Current glycoconjugate vaccines are synthesized empirically, without scientifically based optimization of antigen presentation. We propose to establish a new generation of knowledge- based, target-specific, structurally designed, highly immunogenic and protective vaccines that can be produced at much lower cost, allowing for much wider use on a global scale. We anticipate that novel insights obtained from our proposed mechanistic studies on antigen processing and presentation, T cell responses, and glycoconjugate vaccine design will redefine the mechanisms by which vaccine design influences T cell activation, which in turn provides B cell help. As the model antigens for our studies, we will use group B streptococcal glycoconjugate vaccines. Our preliminary data show that, contrary to the traditional paradigm, complex glycoconjugate molecules are not handled by the endosomal compartment as previously believed. Consequently, the empirical construction of glycoconjugate vaccines, as presently undertaken by vaccine manufacturers and designers, fails to optimize immunogenic potential. More specifically, current glycoconjugate vaccines are designed without consideration of which epitopes should be presented to T cells for optimal immune responses. Our data show that glycopeptide epitopes of glycoconjugate vaccines, rather than peptide epitopes alone, are actually presented to T cells in the context of major histocompatibility complex class II (MHCII) on the surface of antigen-presenting cells (APCs). In the proposed studies, we will determine whether CD4+ T cells can differentiate glycopeptides from peptides and whether glycopeptide epitopes can induce IgM-to-IgG switching. With this information in hand, we can synthetically mimic optimal epitopes at optimal frequency and density, enhancing vaccine immunogenicity and protection through efficient processing and presentation by APCs and highly specific T cell recognition. On the basis of our data, we believe that, in terms of T cell help, these immunogenic epitopes are glycopeptides. By optimizing the use of the most immunogenic components, we will produce vaccines with greater immunogenicity; longer-lived immunity; lower dosage requirements (and therefore greater safety); and, in all probability, greater immunogenicity and protective capacity in elderly individuals and in children.