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.
Efforts toward vaccine development continue. The number of vaccine candidates has been narrowed to <10 and efforts to identify the specific candidate(s) that widely conserved and induce protective immunity are underway. It is becoming increasingly apparent that vaccine formulation plays a critical role in induction of a protective immune response, particularly in vaccines meant to protect against variant pathogens that establish persistent infection, such as malaria, HIV, and A. marginale. We determined that maintenance of the linkages between the molecules in an immunogen containing multiple proteins greatly improved the antibody response to immunization. Once the protective proteins are identified, this technique can be used to boost the immunogenicity of the vaccine. A manuscript describing these experiments is in preparation. The project is monitored by conference callsm electronic exchange of data, manuscripts and meeting with the prinicap investigator.