Veterinary tuberculosis vaccine development

Wildlife Immune Responses to Mycobacterium bovis and to Bacille of Calmette-Guerin

Bovine tuberculosis (bTB) is a zoonotic bacterial disease presenting public health, veterinary, and economic threats around the globe. Although cattle producers rely on regular testing and management practices to minimize domestic herd exposure, wildlife species around the world continue to be the main reservoirs for disease. Wildlife reservoirs for bTB include the Eurasian badger (Meles meles) in Great Britain and Ireland, the brushtail possum (Trichosurus vulpecula) in New Zealand, wild boar (Sus scrofa) in Spain, as well as white-tailed deer (Odocoileus virginianus) in the United States and red deer (Cervus elaphus) in Spain. Although all reservoir species share the ability to infect cattle, they differ in transmission capability, disease pathogenesis, diagnostic detection, and vaccination strategies. In this review, bTB interactions with these wildlife reservoirs are discussed, illustrating the need to address bTB disease in wildlife hosts to achieve eradication in domestic livestock.

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.

Neonatal and infant immunity for tuberculosis vaccine development: importance of age-matched animal models

Neonatal and infant immunity differs from that of adults in both the innate and adaptive arms, which are critical contributors to immune-mediated clearance of infection and memory responses elicited during vaccination. The tuberculosis (TB) research community has openly admitted to a vacuum of knowledge about neonatal and infant immune responses to Mycobacterium tuberculosis (Mtb) infection, especially in the functional and phenotypic attributes of memory T cell responses elicited by the only available vaccine for TB, the Bacillus Calmette-Guérin (BCG) vaccine. Although BCG vaccination has variable efficacy in preventing pulmonary TB during adolescence and adulthood, 80% of endemic TB countries still administer BCG at birth because it has a good safety profile and protects children from severe forms of TB. As such, new vaccines must work in conjunction with BCG at birth and, thus, it is essential to understand how BCG shapes the immune system during the first months of life. However, many aspects of the neonatal and infant immune response elicited by vaccination with BCG remain unknown, as only a handful of studies have followed BCG responses in infants. Furthermore, most animal models currently used to study TB vaccine candidates rely on adult-aged animals. This presents unique challenges when transitioning to human trials in neonates or infants. In this Review, we focus on vaccine development in the field of TB and compare the relative utility of animal models used thus far to study neonatal and infant immunity. We encourage the development of neonatal animal models for TB, especially the use of pigs.

Use of the Human Vaccine, Mycobacterium bovis Bacillus Calmette Guérin in Deer

The only vaccine ever approved for human tuberculosis was developed a century ago from an isolate of Mycobacterium bovis derived from a tuberculous cow. Initial safety and efficacy studies of an attenuated version of this isolate were conducted in cattle and other animals. In 1921 the first human, an infant, was orally dosed with this attenuated strain that came to be known as M. bovis bacillus Calmette-Guérin (BCG); named for Albert Calmette and Camille Guérin, the two French scientists that developed the strain. Since 1921, billions of people have been vaccinated with BCG making it the oldest, most widely used, and safest vaccine in use today. It is also the tuberculosis vaccine most studied for use in wildlife, including deer. While BCG vaccination of deer may not reliably prevent infection, it consistently decreases lesion severity, minimizing large, necrotic lesions, which often contain large numbers of bacilli. It is believed that decreased lesion severity correlates with decreased disease transmission; however, this hypothesis remains to be proven. Safety studies in white-tailed deer show BCG may persist in lymphoid tissues for up to 12 months; a factor to be considered in deer used for food. Beyond efficacy and safety, methods of vaccine delivery to free-ranging deer are also under investigation, both in the laboratory and in the field. The ideal delivery method is effective, efficient and safe for non-target species, including livestock. Ingestion of BCG by cattle is of special concern as such cattle may present as "false positives" using currently approved diagnostic methods, thus interfering with efforts by animal health agencies to monitor cattle for tuberculosis. An effective BCG vaccine for deer would be of value in regions where free-ranging deer represent a potential source of M. bovis for livestock. Such a vaccine would also be beneficial to farmed deer where M. bovis represents a serious threat to trade and productivity.

