Design of Agonistic Altered Peptides for the Robust Induction of CTL Directed towards H-2Db in Complex with the Melanoma-Associated Epitope gp100

Abstract

Immunogenicity of tumor-associated antigens (TAA) is often weak because many TAA are autoantigens for which the T-cell repertoire is sculpted by tolerance mechanisms. Substitutions at main anchor positions to increase the complementarity between the peptide and the MHC class I (MHC-I) binding cleft constitute a common procedure to improve binding capacity and immunogenicity of TAA. However, such alterations are tailored for each MHC-I allele and may recruit different CTL specificities through conformational changes in the targeted peptides. Comparative analysis of substituted melanomadifferentiation antigen gp100 in complex with H-2D b revealed that combined introduction of glycine and proline residues at the nonanchor positions 2 and 3, respectively, resulted in an agonistic altered peptide with dramatically enhanced binding affinity, stability, and immunogenicity of this TAA. Peptide vaccination using the p2Gp3P-altered peptide version of gp100 induced high frequencies of melanoma-specific CTL in the endogenous CD8 + repertoire. Crystal structure analysis of MHC/peptide complexes revealed that the conformation of the modified p2Gp3P-peptide was similar to the wild-type peptide, and indicated that this mimotope was stabilized through interactions between peptide residue p3P and the tyrosine residue Y159 that is conserved among most known MHC-I molecules throughout mammalian species. Our results may provide an alternative approach to enhance MHC stabilization capacity and immunogenicity of low-affinity peptides for induction of robust tumor-specific CTL. [Cancer Res 2009;69(19):7784-92]

Cytomegalovirus-Based Vaccine Expressing a Modified Tumor Antigen Induces Potent Tumor-Specific CD8+ T-cell Response and Protects Mice from Melanoma

“…(EGSRNQDWL) epitope, and thus is strikingly more immunogenic (37). Therefore, we constructed a recombinant MCMV vector expressing the original gp100 (MCMV-gp100) or gp100 with altered CD8 epitope (MCMV-gp100KGP).…”

Peptide transporter TAP mediates between competing antigen sources generating distinct surface MHC class I peptide repertoires

“…RMA-S cells were cultured for 2 days at 261C to accumulate peptide receptive MHC-I molecules on the cell surface [60]. Cells were washed in serum-free medium and incubated at 2 Â 10 5 cells/well with varying concentrations of peptides for 4 h at 371C.…”

“…Target cells were then incubated with CTLs in a 2:1 ratio with Brefeldin A to retain produced IFN-g intracellularly. Incubation was performed overnight at 371C and percentage of cytokine-producing CTLs was analyzed by flow cytometry as described [60]. …”

Cancer vaccines inducing antibody production: more pros than cons

“…We believe that vaccination with these mimotopes may overcome tolerance-cell mediated immune escape of the natural tumor antigen, as they are similar, but not identical to the original tumor antigen. In addition, mimotopes for T-cell epitopes of tumor antigens have been generated in the past [87][88][89][90]. In fact, the only clinical study so far was successfully performed with T-cell mimotopes in two human patients for cutaneous lymphoma [88].…”

“…Mimotope vaccines for epitope-specific antibody [52,53,60] or T-cell induction [87][88][89][90] need antigen density to achieve immunogenicity. Mimotopes can thus be applied either as multiple antigenic peptides (b) [66], displayed on phages when selected from phage display peptide libraries (c) [86], synthesized and chemically coupled to different carrier systems such as keyhole limpet hemocyanin (d) [60], presented on the surface of adeno-associated viruses (e) [82], as fusion constructs with immunoglobulin Fc-domains (f) [75] or in DNA form (g) [73].…”