKline Biologicals, Rixensart, Belgium) and pentavalent (RotaTeq: MERCK & Co., Inc., Kenilworth, NJ, USA) vaccines may be less effective against non-vaccine strains, which clearly shows the demand for the design of a vaccine that is equally effective against all circulating genotypes. In the present study, a multivalent vaccine was designed from VP4 and VP7 proteins of RVA. Epitopes were screened for antigenicity, allergenicity, homology with humans and anti-inflammatory properties. The vaccine contains four B-cell, three CTL and three HTL epitopes joined via linkers and an N-terminal RGD motif adjuvant. The 3D structure was predicted and refined preceding its docking with integrin. Immune simulation displayed promising results both in Asia and worldwide. In the MD simulation, the RMSD value varied from 0.2 to 1.6 nm while the minimum integrin amino acid fluctuation (0.05-0.1 nm) was observed with its respective ligand. Codon optimization was performed with an adenovirus vector in a mammalian expression system. The population coverage analysis showed 99.0% and 98.47% in South Asia and worldwide, respectively. These computational findings show potential against all RVA genotypes; however, in-vitro/in-vivo screening is essential to devise a meticulous conclusion.

Demystifying particle-based oral vaccines

Introduction: The oral route of vaccination is pain- and needle-free and can induce systemic and mucosal immunity. However, gastrointestinal barriers and antigen degradation impose significant hurdles in the development of oral vaccines. Live attenuated viruses and bacteria can overcome these barriers but at the risk of introducing safety concerns. As an alternative, particles have been investigated for antigen protection and delivery, yet there are no FDA-approved oral vaccines based on particle-based delivery systems. Our objective was to discover underlying determinants that can explain the current inadequacies and identify paradigms that can be implemented in future for successful development of oral vaccines relying on particle-based delivery systems.Areas covered: We reviewed literature related to the use of particles for oral vaccination and placed special emphasis on formulation characteristics and administration schedules to gain an insight into how these parameters impact production of antigen-specific antibodies in systemic and mucosal compartments.Expert opinion: Despite the long history of vaccines, particle-based oral vaccination is a relative new field with the first study published in 1989. Substantial variability exists between different studies with respect to dosing schedules, number of doses, and the amount of vaccine per dose. Most studies have not used adjuvants in the formulations. Better standardization in vaccination parameters is required to improve comparison between experiments, and adjuvants should be used to enhance the systemic and mucosal immune responses and to reduce the number of doses, which will make oral vaccines more attractive.

Future Approaches to DNA Vaccination Against Hemorrhagic Fever Viruses

To date, there is no protective vaccine for Ebola virus infection. Safety concerns have prevented the use of live-attenuated vaccines, and forced researchers to examine new vaccine formulations. DNA vaccination is an attractive method for inducing protective immunity to a variety of pathogens, but the low immunogenicity seen in larger animals and humans has hindered its usage. Various approaches have been used to improve the immunogenicity of DNA vaccines, but the most successful, and widespread, is electroporation. Of increasing interest is the use of molecular adjuvants to produce immunomodulatory signals that can both amplify and direct the immune response. When combined, these approaches have the possibility to push DNA vaccination into the forefront of medicine.

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.

Nanotechnological Approaches for Genetic Immunization

Genetic immunization is one of the important findings that provide multifaceted immunological response against infectious diseases. With the advent of r-DNA technology, it is possible to construct vector with immunologically active genes against specific pathogens. Nevertheless, site-specific delivery of constructed genetic material is an important contributory factor for eliciting specific cellular and humoral immune response. Nanotechnology has demonstrated immense potential for the site-specific delivery of biomolecules. Several polymeric and lipidic nanocarriers have been utilized for the delivery of genetic materials. These systems seem to have better compatibility, low toxicity, economical and capable to delivering biomolecules to intracellular site for the better expression of desired antigens. Further, surface engineering of nanocarriers and targeting approaches have an ability to offer better presentation of antigenic material to immunological cells. This chapter gives an overview of existing and emerging nanotechnological approaches for the delivery of genetic materials.

Construction of an artificial recombinant bicistronic plasmid DNA vaccine against porcine rotavirus