Tuberculosis vaccines and prevention of infection

SUMMARY

Tuberculosis (TB) is a leading cause of death worldwide despite the availability of effective chemotherapy for over 60 years. Although Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccination protects against active TB disease in some populations, its efficacy is suboptimal. Development of an effective TB vaccine is a top global priority that has been hampered by an incomplete understanding of protective immunity to TB. Thus far, preventing TB disease, rather than infection, has been the primary target for vaccine development. Several areas of research highlight the importance of including preinfection vaccines in the development pipeline. First, epidemiology and mathematical modeling studies indicate that a preinfection vaccine would have a high population-level impact for control of TB disease. Second, immunology studies support the rationale for targeting prevention of infection, with evidence that host responses may be more effective during acute infection than during chronic infection. Third, natural history studies indicate that resistance to TB infection occurs in a small percentage of the population. Fourth, case-control studies of BCG indicate that it may provide protection from infection. Fifth, prevention-of-infection trials would have smaller sample sizes and a shorter duration than disease prevention trials and would enable opportunities to search for correlates of immunity as well as serve as a criterion for selecting a vaccine product for testing in a larger TB disease prevention trial. Together, these points support expanding the focus of TB vaccine development efforts to include prevention of infection as a primary goal along with vaccines or other interventions that reduce the rate of transmission and reactivation.

Farmed deer: A veterinary model for chronic mycobacterial diseases that is accessible, appropriate and cost-effective

Although most studies in immunology have used inbred mice as the experimental model to study fundamental immune mechanisms they have been proven to be limited in their ability to chart complex functional immune pathways, such as are seen in outbred populations of humans or animals. Translation of the findings from inbred mouse studies into practical solutions in therapeutics or the clinic has been remarkably unproductive compared with many other areas of clinical practice in human and veterinary medicine. Access to an unlimited array of mouse strains and an increasing number of genetically modified strains continues to sustain their paramount position in immunology research. Since the mouse studies have provided little more than the dictionary and glossary of immunology, another approach will be required to write the classic exposition of functional immunity. Domestic animals such as ruminants and swine present worthwhile alternatives as models for immunological research into infectious diseases, which may be more informative and cost effective. The original constraint on large animal research through a lack of reagents has been superseded by new molecular technologies and robotics that allow research to progress from gene discovery to systems biology, seamlessly. The current review attempts to highlight how exotic animals such as deer can leverage off the knowledge of ruminant genomics to provide cost-effective models for research into complex, chronic infections. The unique opportunity they provide relates to their diversity and polymorphic genotypes and the integrity of their phenotype for a range of infectious diseases.

Oral vaccination of white-tailed deer (Odocoileus virginianus) with Mycobacterium bovis Bacillus Calmette-Guerin (BCG)

Wildlife reservoirs of Mycobacterium bovis represent serious obstacles to the eradication of tuberculosis from livestock, particularly cattle. In Michigan, USA tuberculous white-tailed deer transmit M. bovis to other deer and cattle. One approach in dealing with this wildlife reservoir is to vaccinate deer, thus interfering with the intraspecies and interspecies transmission cycles. Thirty-three white-tailed deer were assigned to one of two groups; oral vaccination with 1 × 10(8) colony-forming units of M. bovis BCG Danish (n = 17); and non-vaccinated (n = 16). One hundred eleven days after vaccination deer were infected intratonsilarly with 300 colony-forming units of virulent M. bovis. At examination, 150 days after challenge, BCG vaccinated deer had fewer gross and microscopic lesions, fewer tissues from which M. bovis could be isolated, and fewer late stage granulomas with extensive liquefactive necrosis. Fewer lesions, especially those of a highly necrotic nature should decrease the potential for dissemination of M. bovis within the host and transmission to other susceptible hosts.

