{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T14:24:06Z","timestamp":1791901446926,"version":"4.3.4"},"reference-count":37,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,4,27]],"date-time":"2026-04-27T00:00:00Z","timestamp":1777248000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"<jats:p>T-cell responses play a critical role in the control of SARS-CoV-2 infections. Here, we examined the T-cell response to a conserved, immunodominant HLA-A*24:02-restricted SARS-CoV-2 spike protein epitope, QI9\/A24 (QYIKWPWYI; residues 1208\u20131216). TCR repertoire analysis revealed that QI9\/A24-specific T cells are highly diverse, with 219 clonotypes isolated and 169 \u03b1\u03b2 TCR pairs identified in six donors. To further characterize this response, we evaluated T-cell recognition of alanine-substituted and homologous coronavirus-derived peptides, using a TCR reconstitution system, and found that QI9\/A24 TCRs tolerated numerous substitutions at the N-terminus and position 3. During peptide synthesis, we unexpectedly discovered that an N-terminally pyroglutamylated QI9\/A24 peptide (pyrQI9) exhibited increased protease resistance, compared with the unmodified peptide. Further analysis revealed that the pyrQI9 peptide was recognized with higher sensitivity than the wild-type sequence and efficiently induced antigen-specific T-cell responses at low concentrations in both vaccinated and convalescent HLA-A*24:02-positive individuals. Moreover, immunization of HLA-A24 transgenic mice with the pyrQI9 peptide elicited antigen-specific T-cell responses more efficiently than the wild-type peptide and conferred superior T-cell\u2013mediated protection. Together, our findings suggest that subtle modifications of antigenic peptides at a tolerable site in the N-terminus with pyroglutamate can enhance T-cell immunity in SARS-CoV-2 infection, providing critical insights into the design of next-generation T-cell-based vaccines against viral infections.<\/jats:p>","DOI":"10.3389\/fimmu.2026.1758642","type":"journal-article","created":{"date-parts":[[2026,4,27]],"date-time":"2026-04-27T05:27:10Z","timestamp":1777267630000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["N-terminal pyroglutamylation of an HLA-A24-restricted immunodominant epitope enhances SARS-CoV-2-specific T-cell responses"],"prefix":"10.3389","volume":"17","author":[{"given":"Yoshiki","family":"Aritsu","sequence":"first","affiliation":[{"name":"Division of Infection and Immunity, Joint Research Center for Human Retrovirus Infection, Kumamoto University","place":["Kumamoto, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Masahiro","family":"Kitabatake","sequence":"additional","affiliation":[{"name":"Department of Immunology, Nara Medical University","place":["Nara, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amiri","family":"Kurose","sequence":"additional","affiliation":[{"name":"Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University","place":["Osaka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hiroshi","family":"Hamana","sequence":"additional","affiliation":[{"name":"Department of Immunology, Faculty of Medicine, Academic Assembly, University of Toyama","place":["Toyama, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takeshi","family":"Nakama","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Joint Research Center for Human Retrovirus Infection, Kumamoto University","place":["Kumamoto, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kyoko","family":"Yamada","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Joint Research Center for Human Retrovirus Infection, Kumamoto University","place":["Kumamoto, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ryutaro","family":"Furukawa","sequence":"additional","affiliation":[{"name":"Department of Immunology, Nara Medical University","place":["Nara, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Noriko","family":"Ouji-Sageshima","sequence":"additional","affiliation":[{"name":"Department of Immunology, Nara Medical University","place":["Nara, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Atsushi","family":"Hara","sequence":"additional","affiliation":[{"name":"Department of Immunology, Nara Medical University","place":["Nara, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kaito","family":"Yasuike","sequence":"additional","affiliation":[{"name":"Department of Immunology, Nara Medical