Identification of Cross-Reactive Peptides Using Combinatorial Libraries Circumvents Tolerance against Her-2/neu-Immunodominant Epitope

Abstract

The majority of the currently defined tumor-associated Ags are often overexpressed products of normal cellular genes. Therefore, tolerance deletes high-affinity T cells directed against the TAAs, leaving only a low-affinity repertoire. We have demonstrated previously that the T cell repertoire against the immunodominant p773–782 A2.1-Her-2/neu-restricted peptide has low affinity in A2xneu mice (Her-2/neu mice crossed with A2.1/Kb mice), compared with A2xFVB mice (A2.1/Kb crossed with FVB-wild-type mice). Immunizations with this peptide have a minor impact in preventing tumor growth in A2xneu mice. Therefore, attempts to expand these responses may be of little clinical value. We hypothesized that if not all possible cross-reactive peptides (CPs) are naturally processed and presented, the possibility exists that T cells against these CPs persist in the repertoire and can be used to induce antitumor responses with higher avidity against native epitopes present on the tumor cells. We have used the positional scanning synthetic peptide combinatorial library methodology to screen the p773–782 T cell clone. The screening data identified potential amino acids that can be substituted in the primary sequences of the p773–782 peptide. The designed CPs induce CTL responses of higher affinity in A2xneu mice compared with the native p773–783 peptide. These CTLs recognize A2+-Her-2/neu+ tumors with high efficiency. Moreover, multiple immunizations with CPs significantly prolonged the survival of tumor-bearing A2xneu mice. These results have demonstrated that it was possible to circumvent tolerance with the identification of CPs and that these peptides could be of significant clinical value.

Erbb2 DNA Vaccine Combined with Regulatory T Cell Deletion Enhances Antibody Response and Reveals Latent Low-Avidity T Cells: Potential and Limits of Its Therapeutic Efficacy

“…In several mouse models, low-avidity T cells alone are enough to suppress the growth of the tumor expressing the Ag (40,41). Collaboration of the humoral and the cellular immune responses in rejection of rErbb2 tumors in transgenic mice has been documented (42).…”

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).…”

Rational optimization of tumor epitopes using in silico analysis‐assisted substitution of TCR contact residues

“…Similarly, several APL with TCR contact residues mutation were originally identified using single specific T-cell clone in vitro, and these APL were much more efficient at expanding and activating the WT specific T-cells pool besides the original T-cell clone [9,14]. These studies and www.eji-journal.eu our findings strongly suggest that a large T-cell repertoire exists in vivo, whose TCR displays common structural features and reactivity patterns to original T-cell clone.…”

“…Similarly, several APL with TCR contact residues mutation were originally identified using single specific T-cell clone in vitro, and these APL were much more efficient at expanding and activating the WT specific T-cells pool besides the original T-cell clone [9,14]. These studies and Mice were sacrificed 11 days after immunization, splenocytes isolated and cultured for 5 days with 10 mg/mL of autologous splenocytes loaded with either WT peptide in the presence/absence of an anti-HLA-A2 antibody derived from BB7.2 or an irrelevant peptide (HIV pol476-484 ).…”

“…To date, there is no convenient method to guide the modification of TCR contact residues of T-cell epitopes to change the affinity between pMHC and the TCR. In the past, only a few APL were identified by methods such as eluting naturally occurring mutant peptides from tumor cells, highthroughput screening of synthetic combinatorial peptides libraries, and random phage displayed peptides libraries; however, these methods are costly and time consuming [14,15]. It is thus necessary to develop a novel rational approach to guide such substitution.…”