Suppository-mediated DNA immunization induces mucosal immunity against bovine herpesvirus-1 in cattle

Recent Development of Ruminant Vaccine Against Viral Diseases

Pathogens of viral origin produce a large variety of infectious diseases in livestock. It is essential to establish the best practices in animal care and an efficient way to stop and prevent infectious diseases that impact animal husbandry. So far, the greatest way to combat the disease is to adopt a vaccine policy. In the fight against infectious diseases, vaccines are very popular. Vaccination's fundamental concept is to utilize particular antigens, either endogenous or exogenous to induce immunity against the antigens or cells. In light of how past emerging and reemerging infectious diseases and pandemics were handled, examining the vaccination methods and technological platforms utilized for the animals may provide some useful insights. New vaccine manufacturing methods have evolved because of developments in technology and medicine and our broad knowledge of immunology, molecular biology, microbiology, and biochemistry, among other basic science disciplines. Genetic engineering, proteomics, and other advanced technologies have aided in implementing novel vaccine theories, resulting in the discovery of new ruminant vaccines and the improvement of existing ones. Subunit vaccines, recombinant vaccines, DNA vaccines, and vectored vaccines are increasingly gaining scientific and public attention as the next generation of vaccines and are being seen as viable replacements to conventional vaccines. The current review looks at the effects and implications of recent ruminant vaccine advances in terms of evolving microbiology, immunology, and molecular biology.

The Key Role of Nucleic Acid Vaccines for One Health

The ongoing SARS-CoV-2 pandemic has highlighted both the importance of One Health, i.e., the interactions and transmission of pathogens between animals and humans, and the potential power of gene-based vaccines, specifically nucleic acid vaccines. This review will highlight key aspects of the development of plasmid DNA Nucleic Acid (NA) vaccines, which have been licensed for several veterinary uses, and tested for a number of human diseases, and will explain how an understanding of their immunological and real-world attributes are important for their efficacy, and how they helped pave the way for mRNA vaccines. The review highlights how combining efforts for vaccine development for both animals and humans is crucial for advancing new technologies and for combatting emerging diseases.

Attempts to induce tolerance to Trichostrongylus colubriformis infection in sheep

BACKGROUND AND OBJECTIVES

The possibility of manipulating the immune response in lambs to the gastrointestinal nematode Trichostrongylus colubriformis to reduce production losses associated with infection was investigated. In a series of four experiments, attempts to immunize sheep via the mucosal route to modify the immune response and induce mucosal tolerance are outlined. Initially, a proof of concept study was conducted with lambs being injected with multiple doses of a somatic T colubriformis antigen without an adjuvant in the rectal submucosa and subsequently challenged with T colubriformis L3 larvae. This was followed by a dose-response study comparing different antigen doses to identify the optimum dose of the nematode antigen for successful induction of mucosal tolerance. The final two studies were conducted to determine the larval stage specificity of the parasite antigen and the most suitable site of delivery required to stimulate mucosal tolerance.

METHODS

In the proof of concept study, lambs either received repeated injections in the rectal submucosa at 3 × weekly intervals with 15 µg of L3, 11 µg of L4 and 21 µg of immature adult (L5) somatic T colubriformis antigens (ANT) or not (INF) prior to infection with T colubriformis. In the dose-rate study, antigen dose rates of 100%, 50%, 10%, 1% or 0% of the antigen concentration used in the proof of concept study were compared while the larval stage study compared antigen from either L3, L4, L5 stages or combination of all (COMB) and the route of administration study compared antigen delivery into either the rectal submucosa (RE) or sub-cutaneous injection (SC).

RESULTS

During infection, lamb growth was improved by antigen treatment between days 21 and 42 in the proof of concept study (P = .009), for groups 10%, 50% and 100% in the dose-rate study (P < .05 for all) and in RE in the route of administration study with no improvement observed in the larval stage study. No differences in faecal egg counts were observed (P > .05 for all). Parasite-specific IgA and IgE showed a dose-response (the dose-rate study), were not affected by larval stage (the larval stage study) and were greater in RE than SC (the route of administration study). IL-4 production following lymphocyte stimulation was greatest in COMB (the larval stage study) and RE (the route of administration study).

CONCLUSIONS

Although antigen treatment improved performance, this was inconsistent and appeared to stimulate immunity rather than induce tolerance. Combined larval stages were more efficient than individual stages, and intra-rectal administration was more effective than sub-cutaneous.

