Superior protection elicited by live-attenuated vaccines in the murine model of paratuberculosis

Characterization of early immune responses elicited by live and inactivated vaccines against Johne's disease in goats

Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) is the causative agent of Johne's disease, a chronic debilitating condition affecting ruminants causing significant economic losses to the dairy industry. Available inactivated vaccines are not effective in controlling the disease and vaccinated animals can continue to infect newly born calves. Recently, we have shown that a live-attenuated vaccine candidate (pgsN) is protective in goats and calves following challenge with virulent strains of M. paratuberculosis. To decipher the dynamics of the immune responses elicited by both live-attenuated and inactivated vaccines, we analyzed key immunological parameters of goats immunized through different routes when a marker-less pgsN vaccine was used. Within a few weeks, the inactivated vaccine triggered the formation of granulomas both at the site of inoculation and in regional lymph nodes, that increased in size over time and persisted until the end of the experiment. In contrast, granulomas induced by the pgsN vaccine were small and subsided during the study. Interestingly, in this vaccine group, histology demonstrated an initial abundance of intra-histiocytic mycobacterial bacilli at the site of inoculation, with recruitment of very minimal T lymphocytes to poorly organized granulomas. Over time, granulomas became more organized, with recruitment of greater numbers of T and B lymphocytes, which coincided with a lack of mycobacteria. For the inactivated vaccine group, mycobacterial bacilli were identified extracellularly within the center of caseating granulomas, with relatively equal proportions of B- and T-lymphocytes maintained across both early and late times. Despite the differences in granuloma-specific lymphocyte recruitment, markers for cell-mediated immunity (e.g., IFN-γ release) were robust in both injected pgsN and inactivated vaccine groups. In contrast, the intranasal live-attenuated vaccine did not elicit any reaction at site of inoculation, nor cell-mediated immune responses. Finally, 80% of animals in the inactivated vaccine group significantly reacted to purified protein derivatives from M. bovis, while reactivity was detected in only 20% of animals receiving pgsN vaccine, suggesting a higher level of cross reactivity for bovine tuberculosis when inactivated vaccine is used. Overall, these results depict the cellular recruitment strategies driving immune responses elicited by both live-attenuated and inactivated vaccines that target Johne's disease.

Peripheral IFN-ɣ Production after Blood Stimulation with Different Mycobacterial Antigens in Goats Vaccinated against Paratuberculosis

Vaccination can be an efficient method for the control of paratuberculosis in ruminants. However, the official tuberculosis control tests cross-interfere with the animals vaccinated against paratuberculosis. In order to test and compare new antigens that could solve this problem, the production of interferon-gamma (IFN-γ) in peripheral blood at different post-vaccination days in experimental kids and adult goats, in field conditions, using the avian and bovine purified protein derivative (PPD), the johnin, two peptide cocktails of Mycobacterium bovis (PC-EC and PC-HP) and the antigens VK 055 and VK 067 of Mycobacterium avium subspecies paratuberculosis (Map) has been analyzed in vitro. The non-specific production of IFN-γ was observed after blood stimulation with the PC-EC and PC-HP cocktail in any sample from vaccinated animals, whereas it was detected when bovine PPD was used. These results support the possible use of these new Mycobacterium bovis antigens in the in the differentiation of animals vaccinated against paratuberculosis or infected with tuberculosis by improving the specificity of bovine PPD. In contrast, the two Map antigens tested in this study did not improve the sensitivity of johnin or avian PPD in the detection of vaccinated or Map-infected goats.

Reduced tissue colonization of Mycobacterium avium subsp. paratuberculosis in neonatal calves vaccinated with a cocktail of recombinant proteins

An increasing prevalence of paratuberculosis supports the need for new efficacious vaccines as an essential management tool. Two separate studies were performed in neonatal calves to evaluate the effectiveness of pooled recombinant Mycobacterium avium subsp. paratuberculosis (MAP) proteins (MAP1087, MAP1204, MAP1272c, MAP2077c) as a potential vaccine. In the first study vaccinated calves were immunized with 400 µg protein cocktail per dose, whereas the second study compared doses of 400 µg and 800 µg of protein cocktail, followed by challenge with live MAP for both vaccinated and nonvaccinated control calves 28 days post-vaccination. At the end of 12 months, tissue colonization with MAP was significantly reduced for the vaccinated calves compared to control animals. A higher dose of vaccine improved protection, with further reductions of MAP burden. Antigen-specific IFN-γ responses and serum antibody responses were similar regardless of vaccination, indicating exposure to MAP invoked conventional host immune responses. Host immunity differed due to vaccination, resulting in increased percentages of CD4+ T cells and B cells after stimulation of PBMCs with antigen. Interestingly, gene expression in PBMCs was similar for both control and vaccinated calves except for significant increases in IFN-γ, IL-12, and IL-17 expression observed in vaccinated calves. Vaccination with a cocktail of immunogenic recombinant MAP proteins was efficacious in reducing the level of infection and fecal shedding of neonatal calves and may be a potential tool for curtailing the spread of Johne's disease.

