An IL-15 adjuvant enhances the efficacy of a combined DNA vaccine against Brucella by increasing the CD8+ cytotoxic T cell response

A Single Nasal Dose Vaccination with a Brucella abortus Mutant Potently Protects against Pulmonary Infection

The Brucella abortus double-mutant (ΔznuA ΔnorD Brucella abortus-lacZ [znBAZ]) was assessed for its protective efficacy after vaccination with a single nasal dose. Superior protection was achieved in znBAZ-vaccinated mice against pulmonary, wild-type B. abortus 2308 challenge when compared with conventional livestock Brucella abortus vaccines, the smooth S19 (smooth B. abortus strain 19 vaccine) and rough RB51 (rough mutant vaccine strain of B. abortus) strains. Nasal znBAZ vaccination reduced splenic and lung colonization by wild-type brucellae by >3-4 logs. In contrast, S19 reduced lung colonization by only 32-fold, and RB51 failed to reduce colonization. One profound attribute of znBAZ vaccination was the >3-fold increase in pulmonary CD8+ T cells when compared with other vaccinated groups. S19 vaccination increased only CD4+ T cells. All vaccines induced IFN-γ and TNF-α production by CD4+ T cells, but only znBAZ vaccination enhanced the recruitment of polyfunctional CD8+ T cells, by >100-fold. IL-17 by both CD4+ and CD8+ T cells was also induced by subsequent znBAZ vaccination. These results demonstrate that, in addition to achieving protective immunity by CD4+ T cells, CD8+ T cells, specifically resident memory T cells, also confer protection against brucellosis. The protection obtained by znBAZ vaccination was attributed to IFN-γ-producing CD8+ T cells, because depletion of CD8+ T cells throughout vaccination and challenge phases abrogated protection. The stimulation of only CD4+ T cells by RB51- and S19-vaccinated mice proved insufficient in protecting against pulmonary B. abortus 2308 challenge. Thus, nasal znBAZ vaccination offers an alternative means to elicit protection against brucellosis.

Recombinant BoHV-5 glycoprotein (rgD5) elicits long-lasting protective immunity in cattle

BoHV-5 is a worldwide distributed pathogen usually associated with a lethal neurological disease in dairy and beef cattle resulting in important economic losses due to the cattle industry. Using recombinant gD5, we evaluated the long-duration humoral immunity of the recombinant vaccines in a cattle model. Here we report that two doses of intramuscular immunization, particularly with the rgD5ISA vaccine, induce long-lasting antibody responses. Recombinant gD5 antigen elicited tightly mRNA transcription of the Bcl6 and the chemokine receptor CXCR5 which mediate memory B cells and long-lived plasma cells in germinal centers. In addition, using an in-house indirect ELISA we observed higher and earlier responses of rgD5-specific IgG antibody and the upregulation of mRNA transcription of IL2, IL4, IL10, IL15, and IFN-γ in rgD5 vaccinated cattle, indicating a mixed immune response. We further show that rgD5 immunization protects against both BoHV -1 and -5. Our findings indicate that the rgD5-based vaccine represents an effective vaccine strategy to induce an efficient control of herpesviruses.

Teleost cytotoxic T cells

Cell-mediated cytotoxicity is one of the major mechanisms by which vertebrates control intracellular pathogens. Two cell types are the main players in this immune response, natural killer (NK) cells and cytotoxic T lymphocytes (CTL). While NK cells recognize altered target cells in a relatively unspecific manner CTLs use their T cell receptor to identify pathogen-specific peptides that are presented by major histocompatibility (MHC) class I molecules on the surface of infected cells. However, several other signals are needed to regulate cell-mediated cytotoxicity involving a complex network of cytokine- and ligand-receptor interactions. Since the first description of MHC class I molecules in teleosts during the early 90s of the last century a remarkable amount of information on teleost immune responses has been published. The corresponding studies describe teleost cells and molecules that are involved in CTL responses of higher vertebrates. These studies are backed by functional investigations on the killing activity of CTLs in a few teleost species. The present knowledge on teleost CTLs still leaves considerable room for further investigations on the mechanisms by which CTLs act. Nevertheless the information on teleost CTLs and their regulation might already be useful for the control of fish diseases by designing efficient vaccines against such diseases where CTL responses are known to be decisive for the elimination of the corresponding pathogen. This review summarizes the present knowledge on CTL regulation and functions in teleosts. In a special chapter, the role of CTLs in vaccination is discussed.

