High Peptide Dose Vaccination Promotes the Early Selection of Tumor Antigen-Specific CD8 T-Cells of Enhanced Functional Competence

Abstract

CD8 T-cell response efficiency critically depends on the TCR binding strength to peptide-MHC, i.e., the TCR binding avidity. A current challenge in onco-immunology lies in the evaluation of vaccine protocols selecting for tumor-specific T-cells of highest avidity, offering maximal immune protection against tumor cells and clinical benefit. Here, we investigated the impact of peptide and CpG/adjuvant doses on the quality of vaccine-induced CD8 T-cells in relation to binding avidity and functional responses in treated melanoma patients. Using TCR-pMHC binding avidity measurements combined to phenotype and functional assays, we performed a comprehensive study on representative tumor antigen-specific CD8 T-cell clones (n = 454) from seven patients vaccinated with different doses of Melan-A/ELA peptide (0.1 mg vs. 0.5 mg) and CpG-B adjuvant (1-1.3 mg vs. 2.6 mg). Vaccination with high peptide dose favored the early and strong in vivo expansion and differentiation of Melan-A-specific CD8 T-cells. Consistently, T-cell clones generated from those patients showed increased TCR binding avidity (i.e., slow off-rates and CD8 binding independency) readily after 4 monthly vaccine injections (4v). In contrast, the use of low peptide or high CpG-B doses required 8 monthly vaccine injections (8v) for the enrichment of anti-tumor T-cells with high TCR binding avidity and low CD8 binding dependency. Importantly, the CD8 binding-independent vaccineinduced CD8 T-cells displayed enhanced functional avidity, reaching a plateau of maximal function. Thus, T-cell functional potency following peptide/CpG/IFA vaccination may not be further improved beyond a certain TCR binding avidity limit. Our results also indicate that while high peptide dose vaccination induced the early selection of Melan-A-specific CD8 T-cells of increased functional competence, continued serial vaccinations also promoted such high-avidity T-cells. Overall, the systematic assessment of T-cell binding avidity may contribute to optimize vaccine design for improving clinical efficacy.

Altering Antigen Charge to Control Self-Assembly and Processing of Immune Signals During Cancer Vaccination

“…Many antigens expressed on tumors are also expressed on normal tissues; thus T cells specific to many tumor antigens are subject to thymic selection which deletes high avidity T-cells recognizing selfantigen (36). This leaves a repertoire of low avidity T cells that require high doses of antigen to become stimulated (37). This is corroborated by our findings that increasing the antigen concentration by altering Trp2:CpG by was found to correlate with improved T cell functionality.…”

Concurrent delivery of immune checkpoint blockade modulates T cell dynamics to enhance neoantigen vaccine-generated antitumor immunity

“…To investigate neoantigen vaccine induced T cell responses and anti-tumor effects in vivo, we first performed neoantigen vaccine treatment on murine colorectal tumor model MC38, which has well-defined MHC-I restricted immunogenic neoantigens 17 . According to the dose and schedule of recent neoantigen vaccine studies 11 , 17 , 18 , we choose the 9-mer mutated Adpgk peptide (ASMTNMELM) as the neoantigen and formulated it with two Toll-like receptor (TLR) agonists as adjuvants (Poly-ICLC for TLR-3 and CpG 1826 for TLR-9), both of which can activate dendritic cells and have been used in clinical trials 19 – 21 . Two doses of neoantigen Adpgk vaccine displayed moderate anti-tumor effect with delayed tumor growth ( Fig.…”

Use of a Novel Peptide Welding Technology Platform for the Development of B- and T-Cell Epitope-Based Vaccines

“…More recently, the use of multiple peptides and personalized approaches have shown very promising results in the treatment of melanoma [37,38]. The HLA-A2restricted, melanoma-associated ELA epitope is among the peptides that have been used in this context [39]. Conjugation of this peptide to a PWT scaffold in the present study allowed the in vitro priming of epitope-specific CD8 + T cells.…”