Altered Peptide Ligands Revisited: Vaccine Design through Chemically Modified HLA-A2–Restricted T Cell Epitopes

Abstract

Virus or tumor Ag–derived peptides that are displayed by MHC class I molecules are attractive starting points for vaccine development because they induce strong protective and therapeutic cytotoxic T cell responses. In thus study, we show that the MHC binding and consequent T cell reactivity against several HLA-A*02 restricted epitopes can be further improved through the incorporation of nonproteogenic amino acids at primary and secondary anchor positions. We screened more than 90 nonproteogenic, synthetic amino acids through a range of epitopes and tested more than 3000 chemically enhanced altered peptide ligands (CPLs) for binding affinity to HLA-A*0201. With this approach, we designed CPLs of viral epitopes, of melanoma-associated Ags, and of the minor histocompatibility Ag UTA2-1, which is currently being evaluated for its antileukemic activity in clinical dendritic cell vaccination trials. The crystal structure of one of the CPLs in complex with HLA-A*0201 revealed the molecular interactions likely responsible for improved binding. The best CPLs displayed enhanced affinity for MHC, increasing MHC stability and prolonging recognition by Ag-specific T cells and, most importantly, they induced accelerated expansion of antitumor T cell frequencies in vitro and in vivo as compared with the native epitope. Eventually, we were able to construct a toolbox of preferred nonproteogenic residues with which practically any given HLA-A*02 restricted epitope can be readily optimized. These CPLs could improve the therapeutic outcome of vaccination strategies or can be used for ex vivo enrichment and faster expansion of Ag-specific T cells for transfer into patients.

Definition of Proteasomal Peptide Splicing Rules for High-Efficiency Spliced Peptide Presentation by MHC Class I Molecules

“…To investigate the affinity of spliced N1.1 products for HLA-A2.1, binding curves of all products, which consisted of 14 residues or fewer and contained at least one anchor residue (L/M/I at P2 and/or V/L/I as C-terminal residue), were measured using an FP assay (26,31) (Fig. 2B).…”

DNA vaccines for prostate cancer

“…The first of these approaches has been to make epitope-specific changes encoded within the DNA (altered peptide ligand, APL) to modify MHC-I affinity as a means to improve antigen presentation (Hoppes et al, 2014; Lazoura et al, 2006; Ma & Kapp, 2001). We recently assessed the ability of an MHC-I-optimized DNA vaccine targeting SSX2 by making sequence-specific modifications to anchor residues of HLA-A2 epitopes to enhance their HLA-A2 binding.…”

Minor histocompatibility Ags: identification strategies, clinical results and translational perspectives

“…78 Moreover, with the introduction of synthetic modifications in the short mHag peptides, their immunogenicity can be further improved, leading to more potent mHag-specific responses in preclinical models. 79,80 On the other hand, there is a growing conviction that vaccination with long peptides would give rise to superior T-cell responses as these would lead to prolonged Ag presentation in comparison with short peptides. Furthermore, the long peptides may induce not only CD8+ CTLs but also CD4+ T-cell responses, which are considered to provide essential signals for licensing of CD8+ CTLs.…”