Enhanced immunogenicity of a T cell immunogenic peptide by modifications of its N and C termini

Abstract

The modification of the terminal ionizable charges of an immunogenic peptide, HEL (46-61), was found to greatly increase the immunogenicity of the peptide. The modified peptide had 100- to 1000-fold enhanced activity in both in vitro and in vivo T cell assays. The mechanism of the enhancement was investigated by determining the binding affinities to I-Ak as well as circular dichroism (CD) studies. The native and enhanced peptides had indistinguishable binding affinities, as well as similar kinetics. The CD studies revealed that in aqueous solution, neither peptide had any detectable helicity; however, the addition of trifluoroethanol did result in significant helicity; with the two peptides being indistinguishable. These same modifications were also shown to enhance other immunogenic peptides if they contained a basic carboxy-terminal amino acid residue. Thus, by modifying the termini of T cell epitopes, their immunogenicity can be dramatically increased, but the molecular basis for this enhancement is still unclear.

Modification of the Amino Terminus of a Class II Epitope Confers Resistance to Degradation by CD13 on Dendritic Cells and Enhances Presentation to T Cells

“…However, more simply, as shown in the current study, modification of the amino terminus by acetylation can interfere with enzymatic cleavage and selectively enhance class II MHC presentation of peptides by dendritic cells more than 10-fold. This is consistent with an earlier report by Allen et al (44) showing that modifications of the amino and carboxy termini of peptides which bind to class II MHC greatly enhanced their antigenicity both in vitro and in vivo. In that study, no mechanism to explain the enhanced presentation was offered.…”

Identification of two distinct properties of class II major histocompatibility complex-associated peptides.

“…This was done in an initial attempt to establish some structural features responsible for producing the stable peptide-MHC complex. Previously, our laboratory had studied peptides which instead of threonine at position 51 contained glutamic acid or lysine (23). The addition of glutamic acid but not lysine had markedly increased the immunogenicity of the core peptide 52-61 (23), a point of importance in the context of the present results.…”

“…Previously, our laboratory had studied peptides which instead of threonine at position 51 contained glutamic acid or lysine (23). The addition of glutamic acid but not lysine had markedly increased the immunogenicity of the core peptide 52-61 (23), a point of importance in the context of the present results. Here, we found that the HEL peptide 51-61 (T-52-61) resulted in a heterogeneous pattern, with most complexes being stable but a minority dissociating (Fig.…”

“…The last column shows the relative inhibitory capacity of each peptide. *The inhibitory capacity was reported before (23 Identical results were obtained by using a protocol in which the labeled peptides were fed directly to APCs and then the I-Ak molecules were isolated. The core peptide 52-61 bound to I-Ak but dissociated in SDS/PAGE (Fig.…”

Cellular mechanisms of antigen processing and the function of class I and II major histocompatibility complex molecules.

“…Peptides bind to MHC-11 molecules in a saturable and homogeneous binding reaction with binding affinities in the micromolar range (Babbitt et aL, 1985). The binding is characterized by a slow on-rate and by a very slow rate of dissociation (Buus et al, 1986;Allen et al, 1989;SadeghNasseri and McConnell, 1989;Roof et al, 1990). Some peptides, once bound, will practically not dissociate unless the MHC-11 molecules are drastically denatured.…”