The attenuated Salmonella typhimurium χ4550 strain was used to harbour a reconstructed bicistronic DNA vaccine against porcine rotavirus, which carried the rotavirus nonstructural protein 4 (NSP4) and VP7 genes simultaneously. Using a balanced lethal system, the kanamycin resistance gene of expressing eukaryotic plasmids pVAX1 and pVAXD were replaced by the aspartate β-semialdehyde dehydrogenase (asd) gene. The NSP4 cleavage product (259-525) of rotavirus OSU strain and VP7 full-length genes were amplified by reverse transcription polymerase chain reaction and then inserted into the eukaryotic single-expression plasmid, pVAX1-asd, and the eukaryotic dual-expression plasmid, pVAXD-asd, respectively. The recombinant plasmids pVAX1-asd-NSP4, pVAX1-asd-VP7 and pVAXD-asd-NSP4-VP7 were transformed into the attenuated S. typhimurium χ4550 strain by electrotransformation. An indirect immunofluorescence assay of the expressed COS-7 cell suggested that the recombinant S. typhimurium χ4550 strain was constructed successfully. The recombinant S. typhimurium χ4550 strain was orally administered to BALB/c mice. The group immunised with dual- expression plasmids produced a significantly higher level of serum Immunoglobulin G (IgG) and intestinal Immunoglobulin A (IgA) than the group immunised with single-expression plasmids. These results indicated that eukaryotic bicistronic plasmid DNA vaccines could be successfully constructed to enhance humoural, mucosal and cellular immune response against rotavirus infection.

Expression of human rotavirus chimeric fusion proteins from replicating but non disseminating adenovectors and elicitation of rotavirus-specific immune responses in mice

The aim of this study was to evaluate the usefulness of replicating but non disseminating adenovirus vectors (AdVs) as vaccine vector using human rotavirus (HRV) as a model pathogen. HRV VP7, VP4, or VP4Δ (N-terminal 336 amino acids of VP4) structural proteins as well as the VP4Δ::VP7 chimeric fusion protein were expressed in mammalian cells when delivered with the AdVs. A preliminary experiment demonstrated that VP4Δ was able to induce a HRV-specific IgG response in BALB/c mice inoculated intramuscularly with AdVs expressing the rotaviral protein. Moreover, an AdV-prime/plasmid DNA-boost regimen of vectors resulted in VP4Δ-specific antibody (Ab) titers ~4 times higher than those obtained from mice immunized with AdVs alone. Subsequently, the various HRV protein-encoding AdVs were compared using the AdV-prime/plasmid DNA-boost regimen. Higher IgG and IgA responses to HRV were obtained when VP4Δ::VP7 fusion protein was used as an immunogen as compared to VP7 or VP4 alone or to a mix of both proteins delivered independently by AdVs. A synergetic effect in terms of Ab was obtained with VP4Δ::VP7. In conclusion, this study demonstrated for the first time the suitability of using replicating but non disseminating AdVs as vaccine vector and the VP4Δ::VP7 fusion protein as an immunogen for vaccination against HRV.

Cysteine proteases as potential antigens in antiparasitic DNA vaccines

Cysteine proteases in parasites are potent inducers of vertebrate host immune responses and may under certain circumstances take part in the pathogen's immune evasion strategies. These capacities place these parasite molecules as interesting candidate antigens in antiparasitic vaccines for use in vertebrates. Parasite cysteine proteases are able to skew the Th1/Th2 profile in mammals towards a response which allows sustainable parasite burdens in the host. DNA vaccines are also able to skew the Th1/Th2 profile by different administration techniques and the use of cysteine proteases in these genetic immunizations open perspectives for manipulation of the host immune response towards higher protection.

Intestinal delivery of non-viral gene therapeutics: physiological barriers and preclinical models

The future of nucleic acid-based therapeutics is dependent on achieving successful delivery. Recently, there has been an increasing interest in delivery via the gastrointestinal tract. Gene therapy via this route has many advantages, including non-invasive access and the versatility to treat local diseases, such as inflammatory bowel disease, as well as systemic diseases, such as haemophilia. However, the intestine presents several distinct barriers and, therefore, the design of robust non-viral delivery systems is key to future success. Several non-viral delivery strategies have provided evidence of activity in vivo. To facilitate the design of more efficient and safe gene medicines, more physiologically relevant models, at both the in vitro and in vivo levels, are essential.

Progress towards a needle-free hepatitis B vaccine

Hepatitis B virus (HBV) infection is a worldwide public health problem. Vaccination is the most efficient way to prevent hepatitis B. Despite the success of the currently available vaccine, there is a clear need for the development of new generation of HBV vaccines. Needle-free immunization is an attractive approach for mass immunization campaigns, since avoiding the use of needles reduces the risk of needle-borne diseases and prevents needle-stick injuries and pain, thus augmenting patient compliance and eliminating the need for trained medical personnel. Moreover, this kind of immunization was shown to induce good systemic as well as mucosal immunological responses, which is important for the creation of both a prophylactic and therapeutic vaccine. In order to produce a better, safer, more efficient and more suitable vaccine, adjuvants have been used. In this article, several adjuvants tested over the years for their potential to help create a needle-free vaccine against HBV are reviewed.