Adjuvantation of inactivated Foot and Mouth Disease Virus vaccine with IL-15 expressing plasmid improves the immune response in Guinea Pigs

Foot and mouth disease is a highly contagious disease affecting cloven footed animals. Vaccination using inactivated virus is followed to control the disease. As the immune response conferred by the inactivated vaccine is short lived, there is a need for an alternate vaccine with increased duration of immunity. Inclusion of adjuvant which enhances B and T cell responses is one of the strategies to increase the duration of immune responses of the vaccine. Interleukin 15 is one such a cytokine which improves the cell mediated immune response and also involved in the maintenance of memory T and B cells. In the present communication, we evaluated the role of bovine IL-15 as an adjuvant to inactivated FMD vaccine in guinea pig model. Animals injected with FMD inactivated vaccine and IL-15 plasmid showed improved levels of neutralizing antibodies which were maintained up to 6 months (as the level of neutralizing antibodies is more >1.5 which is considered to give protection). Increased Th1 and Th2 responses (by measuring the level of IL-4 and IFN- gamma responses) were seen in IL-15 adjuvanted guinea pigs compared to animals injected with inactivated vaccine alone.

Safety and Immunological Efficacy of a DNA Vaccine Encoding the Androgen Receptor Ligand-Binding Domain (AR-LBD)

BACKGROUND

The androgen receptor (AR) is a key oncogenic driver of prostate cancer, and has been the primary focus of prostate cancer treatment for several decades. We have previously demonstrated that the AR is also an immunological target antigen, recognized in patients with prostate cancer, and targetable by means of vaccines in rodent models with delays in prostate tumor growth. The current study was performed to determine the safety and immunological efficacy of a GMP-grade plasmid DNA vaccine encoding the ligand-binding domain (LBD) of the AR, pTVG-AR.

METHODS

Groups of male mice (n = 6-10 per group) were evaluated after four or seven immunizations, using different schedules and inclusion of GM-CSF as a vaccine adjuvant. Animals were assessed for toxicity using gross observations, pathological analysis, and analysis of serum chemistries. Animals were analyzed for evidence of vaccine-augmented immunity by tetramer analysis. Survival studies using different immunization schedules and inclusion of GM-CSF were conducted in an autochthonous genetically engineered mouse model.

RESULTS

No significant toxicities were observed in terms of animal weights, histopathology, hematological changes, or changes in serum chemistries, although there was a trend to lower serum glucose in animals treated with the vaccine. There was specifically no evidence of toxicity in other tissues that express AR, including liver, muscle, hematopoietic, and brain. Vaccination was found to elicit AR LBD-specific CD8+ T cells. In a subsequent study of tumor-bearing animals, animals treated with vaccine had prolonged survival compared with control-immunized mice.

CONCLUSIONS

These studies demonstrate that, in immunocompetent mice expressing the target antigen, immunization with the pTVG-AR vaccine was both safe and effective in eliciting AR-specific cellular immune responses, and prolonged the survival of prostate tumor-bearing mice. These findings support the clinical evaluation of pTVG-AR in patients with recurrent prostate cancer. Prostate 77:812-821, 2017. © 2017 Wiley Periodicals, Inc.

Meta-Analysis and Advancement of Brucellosis Vaccinology

Background/Objectives

In spite of all the research effort for developing new vaccines against brucellosis, it remains unclear whether these new vaccine technologies will in fact become widely used. The goal of this study was to perform a meta-analysis to identify parameters that influence vaccine efficacy as well as a descriptive analysis on how the field of Brucella vaccinology is advancing concerning type of vaccine, improvement of protection on animal models over time, and factors that may affect protection in the mouse model.

Methods

A total of 117 publications that met the criteria were selected for inclusion in this study, with a total of 782 individual experiments analyzed.

Results

Attenuated (n = 221), inactivated (n = 66) and mutant (n = 102) vaccines provided median protection index above 2, whereas subunit (n = 287), DNA (n = 68), and vectored (n = 38) vaccines provided protection indexes lower than 2. When all categories of experimental vaccines are analyzed together, the trend line clearly demonstrates that there was no improvement of the protection indexes over the past 30 years, with a low negative and non significant linear coefficient. A meta-regression model was developed including all vaccine categories (attenuated, DNA, inactivated, mutant, subunit, and vectored) considering the protection index as a dependent variable and the other parameters (mouse strain, route of vaccination, number of vaccinations, use of adjuvant, challenge Brucella species) as independent variables. Some of these variables influenced the expected protection index of experimental vaccines against Brucella spp. in the mouse model.

Conclusion

In spite of the large number of publication over the past 30 years, our results indicate that there is not clear trend to improve the protective potential of these experimental vaccines.

