IMMUNOGENICITY OF T-EPITOPE-CONTAINING CYCLIC-PEPTIDES - INCREASING NEUTRALIZING ANTIBODY-RESPONSES BY INTRODUCING FINE CHEMICAL-CHANGES

We showed previously that the disulfide-containing T peptide 24-41C fr om a highly structured snake toxin elicits, in a free state, Abs that neutralize the toxin, and only a turn structure commonly exists in 24- 41C and the corresponding toxin region. To tentatively increase the ne utralizing capacity of antipeptide Abs, we 1) replaced Gly-40 by an am inoisobutyric moiety (24-41Aib), 2) substituted the half cystines 24 a nd 41 by penicillamine moieties (24-41Pen), and 3) introduced an amide bond between the epsilon NH2 of Lys-27 and the gamma-COOH of Glu-38 ( 24-41K-E). A solution ELISA made with antitoxin Abs revealed that 24-4 1Pen is more antigenic than 24-41Aib and 24-41C, which are more antige nic than 24-41K-E, suggesting that the conformation of 24-41Pen is mos t closely related to the corresponding region in the native toxin. The peptides 24-41Pen, 24-41Aib, and 24-41C stimulate T cells from BALB/c mice, whereas 24-41K-E has lost this property and thereby fails to el icit Abs. Finally, anti-24-41Pen Abs are more potent at neutralizing t he native toxin than anti-24-41C Abs, which are more patent than anti- 24-41Aib Abs. The efficacy of anti-24-41Pen Abs was similar to that of a toxin specific mAb. Therefore, introduction of appropriate constrai nts makes it possible to improve the neutralizing Ab response raised b y a synthetic peptide. Such observations should be of interest for the design of efficient synthetic vaccines.