A Protective Vaccine against Johne's Disease in Cattle

Johne’s disease (JD) caused by Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) is a chronic infection characterized by the development of granulomatous enteritis in wild and domesticated ruminants. It is one of the most significant livestock diseases not only in the USA but also globally, accounting for USD 200–500 million losses annually for the USA alone with potential link to cases of Crohn’s disease in humans. Developing safe and protective vaccines is of a paramount importance for JD control in dairy cows. The current study evaluated the safety, immunity and protective efficacy of a novel live attenuated vaccine (LAV) candidate with and without an adjuvant in comparison to an inactivated vaccine. Results indicated that the LAV, irrespective of the adjuvant presence, induced robust T cell immune responses indicated by proinflammatory cytokine production such as IFN-γ, IFN-α, TNF-α and IL-17 as well as strong response to intradermal skin test against M. paratuberculosis antigens. Furthermore, the LAV was safe with minimal tissue pathology. Finally, calves vaccinated with adjuvanted LAV did not shed M. paratuberculosis post-challenge, a much-desired characteristic of an effective vaccine against JD. Together, this data suggests a strong potential of testing LAV in field trials to curb JD in dairy herds.

Preclinical Models of Nontuberculous Mycobacteria Infection for Early Drug Discovery and Vaccine Research

Nontuberculous mycobacteria (NTM) represent an increasingly prevalent etiology of soft tissue infections in animals and humans. NTM are widely distributed in the environment and while, for the most part, they behave as saprophytic organisms, in certain situations, they can be pathogenic, so much so that the incidence of NTM infections has surpassed that of Mycobacterium tuberculosis in developed countries. As a result, a growing body of the literature has focused attention on the critical role that drug susceptibility tests and infection models play in the design of appropriate therapeutic strategies against NTM diseases. This paper is an overview of the in vitro and in vivo models of NTM infection employed in the preclinical phase for early drug discovery and vaccine development. It summarizes alternative methods, not fully explored, for the characterization of anti-mycobacterial compounds.

Influence of vaccination against paratuberculosis on the diagnosis of caprine tuberculosis during official eradication programmes in Castilla y León (Spain)

The information generated from the official eradication programmes of caprine tuberculosis (TB) in Castilla y León, Spain, during 2018, has been used to assess the effect of vaccination against paratuberculosis (PTB) and the presence of this infection, on the single intradermal tuberculin (SIT) test results. Data from 121,665 goats belonging to 1936 different herds were analysed using generalized linear models. An epidemiological survey was conducted to know the herd immunization status against PTB and the date of last vaccination. All SIT test-positive animals were further investigated in order to confirm the diagnosis of TB, through bacterial culture, and PTB, by histopathological and qPCR analyses. SIT positivity was found in 39 (2.01%) herds and 507 (0.41%) goats. TB was confirmed by M. caprae or M. bovis isolation in 10 (0.51%) herds and 46 (0.038%) goats. PTB was diagnosed in 13 (33.33%) and 55 (10.84%) of the SIT test-positive herds and goats, respectively. Vaccination against PTB showed a significant influence on the results of the SIT test at herd level, with higher positivity detected among those herds vaccinated. However, this effect was not observed when the total number of animals was considered, where the highest positivity was found in unvaccinated goats. The time elapsed between vaccination and SIT test performance also influenced the results. The strongest effect was found when less than eight months elapsed between performing both activities, and to a lesser extent between 8 and 12 months. Conversely, no positive herds or animals were found when the time elapsed was higher than one year. No significant effect of the presence of PTB was observed. These findings demonstrate that the use of PTB vaccine does not result in false positives to a SIT test at individual level, provided that the time elapsed between the performance of both practices is higher than 12 months.

