Improved Immunogenicity of an Immunodominant Epitope of the Her-2/neu Protooncogene by Alterations of MHC Contact Residues

Abstract

The HER-2/neu (HER-2) oncogene is expressed in normal epithelial surfaces at low levels and overexpressed in several types of tumors. The low immunogenicity against this self tumor Ag can be improved by developing epitopes with amino acid replacements in their sequences. In this study, three HER-2/neu.369 (HER-2.369) analogue peptides, produced by modifying both anchor positions by introducing L, V, or T at position 2 and V at the C terminus, were analyzed for their capacity to induce CTLs in vitro from human PBMC and in vivo in HLA-A2.1/Kb transgenic mice. One of the analogues (HER-2.369 V2V9) sensitized target cells for HER-2-specific recognition by human CTLs and induced specific CTLs in vitro at 100-fold lower concentrations than the HER-2.369 wild-type epitope. These CTLs were also able to recognize the wild-type epitope and HER-2-expressing tumors in an MHC-restricted manner. Furthermore, a 100-fold lower amount of the HER-2.369 V2V9 analogue compared with the wild-type epitope was required to induce CTLs in HLA-A2.1/Kb transgenic mice. However, the V2V9 analogue demonstrated only marginally better binding to the MHC class I A2 allele compared with wild type. To establish thermodynamic parameters, we developed radiolabeled F3*Y analogues from both the HER-2.369 epitope and the V2V9 analogue. Our results indicate that the high biological activity of the HER-2.369 V2V9 epitope is associated with a slower dissociation kinetic profile, resulting in an epitope with greater HLA-A2 stability.

CTLs Directed against HER2 Specifically Cross-React with HER3 and HER4

“…The efficacy of generating tumorlytic T cells against this or other HER2 epitopes may be also enhanced by using altered or cross-reactive peptides for stimulating T cells in vitro (45,(55)(56)(57).…”

Vaccination with Human HER-2/neu(435-443) CTL Peptide Induces Effective Antitumor Immunity against HER-2/neu-Expressing Tumor CellsIn vivo

“…Efforts to use unmodified forms of peptide immunogens to elicit antitumor responses in vivo have been largely unsuccessful, leading investigators to modify naturally occurring tumor antigens. Indeed, several peptide analogues capable of eliciting enhanced immunity to tumor-associated epitopes have been developed (18)(19)(20). In the present study, we have tested the capacity of hHER-2 (9 435 ), which differs from its murine homologue by one amino acid substitution at position 4, to function both as a protective and as a therapeutic vaccine in HHD mice inoculated with transplantable ALC tumor cells.…”

Identification of a Novel Immunogenic HLA-A*0201-Binding Epitope of HER-2/neu with Potent Antitumor Properties

“…Thus, the strong immunogenicity of HER-2(10 85 ) might be explained by its enhanced ability to remain bound to MHC class I molecules on APC for a longer period, allowing better presentation to CTLs. It is also possible that the increased immunogenicity of HER-2(10 85 ) might be related to increased functional binding activity for T cells (36). This might be the indirect result of the increased stability of the complexes (i.e., TCR-MHC-peptide), allowing more avid TCR contact.…”