Development of a Bacillus subtilis-based rotavirus vaccine

Bacillus subtilis vaccine strains engineered to express either group A bovine or murine rotavirus VP6 were tested in adult mice for their ability to induce immune responses and provide protection against rotavirus challenge. Mice were inoculated intranasally with spores or vegetative cells of the recombinant strains of B. subtilis. To enhance mucosal immunity, whole cholera toxin (CT) or a mutant form (R192G) of Escherichia coli heat-labile toxin (mLT) were included as adjuvants. To evaluate vaccine efficacy, the immunized mice were challenged orally with EDIM EW murine rotavirus and monitored daily for 7 days for virus shedding in feces. Mice immunized with either VP6 spore or VP6 vegetative cell vaccines raised serum anti-VP6 IgG enzyme-linked immunosorbent assay (ELISA) titers, whereas only the VP6 spore vaccines generated fecal anti-VP6 IgA ELISA titers. Mice in groups that were immunized with VP6 spore vaccines plus CT or mLT showed significant reductions in virus shedding, whereas the groups of mice immunized with VP6 vegetative cell vaccines showed no difference in virus shedding compared with mice immunized with control spores or cells. These results demonstrate that intranasal inoculation with B. subtilis spore-based rotavirus vaccines is effective in generating protective immunity against rotavirus challenge in mice.

Veterinary vaccines: alternatives to antibiotics?

The prevention of infectious diseases of animals by vaccination has been routinely practiced for decades and has proved to be one of the most cost-effective methods of disease control. However, since the pioneering work of Pasteur in the 1880s, the composition of veterinary vaccines has changed very little from a conceptual perspective and this has, in turn, limited their application in areas such as the control of chronic infectious diseases. New technologies in the areas of vaccine formulation and delivery as well as our increased knowledge of disease pathogenesis and the host responses associated with protection from disease offer promising alternatives for vaccine formulation as well as targets for the prevention of bacterial disease. These new vaccines have the potential to lessen our reliance on antibiotics for disease control, but will only reach their full potential when used in combination with other intervention strategies.

Polymeric Materials for Gene Delivery and DNA Vaccination

Gene delivery holds great potential for the treatment of many different diseases. Vaccination with DNA holds particular promise, and may provide a solution to many technical challenges that hinder traditional vaccine systems including rapid development and production and induction of robust cell-mediated immune responses. However, few candidate DNA vaccines have progressed past preclinical development and none have been approved for human use. This Review focuses on the recent progress and challenges facing materials design for nonviral DNA vaccine drug delivery systems. In particular, we highlight work on new polymeric materials and their effects on protective immune activation, gene delivery, and current efforts to optimize polymeric delivery systems for DNA vaccination.

DNA vaccines: ready for prime time?

Since the discovery, over a decade and a half ago, that genetically engineered DNA can be delivered in vaccine form and elicit an immune response, there has been much progress in understanding the basic biology of this platform. A large amount of data has been generated in preclinical model systems, and more sustained cellular responses and more consistent antibody responses are being observed in the clinic. Four DNA vaccine products have recently been approved, all in the area of veterinary medicine. These results suggest a productive future for this technology as more optimized constructs, better trial designs and improved platforms are being brought into the clinic.

Oral Plasmid DNA Delivery Systems for Genetic Immunisation

The use and optimisation of plasmid DNA delivery systems for the purposes of eliciting transgene specific immune responses to orally administered DNA encoded antigen represents a significant challenge. Here, we have outlined a multicomponent polymer modified liposomal delivery system that offers potential for oral administration of plasmid DNA. It is shown that the polymer/liposome formulated DNA is able to elicit markedly enhanced transgene specific cytokine production following in vitro restimulation of splenocytes with recombinant antigen. This is discussed with reference to recent publications and the potential of plasmid DNA delivery systems for the purposes of genetic immunisation, as reported in selected literature, is assessed.

Comparative ability of various plasmid-based cytokines and chemokines to adjuvant the activity of HIV plasmid DNA vaccines

The effectiveness of plasmid DNA (pDNA) vaccines can be improved by the co-delivery of plasmid-encoded molecular adjuvants. We evaluated pDNAs encoding GM-CSF, Flt-3L, IL-12 alone, or in combination, for their relative ability to serve as adjuvants to augment humoral and cell-mediated immune responses elicited by prototype pDNA vaccines. In Balb/c mice we found that co-administration of plasmid-based murine GM-CSF (pmGM-CSF), murine Flt-3L (pmFlt-3L) or murine IL-12 (pmIL-12) could markedly enhance the cell-mediated immune response elicited by an HIV-1 env pDNA vaccine. Plasmid mGM-CSF also augmented the immune response elicited by DNA vaccines expressing HIV-1 Gag and Nef-Tat-Vif. In addition, the use of pmGM-CSF as a vaccine adjuvant appeared to markedly increase antigen-specific proliferative responses and improved the quality of the resulting T-cell response by increasing the percentage of polyfunctional memory CD8(+) T cells. Co-delivery of pmFlt-3L with pmGM-CSF did not result in a further increase in adjuvant activity. However, the co-administration of pmGM-CSF with pmIL-12 did significantly enhance env-specific proliferative responses and vaccine efficacy in the murine vaccinia virus challenge model relative to mice immunized with the env pDNA vaccine adjuvanted with either pmGM-CSF or pmIL-12 alone. These data support the testing of pmGM-CSF and pmIL-12, used alone or in combination, as plasmid DNA vaccine adjuvants in future macaque challenge studies.