Inducing cellular immune responses with a marked Mycobacterium avium subsp. paratuberculosis strain in dairy calves

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Johne's disease, a chronic granulomatous enteritis with a high global prevalence in dairy cattle. This disease causes significant economic loss in the dairy industry and has been challenging to control, as current diagnostic assays are low in sensitivity and specificity, and previously developed vaccines do not prevent infection and face regulatory concerns due to interference with bovine tuberculosis diagnostics. To remediate this issue, positive and negative immune markers were created in a MAP strain as a step towards a vaccine capable of differentiating infected from vaccinated animals (DIVA). A gene coding for an immunogenic protein (MAP1693c) in the MAP genome was replaced with a library of epitope-tagged immunogenic genes (pepA) via a stable allelic exchange method. These markers were evaluated in a calf infection trial, where Holstein-Friesian dairy calves were inoculated at two weeks of age with either the marked strain or the parent strain, or remained uninfected controls. Cellular immune responses to the markers were measured using an interferon gamma release assay (IGRA). There were no MAP1693c marker-specific differences in cellular immune responses between infection groups. A scrambled version of the HA (human influenza hemagglutinin) epitope, but not the actual HA epitope, induced a significant IFN-γ response in marker-infected calves compared to WT-infected and uninfected groups at 4.5 months post-inoculation. This scrambled HA epitope thus holds potential as a diagnostic tool as part of a DIVA vaccine for Johne's disease.

A single dose polyanhydride-based nanovaccine against paratuberculosis infection

Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) causes Johne’s disease in ruminants and is characterized by chronic gastroenteritis leading to heavy economic losses to the dairy industry worldwide. The currently available vaccine (inactivated bacterin in oil base) is not effective in preventing pathogen shedding and is rarely used to control Johne’s disease in dairy herds. To develop a better vaccine that can prevent the spread of Johne’s disease, we utilized polyanhydride nanoparticles (PAN) to encapsulate mycobacterial antigens composed of whole cell lysate (PAN-Lysate) and culture filtrate (PAN-Cf) of M. paratuberculosis. These nanoparticle-based vaccines (i.e., nanovaccines) were well tolerated in mice causing no inflammatory lesions at the site of injection. Immunological assays demonstrated a substantial increase in the levels of antigen-specific T cell responses post-vaccination in the PAN-Cf vaccinated group as indicated by high percentages of triple cytokine (IFN-γ, IL-2, TNF-α) producing CD8⁺ T cells. Following challenge, animals vaccinated with PAN-Cf continued to produce significant levels of double (IFN-γ, TNF-α) and single cytokine (IFN-γ) secreting CD8⁺ T cells compared with animals vaccinated with an inactivated vaccine. A significant reduction in bacterial load was observed in multiple organs of animals vaccinated with PAN-Cf, which is a clear indication of protection. Overall, the use of polyanhydride nanovaccines resulted in development of protective and sustained immunity against Johne’s disease, an approach that could be applied to counter other intracellular pathogens.

Protection efficacy of Argentinian isolates of Mycobacterium avium subsp. paratuberculosis with different genotypes and virulence in a murine model

Paratuberculosis is a chronic disease caused by Mycobacterium avium subsp. paratuberculosis (Map). The disease causes economic losses and, therefore, it is imperative to follow proper control strategies, which should include an effective vaccine. Several strategies have assessed the virulence and immune response of Map strains that could be used as a vaccine. This study evaluates the degree of virulence, immune response, and protection of Argentinian strains of Map with different genotype in a murine model. Four local isolates (Cattle type) with different genotypes (analyzed by MIRU-VNTR and SSRs) were selected and evaluated in a virulence assay in BALB/c mice. This assay allowed us to differentiate virulent and low-virulence Map strains. The less virulent strains (1543/481 and A162) failed to induce a significant production of the proinflammatory cytokine IFNg, whereas the virulent strain 6611 established infection along with a proinflammatory immune response. On the other hand, the virulent strain 1347/498 was efficient in establishing a persistent infection, but failed to promote an important Th1 response compared with 6611 at the evaluated time. We selected the low-virulence strain 1543/498 as a live vaccine and the virulent strain 6611 as a live and inactivated vaccine in a protection assay in mice. Strain 1543/481 failed to protect the animals from challenge, whereas strain 6611, in its live and inactivated form, significantly reduced the CFUs count in the infected mice, although they had different immunological response profiles. The inactivated virulent strain 6611 is a potential vaccine candidate against paratuberculosis to be tested in cattle.