Mucosal Vaccine Approaches for Prevention of HIV and SIV Transmission

Optimal protective immunity to HIV will likely require that plasma cells, memory B cells and memory T cells be stationed in mucosal tissues at portals of viral entry. Mucosal vaccine administration is more effective than parenteral vaccine delivery for this purpose. The challenge has been to achieve efficient vaccine uptake at mucosal surfaces, and to identify safe and effective adjuvants, especially for mucosally administered HIV envelope protein immunogens. Here, we discuss strategies used to deliver potential HIV vaccine candidates in the intestine, respiratory tract, and male and female genital tract of humans and nonhuman primates. We also review mucosal adjuvants, including Toll-like receptor agonists, which may adjuvant both mucosal humoral and cellular immune responses to HIV protein immunogens.

Immunity to bovine herpesvirus 1: II. Adaptive immunity and vaccinology

Bovine herpesvirus 1 (BHV-1) infection is widespread and causes a variety of diseases. Although similar in many respects to the human immune response to human herpesvirus 1, the differences in the bovine virus proteins, immune system components and strategies, physiology, and lifestyle mean the bovine immune response to BHV-1 is unique. The innate immune system initially responds to infection, and primes a balanced adaptive immune response. Cell-mediated immunity, including cytotoxic T lymphocyte killing of infected cells, is critical to recovery from infection. Humoral immunity, including neutralizing antibody and antibody-dependent cell-mediated cytotoxicity, is important to prevention or control of (re-)infection. BHV-1 immune evasion strategies include suppression of major histocompatibility complex presentation of viral antigen, helper T-cell killing, and latency. Immune suppression caused by the virus potentiates secondary infections and contributes to the costly bovine respiratory disease complex. Vaccination against BHV-1 is widely practiced. The many vaccines reported include replicating and non-replicating, conventional and genetically engineered, as well as marker and non-marker preparations. Current development focuses on delivery of major BHV-1 glycoproteins to elicit a balanced, protective immune response, while excluding serologic markers and virulence or other undesirable factors. In North America, vaccines are used to prevent or reduce clinical signs, whereas in some European Union countries marker vaccines have been employed in the eradication of BHV-1 disease.

Cell-mediated immune responses induced by BHV-1: rational vaccine design

Bovine herpesvirus-1 (BHV-1) is one of the major respiratory pathogens in cattle worldwide. Although antibodies have been correlated with protection and recovery from BHV-1 infection, the cell-mediated immune response is also a critical defense mechanism because cell-to-cell spread occurs before hematogenous spread. Furthermore, induction of robust T-cell memory is critical for the long-term duration of immunity. Among current commercial vaccines, the attenuated conventional vaccines induce a balanced immune response and long-term memory but may result in viral shedding. By contrast, inactivated vaccines primarily elicit a humoral immune response and relative short-term memory. These vaccines do not allow differentiation of vaccinated from infected cattle. Recent efforts are focusing on the development of vaccines that induce a balanced immune response and long-term memory, as well as having differentiation markers. This includes well-defined genetically engineered gene-deleted, subunit and vectored vaccines.

Development of liposome gel based formulations for intravaginal delivery of the recombinant HIV-1 envelope protein CN54gp140

Mucosally-administered vaccine strategies are widely investigated as a promising means of preventing HIV infection. This study describes the development of liposomal gel formulations, and novel lyophilised variants, comprising HIV-1 envelope glycoprotein, CN54gp140, encapsulated within neutral, positively charged or negatively charged liposomes. The CN54gp140 liposomes were evaluated for mean vesicle diameter, polydispersity, morphology, zeta potential and antigen encapsulation efficiency before being incorporated into hydroxyethyl cellulose (HEC) aqueous gel and subsequently lyophilised to produce a rod-shaped solid dosage form for practical vaginal application. The lyophilised liposome-HEC rods were evaluated for moisture content and redispersibility in simulated vaginal fluid. Since these rods are designed to revert to gel form following intravaginal application, mucoadhesive, mechanical (compressibility and hardness) and rheological properties of the reformed gels were evaluated. The liposomes exhibited good encapsulation efficiency and the gels demonstrated suitable mucoadhesive strength. The freeze-dried liposome-HEC formulations represent a novel formulation strategy that could offer potential as stable and practical dosage form.

Vaginal delivery of the recombinant HIV-1 clade-C trimeric gp140 envelope protein CN54gp140 within novel rheologically structured vehicles elicits specific immune responses

Rheologically structured vehicle (RSV) gels were developed as delivery systems for vaginal mucosal vaccination with an HIV-1 envelope glycoprotein (CN54gp140). RSVs comprised a mucoadhesive matrix-forming and vaginal fluid absorbing polymer. The mucoadhesive and rheological properties of the RSVs were evaluated in vitro, and the distribution, antigenicity and release of CN54gp140 were analysed by ELISA. CN54gp140 was uniformly distributed within the RSVs and continuously released in vitro in an antigenically intact form over 24 h. Vaginal administration to rabbits induced specific serum IgG, and IgG and IgA in genital tract secretions. The RSVs are a viable delivery modality for vaginal immunization.