Past, present, and future technologies for oral delivery of therapeutic proteins

Biological drugs are usually complex proteins and cannot be orally delivered due to problems related to degradation in the acidic and protease-rich environment of the gastrointestinal (GI) tract. The high molecular weight of these drugs often results in poor absorption into the periphery when administered orally. The most common route of administration for these therapeutic proteins is injection. Most of these proteins have short serum half-lives and need to be administered frequently or in high doses to be effective. So, difficulties in the administration of protein-based drugs provides the motivation for developing drug delivery systems (DDSs) capable of maintaining therapeutic drug levels without side effects as well as traversing the deleterious mucosal environment. Employing a polymer as an entrapment matrix is a common feature among the different types of systems currently being pursued for protein delivery. Protein release from these matrices can occur through various mechanisms, such as diffusion through or erosion of the polymer matrix, and sometimes a combination of both. Encapsulation of proteins in liposomes has also been a widely investigated technology for protein delivery. All of these systems have merit and our worthy of pursuit.

Current progress of DNA vaccine studies in humans

Despite remarkable progress in the field of DNA vaccine research since its discovery in the early 1990 s, the formal acceptance of this novel technology as a new modality of human vaccines depends on the successful demonstration of its safety and efficacy in advanced clinical trials. Although clinical trials conducted so far have provided overwhelming evidence that DNA vaccines are well tolerated and have an excellent safety profile, the early designs of DNA vaccines failed to demonstrate sufficient immunogenicity in humans. However, studies conducted over the last few years have led to promising results, particularly when DNA vaccines were used in combination with other forms of vaccines. Here, we provide a review of the data from reported DNA vaccine clinical studies with an emphasis on the ability of DNA vaccines to elicit antigen-specific, cell-mediated and antibody responses in humans. The majority of these trials are designed to test candidate vaccines against several major human pathogens and the remaining studies tested the immunogenicity of therapeutic vaccines against cancer.

The relative immunogenicity of DNA vaccines delivered by the intramuscular needle injection, electroporation and gene gun methods

Immunogenicity of DNA vaccines varies significantly due to many factors including the inherent immunogenicity of the protein antigen encoded in the DNA vaccine, the optimal immune responses that can be achieved in different animal models and in humans with different genetic backgrounds and, to a great degree, the delivery methods used to administer the DNA vaccines. Based on published results, only the gene gun-mediated delivery approach has been able to elicit protective levels of immune responses in healthy, adult volunteers by DNA immunization alone without the use of another vaccine modality as a boost. Recent results from animal studies suggest that electroporation is also effective in eliciting high level immune responses. However, there have been no reports to identify the similarities and differences between these two leading physical delivery methods for DNA vaccines against infectious disease targets. In the current study, we compared the relative immunogenicity of a DNA vaccine expressing a hemagglutinin (HA) antigen from an H5N1 influenza virus in two animal models (rabbit and mouse) when delivered by either intramuscular needle immunization (IM), gene gun (GG) or electroporation (EP). HA-specific antibody, T cell and B cell responses were analyzed. Our results indicate that, overall, both the GG and EP methods are more immunogenic than the IM method. However, EP and IM stimulated a Th-1 type antibody response and the antibody response to GG was Th-2 dominated. These findings provide important information for the further selection and optimization of DNA vaccine delivery methods for human applications.

Oral vaccination: where we are?

As early as 900 years ago, the Bedouins of the Negev desert were reported to kill a rabid dog, roast its liver and feed it to a dog-bitten person for three to five days according to the size and number of bites [1] . In sixteenth century China, physicians routinely prescribed pills made from the fleas collected from sick cows, which purportedly prevented smallpox. One may dismiss the wisdom of the Bedouins or Chinese but the Nobel laureate, Charles Richet, demonstrated in 1900 that feeding raw meat can cure tuberculous dogs - an approach he termed zomotherapy. Despite historical clues indicating the feasibility of oral vaccination, this particular field is notoriously infamous for the abundance of dead-end leads. Today, most commercial vaccines are delivered by injection, which has the principal limitation that recipients do not like needles. In the last few years, there has been a sharp increase in interest in needle-free vaccine delivery; new data emerges almost daily in the literature. So far, there are very few licensed oral vaccines, but many more vaccine candidates are in development. Vaccines delivered orally have the potential to take immunization to a fundamentally new level. In this review, the authors summarize the recent progress in the area of oral vaccines.

Polymeric nano- and microparticle technologies for oral gene delivery

Gene therapy refers to local or systemic administration of a nucleic acid construct that can prevent, treat and even cure diseases by changing the expression of genes that are responsible for the pathological condition. Oral gene therapy has significant promise for treatment of local diseases such as inflammatory bowel disease and for systemic absorption of the expressed protein therapeutics. In addition, efficient oral delivery of DNA vaccines can have significant impact in disease prevention. The use of polymeric gene delivery vectors promises the translation of this experimental medical concept into clinical reality. This review addresses the challenges and opportunities in the development of polymer-based nano- and microparticle technologies for oral gene therapy. Specifically, the discussion is focused on different synthetic and natural polymers used for formulating nano- and microparticle technologies and the use of these delivery systems for oral DNA administration for therapeutic and vaccination purposes.

Delivery systems and adjuvants for oral vaccines

The oral route is the ideal means of delivering prophylactic and therapeutic vaccines, offering significant advantages over systemic delivery. Most notably, oral delivery is associated with simple administration and improved safety. In addition, unlike systemic immunisation, oral delivery can induce mucosal immune responses. However, the oral route of vaccine delivery is the most difficult because of the numerous barriers posed by the gastrointestinal tract. To facilitate effective immunisation with peptide and protein vaccines, antigens must be protected, uptake enhanced and the innate immune response activated. Numerous delivery systems and adjuvants have been evaluated for oral vaccine delivery, including live vectors, inert particles and bacterial toxins. Although developments in oral vaccines have been disappointing so far, in terms of the generation of products, the availability of a range of novel delivery systems offers much greater hope for the future development of improved oral vaccines.

DNA vaccines for HIV: challenges and opportunities

In December 2005, the UNAIDS and WHO reported that the global epidemic known as acquired immunodeficiency syndrome (AIDS) has claimed the lives of more than 25 million adults and children over the past 26 years. These figures included an estimated 3.1 million AIDS-related deaths in 2005. Despite enormous efforts to control the spread of human immunodeficiency virus (HIV) new infection rates are on the rise. An estimated 40.3 million people are now living with HIV, including 4.9 million new infections this past year. Nearly half of new HIV infections are in young people between the ages of 15 and 24. While drug therapies have helped sustain the lives of infected individuals in wealthy regions, they are relatively unavailable to the poorest global regions. This includes sub-Saharan Africa which has approximately 25.8 million infected individuals, more than triple the number of infections of any other region in the world. It is widely believed that the greatest hope for controlling this devastating pandemic is a vaccine. In this review, we will discuss the current state of DNA-based vaccines and how they compare to other vaccination methods currently under investigation. We will also discuss innovative ideas for enhancing DNA vaccine efficacy and the progress being made toward developing an effective vaccine.

Nanoparticles as potential oral delivery systems of proteins and vaccines: a mechanistic approach

Peptides and proteins remain poorly bioavailable upon oral administration. One of the most promising strategies to improve their oral delivery relies on their association with colloidal carriers, e.g. polymeric nanoparticles, stable in gastrointestinal tract, protective for encapsulated substances and able to modulate physicochemical characteristics, drug release and biological behavior. The mechanisms of transport of these nanoparticles across intestinal mucosa are reviewed. In particular, the influence of size and surface properties on their non-specific uptake or their targeted uptake by enterocytes and/or M cells is discussed. Enhancement of their uptake by appropriate cells, i.e. M cells by (i) modeling surface properties to optimize access to and transport by M cells (ii) identifying surface markers specific to human M cell allowing targeting to M cells and nanoparticles transcytosis is illustrated. Encouraging results upon in vivo testing are reported but low bioavailability and lack of control on absorbed dose slow down products development. Vaccines are certainly the most promising applications for orally delivered nanoparticles.

DNA vaccines against enteric infections

The first DNA vaccines for prevention of infectious diseases were described in 1993 and have since been shown to generate protective humoral and cellular immune responses to numerous infectious agents. For enteric infections, protective immunity has been obtained with DNA vaccines against several enteric viral, bacterial, and parasitic agents. Inoculation of DNA vaccines has generally been by intramuscular injection or by gene gun delivery of vaccine DNA-coated gold microparticles into the skin. Administration of DNA vaccines by the oral route would target the vaccines to enteric mucosal tissues, as well as providing a convenient means for vaccine delivery. Orally administered plasmid DNAs encapsulated in polymeric microparticles or inserted in live bacterial vectors have been effective in animal models for rotavirus DNA vaccines and Listeria monocytogenes DNA vaccines, respectively. Human trials of enteric DNA vaccines have not been initiated, but trials of veterinary vaccines have shown promise.

Mucosal delivery of vaccines in domestic animals

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although highly beneficial for achieving protective immunity, the induction of mucosal immunity, especially in the gastro-intestinal tract, still remains a difficult task. As a result, only very few mucosal vaccines are commercially available for domestic animals. Here, we critically review various strategies for mucosal delivery of vaccines in domestic animals. This includes live bacterial and viral vectors, particulate delivery-systems such as polymers, alginate, polyphosphazenes, immune stimulating complex and liposomes, and receptor mediated-targeting strategies to the mucosal tissues. The most commonly used routes of immunization, strategies for delivering the antigen to the mucosal surfaces, and future prospects in the development of mucosal vaccines are discussed.

