VIDO research program area: Bacterial Vaccine Development
Overview: Despite numerous efforts, environmental and contagious types of bovine mastitis continue to be the most economically important infectious disease affecting dairy producers worldwide. In Canada alone, annual losses due to this disease amount to $300 million (Canadian Bovine Mastitis Research Network). The most prevalent infectious bacteria isolated from mammary gland secretions are Staphylococcus aureus and coagulase-negative Staphylococci. Currently our research focuses on two related surface proteins of S. aureus, GapB and GapC, since we and others have shown that GapC is effective as a vaccine against a variety of other pathogens.
Background:
Despite numerous efforts, bovine mastitis continues to be the most economically important infectious disease affecting dairy producers worldwide. In Canada alone, annual losses due to this disease amount to more than $350 million.
In the past, our research has focused on the characterization of surface proteins of the environmental pathogens S. uberis and S. dysgalactiae that might play a role in virulence and have potential for use as targets for vaccine development. Our efforts have been directed towards:
the lactoferrin-binding protein of S. uberis and S. dysgalactiae
the Mig Fc-receptor of S. dysgalactiae
the CAMP factor of S. agalactiae and S. uberis
and finally the plasmin receptor GapC of S. uberis and S. dysgalactiae.
We have used single and chimeric proteins in vaccine trials to demonstrate protection against experimental challenges with heterologous strains of S. uberis and S. dysgalactiae.
The most prevalent infectious bacteria isolated from mammary gland secretions are Staphylococcus aureus and coagulase-negative Staphylococci. The success rate of conventional control methods for these organisms is variable, emphasizing the need for alternative methods of preventing infections. Vaccination is currently used as one such measure with most vaccines composed of killed bacterial cells or bacterial products that elicit protection against a limited number of strains.
Currently our research focuses on two related surface proteins of S. aureus, GapB and GapC, since we and others have shown that GapC is effective as a vaccine against a wide variety of other pathogens.
It is evident that both systemic and local humoral (antibody) immune responses can contribute to mammary gland immune defences. There is much less evidence, however, that T cells--a type of immune cell--play a direct role in the prevention or clearance of mammary gland infections in ruminants. CD8 + T cells have been identified in ruminant mammary tissue but there is no direct evidence that these cells can respond to an infectious agent.
Historically, mastitis vaccination strategies have focused on the enhancement of humoral immunity. Vaccination strategies that can also enhance cell-mediated immunity in the mammary gland have not been pursued. Furthermore, vaccination strategies should also consider how immune defences change during the lactation cycle. This work will contribute significantly to our knowledge of basic immune mechanisms in the mammary gland and also to the development of strategies to enhance local immunity that can be easily adopted by dairy producers.
Objectives:
The main goal of this research is to optimize methods of stimulating local immunity in the mammary gland both quantitatively and qualitatively using a prototype S. aureus vaccine composed of the GapB and GapC antigens. In the short term, we will:
1. Compare the ability of formulations containing these antigens in combination with CpG oligonucleotides and metabolizable polymers to induce immune responses in cattle.
2. Determine the effect of the site of immunization on local immunity in the mammary gland using the optimal formulation.
3. Determine the importance of cell-mediated immunity in the mammary gland using DNA-based vaccines.
Progress:
The objective of this research program is to develop a comprehensive vaccine for bovine mastitis caused by contagious and environmental organisms. Antigens will be identified that can be used to reduce colonization of the gland and thereby reduce the incidence of mastitis.
For simplicity of vaccine delivery, we are determining whether antigens can be effectively delivered as protein chimeras. In a pilot trial we found that the S. uberis GapC protein and the CAMP/GapC chimera both protected immunized animals against a challenge with a heterologous strain of S. uberis. Likewise, immune responses to a S. aureus GapC/B chimera were not significantly different to the responses obtained with the individual antigens.
Proof of concept trial using GapC and CAMP3 chimeras. Results of the trial were not encouraging, likely due to the heterogeneity of the response by animals in the Agassiz facility. Testing of S. dysgalactiae GapC and Mig as targets for vaccines. The somatic cell counts from teat secretions were significantly decreased in both the GapC and Mig vaccinates indicating the presence of protective immune responses. Identification of surface-exposed S. aureus protein antigens. We have cloned and expressed the genes coding for GapB and GapC in Escherichia coli in order to produce the material needed to conduct vaccine trials. In mouse immunization experiments, we found that there were no differences between the immune responses to the individual proteins and the chimera. Plasmid DNA as a vaccine component. We found that DNA vaccination against S. aureus without a boost with the recombinant proteins was unable to elicit a significant humoral response and barely able to elicit a detectable cell-mediated response to the recombinant antigens, even when the antigens were expressed on the cell surface. However, we found that a boost with the recombinant proteins resulted in a significant humoral and cell-mediated immune response to the antigens. In addition, we find that DNA vaccination using a plasmid encoding the GapC/B chimera followed by a boost with the same protein, although successful, is slightly less effective than priming with plasmids encoding GapB or GapC followed by a boost with the individual antigens. Duration of immunity in dairy cows. We found that vaccination against S. aureus with the GapC/B chimera formulated with 30% VSA3 resulted in the highest level and duration of the immune response as measured by antibody titres in serum and milk of dairy cows. Optimization of the immune response. We also compared the immune response to the GapC/B chimera when used to immunize dry dairy cows either by the intradermal or subcutaneous route targeting either the parotid or the supramammary lymph nodes. We found that there were no significant differences in the antibody titres to GapC/B regardless of the immunization method and the lymphatic node targeted.
Project Leader:
