Frequency of IFN-gamma producing cells correlates with adjuvant enhancement of bacille Calmette-Guèrin induced protection against Mycobacterium bovis

Prime Vaccination with Chitosan-Coated Phipps BCG and Boosting with CFP-PLGA against Tuberculosis in a Goat Model

Simple Summary

Bovine tuberculosis is a disease that affects cattle and other animal species worldwide and represents a risk to public health. Even though there is a vaccine that has been used to control tuberculosis in humans for almost 100 years, up to now, it has not been used in animals. The reason is that vaccination interferes with the tuberculin test, the current test to diagnose tuberculosis in the field, and shows an inconsistent efficacy in animals. Recent studies report that prime vaccinating with BCG and boosting with proteins vaccinations perform better. In addition, there are reports that some polymers increase the immune response against various infectious diseases; therefore, testing a vaccine formula with polymers sounds like a wise thing to do. In this study, we showed that priming with BCG and boosting with a culture filtrate protein, alone or in combination with a polymer, the number of animals with lesions, the number of lesions per animal, and the size of the lesions in vaccinated animals, compared with those not vaccinated or those vaccinated with BCG alone, are significantly reduced. Our results mean that a vaccination used as a complement of actual tuberculosis control programs in animal populations can be useful to reduce tuberculosis dissemination.

Abstract

Attempts to improve the immune response and efficacy of vaccines against tuberculosis in cattle, goats, and other animal species have been the focus of research in this field during the last two decades. Improving the vaccine efficacy is essential prior to running long-lasting and expensive field trials. Studies have shown that vaccine protocols utilizing boosting with proteins improve the vaccine efficacy. The use of polymers such as chitosan and PolyLactic-co-Glycolic Acid (PLGA) improves the immune response against different diseases by improving the interaction of antigens with the cellular immune system and modulating the host immune response. This study shows that the prime BCG vaccination, boosted with a culture filtrate protein (CFP), alone or in combination with chitosan and PolyLactic-co-Glycolic Acid (PLGA), have the potential to reduce tuberculosis (TB) dissemination by reducing the number of animals with lesions, the number of lesions per animal, and the size of the lesions in vaccinated animals, compared with those not vaccinated or those vaccinated with BCG alone. The vaccinated groups showed significantly higher Interferon-γ levels in the blood compared to the control, nonvaccinated group after vaccination, after boosting, and after the challenge with the wild-type Mycobacterium bovis strain.

The effect of BCG vaccination on macrophage phenotype in a mouse model of intranasal Mycobacterium bovis challenge

In order to develop improved vaccinations against tuberculosis, it is essential to understand the effect of vaccination on the immune response, and to overcome the mechanisms by which mycobacteria regulate this immune response. In this study, we examine the effect of intradermal vaccination with Mycobacterium bovis bacille Calmette-Guèrin on macrophage phenotype following intranasal challenge with virulent Mycobacterium bovis. Preserved lung tissues used in the present study were obtained from a previous vaccination trial in BALB/c mice. Vaccinated mice showed less extensive pulmonary lesions along with a significant decrease in bacterial lung burden when compared to control mice. Immunohistochemical markers of classically activated macrophages (iNOS) and alternatively activated macrophages (Arg1, FIZZ1) were applied to lung sections. Vaccination led to a statistically significant decrease in the number of Arg1+ macrophages. The presence of macrophages that expressed Arginase 1 in pulmonary lesions was much smaller than the presence of macrophages expressing iNOS. The low presence of Arg1+ macrophages induced by vaccination may be caused by Th1 polarization and may reduce alternative activation of macrophages, with an overall more effective intracellular killing of bacteria.

Lactation-Based Maternal Educational Immunity Crosses MHC Class I Barriers and Can Impart Th1 Immunity to Th2-Biased Recipients

We have previously demonstrated lactational transfer of T cell-based immunity from dam to foster pup. In the short term, a significant part of transferred immunity is passive cellular immunity. However, as time progresses, this is replaced by what we have described as maternal educational immunity such that by young adulthood, all immune cells responding to a foster dam immunogen are the product of the foster pup's thymus. To reduce confounding factors, this original demonstration used congenic/syngeneic dam and foster pup pairs. In this study, we investigated lactational transfer of immunity to Mycobacterium tuberculosis in MHC class I-mismatched animals, as well as from Th1-biased dams to Th2-biased foster pups. Using immunized C57BL/6J dams, lactational transfer to nonimmunized BALB/cJ foster pups resulted in much greater immunity than direct immunization in 5-wk-old pups (ex vivo assay of pup splenocytes). At this age, 82% of immunogen-responding cells in the pup spleen were produced through maternal educational immunity. FVB/NJ nonimmunized foster recipients had a greater number of maternal cells in the spleen and thymus but a much larger percentage was Foxp3⁺, resulting in equivalent immunity to direct immunization. Depletion of maternal Foxp3⁺ cells from pup splenocytes illustrated a substantial role for lactationally transferred dam regulatory T cells in suppression of the ex vivo response in FVB/NJ, but not BALB/cJ, recipients. We conclude that lactational transfer of immunity can cross MHC class I barriers and that Th1 immunity can be imparted to Th2-biased offspring; in some instances, it can be greater than that achieved by direct immunization.

Testing the H56 Vaccine Delivered in 4 Different Adjuvants as a BCG-Booster in a Non-Human Primate Model of Tuberculosis

The search for new and improved tuberculosis (TB) vaccines has focused on IFN-γ both for selecting antigens and for evaluating vaccine delivery strategies. The essential role of IFN-γ in endogenous host protection is well established, but it is still uncertain whether this also holds true for vaccine protection. Here we evaluate the H56 fusion protein vaccine as a BCG booster in a non-human primate (NHP) model of TB that closely recapitulates human TB pathogenesis. To date, only a handful of novel adjuvants have been tested in the NHP model of TB, and therefore we administered H56 in 3 novel cationic liposome adjuvants of increasing immunogenicity (CAF01, CAF04, CAF05) and compared them to H56 in the IC31^® adjuvant previously reported to promote protection in this model. The individual clinical parameters monitored during infection (weight, ESR, X-ray) all correlated with survival, and boosting BCG with H56 in all adjuvants resulted in better survival rates compared to BCG alone. The adjuvants promoted IFN-γ-responses of increasing intensity as measured by ELISPOT in the peripheral blood, but the level of vaccine-specific IFN-γ production did not correlate with or predict disease outcome. This study’s main outcome underscores the importance of the choice of adjuvant for TB subunit vaccines, and secondly it highlights the need for better correlates of protection in preclinical models of TB.

Parenteral adenoviral boost enhances BCG induced protection, but not long term survival in a murine model of bovine TB

Boosting BCG using heterologous prime-boost represents a promising strategy for improved tuberculosis (TB) vaccines, and adenovirus (Ad) delivery is established as an efficacious boosting vehicle. Although studies demonstrate that intranasal administration of Ad boost to BCG offers optimal protection, this is not currently possible in cattle. Using Ad vaccine expressing the mycobacterial antigen TB10.4 (BCG/Ad-TB10.4), we demonstrate, parenteral boost of BCG immunised mice to induce specific CD8(+) IFN-γ producing T cells via synergistic priming of new epitopes. This induces significant improvement in pulmonary protection against Mycobacterium bovis over that provided by BCG when assessed in a standard 4week challenge model. However, in a stringent, year-long survival study, BCG/Ad-TB10.4 did not improve outcome over BCG, which we suggest may be due to the lack of additional memory cells (IL-2(+)) induced by boosting. These data indicate BCG-prime/parenteral-Ad-TB10.4-boost to be a promising candidate, but also highlight the need for further understanding of the mechanisms of T cell priming and associated memory using Ad delivery systems. That we were able to generate significant improvement in pulmonary protection above BCG with parenteral, rather than mucosal administration of boost vaccine is critical; suggesting that the generation of effective mucosal immunity is possible, without the risks and challenges of mucosal administration, but that further work to specifically enhance sustained protective immunity is required.

Construction and immunogenicity of a new Fc-based subunit vaccine candidate against Mycobacterium tuberculosis

