Novel modifications to the C-terminus of LTB that facilitate site-directed chemical coupling of antigens and the development of LTB as a carrier for mucosal vaccines

To facilitate site-directed chemical coupling of antigens to the heat labile enterotoxin B subunit of Escherichia coli (LTB), a series of genetically modified fusion proteins of LTB were constructed. The LTB fusion proteins had modified versions of a short (14 amino acid) spacer epitope called the Pk tag attached at their C termini. The LTB-Pk.cys mutants differed from each other in the position of a single cysteine residue within the Pk tag. The presence of a cysteine residue at any position within the Pk spacer tag did not prevent the LTB-Pk.cys proteins from forming pentamers or binding to GM1 gangliosides, but the position of the cysteine had variable impact on the yield of the fusion proteins. Following site-directed chemical coupling of antigens to the cysteine residue within the Pk tag, the LTB-antigen conjugates retained their ability to bind GM1 on the surface of eukaryotic cells. Intranasal immunisation of mice with an experimental antigen (HRP) chemically linked to LTB-Pk.cys induced high levels of anti-HRP antibodies that could be detected in the serum, saliva and nasal and lung washes. No antibody responses to HRP were detected when HRP was co-administered with, but not linked to, LTB-Pk.cys. (C) 1999 Elsevier Science Ltd. All rights reserved.