University","place":["Nara, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Suzu","family":"Itami","sequence":"additional","affiliation":[{"name":"Graduate School of Science and Engineering, Kindai University","place":["Osaka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Huanyu","family":"Li","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Joint Research Center for Human Retrovirus Infection, Kumamoto University","place":["Kumamoto, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keiko","family":"Udaka","sequence":"additional","affiliation":[{"name":"Department of Immunology, Kochi University","place":["Kochi, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hiroyuki","family":"Kishi","sequence":"additional","affiliation":[{"name":"Department of Immunology, Faculty of Medicine, Academic Assembly, University of Toyama","place":["Toyama, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takamasa","family":"Ueno","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Joint Research Center for Human Retrovirus Infection, Kumamoto University","place":["Kumamoto, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"So","family":"Nakagawa","sequence":"additional","affiliation":[{"name":"Department of Molecular Life Science, Tokai University School of Medicine","place":["Kanagawa, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Toshihiro","family":"Ito","sequence":"additional","affiliation":[{"name":"Department of Immunology, Nara Medical University","place":["Nara, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Norihito","family":"Kawashita","sequence":"additional","affiliation":[{"name":"Department of Energy and Materials, Faculty of Science and Engineering, Kindai University","place":["Osaka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mizuki","family":"Kitamatsu","sequence":"additional","affiliation":[{"name":"Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University","place":["Osaka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chihiro","family":"Motozono","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Joint Research Center for Human Retrovirus Infection, Kumamoto University","place":["Kumamoto, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,4,27]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.1038\/nri3084","article-title":"Towards a systems understanding of MHC class I and MHC class II antigen presentation","volume":"11","author":"Neefjes","year":"2011","journal-title":"Nat Rev Immunol"},{"key":"B2","doi-asserted-by":"publisher","first-page":"996","DOI":"10.1016\/j.cell.2020.09.038","article-title":"Antigen-specific adaptive immunity to SARS-CoV-2 in acute COVID-19 and associations with age and disease severity","volume":"183","author":"Rydyznski Moderbacher","year":"2020","journal-title":"Cell"},{"key":"B3","doi-asserted-by":"publisher","DOI":"10.1016\/j.celrep.2021.108728","article-title":"Early induction of functional SARS-CoV-2-specific T cells associates with rapid viral clearance and mild disease in COVID-19 patients","volume":"34","author":"Tan","year":"2021","journal-title":"Cell Rep"},{"key":"B4","doi-asserted-by":"publisher","DOI":"10.1038\/s41586-023-06331-x","article-title":"A common allele of HLA is associated with asymptomatic SARS-CoV-2 infection","volume":"620","author":"Augusto","year":"2023","journal-title":"Nature"},{"key":"B5","doi-asserted-by":"publisher","DOI":"10.1016\/j.immuni.2021.04.009","article-title":"CD8(+) T cells specific for an immunodominant SARS-CoV-2 nucleocapsid epitope display high naive precursor frequency and TCR promiscuity","volume":"54","author":"Nguyen","year":"2021","journal-title":"Immunity"},{"key":"B6","doi-asserted-by":"publisher","DOI":"10.1016\/j.cell.2020.05.015","article-title":"Targets of T cell responses to SARS-CoV-2 coronavirus in humans with COVID-19 disease and unexposed individuals","volume":"181","author":"Grifoni","year":"2020","journal-title":"Cell"},{"key":"B7","doi-asserted-by":"publisher","DOI":"10.1093\/nar\/gkz1029","article-title":"Allele frequency net database (AFND) 2020 update: Gold-standard data classification, open access genotype data and new query tools","volume":"48","author":"Gonzalez-Galarza","year":"2020","journal-title":"Nucleic Acids Res"},{"key":"B8","doi-asserted-by":"publisher","DOI":"10.1016\/j.chom.2021.06.006","article-title":"SARS-CoV-2 spike L452R variant evades cellular immunity and increases infectivity","volume":"29","author":"Motozono","year":"2021","journal-title":"Cell Host