As an ancient disease, tuberculosis (TB) is a major global health threat. Therefore, there is an urgent need for an effective and safe anti-TB vaccine. In the current study, a delivery system of Fc domain of mouse IgG2a and early secreted antigenic target protein 6 (ESAT-6) was evaluated for the selective uptake of antigens by antigen-presenting cells (APCs). Thus, it was based on the immunogenicity of a fusion protein. The study was initiated by the transfer of recombinant expression vectors of pPICZαA-ESAT-6:Fcγ2a and pPICZαA-ESAT-6: His into Pichia pastoris (P. pastoris). Recombinant proteins were assessed for immunogenicity following the immunoblotting analysis. High levels of IFN-γ and IL-12 were produced to induce Th1-type cellular responses through vaccination with both recombinant proteins [ESAT-6:Fcγ2a (EF) and ESAT-6:His (EH)]. The Fc-tagged recombinant protein induced more effective Th1-type cellular responses with a low increment in IL-4 compared to PBS, BCG, and EH groups. Although in all the immunized groups, the ratio of IFN-γ/IL-4 was in favor of Th1 responses, the highest Th1/Th2 balance was observed in EF immunized group. Fc fragment of mouse IgG2a may induce a selective uptake of APCs towards the cross-presentation and formation of Th1 responses in favor of an appropriate protective anti-tuberculosis reaction. Thus, further research on Fc-fusion proteins is required to develop Fc-based TB vaccines.

BALB/c mice display more enhanced BCG vaccine induced Th1 and Th17 response than C57BL/6 mice but have equivalent protection

It is generally assumed that the inbred mouse strains BALB/c (H-2(d)) and C57BL/6 (H-2(b)) respond to mycobacterial infection with distinct polarisation of T helper responses, with C57BL/6 predisposed to Th1 and BALB/c to Th2. We investigated this in a BCG-immunisation, Mycobacterium bovis challenge model. Following immunisation, lung and spleen cell cytokine responses to in vitro re-stimulation with a cocktail of seven secreted, immunogenic, recombinant mycobacterial proteins were determined. In both lung and spleen, BALB/c cells produced at least 2-fold more IFN-γ, and up to 7-fold more IL-2 and IL-17 than C57BL/6 cells, whereas IL-10 production was reciprocally increased in C57BL/6 mice. These data suggest that, contrary to reports in the literature, specific mycobacterial antigens are able to induce strong Th1 and Th17 responses in BALB/c mice following BCG vaccination, whilst in C57BL/6 mice, the Th1 response is partly counterbalanced by IL-10. After subsequent M. bovis low dose challenge, protection, as measured in the lungs and dissemination to the spleen, was equivalent in BALB/c and C57BL/6 mice, indicating that BCG-induced immunity was equivalent in both strains. Thus, the differential immune responses do not appear to have a role in protection, but further, as yet unidentified, specific immune responses play a significant role.

Efficacy of a vaccine formula against tuberculosis in cattle

"Test-and-slaughter" has been successful in industrialized countries to control and eradicate tuberculosis from cattle; however, this strategy is too expensive for developing nations, where the prevalence is especially high. Vaccination with the Calmette-Guérin (BCG) strain has been shown to protect against the development of lesions in vaccinated animals: mouse, cattle and wildlife species. In this study, the immune response and the pathology of vaccinated (BCG-prime and BCG prime-CFP-boosted) and unvaccinated (controls) calves were evaluated under experimental settings. A 10(6) CFU dose of the BCG strain was inoculated subcutaneously on the neck to two groups of ten animas each. Thirty days after vaccination, one of the vaccinated groups was boosted with an M. bovis culture filtrate protein (CFP). Three months after vaccination, the three groups of animals were challenged with 5×10(5) CFU via intranasal by aerosol with a field strain of M. bovis. The immune response was monitored throughout the study. Protection was assessed based on immune response (IFN-g release) prechallenge, presence of visible lesions in lymph nodes and lungs at slaughter, and presence of bacilli in lymph nodes and lung samples in histological analysis. Vaccinated cattle, either with the BCG alone or with BCG and boosted with CFP showed higher IFN-g response, fewer lesions, and fewer bacilli per lesion than unvaccinated controls after challenge. Animals with low levels of IFN-g postvaccine-prechallenge showed more lesions than animals with high levels. Results from this study support the argument that vaccination could be incorporated into control programs to reduce the incidence of TB in cattle in countries with high prevalence.

