ENDEMIC AND OUTBREAK STRAIN GUIDANCE IN THE DEVELOPMENT OF AN ANAPLASMA MARGINALE VACCINE
Animal Diseases Research
2012 Annual Report
1a.Objectives (from AD-416):
Develop effective vaccines for anaplasmosis using an integrated genomic and proteomic approach to identify the essential immunogens within the immunoprotective Anaplasma marginale surface protein complex. This research will test whether intermolecular linkages between outer membrane proteins are required for induction of strong memory/effector CD4+ T lymphocyte, high titer IgG2 responses, and protective immunity. The identified immunogens will be tested for conservation among multiple A. marginale strains from endemic regions.
1b.Approach (from AD-416):
The structural requirements for induction of memory/effector CD4+ T lymphocytes, high titer IgG2, and protective immunity will be tested using the surface protein immunogen with either intact intermolecular linkages (cross-linked) or disrupted linkages (cross-linked then reduced). Mapping the B and T cell immunogenicity of protein partners within the cross-linked complex will define the minimal contributions required for protection. This is essential as the minimal immunogen will be more amenable to both standardization and development of low-cost vaccine. To ensure that the epitopes required for immunity are broadly represented among currently transmitted strains (rather than only “historical” strains isolated between 1950 and 1995), both outbreak and endemic strains will be isolated, genotyped, and the sequences of the relevant immunogenic proteins determined by targeted sequencing of their encoded genes. The strains will be isolated from endemic regions in United States and from regions in Mexico that export cattle to the U.S. The relevance of strain-specific polymorphisms to protective immunity and vaccine efficacy will be determined using CD4+ T lymphocytes and IgG2 antibody from immunized animals and immunologic differences confirmed by vaccine trials with heterologous strain challenge.
This work related to objective 3 of parent project by provision of data supporting vaccine development for anaplasmosis. Through a variety of genomic and proteomic approaches, the number of vaccine candidates have been narrowed to less than 20 in the last few years. However, several challenges remain, including the narrowing of the vaccine candidates to identify the minimum number of proteins that can induce protective immunity, and determine if one set of antigens will be protective against a wide variety of strains or if vaccines must be tailored based on the strains within a region. In order to address this second challenge, genes encoding several primary vaccine candidate proteins have been sequenced from endemic and outbreak strains from the U.S., Australia, Mexico, and Puerto Rico. All vaccine candidates to date are highly conserved among widely separate geographic regions. These findings suggest that one vaccine formulation may provide broad protection to a variety of strains. Information is exchanged relative to this work by regular face to face meetings and email.