Oral re-vaccination of Eurasian wild boar with Mycobacterium bovis BCG yields a strong protective response against challenge with a field strain

Background

Field vaccination trials with Mycobacterium bovis BCG, an attenuated mutant of M. bovis, are ongoing in Spain, where the Eurasian wild boar (Sus scrofa) is regarded as the main driver of animal tuberculosis (TB). The oral baiting strategy consists in deploying vaccine baits twice each summer, in order to gain access to a high proportion of wild boar piglets. The aim of this study was to assess the response of wild boar to re-vaccination with BCG and to subsequent challenge with an M. bovis field strain.

Results

BCG re-vaccinated wild boar showed reductions of 75.8% in lesion score and 66.9% in culture score, as compared to unvaccinated controls. Only one of nine vaccinated wild boar had a culture-confirmed lung infection, as compared to seven of eight controls. Serum antibody levels were highly variable and did not differ significantly between BCG re-vaccinated wild boar and controls. Gamma IFN levels differed significantly between BCG re-vaccinated wild boar and controls. The mRNA levels for IL-1b, C3 and MUT were significantly higher in vaccinated wild boar when compared to controls after vaccination and decreased after mycobacterial challenge.

Conclusions

Oral re-vaccination of wild boar with BCG yields a strong protective response against challenge with a field strain. Moreover, re-vaccination of wild boar with BCG is not counterproductive. These findings are relevant given that re-vaccination is likely to happen under real (field) conditions.

Oral vaccination against bovine tuberculosis with Mycobacterium bovis BCG

The use of a bacillus Calmette-Guerin (BCG)-based vaccine could represent a viable strategy for controlling bovine tuberculosis (TB), principally in those cases where a wildlife disease vector exists. This article focuses on recent progress in animal TB vaccinology, outlining that oral-route vaccination represents the most feasible means of distributing a vaccine to control disease in wildlife. Drawing on historical successes of previous wildlife vaccination programs, the article suggests how, and in what form, an oral-delivery BCG-based vaccine might become operational, considering the wide diversity of TB reservoir species and the inherent problems associated with field delivery of a live-attenuated microbial vaccine.

Factors influencing the protective efficacy of a BCG homologous prime-boost vaccination regime against tuberculosis

Tuberculosis due to Mycobacterium spp. continues to represent a major threat to human and animal health, prompting the search for effective vaccines. We have previously reported a sequential prime and boost homologous vaccination regime, using live avirulent M. bovis bacille Calmette-Guerin (BCG) strain 1173P2, that can provide significant protection to red deer (Cervus elaphus) against virulent M. bovis infection. Here, we have investigated the influence of varying the time-periods during and following the vaccination regime on the subsequent outcome of disease following post-vaccination pathogen challenge. Deer vaccinated using the standard regime of BCG-prime (week 0) and BCG-boost (week 8) followed by M. bovis challenge (week 14-16) were highly protected, showing significant reductions in the incidence of M. bovis infection and tuberculous lesions, as well as reduced pathogen burdens in sentinel lymphatic tissues. Decreasing the time-period between primary and secondary immunisations from 8 to 4 weeks had no significant impact on the protective efficacy afforded by BCG vaccination, while increasing this period to 43 weeks largely ablated protection. Increasing the time-period between secondary immunisation and M. bovis challenge from 6 to 26 or 52 weeks also had no significant impact on protection, suggesting that an appropriately timed BCG prime-boost vaccination regime can establish long-lasting protective immunological memory in deer. Finally, increasing the time-period between virulent M. bovis challenge and the subsequent post-mortem examination of disease outcome indicated that - once vaccinated by the standard prime-boost regime - deer remain refractory to disease if challenged and maintained for up to 52 weeks, suggesting that vaccinated animals harbouring low numbers of virulent M. bovis organisms do not succumb to disease activation over time. These findings are discussed in relation to concurrent measurements of in vivo and ex vivo immunological markers of disease and protection, as well as the wider implications of a standardised vaccine regimen for practical use in animal health.

