CYCLIC V3-LOOP-RELATED HIV-1 CONJUGATE VACCINES - SYNTHESIS, CONFORMATION AND IMMUNOLOGICAL PROPERTIES

Branched undecapeptides with sequences related to the virus glycoprote in V3 domain sequences of the MN and IIIB variants of HIV-1 were synth esized and cyclized with a peptide (amide) closure to cyclic decapepti des. Two-dimensional NMR studies allowed protons for the MN variant-re lated cycle (L-697,250) to be assigned. Molecular modelling with dista nce geometry methods permitted a conformation to be identified which s howed good agreement with ROESY and 2D NMR study data. A molecular dyn amics simulation showed that the highly conserved loop tip sequence (G ly-Pro-Gly-Arg) was in a conventional beta-turn less than 50% of the t ime. For evaluation of immunogenicity and antibody characterization st udies, covalent carrier conjugates were prepared. 3-Maleimidopropionyl ation of the Nle amino group of the cyclic peptides gave an electrophi lic tether which captured a thiol group from a thiolated carrier prote in, OMPC (outer membrane protein complex of Neisseria meningitidis). T hrough the use of a novel co-conjugation procedure, soluble immunogen- carrier molecules were prepared which had suitable physical properties for use as a vaccine. These V3-loop-based vaccines could elicit neutr alizing antibody, but not consistently in all animals. Characterizatio n of sera showed that responses were broadly virus neutralizing.