Nasal vaccination stimulates CD8(+) T cells for potent protection against mucosal Brucella melitensis challenge

Brucellosis remains a significant zoonotic threat worldwide. Humans and animals acquire infection via their oropharynx and upper respiratory tract following oral or aerosol exposure. After mucosal infection, brucellosis develops into a systemic disease. Mucosal vaccination could offer a viable alternative to conventional injection practices to deter disease. Using a nasal vaccination approach, the ΔznuA B. melitensis was found to confer potent protection against pulmonary Brucella challenge, and reduce colonization of spleens and lungs by more than 2500-fold, with more than 50% of vaccinated mice showing no detectable brucellae. Furthermore, tenfold more brucellae-specific, IFN-γ-producing CD8⁺ T cells than CD4⁺ T cells were induced in the spleen and respiratory lymph nodes. Evaluation of pulmonary and splenic CD8⁺ T cells from mice vaccinated with ΔznuA B. melitensis revealed that these expressed an activated effector memory (CD44^hiCD62L^loCCR7^lo) T cells producing elevated levels of IFN-γ, TNF-α, perforin, and granzyme B. To assess the relative importance of these increased numbers of CD8⁺ T cells, CD8^−/− mice were challenged with virulent B. melitensis, and they showed markedly increased bacterial loads in organs in contrast to similarly challenged CD4^−/− mice. Only ΔznuA B. melitensis- and Rev-1-vaccinated CD4^−/− and wild-type mice, not CD8^−/− mice, were completely protected against Brucella challenge. Determination of cytokines responsible for conferring protection showed the relative importance of IFN-γ, but not IL-17. Unlike wild-type mice, IL-17 was greatly induced in IFN-γ^−/− mice, but IL-17 could not substitute for IFN-γ’s protection, although an increase in brucellae dissemination was observed upon in vivo IL-17 neutralization. These results show that nasal ΔznuA B. melitensis vaccination represents an attractive means to stimulate systemic and mucosal immune protection via CD8⁺ T cell engagement.

Differential effects of IL-15 on the generation, maintenance and cytotoxic potential of adaptive cellular responses induced by DNA vaccination

IL-15 is an important cytokine for the regulation of lymphocyte homeostasis. However, the role of IL-15 in the generation, maintenance and cytotoxic potential of antigen specific T cells is not fully understood. Because the route of antigenic delivery and the vaccine modality could influence the IL-15 requirement for mounting and preserving cytotoxic T cell responses, we have investigated the immunogenicity of DNA-based vaccines in IL-15 KO mice. DNA vaccination with SIV Gag induced antigen-specific CD4(+) and CD8(+) T cells in the absence of IL-15. However, the absolute number of antigen-specific CD8(+) T cells was decreased in IL-15 KO mice compared to WT animals, suggesting that IL-15 is important for the generation of maximal number of antigen-specific CD8(+) T cells. Interestingly, antigen-specific memory CD8 cells could be efficiently boosted 8 months after the final vaccination in both WT and KO strains of mice, suggesting that the maintenance of antigen-specific long-term memory T cells induced by DNA vaccination is comparable in the absence and presence of IL-15. Importantly, boosting by DNA 8-months after vaccination revealed severely reduced granzyme B content in CD8(+) T cells of IL-15 KO mice compared to WT mice. This suggests that the cytotoxic potential of the long-term memory CD8(+) T cells is impaired. These results suggest that IL-15 is not essential for the generation and maintenance of adaptive cellular responses upon DNA vaccination, but it is critical for the preservation of maximal numbers and for the activity of cytotoxic CD8(+) T cells.

Adjuvant effects of recombinant giant panda (Ailuropoda melanoleuca) IL-18 on the canine distemper disease vaccine in mice

Canine distemper virus (CDV) is a morbillivirus known to cause morbidity and mortality in a broad range of animals. Giant pandas (Ailuropoda melanoleuca), especially captive ones, are susceptible to natural infection with CDV. Interleukin-18 (IL-18) is a powerful adjuvant molecule that can enhance the development of antigen-specific immunity and vaccine efficacy. In this study, a giant panda IL-18 gene eukaryotic expression plasmid (pcAmIL-18) was constructed. Female BALB/c mice were muscularly inoculated with the plasmids pcAmIL-18, pcDNA3.1 and PBS, respectively. They were subsequently injected with an attenuated CDV vaccine for dogs, and the induced humoral and cellular responses were evaluated. The results showed that pcAmIL-18 remarkably improved the level of specific antibody, IFN-γ and IL-2 in mice sera, the T lymphocyte proliferation index and the percentage of CD4⁺ and CD8⁺ cells. These data indicated that pcAmIL-18 is a potential adjuvant that promotes specific immunity.