Microbe"},{"key":"B9","doi-asserted-by":"publisher","first-page":"5440","DOI":"10.1038\/s41467-022-33068-4","article-title":"The SARS-CoV-2 Omicron BA.1 spike G446S mutation potentiates antiviral T-cell recognition","volume":"13","author":"Motozono","year":"2022","journal-title":"Nat Commun"},{"key":"B10","doi-asserted-by":"publisher","first-page":"50","DOI":"10.1186\/s41232-022-00239-1","article-title":"Association of cellular immunity with severity of COVID-19 from the perspective of antigen-specific memory T cell responses and cross-reactivity","volume":"42","author":"Fujii","year":"2022","journal-title":"Inflammation Regener"},{"key":"B11","doi-asserted-by":"publisher","first-page":"990","DOI":"10.1111\/imcb.12482","article-title":"SARS-CoV-2-specific CD8(+) T-cell responses and TCR signatures in the context of a prominent HLA-A*24:02 allomorph","volume":"99","author":"Rowntree","year":"2021","journal-title":"Immunol Cell Biol"},{"key":"B12","doi-asserted-by":"publisher","first-page":"5251","DOI":"10.1038\/s41467-022-32989-4","article-title":"Long-term memory CD8(+) T cells specific for SARS-CoV-2 in individuals who received the BNT162b2 mRNA vaccine","volume":"13","author":"Kuse","year":"2022","journal-title":"Nat Commun"},{"key":"B13","doi-asserted-by":"publisher","DOI":"10.1172\/JCI145476","article-title":"SARS-CoV-2-specific CD8+ T cell responses in convalescent COVID-19 individuals","volume":"131","author":"Kared","year":"2021","journal-title":"J Clin Invest"},{"key":"B14","doi-asserted-by":"publisher","DOI":"10.1038\/s41590-024-02051-0","article-title":"T cell immune evasion by SARS-CoV-2 JN.1 escapees targeting two cytotoxic T cell epitope hotspots","volume":"26","author":"Tian","year":"2025","journal-title":"Nat Immunol"},{"key":"B15","doi-asserted-by":"publisher","first-page":"1365","DOI":"10.1038\/s42003-021-02885-6","article-title":"Identification of TCR repertoires in functionally competent cytotoxic T cells cross-reactive to SARS-CoV-2","volume":"4","author":"Shimizu","year":"2021","journal-title":"Commun Biol"},{"key":"B16","doi-asserted-by":"publisher","DOI":"10.1016\/j.celrep.2021.110218","article-title":"The SARS-CoV-2 Lambda variant exhibits enhanced infectivity and immune resistance","volume":"38","author":"Kimura","year":"2022","journal-title":"Cell Rep"},{"key":"B17","doi-asserted-by":"publisher","DOI":"10.1016\/j.immuni.2023.04.010","article-title":"Recruitment of epitope-specific T cell clones with a low-avidity threshold supports efficacy against mutational escape upon re-infection","volume":"56","author":"Straub","year":"2023","journal-title":"Immunity"},{"key":"B18","doi-asserted-by":"publisher","first-page":"393","DOI":"10.1007\/s00251-005-0004-2","article-title":"Classification of A1- and A24-supertype molecules by analysis of their MHC-peptide binding repertoires","volume":"57","author":"Sidney","year":"2005","journal-title":"Immunogenetics"},{"key":"B19","doi-asserted-by":"publisher","DOI":"10.1097\/00002371-200405000-00001","article-title":"Preventing the spontaneous modification of an HLA-A2-restricted peptide at an N-terminal glutamine or an internal cysteine residue enhances peptide antigenicity","volume":"27","author":"Thompson","year":"2004","journal-title":"J Immunother"},{"key":"B20","doi-asserted-by":"publisher","DOI":"10.1016\/j.molimm.2003.10.015","article-title":"Stabilization of peptide Guinea pig myelin basic protein 72\u201385 by N-terminal acetylation-implications for immunological studies","volume":"40","author":"de Haan","year":"2004","journal-title":"Mol Immunol"},{"key":"B21","doi-asserted-by":"publisher","DOI":"10.1172\/jci91512","article-title":"Peptide mimic for influenza vaccination using nonnatural combinatorial chemistry","volume":"128","author":"Miles","year":"2018","journal-title":"J Clin Invest"},{"key":"B22","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0407677102","article-title":"Partial D-amino acid substitution: Improved enzymatic stability and preserved Ab recognition of a MUC2 epitope peptide","volume":"102","author":"Tugyi","year":"2005","journal-title":"Proc Natl Acad Sci USA"},{"key":"B23","doi-asserted-by":"publisher","DOI":"10.4049\/jimmunol.175.6.3810","article-title":"T cell determinants incorporating beta-amino acid residues are protease resistant and remain immunogenic in vivo","volume":"175","author":"Webb","year":"2005","journal-title":"J Immunol"},{"key":"B24","doi-asserted-by":"publisher","DOI":"10.1126\/sciadv.abh3827","article-title":"A lethal mouse model for evaluating vaccine-associated enhanced