Challenges in mucosal vaccination of cattle

Recognition of the mucosal portal of entry for many infectious diseases and of the relevance of mucosal immune response to protection has encouraged the development of vaccines administered by mucosal routes, principally oral and intranasal, for stimulation of intestinal and nasopharyngeal lymphoid tissues respectively. The oral route is problematic in cattle and other ruminants where antigen degradation in the rumen is likely, prior to transit to the intestine. On the other hand, rumination can be exploited for exposure of nasopharyngeal tissues during cudding if vaccine antigen is expressed by a fibrous feed like alfalfa. An increase in anti-leukotoxin (Lkt) IgA was demonstrated in nasal secretions of calves following feeding of alfalfa expressing a truncated Lkt50 from Mannheimia haemolytica, and there is evidence suggesting that such vaccination may protect against experimentally induced pneumonia. Intranasal vaccination is an alternative approach for use in pre-ruminating calves. Intranasal administration of ISCOMs carrying soluble antigens of M. haemolytica, including native Lkt, induced Lkt specific IgA in nasal secretions after vaccination at 4 and 6 weeks of age. Subcutaneous (s.c.) administration of the same vaccine induced Lkt specific IgG in both serum and nasal secretions, whereas s.c. administration of a commercial M. haemolytica vaccine did not. Regardless of the vaccination strategy employed it is difficult to assess the immunogenicity of mucosally administered vaccines because production of secreted antibodies tends to be transient, and they do not persist on the mucosal surface in the absence of ongoing antigenic stimulation. An additional challenge is demonstration of vaccine efficacy in response to experimental infection. Protection of the mucosally vaccinated animal will most probably result from recall response, which may not amplify sufficiently to counter the effects of experimental pulmonary delivery of a large bolus of virulent bacteria, even though the response would suffice over the more prolonged and gradual infection that occurs in natural induction of pneumonia.

DNA vaccines and their applications in veterinary practice: current perspectives

Inoculation of plasmid DNA, encoding an immunogenic protein gene of an infectious agent, stands out as a novel approach for developing new generation vaccines for prevention of infectious diseases of animals. The potential of DNA vaccines to act in presence of maternal antibodies, its stability and cost effectiveness and the non-requirement of cold chain have heightened the prospects. Even though great strides have been made in nucleic acid vaccination, still there are many areas that need further research for its wholesome practical implementation. Major areas of concern are vaccine delivery, designing of suitable vectors and cytotoxic T cell responses. Also, the induction of immune responses by DNA vaccines is inconclusive due to the lack of knowledge regarding the concentration of the protein expressed in vivo. Alternative delivery systems having higher transfection efficiency and the use of cytokines, as immunomodulators, needs to be further explored. Recently, efforts are being made to modulate and prolong the active life of dendritic cells, in order to make antigen presentation a more efficacious one. For combating diseases like acquired immunodeficiency syndrome (AIDS), influenza, malaria and tuberculosis in humans; and foot and mouth disease, Aujesky’s disease, swine fever, rabies, canine distemper and brucellosis in animals, DNA vaccine clinical trials are underway. This review highlights the salient features of DNA vaccines, and measures to enhance their efficacy so as to devise an effective and novel vaccination strategy against animal diseases.

Prime-boost strategies combining DNA and inactivated vaccines confer high immunity and protection in cattle against bovine herpesvirus-1

DNA vaccines have frequently been associated with poor efficacy in large animals. In the present study, one administration of an inactivated marker vaccine to cattle considerably boosted both humoral and cellular arms of the immune response primed with Bovine herpesvirus-1 (BoHV-1) DNA vaccines encoding glycoprotein D (gD) or gC+gD. Calves vaccinated according to the DNA prime-inactivated boost also showed significantly enhanced virological protection as compared to controls. The 4-logarithms reduction of virus shedding observed in primed-boosted animals was comparable to the one previously reported in calves immunized twice with marker vaccines. Intradermal immunization of cattle with DNA vaccines promoted a Th2-biased immune response but also primed a cellular component that was further boosted by the inactivated vaccine. Individual IgG2 titers of vaccinated calves were significantly correlated to IFN-gamma production. The immunization protocol described in the present study demonstrates the complementarity between DNA and conventional marker vaccines.