Systemic BCG immunization induces persistent lung mucosal multifunctional CD4 T(EM) cells which expand following virulent mycobacterial challenge

To more closely understand the mechanisms of how BCG vaccination confers immunity would help to rationally design improved tuberculosis vaccines that are urgently required. Given the established central role of CD4 T cells in BCG induced immunity, we sought to characterise the generation of memory CD4 T cell responses to BCG vaccination and M. bovis infection in a murine challenge model. We demonstrate that a single systemic BCG vaccination induces distinct systemic and mucosal populations of T effector memory (T_EM) cells in vaccinated mice. These CD4⁺CD44^hiCD62L^loCD27⁻ T cells concomitantly produce IFN-γ and TNF-α, or IFN-γ, IL-2 and TNF-α and have a higher cytokine median fluorescence intensity MFI or ‘quality of response’ than single cytokine producing cells. These cells are maintained for long periods (>16 months) in BCG protected mice, maintaining a vaccine–specific functionality. Following virulent mycobacterial challenge, these cells underwent significant expansion in the lungs and are, therefore, strongly associated with protection against M. bovis challenge. Our data demonstrate that a persistent mucosal population of T_EM cells can be induced by parenteral immunization, a feature only previously associated with mucosal immunization routes; and that these multifunctional T_EM cells are strongly associated with protection. We propose that these cells mediate protective immunity, and that vaccines designed to increase the number of relevant antigen-specific T_EM in the lung may represent a new generation of TB vaccines.

Protection of Eurasian badgers (Meles meles) from tuberculosis after intra-muscular vaccination with different doses of BCG

Mycobacterium bovis infection is widespread in Eurasian badger (Meles meles) populations in Great Britain and the Republic of Ireland where they act as a wildlife reservoir of infection for cattle. Removal of infected badgers can significantly reduce the incidence of bovine tuberculosis (TB) in local cattle herds. However, control measures based on culling of native wildlife are contentious and may even be detrimental to disease control. Vaccinating badgers with bacillus Calmette-Guerin (BCG) has been shown to be efficacious against experimentally induced TB of badgers when administered subcutaneously and orally. Vaccination may be an alternative or complementary strategy to other disease control measures. As the subcutaneous route is impractical for vaccinating wild badgers and an oral vaccine bait formulation is currently unavailable, we evaluated the intramuscular (IM) route of BCG administration. It has been demonstrated that the IM route is safe in badgers. IM administration has the practical advantage of being relatively easy to perform on trapped wild badgers without recourse to chemical immobilisation. We report the evaluation of the efficacy of IM administration of BCG Danish strain 1331 at two different doses: the dose prescribed for adult humans (2-8×10(5)colony forming units) and a 10-fold higher dose. Vaccination generated a dose-dependent cell-mediated immune response characterised by the production of interferon-γ (IFNγ) and protection against endobronchial challenge with virulent M. bovis. Protection, expressed in terms of a significant reduction in the severity of disease, the number of tissues containing acid-fast bacilli, and reduced bacterial excretion was statistically significant with the higher dose only.

Viral reservoir is suppressed but not eliminated by CD8 vaccine specific lymphocytes

It has long been postulated that while CD8 lymphocytes are capable of suppressing human immunodeficiency virus (HIV)-1 replication it is unlikely that the viral reservoirs once formed can be cleared. Our previous studies demonstrate that co-immunizing cynomologous macaques with a simian/human immunodeficiency virus (SHIV) DNA-based vaccines induces a strong cellular immune response that is able to suppress viral replication. We further demonstrated that interleukin (IL)-12 could significantly enhance the vaccine specific CD8 lymphocyte response. In this manuscript cynomologous macaques were vaccinated with a SHIV DNA-based vaccine co-delivered with IL-12. The macaques were then challenged with SHIV89.6p. Two years post-immunization and viral challenge we transiently depleted CD8(+) T cells. Plasma viral load increased, demonstrating the central role of CD8(+) T cells in viral suppression yet an inability to clear the viral reservoirs. Furthermore, in the data presented here, we found a higher number of IFN-gamma producing vaccine specific cells did not enhance suppression of viral replication.

Enhanced protection against bovine tuberculosis after coadministration of Mycobacterium bovis BCG with a Mycobacterial protein vaccine-adjuvant combination but not after coadministration of adjuvant alone

