Irrespective of its target, a vaccine usually contains a mix of antigens and an adjuvant, that is required to stimulate the immune system. The exact molecular composition of existing vaccines is largely unknown, complicating the improvement of these vaccines. A promising strategy to generate novel vaccine modalities, having a well-defined and tunable mode of action, entails the conjugation of oligopeptide antigens to innate immunostimulatory agents, such as Toll-like receptor ligands. So far, several TLR agonists have been conjugated to antigenic peptides. Strikingly, the TLR4-ligand Lipid A, one of the most potent immunostimulating agens known to date, has not been explored in peptide-conjugate vaccine modalities . Based on the structure of lipid A, a new class of potent monosaccharide adjuvants has been discovered, the aminoalkyl glucosamine 4-phosphates (AGPs), in which the reducing end glucosamine of lipid A is substituted with a functionalized serine residue [1, 2]. CRX-527 is one of the most potent AGPs and was therefore selected to use as a built-in adjuvant for the generation of novel conjugate vaccine modalities.
Herein, we describe the design, synthesis and immunological evaluation of synthetic long peptide vaccine conjugates 1-4 composed of an antigenic MHC-I peptide (SIINFEKL) and CRX-527 as built-in adjuvant (Figure 1). For its generation we improved the syntheses of the potent TLR4 agonist CRX-527 and (R)-3-alkyloxytetradecanoic acids and developed an efficient conjugation and purification strategy. Immunological evaluation shows that these covalent conjugates effectively initiate dendritic cell maturation and activation through TLR4 leading to enhanced cross presentation. Initial in vivo evaluation of the first AGP-based conjugates has shown the best strategy for this type of conjugates.
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