The vagina as a route for systemic drug delivery

Exhaustive efforts have been made toward the administration of drugs, via alternative routes, that are poorly absorbed after the oral administration. The vagina as a route of drug delivery has been known since ancient times. In recent years, the vaginal route has been rediscovered as a potential route for systemic delivery of peptides and other therapeutically important macromolecules. However, successful delivery of drugs through the vagina remains a challenge, primarily due to the poor absorption across the vaginal epithelium. The rate and extent of drug absorption after intravaginal administration may vary depending on formulation factors, vaginal physiology, age of the patient and menstrual cycle. Suppositories, creams, gels, tablets and vaginal rings are commonly used vaginal drug delivery systems. The purpose of this communication is to provide the reader with a summary of advances made in the field of vaginal drug delivery. This report, therefore, summarizes various vaginal drug delivery systems with an introduction to vaginal physiology and factors affecting drug absorption from the vaginal route.

DNA vaccination against tumors

DNA vaccines have been used to generate protective immunity against tumors in a variety of experimental models. The favorite target antigens have been those that are frequently expressed by human tumors, such as carcinoembryonic antigen (CEA), ErbB2/neu, and melanoma-associated antigens. DNA vaccines have the advantage of being simple to construct, produce and deliver. They can activate all arms of the immune system, and allow substantial flexibility in modifying the type of immune response generated through codelivery of cytokine genes. DNA vaccines can be applied by intramuscular, dermal/epidermal, oral, respiratory and other routes, and pose relatively few safety concerns. Compared to other nucleic acid vectors, they are usually devoid of viral or bacterial antigens and can be designed to deliver only the target tumor antigen(s). This is likely to be important when priming a response against weak tumor antigens. DNA vaccines have been more effective in rodents than in larger mammals or humans. However, a large number of methods that might be applied clinically have been shown to ameliorate these vaccines. This includes in vivo electroporation, and/or inclusion of various immunostimulatory molecules, xenoantigens (or their epitopes), antigen-cytokine fusion genes, agents that improve antigen uptake or presentation, and molecules that activate innate immunity mechanisms. In addition, CpG motifs carried by plasmids can overcome the negative effects of regulatory T cells. There have been few studies in humans, but recent clinical trials suggest that plasmid/virus, or plasmid/antigen-adjuvant, prime-boost strategies generate strong immune responses, and confirm the usefulness of plasmid-based vaccination.

Strategies for improved formulation and delivery of DNA vaccines to veterinary target species

Interest in DNA immunization of animals continues, despite the fact that immune responses induced by DNA vaccines are generally lower than those elicited by conventional vaccines. In attempts to enhance the immune response to DNA vaccines, individuals have tried a variety of immune modulators, cytokines, and costimulatory molecules, but these only boost immune responses marginally. These results clearly demonstrate that the major challenge to improving DNA-based vaccines is to improve the transfection efficiency. Gene gun and electroporation can increase transfection and improve immune responses significantly, but these technologies have not yet advanced to the stage of routine use in livestock. Hopefully, transfection efficiency can be increased further in a user-friendly manner to ensure that the benefits of using DNA vaccines become a reality.

Modulation of immune responses to bovine herpesvirus-1 in cattle by immunization with a DNA vaccine encoding glycoprotein D as a fusion protein with bovine CD154

The objective of this study was to determine whether a DNA vaccine encoding bovine CD154 linked to a truncated version of bovine herpesvirus-1 (BHV-1) glycoprotein D (tgD-CD154) induces enhanced tgD-specific immune responses in cattle. In vitro characterization demonstrated that tgD and tgD-CD154 both bind to cultured bovine B cells, whereas only tgD-CD154 induces interleukin-4-dependent proliferation, suggesting that tgD-CD154 specifically binds the CD40 receptor and induces receptor signalling. Calves were immunized with plasmid encoding either tgD or tgD-CD154 by intradermal injection with a needle-free device. After two immunizations, tgD-specific immune responses were observed in both vaccinated groups and after challenge with BHV-1 these responses further increased. Animals immunized with plasmid encoding tgD-CD154 had significantly higher tgD-specific serum titres of immunoglobulins G and A but significantly lower numbers of tgD-specific interferon-gamma-secreting cells than animals immunized with plasmid encoding tgD after BHV-1 challenge. This suggests that the expression of an antigen as a chimeric protein with CD154 can qualitatively alter immune responses in cattle. Since we previously showed that plasmid encoding tgD-CD154 induces significantly enhanced secondary tgD-specific antibody responses in sheep, there appear to be interspecies differences in the immune responses induced by tgD-CD154, which suggests that both proteins in the chimeric molecule may influence protein targeting and the induction of an immune response.