Current efforts are aimed at optimizing the protective efficacy of Mycobacterium bovis BCG by the use of vaccine combinations. We have recently demonstrated that the protection afforded by BCG alone is enhanced by vaccinating cattle with a combination of vaccines comprising BCG and a protein tuberculosis vaccine, namely, culture filtrate proteins (CFPs) from M. bovis plus an adjuvant. In the current study, three different adjuvant systems were compared. The CFP was formulated with a depot adjuvant, dimethyldioctadecyl ammonium bromide (DDA), together with one of three different immunostimulants: monophosphoryl lipid A (MPL), a synthetic mycobacterial phosphatidylinositol mannoside-2 (PIM2), and a synthetic lipopeptide (Pam3Cys-SKKKK [Pam(3)CSK(4)]). Groups of cattle (n = 10/group) were vaccinated with BCG-CFP-DDA-PIM2, BCG-CFP-DDA-MPL, or BCG-CFP-DDA-Pam(3)CSK(4). Two additional groups (n = 10) were vaccinated with BCG alone or BCG-adjuvant (DDA-MPL), and a control group was left unvaccinated. Protection was assessed by challenging the cattle intratracheally with M. bovis. Groups of cattle vaccinated with BCG-CFP-DDA-PIM2, BCG-CFP-DDA-MPL, BCG-CFP-DDA-Pam(3)CSK(4), and BCG alone showed significant reductions in three, three, five, and three pathological and microbiological disease parameters, respectively, compared to the results for the nonvaccinated group. Vaccination with the combination of BCG and the DDA-MPL adjuvant alone abrogated the protection conferred by BCG alone. The profiling of cytokine gene expression following vaccination, prior to challenge, did not illuminate significant differences which could explain the latter result. Vaccination of cattle with a combination of BCG and protein tuberculosis vaccine enhances protection against tuberculosis.

Lactoferrin enhanced efficacy of the BCG vaccine to generate host protective responses against challenge with virulent Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is a disease with world wide consequences, affecting nearly a third of the world's population. The established vaccine for TB, an attenuated strain of Mycobacterium bovis Calmette Guerin (BCG), has existed since 1921. Lactoferrin, an iron-binding protein found in mucosal secretions and granules of neutrophils was hypothesized to be an ideal adjuvant to enhance the efficacy of the BCG vaccine, specifically because of previous reports of lactoferrin enhancement of IL-12 production from macrophages infected with BCG. Different vaccination protocols were investigated for generation of host protective responses against MTB infection using lactoferrin admixed to the BCG vaccine. Resulting effects demonstrate that BCG/lactoferrin increased host protection against MTB infection by decreasing organ bacterial load and reducing lung histopathology; significant reduction in tissue CFUs and pathology were observed post-challenge compared to those seen with BCG alone. Addition of lactoferrin to the vaccine led to reduced pathological damage upon subsequent infection with virulent MTB, with positive results demonstrated when admixed in oil-based vehicle (incomplete Freund's adjuvant, IFA) or when given with BCG in saline. The observed post-challenge results paralleled increasing production of IFN-gamma and IL-6, but only limited changes to proinflammatory mediators TNF-alpha or IL-1beta from BCG-stimulated splenocytes. Overall, these studies indicate that lactoferrin is a useful and effective adjuvant to improve efficacy of the BCG vaccine, with potential to reduce related tissue damage and pulmonary histopathology.

Vaccination of cattle with Danish and Pasteur strains of Mycobacterium bovis BCG induce different levels of IFNgamma post-vaccination, but induce similar levels of protection against bovine tuberculosis

A number of studies have demonstrated significant protection of cattle against bovine tuberculosis following vaccination with the Pasteur strain of Mycobacterium bovis bacille Calmete-Guerin (BCG). However, it is unclear if other daughter strains of BCG are as effective, which is an important issue to resolve for a variety of regulatory compliance issues. This study compared the protective immune responses to bovine tuberculosis induced in cattle vaccinated with BCG Danish with those induced by BCG Pasteur. Groups of calves (n=10) were vaccinated with 10(6) colony forming units (CFU) BCG Pasteur prepared from a fresh liquid culture, 10(6) CFU BCG Danish prepared from a fresh liquid culture or 0.4 mg of reconstituted freeze-dried culture of BCG Danish. Another group (n=10) served as non-vaccinated controls. BCG Pasteur induced significantly higher and more sustained levels of bovine purified protein derivative (PPD)-specific gamma interferon (IFN-gamma) in whole-blood cultures following vaccination compared to either fresh culture BCG Danish or freeze-dried BCG Danish. Vaccination with a fresh culture of BCG Pasteur, fresh culture BCG Danish and freeze-dried BCG Danish gave a significant enhancement in three, four and three pathological and microbiological parameters of protection, respectively, compared to the non-vaccinated group. These results demonstrate the Danish strain of BCG is a viable alternative to BCG Pasteur for vaccination of cattle as both strains had similar efficacy and there was little difference between freshly cultured and freeze-dried formulation of BCG Danish. The results also show that post-vaccination antigen-specific IFN-gamma levels in whole blood is not always a reliable indicator of protection against a subsequent virulent challenge.