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

Plasmid expressing HBV small envelope antigen was formulated with poly(lactide-co-glycolide-acid) (PLGA) and cetyltrimethylammonium bromide (CTAB) to generate highly uniform microparticles. Controlled release of DNA from these microparticles was demonstrated in vitro and in vivo using flow cytometry and confocal laser scanning microscopy with the focus on localization and quantitatively evaluation of antigen-presenting cells (APCs) involved in the expression of target antigen. Compared to mice vaccinated with naked DNA, mice immunized with PLGA-CTAB-DNA microparticles displayed a much higher percentage of CD11c+, HBsAg-expressing APCs in the draining lymph nodes at 24 h and day 14 postinoculation. In addition, a prolonged transcription of plasmid DNA was detected by RT-PCR in mice immunized with the microparticles. A significantly enhanced immunogenicity of PLGA-CTAB-DNA over naked DNA was observed in immunized mice, including higher levels of antibody production, interferon gamma (IFN-gamma) secretion and cytotoxic T lymphocyte activity. Mice immunized with PLGA-CTAB-DNA microparticles also showed greater efficacy of immunoprotection against challenge of transplanted HBsAg-expressing tumor cells. Our data suggest that controlled release of the PLGA-CTAB-DNA microparticles might involve in the mechanisms of its augmented immunogenicity and enhanced immunoprotection.

Mannosylated niosomes as adjuvant–carrier system for oral genetic immunization against Hepatitis B

Aim of the present study was to develop mannosylated niosomes as oral DNA vaccine carriers for the induction of humoral, cellular and mucosal immunity. Niosomes composed of span 60, cholesterol and stearylamine as constitutive lipids were prepared by reverse phase evaporation method and were coated with a modified polysaccharide o-palmitoyl mannan (OPM) in order to protect them from bile salt caused dissolution and enzymatic degradation in the gastrointestinal tract and to enhance their affinity towards the antigen presenting cells of Peyer's patches. Prepared niosomes were characterized in vitro for their size, shape, entrapment efficiency, ligand binding specificity and stability in simulated gastric fluid and simulated intestinal fluid. OPM coated niosomes were found to better stable in simulated GIT conditions. The immune stimulating activity was studied by measuring serum anti-HBsAg titer, secretory IgA level in intestinal and salivary secretions and cyokines level (IL-2 and IFN-gamma) in spleen homogenates following oral administration of niosomal formulations in Balb/c mice and compared with naked DNA as well as pure recombinant HBsAg injected intramuscularly. The serum anti-HBsAg titer obtained after oral administration of OPM coated niosomal formulations was although less as compared to that elicited by naked DNA and pure HBsAg administered intramuscularly, but the mice were seroprotective within 2 weeks and antibody level far above the clinically protective limit for humans was achieved. Intramuscular naked DNA and recombinant HBsAg did not elicited sIgA titer in mucosal secretions that was induced by oral administration of OPM coated niosomes. Similarly, cellular response (cytokines level) was absent in pure HBsAg treated animals. OPM coated niosomes produced humoral (both systemic and mucosal) and cellular immune response upon oral administration. The study signifies the potential of OPM coated niosomes as DNA vaccine carrier and adjuvant for effective oral immunization.

Microparticles for oral delivery of vaccines

Nonreplicating antigens are poorly immunogenic when given orally, either due to their degradation in the gastrointestinal tract or because they are not efficiently taken up in the gut. Studies in laboratory animals have clearly demonstrated that microparticles can significantly improve the immunogenicity of orally administered antigens. However, the oral delivery of vaccines using microparticles has not been explored extensively in humans and large animals. In this article the progress in oral microparticle antigen delivery will be reviewed and, where possible, studies in humans and large animals will be highlighted. In addition, possible approaches that have the potential to significantly improve microparticle delivery of oral vaccines will be suggested.

Mucosal and systemic antibody responses and protection induced by a prime/boost rotavirus-DNA vaccine in a gnotobiotic pig model

A live rotavirus prime/DNA boost vaccine regimen was evaluated in a gnotobiotic pig model for human rotavirus (HRV) diarrhea. Plasmid DNA expressing rotavirus inner capsid VP6 was administered to pigs intramuscularly (IM) twice after oral priming with attenuated (Att) Wa strain HRV (AttHRV/VP6DNA2x). Other groups included: (1) VP6 DNA IM 2x then AttHRV orally (VP6DNA2x/AttHRV); (2) VP6 DNA IM 3x (VP6DNA3x) and controls. Significant protection (70%) against virus shedding, but lower protection against diarrhea (30%) was achieved only in the AttHRV/VP6DNA2x group after challenge (virulent Wa HRV). The other vaccines (VP6DNA2x/AttHRV and VP6DNA3x) were less effective. Higher protection rates were associated with the highest IgA antibody responses induced by the AttHRV/VP6DNA2x regimen. Interestingly, the VP6 DNA vaccine, although not effective when administered alone, boosted neutralizing and VP4 antibody titers in pigs previously primed with AttHRV, possibly mediated by cross-reactive T helper cells.