Alternative routes of mucosal immunization in large animals

Mucosal immunization regimes that employ the oral route of delivery are often compromised by antigen degradation in the stomach. Moreover, tolerance or immunological unresponsiveness to orally delivered vaccine antigens is also a major problem associated with this route of immunization. Immunization by alternative routes including intrarectal (i.r.) and intranasal (i.n.) is becoming increasingly recognized in large animals for generating protective antibody responses at mucosal surfaces. These approaches are particularly useful in ruminant species which have four stomachs that can potentially interfere with antigen presentation to mucosal inductive sites of the gut. Modifications to enhance existing mucosal immunization regimes have also been explored through the use of alternative antigen delivery systems and mucosal adjuvants. The combination of alternative immunization routes and the use of appropriate antigen delivery systems appear to be a rational approach for providing protective immunity at mucosal surfaces. There has been a considerable amount of research conducted on evaluating the efficacy of emerging antigen delivery systems and novel adjuvants for improved immunity to mucosal immunization but very little of this work has been specific to the mucosal compartment of large animals. The aim of this review is therefore to assess the feasibility and practicality of using large animals (particularly sheep, cattle and pigs) for inducing and detecting specific immune responses to alternative mucosal routes of immunization.

Recent advances in veterinary vaccine adjuvants

Next generation veterinary vaccines are going to mainly comprise of either subunit or inactivated bacteria/viruses. These vaccines would require optimal adjuvants and delivery systems to accord long-term protection from infectious diseases in animals. There is an urgent need for the development of new and improved veterinary and human vaccine adjuvants. Adjuvants can be broadly divided into two classes, based on their principal mechanisms of action: vaccine delivery systems and 'immunostimulatory adjuvants'. Vaccine delivery systems are generally particulate e.g. emulsions, microparticles, ISCOMS and liposomes, and mainly function to target associated antigens into antigen presenting cells (APC). In contrast, immunostimulatory adjuvants are predominantly derived from pathogens and often represent pathogen associated molecular patterns, e.g. LPS, MPL and CpG DNA, which activate cells of the innate immune system. Recent progress in innate immunity is beginning to yield insight into the initiation of immune responses and the ways in which immunostimulatory adjuvants might enhance this process in animals and humans alike.

Augmentation of cellular immune responses to bovine herpesvirus-1 glycoprotein D by vaccination with CpG-enhanced plasmid vectors

The potential of CpG-enhanced plasmid DNA vectors encoding a truncated secreted form of bovine herpesvirus-1 (BHV-1) glycoprotein D (tgD) to induce enhanced immune responses in cattle was investigated. We created tgD expression plasmids containing 0, 40 or 88 copies of the hexamer 5' GTCGTT 3', a known pan-activating CpG motif in several species. The total tgD-specific IgG titre of calves immunized with these plasmids did not correlate with the CpG content of the plasmid backbone. However, the pBISIA88-tgD-vaccinated group showed a significantly lower IgG1:IgG2 ratio than calves immunized with pBISIA40-tgD or pMASIA-tgD, which has no CpG motifs inserted. Antigen-specific lymphocyte proliferation and IFN-gamma secretion by peripheral blood mononuclear cells correlated positively with the CpG content of the vectors. In contrast, calves that received a killed BHV-1 vaccine had an IgG1-predominant isotype and low lymphocyte proliferation and IFN-gamma levels. Following challenge, the pBISIA88-tgD-immunized group developed the greatest anamnestic response, the highest BHV-1 neutralization titres in serum and a significantly lower level of virus shedding than the saline control group. However, there were no significant differences in clinical symptoms of infection between the DNA-immunized groups and the saline control group. These data indicate that CpG-enhanced plasmids induce augmented immune responses and could be used to vaccinate against pathogens requiring a strong cellular response for protection.

The application of nucleic acid vaccines in veterinary medicine

Nucleic acid immunisation entails the delivery of DNA (or RNA) encoding a vaccine antigen to the recipient. The DNA is taken up by host cells and transcribed to mRNA, from which the vaccine proteins are then translated. The expressed proteins are recognised as foreign by the host immune system and elicit an immune response, which may have both cell-mediated and humoral components. DNA vaccines offer a number of advantages over conventional vaccines, including ease of production, stability and cost. They also allow the production of vaccines against organisms which are difficult or dangerous to culture in the laboratory. This review describes the principles of DNA vaccination and the application of DNA vaccines to veterinary species. Although a great deal of developmental work is required before the technology can give rise to commercial vaccines in domestic animals, there is ongoing research in many fields and it is expected that a number of exciting developments will arise in the next decade.