Linear PADRE T helper epitope and carbohydrate B cell epitope conjugates induce specific high titer IgG antibody responses

Linear carbohydrate-peptide constructs based on the 13 amino acid nonnatura l pan DR epitope (PADRE) and carbohydrate B cell epitopes are demonstrated to be potent immunogens. These data support our belief that PADRE should be considered as an alternative to more complex carriers for use in prophylax is and therapeutic vaccines. Two model carbohydrate-PADRE glycoconjugates w ere used to demonstrate that PADRE could effectively provide T cell help fo r carbohydrate-specific Ab responses. Conjugates of PADRE covalently linked to the human milk oligosaccharide, lacto-N-fucopentose II or a dodecasacch aride derived from Salmonella typhimurium O-Ag induced high titer IgG Ab re sponses in mice, which were comparable to glycoconjugates employing human s erum albumin (HSA) as the carrier protein. Different adjuvants, in combinat ion with PADRE conjugates, allowed for the modulation of the isotype profil e with alum supporting an IgG1 profile; QS-21 an IgG2a, 2b profile, while a n alum/QS-21 mixture generated a balanced IgG1/IgG2b isotype profile. As de fined by binding to synthetic glycoconjugates, dodecasaccharide-specific Ab s exhibited fine specificity similar to protective polyclonal Ab responses previously reported for dodecasaccharide-protein conjugates, The same Abs b ound to intact S. typhimurium cells, suggesting that biologically relevant specificities were produced, The affinity of the dodecasaccharide-specific Abs was further shown to be comparable to that of a well-characterized, hig h affinity monoclonal anti-carbohydrate Ab recognizing the same epitope.