Induction of mucosal and systemic immune response by single-dose oral immunization with biodegradable microparticles containing DNA encoding HBsAg

The purpose of this work was to assess the ability of plasmid DNA encoding hepatitis B virus (HBV) HBsAg encapsulated in poly(dl-lactide-co-glycolic acid) (PLGA) microparticles to induce local and systemic HBsAg-specific immunity following a single dose of oral immunization. RT-PCR analysis demonstrated prolonged transcription of plasmid DNA, consistent with the sustained expression and presentation of target antigen observed by confocal laser scanning microscopy, in gut-associated lymphocyte tissue (GALT) from mice immunized orally with plasmid DNA encapsulated into PLGA microparticles. Oral administration of PLGA-DNA microparticles induced a long-lasting and stable antigen-specific antibody response, both serum total antibody and intestinal IgA, in BALB/c mice. Mice immunized orally exhibited antigen-specific gamma interferon production and cytotoxic T lymphocyte responses in spleen and GALT after restimulation in vitro with HBsAg or tumour cells stably expressing HBsAg. In contrast, naked DNA vaccines given by intramuscular injection induced only systemic cellular and humoral responses to HBsAg, which were much lower than the responses elicited by oral DNA encapsulated in PLGA microparticles at equivalent doses. The results are encouraging with regard to obtaining good compliance and vaccination coverage with candidate plasmid DNA vaccines, especially in developing countries.

Humoral immune response to rotavirus NSP4 enterotoxin in Spanish children

The rotavirus non-structural protein 4 (NSP4) has been shown to play a crucial role in rotavirus-induced diarrhea, acting as a viral enterotoxin. It has also been demonstrated that antibody to NSP4 can reduce the severity of rotavirus-induced diarrhea in newborn mice. Two recombinant baculoviruses, expressing the NSP4 protein from the SA11 and Wa rotavirus strains, genotypes A and B, respectively, were used to produce and purify these glycoproteins, which were applied as antigen in an enzyme-linked immunosorbent assay (ELISA) to test the specific antibody response to NSP4 in human sera. Serum samples from 30 children convalescing from a rotavirus infection, from 54 healthy children under 5-years-old, and from 49 adults were tested to determine the presence of antibodies to the viral enterotoxin and to rotavirus structural proteins. Seventy percent of the sera from rotavirus-infected children showed an IgG antibody response to either one or both NSP4 proteins used in this study, although the response was weak. However, IgG antibodies towards either one or both NSP4 proteins were only detected in 26% of the non-convalescent healthy children and in only 18% of the adults. No serum IgA antibodies towards NSP4 were found in this study. IgG antibody recognition of the NSP4 protein from the SA11 and Wa rotavirus strains was not always heterotypic.

DNA vaccine

The DNA vaccine has proven to be one of the most promising applications in the field of gene therapy. Due to its unique ability to readily induce humoral as well as cellular immune responses, it attracted great interest when the concept was first confirmed in the early 1990s. After thousands of articles related to the DNA vaccine were published, scientists began to realize that although the DNA vaccine is very effective in small animal models, its effectiveness in recent clinical trails is rather disappointing. Therefore, current effort has been shifted to understanding the different performance of the DNA vaccine in mouse and large animal models and on how to transfer the success of the DNA vaccine in small animals to large animals and humans.

Enhancement of vaccine potency through improved delivery

The need for more potent, safe and well-characterised vaccines has necessitated the discovery and development of new vaccine technologies. These include adjuvants to target the innate immune system to provide a stimulus that potentiates the development of an antigen-specific immune response, and delivery systems to ensure that the antigen and adjuvant are localised to the appropriate immune compartments. Several such technologies are being tested in human clinical trials and a few have been licensed for limited use in human vaccines. This review will highlight some of the promising technologies that may have an impact on how vaccines are administered.

An assessment of different DNA delivery systems for protection against respiratory syncytial virus infection in the murine model: gene-gun delivery induces IgG in the lung

Immunization with plasmid DNA (pDNA) has the potential to overcome the difficulties of neonatal vaccination that may be required for protection against infection with respiratory syncytial virus (RSV); however, little is known about optimal delivery modalities. In this pilot study we compared mucosal delivery of pDNA encoding RSV F protein encapsulated in poly(DL-lactide-co-glycolide) with delivery of pDNA by gene-gun for the induction of immunity in mice. Intra-gastric or intra-nasal immunization with various doses of microparticles induced weak low levels of RSV-specific serum antibodies in a proportion of mice; in contrast, gene-gun vaccination led to protective immunity associated with a humoral response. Interestingly, RSV-specific antibody was detected in lung fragment cultures following intradermal vaccination with the gene-gun.

