{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,2]],"date-time":"2026-06-02T06:14:43Z","timestamp":1780380883096,"version":"3.54.1"},"reference-count":44,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,9,5]],"date-time":"2025-09-05T00:00:00Z","timestamp":1757030400000},"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:sec><jats:title>Introduction<\/jats:title><jats:p>T-cell responses to SARS-CoV-2 remain largely preserved across variants despite waning neutralizing antibodies. However, T-cell immunity may vary with the host\u2019s immune status, and data on T-cell responses in post-vaccine infections (PVI) are limited.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>We assessed Spike-specific T-cell responses in 32 vaccinated individuals, 16 of whom experienced PVI. Immune responses were evaluated at three time points: 1 month after the second vaccine dose (T1), 1 month after the booster dose (T2), and, in the PVI group, 1\u20133 months after the first positive nasal swab (T3). Additionally, we evaluated anti-spike antibody levels, T-cell exhaustion markers, and natural killer cell subsets, focusing on memory-like CD57<jats:sup>+<\/jats:sup> NKG2C<jats:sup>+<\/jats:sup> cells.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Subjects who developed PVI exhibited significantly reduced Spike-specific CD4 T-cell responses following the booster dose compared to vaccinated individuals who remained uninfected. This was accompanied by increased frequencies of LAG-3<jats:sup>+<\/jats:sup> CD4<jats:sup>+<\/jats:sup> and CD8<jats:sup>+<\/jats:sup> T-cells. A positive correlation was observed between AIM<jats:sup>+<\/jats:sup> CD4<jats:sup>+<\/jats:sup> T-cells and NKG2C<jats:sup>+<\/jats:sup> NK cells at T2 in PVI subjects. Following natural infection, T-cell responses were enhanced and associated with an expansion of NKG2C<jats:sup>+<\/jats:sup> NK cells.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>Individuals experiencing PVI displayed impaired booster-induced CD4<jats:sup>+<\/jats:sup> T-cell responses and increased expression of the immune checkpoint LAG-3. Natural infection restored and enhanced cellular immunity, particularly through the expansion of Spike-specific T-cells and memory NK cell populations. This study identifies an immune profile characterized by low spike-specific responses, which are associated with an increased susceptibility to breakthrough infections.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fimmu.2025.1657082","type":"journal-article","created":{"date-parts":[[2025,9,5]],"date-time":"2025-09-05T05:23:53Z","timestamp":1757049833000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":3,"title":["Reduced spike specific T-cell responses in COVID-19 vaccinated subjects undergoing SARS-CoV-2 breakthrough infection"],"prefix":"10.3389","volume":"16","author":[{"given":"Stefania","family":"Varchetta","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Federica 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