Knowledge gaps that hamper prevention and control of Mycobacterium avium subspecies paratuberculosis infection

In the last decades, many regional and country-wide control programmes for Johne's disease (JD) were developed due to associated economic losses, or because of a possible association with Crohn's disease. These control programmes were often not successful, partly because management protocols were not followed, including the introduction of infected replacement cattle, because tests to identify infected animals were unreliable, and uptake by farmers was not high enough because of a perceived low return on investment. In the absence of a cure or effective commercial vaccines, control of JD is currently primarily based on herd management strategies to avoid infection of cattle and restrict within-farm and farm-to-farm transmission. Although JD control programmes have been implemented in most developed countries, lessons learned from JD prevention and control programmes are underreported. Also, JD control programmes are typically evaluated in a limited number of herds and the duration of the study is less than 5 year, making it difficult to adequately assess the efficacy of control programmes. In this manuscript, we identify the most important gaps in knowledge hampering JD prevention and control programmes, including vaccination and diagnostics. Secondly, we discuss directions that research should take to address those knowledge gaps.

Superior Protection from Live-Attenuated Vaccines Directed against Johne's Disease

Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) is the etiological agent of Johne's disease in ruminants. Johne's disease is an important enteric infection causing large economic losses associated with infected herds. In an attempt to fight this infection, we created two novel live-attenuated vaccine candidates with mutations in sigH and lipN (pgsH and pgsN, respectively). Earlier reports in mice suggested these vaccines are promising candidates to fight Johne's disease in ruminants. In this study, we tested the performances of the two constructs as vaccine candidates using the goat model of Johne's disease. Both vaccines appeared to provide significant immunity to goats against challenge from wild-type M. paratuberculosis The pgsH and pgsN constructs showed a significant reduction in histopathological lesions and tissue colonization compared to nonvaccinated goats and those vaccinated with an inactivated vaccine. Unlike the inactivated vaccine, the pgsN construct was able to eliminate fecal shedding from challenged animals, a feature that is highly desirable to control Johne's disease in infected herds. Furthermore, strong initial cell-mediated immune responses were elicited in goats vaccinated with pgsN that were not demonstrated in other vaccine groups. Overall, the results indicate the potential use of live-attenuated vaccines to control intracellular pathogens, including M. paratuberculosis, and warrant further testing in cattle, the main target for Johne's disease control programs.

Vaccination sequence effects on immunological response and tissue bacterial burden in paratuberculosis infection in a rabbit model

Paratuberculosis (PTB), a chronic granulomatous enteritis produced by Mycobacterium avium subspecies paratuberculosis (MAP), is considered as one of the diseases with the highest economic impact in the ruminant industry. Vaccination against MAP is recommended during the first months after birth on the basis that protection would be conferred before the first contact with mycobacteria. However, little is known about the therapeutic effect of MAP vaccination in controlled experimental conditions. The current study was designed to evaluate the efficacy of vaccination before and after challenge with MAP in a rabbit infection model. The rabbits were divided into four groups: non-infected control (NIC, n = 4), infected control challenged with MAP (IC, n = 5), vaccinated and challenged 1 month after with MAP (VSI, n = 5) and challenged with MAP and vaccinated 2 months later (IVS, n = 5). The results from this study show a quick increase in IFN-γ release upon stimulation with bovine, avian and johnin PPD in animals vaccinated before MAP challenge. All vaccinated animals show an increased humoral response as seen by western blot and ELISA. The final bacteriology index (considering tissue culture and qPCR) shows that the IC group was the most affected. Vaccination after infection (IVS) produced the lowest bacteriology index showing significant differences with the IC group (p = 0.034). In conclusion, vaccination against MAP shows positive effects in a rabbit model. However, vaccination after infection shows a slightly stronger protective effect compared to vaccination before infection, suggesting a therapeutic effect. This feature could be applied to previously infected adult animals under field conditions.

Development of vaccines to Mycobacterium avium subsp. paratuberculosis infection

Johne's disease or paratuberculosis is a chronic debilitating disease in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). The disease causes significant economic losses in livestock industries worldwide. There are no effective control measures to eradicate the disease because there are no appropriate diagnostic methods to detect subclinically infected animals. Therefore, it is very difficult to control the disease using only test and cull strategies. Vaccination against paratuberculosis has been considered as an alternative strategy to control the disease when combined with management interventions. Understanding host-pathogen interactions is extremely important to development of vaccines. It has long been known that Th1-mediated cellular immune responses are play a crucial role in protection against MAP infection. However, recent studies suggested that innate immune responses are more closely related to protective effects than adaptive immunity. Based on this understanding, several attempts have been made to develop vaccines against paratuberculosis. A variety of ideas for designing novel vaccines have emerged, and the tests of the efficacy of these vaccines are conducted constantly. However, no effective vaccines are commercially available. In this study, studies of the development of vaccines for MAP were reviewed and summarized.