M cell DNA vaccination for CTL immunity to HIV

To facilitate invasion, reovirus has evolved to attach to M cells, a specialized epithelium residing within the follicle-associated epithelium that covers mucosal inductive tissues. Thus, we questioned adapting reovirus protein sigma1 to ferry DNA vaccines to the mucosa to immunize against HIV. Three expression plasmids encoding HIV(Ba-L) gp160, cytoplasmic gp140, and secreted gp140 were tested in mice as protein sigma1-poly-L-lysine-DNA complexes (formulated vaccine) via the intranasal route. Evaluation of cell-mediated immunity showed that the formulated gp160 DNA vaccine was more effective for stimulating envelope (Env)-specific CTL responses in lungs, lower respiratory lymph nodes (LN), cervical LN, submaxillary gland LN, and spleens. Three doses of vaccine were required for CTL responses, and intranasal naked DNA immunizations were ineffective. The greatest CTL activity was observed between weeks 8 and 10 for gp160-vaccinated mice, and activity remained detectable by week 16. These Env-specific CTL responses were perforin dependent in peripheral tissues, but mostly Fas dependent in the lungs. These Env-specific CTLs also produced IFN-gamma. Mice vaccinated with the formulated gp160 DNA vaccine showed potent antiviral immunity against vaccinia virus-env replication in ovaries. Thus, compared with live vectors, protein sigma1-mediated DNA delivery represents an alternative mucosal formulation for inducing cellular immunity against HIV-1.

Oral immunization with rotavirus VP7 expressed in transgenic potatoes induced high titers of mucosal neutralizing IgA

Rotaviruses (RV) are a common cause of severe diarrhea in young children, resulting in nearly one million deaths worldwide annually. Rotavirus VP7 was the rotavirus neutralizing protein. Previous study reported that VP7 DNA vaccine can induce high levels of IgG in mice but cannot protect mice against challenge (Choi, A.H., Basu, M., Rae, M.N., McNeal, M.M., Ward, R.L., 1998. Virology 250, 230-240). We found that rotavirus VP7 could maintain its neutralizing immunity when it was transformed into the potato genome. Mice immunized with the transformed tubers successfully elicited serum IgG and mucosal IgA specific for VP7. The mucosal IgA titer was as high as 1000, while serum IgG titer was only 600. Neutralizing assays indicated that IgA could neutralize rotavirus. These results indicate the potential usefulness of plants for production and delivery of edible rotavirus vaccines.

Formulations containing poly(lactide-co-glycolide) and plasmid DNA expression vectors

DNA expression vectors have the potential to be useful therapeutics for a wide variety of applications. However, development has been hindered by the lack of systems that provide protection from nuclease-based attack, enable cell or tissue localisation, promote adequate gene expression or provide for controlled release. At least one synthetic polymer, poly(lactide-co-glycolide) (PLG), may provide benefit in this regard. This polymer has a history of safe use in humans, has been demonstrated effective as a delivery system, its use is not hindered by composition patents, and Good Manufacturing Practices grade material is readily available from commercial sources. Safety and applicability to clinical medicine have been proven by use of the polymer as a microparticle delivery vehicle for peptides (luteinizing hormone releasing hormone agonist peptides; Lupron Depot [TAP Pharmaceuticals]; Zoladex [AstraZeneca]) and proteins (human growth hormone recombinant protein, Nutropin Depot [Genentech]). This report focuses on the expanding field of PLG-based DNA delivery and provides a review on research and clinical experience with PLG-plasmid formulations.

Mechanisms of increased immunogenicity for DNA-based vaccines adsorbed onto cationic microparticles

Investigation into the mechanism of action of vaccine adjuvants provides opportunities to define basic immune principles underlying the induction of strong immune responses and insights useful for the rational development of subunit vaccines. A novel HIV vaccine composed of plasmid DNA-encoding p55 gag formulated with poly-lactide-co-glycolide microparticles (PLG) and cetyl trimethyl ammonium bromide (CTAB) elicits both serum antibody titers and cytotoxic lymphocyte activity in mice at doses two orders of magnitude lower than those required for comparable response to plasmid DNA in saline. Using this model, we demonstrated the increase in potency requires the DNA to be complexed to the PLG-CTAB microparticles. Furthermore, the PLG-CTAB-DNA formulation increased the persistence of DNA at the injection site, recruited mononuclear phagocytes to the site of injection, and activated a population of antigen presenting cells. Intramuscular immunization with the PLG-CTAB-DNA complex induced antigen expression at both the injection site and the draining lymph node. These findings demonstrate that the PLG-CTAB-DNA formulation exhibits multiple mechanisms of immunopotentiation.