respiratory disease during SARS-CoV-2 infection","volume":"8","author":"Iwata-Yoshikawa","year":"2022","journal-title":"Sci Adv"},{"key":"B25","doi-asserted-by":"publisher","DOI":"10.4049\/jimmunol.166.5.3028","article-title":"Potent cytolytic response by a CD8+ CTL clone to multiple peptides from the same protein in association with an allogeneic class I MHC molecule","volume":"166","author":"Kageyama","year":"2001","journal-title":"J Immunol"},{"key":"B26","doi-asserted-by":"publisher","DOI":"10.1038\/nri3279","article-title":"Why must T cells be cross-reactive","volume":"12","author":"Sewell","year":"2012","journal-title":"Nat Rev Immunol"},{"key":"B27","doi-asserted-by":"publisher","first-page":"169","DOI":"10.1146\/annurev-immunol-032414-112334","article-title":"T cell antigen receptor recognition of antigen-presenting molecules","volume":"33","author":"Rossjohn","year":"2015","journal-title":"Annu Rev Immunol"},{"key":"B28","doi-asserted-by":"publisher","DOI":"10.1002\/eji.200425369","article-title":"Mechanism of modulation of T cell responses by N-palmitoylated peptides","volume":"34","author":"Bueno","year":"2004","journal-title":"Eur J Immunol"},{"key":"B29","doi-asserted-by":"publisher","DOI":"10.1021\/acs.jmedchem.4c02247","article-title":"Targeting QPCTL: An emerging therapeutic opportunity","volume":"68","author":"Yu","year":"2025","journal-title":"J Med Chem"},{"key":"B30","doi-asserted-by":"publisher","DOI":"10.1016\/s0021-9258(18)47446-7","article-title":"An enzyme(s) that converts glutaminyl-peptides into pyroglutamyl-peptides. Presence in pituitary, brain, adrenal medulla, and lymphocytes","volume":"262","author":"Busby","year":"1987","journal-title":"J Biol Chem"},{"key":"B31","doi-asserted-by":"publisher","DOI":"10.4049\/jimmunol.1300483","article-title":"HLA-A*01:03, HLA-A*24:02, HLA-B*08:01, HLA-B*27:05, HLA-B*35:01, HLA-B*44:02, and HLA-C*07:01 monochain transgenic\/H-2 class I null mice: Novel versatile preclinical models of human T cell responses","volume":"191","author":"Boucherma","year":"2013","journal-title":"J Immunol"},{"key":"B32","doi-asserted-by":"publisher","first-page":"197","DOI":"10.1007\/s00251-006-0185-3","article-title":"Identification of CTL epitopes in hepatitis C virus by a genome-wide computational scanning and a rational design of peptide vaccine","volume":"59","author":"Mashiba","year":"2007","journal-title":"Immunogenetics"},{"key":"B33","doi-asserted-by":"publisher","first-page":"30494","DOI":"10.2807\/1560-7917.es.2017.22.13.30494","article-title":"GISAID: Global initiative on sharing all influenza data - from vision to reality","volume":"22","author":"Shu","year":"2017","journal-title":"Euro Surveill"},{"key":"B34","doi-asserted-by":"publisher","DOI":"10.1016\/j.heliyon.2025.e42613","article-title":"SGV-caller: SARS-CoV-2 genome variation caller","volume":"11","author":"Wu","year":"2025","journal-title":"Heliyon"},{"key":"B35","doi-asserted-by":"publisher","DOI":"10.1016\/j.bbrc.2016.05.015","article-title":"A novel, rapid and efficient method of cloning functional antigen-specific T-cell receptors from single human and mouse T-cells","volume":"474","author":"Hamana","year":"2016","journal-title":"Biochem Biophys Res Commun"},{"key":"B36","doi-asserted-by":"publisher","first-page":"136","DOI":"10.1038\/s41392-021-00552-0","article-title":"Gender associates with both susceptibility to infection and pathogenesis of SARS-CoV-2 in Syrian hamster","volume":"6","author":"Yuan","year":"2021","journal-title":"Signal Transduct Target Ther"},{"key":"B37","doi-asserted-by":"publisher","first-page":"493","DOI":"10.1038\/s41586-024-07487-w","article-title":"Accurate structure prediction of biomolecular interactions with AlphaFold 3","volume":"630","author":"Abramson","year":"2024","journal-title":"Nature"}],"container-title":["Frontiers in Immunology"],"original-title":[],"link":[{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fimmu.2026.1758642\/full","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,27]],"date-time":"2026-04-27T05:27:11Z","timestamp":1777267631000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fimmu.2026.1758642\/full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,27]]},"references-count":37,"alternative-id":["10.3389\/fimmu.2026.1758642"],"URL":"https:\/\/doi.org\/10.3389\/fimmu.2026.1758642","relation":{},"ISSN":["1664-3224"],"issn-type":[{"value":"1664-3224","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,27]]},"article-number":"1758642"}}