CD8 knockout mice are protected from challenge by vaccination with WR201, a live attenuated mutant of Brucella melitensis

CD8+ T cells have been reported to play an important role in defense against B. abortus infection in mouse models. In the present report, we use CD8 knockout mice to further elucidate the role of these cells in protection from B. melitensis infection. Mice were immunized orally by administration of B. melitensis WR201, a purine auxotrophic attenuated vaccine strain, then challenged intranasally with B. melitensis 16M. In some experiments, persistence of WR201 in the spleens of CD8 knockout mice was slightly longer than that in the spleens of normal mice. However, development of anti-LPS serum antibody, antigen-induced production of γ-interferon (IFN-γ) by immune splenic lymphocytes, protection against intranasal challenge, and recovery of nonimmunized animals from intranasal challenge were similar between normal and knockout animals. Further, primary Brucella infection was not exacerbated in perforin knockout and Fas-deficient mice and these animals' anti-Brucella immune responses were indistinguishable from those of normal mice. These results indicate that CD8+ T cells do not play an essential role as either cytotoxic cells or IFN-γ producers, yet they do participate in a specific immune response to immunization and challenge in this murine model of B. melitensis infection.

A history of the development of Brucella vaccines

Brucellosis is a worldwide zoonosis affecting animal and human health. In the last several decades, much research has been performed to develop safer Brucella vaccines to control the disease mainly in animals. Till now, no effective human vaccine is available. The aim of this paper is to review and discuss the importance of methodologies used to develop Brucella vaccines in pursuing this challenge.

Association of interleukin-15 single nucleotide polymorphisms with resistance to brucellosis among Iranian patients

Interleukin (IL)-15, a Th1-related cytokine, triggers inflammatory cells' recruitment and increases the expression of interferon gamma (IFN-γ), which is an important cytokine in the immunity against brucellosis. Different single-nucleotide polymorphisms (SNPs) have been observed in the IL-15 gene, so this study aimed to investigate the probable association between these SNPs and susceptibility to brucellosis among Iranian patients. A total of 190 patients with brucellosis and 83 healthy milk farmers who consumed contaminated raw milk and dairy products from animals involved with brucellosis were included in this study. All the patients and the controls were genotyped for four IL-15 polymorphisms at positions 267, 367, 13687 and 14035 using polymerase chain reaction-restriction fragment length polymorphisms. The 267C and 13687A alleles, haplotypes CGCT and CAAA and the 267CC and 13687AA genotypes were significantly more frequent in the controls than in the patients (P = 0.014, 0.03, 0.006, 0.024, 0.026 and 0.01, respectively), so the variation in the IL-15 gene may be one of the factors affecting the resistance to brucellosis. In contrast, the frequency of haplotypes CGCA and TACT was significantly higher in patients compared with controls (P = 0.015 and 0.007, respectively), and interestingly the last one was observed only in the patients; therefore, it may serve as a predictive factor for brucellosis. In conclusion, it could be suggested that IL-15 genetic variants can affect resistance or susceptibility to human brucellosis among Iranian patients.

The role of interleukin-15 in inflammation and immune responses to infection: implications for its therapeutic use

Interleukin-15 (IL-15) is a pleiotropic cytokine with a broad range of biological functions in many diverse cell types. It plays a major role in the development of inflammatory and protective immune responses to microbial invaders and parasites by modulating immune cells of both the innate and adaptive immune systems. This review provides an overview of the mechanisms by which IL-15 modulates the host response to infectious agents and its utility as a cytokine adjuvant in vaccines against infectious pathogens.

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.

A chimeric HIV-1 envelope glycoprotein trimer with an embedded granulocyte-macrophage colony-stimulating factor (GM-CSF) domain induces enhanced antibody and T cell responses

An effective HIV-1 vaccine should ideally induce strong humoral and cellular immune responses that provide sterilizing immunity over a prolonged period. Current HIV-1 vaccines have failed in inducing such immunity. The viral envelope glycoprotein complex (Env) can be targeted by neutralizing antibodies to block infection, but several Env properties limit the ability to induce an antibody response of sufficient quantity and quality. We hypothesized that Env immunogenicity could be improved by embedding an immunostimulatory protein domain within its sequence. A stabilized Env trimer was therefore engineered with the granulocyte-macrophage colony-stimulating factor (GM-CSF) inserted into the V1V2 domain of gp120. Probing with neutralizing antibodies showed that both the Env and GM-CSF components of the chimeric protein were folded correctly. Furthermore, the embedded GM-CSF domain was functional as a cytokine in vitro. Mouse immunization studies demonstrated that chimeric Env(GM-CSF) enhanced Env-specific antibody and T cell responses compared with wild-type Env. Collectively, these results show that targeting and activation of immune cells using engineered cytokine domains within the protein can improve the immunogenicity of Env subunit vaccines.