A review of M. bovis BCG protection against TB in cattle and other animals species

Bovine tuberculosis (TB) causes severe economic losses in livestock due to low production, animal deaths and condemnation of carcasses. It is also an important constraint in international trade of animals and animal products. A scientific committee in Great Britain in 1997 concluded that the development of a cattle vaccine would be the best option for long-term control of TB. However, vaccination of cattle currently is not accepted because the vaccine interferes with the skin reaction to the tuberculin test in the field. Efficacy of M. bovis BCG in protecting bovine and other animal species against tuberculous infection has received much study. Vaccination of cattle prevents the spread of the disease in populations by reducing the number and size of the lesions, and the load of bacteria (rather than by preventing infection). We review the literature about the efficacy of BCG in protecting cattle and other animal species against infection with field strains of M. bovis and discusses its potential use in programs of TB control in high-prevalence populations.

Analysis of the antigen-specific IFN-gamma producing T-cell subsets in cattle experimentally infected with Mycobacterium bovis

Three 10 months old cattle were infected by the intratracheal route with 10(6)cfu of a field strain of Mycobacterium bovis. Blood samples were regularly collected for in vitro IFN-gamma production after antigenic stimulation. Peripheral blood cells of infected animals produced IFN-gamma in response to crude M. bovis antigens (live and heat-inactivated BCG and protein-purified derivative (PPD)) 3-4 weeks after infection. The ratio of the response to bovine PPD versus avian PPD indicated a specific sensitisation for M. bovis antigens. Three months post-infection (PI), animals were culled and M. bovis was cultured from tubercle lesions. At different time points, the frequency of specific M. bovis IFN-gamma producing CD4+, CD8+ and WC1+ T-cells in the peripheral blood was examined by flow cytometry. Two colour immunofluorescence staining of intracellular IFN-gamma and bovine cell surface molecules showed that both CD4+ and CD8+, but not WC1+, T-cells produced IFN-gamma following stimulation with PPD, live or killed BCG. In two animals analysed, the relative percentage of circulating IFN-gamma producing CD8+ cells decreased between week 5 and week 9 PI. The same evolution was not observed for IFN-gamma secreting CD4+ cells. Magnetic positive selection of T-cells from infected animals showed that CD4+ T-cells produced specific IFN-gamma only in the presence of antigen presenting cells (APCs). Positively selected CD8+ T-cells secreted IFN-gamma only in the presence of recombinant human IL-2 and APCs. In vitro depletion of the CD4+ T-cells, but not the depletion of CD8+ or WC1+ T-cells, resulted in abrogation of the specific IFN-gamma production showing the key role of this cell population for the specific IFN-gamma production.

Tuberculosis in deer: perceptions, problems and progress

Since the emergence of deer farming as an alternative farming enterprise over the past 30 years, there has been an increasing awareness of the potential threat posed by tuberculosis (TB) to domesticated deer. TB, caused by Mycobacterium bovis, has been found in deer in every country involved with deer farming. Different types of TB control policies, which vary from whole-herd depopulation to selective testing and slaughter of reactor animals, have been implemented. Extensive research has been carried out, incorporating modern microbiological and immunological concepts and advanced molecular methodologies, to find new solutions for the eradication of TB from domesticated deer. This work has resulted in valuable new insights into the aetiology, transmission, pathogenesis, diagnosis, prevention and heritability of resistance to M. bovis infection in ruminants. This knowledge has complemented the existing literature database on bovine and human TB and will provide new strategies for improved diagnosis, vaccination and selective breeding to control TB, which should be relevant for human, domestic livestock and wildlife populations.