Molecular Mechanisms for Carbohydrate Presentation to CD4+ T cells by MHCII Pathway

项目总结/文摘

Project Summary/Abstract Most pathogenic bacteria express surface carbohydrates called capsular polysaccharides (CPSs). CPSs are important vaccine candidates given that they are located on the outermost surface of bacteria and they have distinct structures. These two features make them easily accessible and distinctly recognizable by immune surveillance, therefore resulting in production of CPS specific antibodies by B cells. To induce a CPS specific adaptive immune response (i.e., T cell-mediated B cell response), CPSs are conjugated with carrier proteins, and the conjugation products are called glycoconjugate vaccines. Due to insufficient understanding of their immune activation mechanisms, current glycoconjugate vaccine strategies have reached saturation and are largely modifications of past empirical conjugation methods. The production of the current generation of glycoconjugate vaccines is based on trial and error and does not make use of specific scientific knowledge to maximize stimulation of critical immune cells (i.e., helper T cells) involved in producing protective IgG antibodies. A new perspective to carbohydrate-based vaccine research is much needed. With the potential of establishing a new paradigm, our previous discovery and preliminary data demonstrate that the mammalian CD4+ T cell repertoire contains a population of carbohydrate-specific T cells (i.e., Tcarbs) that recognize carbohydrate epitopes. Here, we propose to expand on our previous discovery and define the molecular mechanisms for Tcarb activation by carbohydrate epitopes from a model glycoconjugate vaccine. In Aim 1 of this proposal we will elucidate structural requirements for carbohydrate presentation by major histocompatibility complex class II (MHCII) proteins on the surface of antigen presenting cells (APCs) or as purified MHCII proteins via interaction studies. In Aim 2 we will structurally and functionally characterize T cell receptor (TCR) recognition of glycan epitopes by Tcarbs. We believe our proposed studies will create a new platform to develop knowledge-based glycoconjugate vaccines that are enriched for functional Tcarb epitopes. Using the discovery of Tcarb activation mechanisms and of structures of glycan epitopes, we can design and develop new-generation glycoconjugate vaccines that will elicit strong and long lasting immune response to protect from bacterial infections.