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Research Article: N-terminal pyroglutamylation of an HLA-A24-restricted immunodominant epitope enhances SARS-CoV-2-specific T-cell responses

Date Published: 2026-04-27

Abstract:
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 1208–1216). TCR repertoire analysis revealed that QI9/A24-specific T cells are highly diverse, with 219 clonotypes isolated and 169 ?? 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–mediated 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.

Introduction:
T-cell receptors (TCRs) on cytotoxic CD8 + T lymphocytes (CTLs) recognize complexes formed by short peptide fragments bound to HLA class I molecules. These peptides are typically generated by proteasomes from cytosolic proteins within target cells and then transported into the lumen of the endoplasmic reticulum (ER) by the transporter associated with antigen presentation (TAP), where they are loaded onto HLA class I molecules ( 1 ). The peptide-HLA (pHLA) complexes are then translocated to the cell surface for…

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