biostudies-literatureCai CEuropean Research CouncilNIAID NIH HHSeadh0687https://www.ebi.ac.uk/biostudies/studies/S-EPMC7615587biostudies-literatureUnknown8(90)T cells are critical for immune protection against severe COVID-19, but it has remained unclear whether repeated exposure to SARS-CoV-2 antigens delivered in the context of vaccination fuels T cell exhaustion or reshapes T cell functionality. Here, we sampled convalescent donors with a history of mild or severe COVID-19 before and after SARS-CoV-2 vaccination to profile the functional spectrum of hybrid T cell immunity. Using combined single-cell technologies and high-dimensional flow cytometry, we found that the frequencies and functional capabilities of spike-specific CD4⁺ and CD8⁺ T cells in previously infected individuals were enhanced by vaccination, despite concomitant increases in the expression of inhibitory receptors such as PD-1 and TIM3. In contrast, CD4⁺ and CD8⁺ T cells targeting non-spike proteins remained functionally static and waned over time, and only minimal effects were observed in healthy vaccinated donors experiencing breakthrough infections with SARS-CoV-2. Moreover, hybrid immunity was characterized by elevated expression of IFN-γ, which was linked with clonotype specificity in the CD8⁺ T cell lineage. Collectively, these findings identify a molecular hallmark of hybrid immunity and suggest that vaccination after infection is associated with cumulative immunological benefits over time, potentially conferring enhanced protection against subsequent episodes of COVID-19.Science immunologySARS-CoV-2 vaccination enhances the effector qualities of spike-specific T cells induced by COVID-19.PMC761558710105712910104148475N93019C00065Bergman PRivera-Ballesteros OSette AHansson LStralin KLlewellyn-Lacey SPrice DAAleman SSandberg JKGrifoni AAdamo SBjorkstrom NKWeiskopf DCai CBuggert MLjunggren HGWherry EJGao YOsterborg AQin CfalseSARS-CoV-2 vaccination enhances the effector qualities of spike-specific T cells induced by COVID-19.T cells are critical for immune protection against severe COVID-19, but it has remained unclear whether repeated exposure to SARS-CoV-2 antigens delivered in the context of vaccination fuels T cell exhaustion or reshapes T cell functionality. Here, we sampled convalescent donors with a history of mild or severe COVID-19 before and after SARS-CoV-2 vaccination to profile the functional spectrum of hybrid T cell immunity. Using combined single-cell technologies and high-dimensional flow cytometry, we found that the frequencies and functional capabilities of spike-specific CD4⁺ and CD8⁺ T cells in previously infected individuals were enhanced by vaccination, despite concomitant increases in the expression of inhibitory receptors such as PD-1 and TIM3. In contrast, CD4⁺ and CD8⁺ T cells targeting non-spike proteins remained functionally static and waned over time, and only minimal effects were observed in healthy vaccinated donors experiencing breakthrough infections with SARS-CoV-2. Moreover, hybrid immunity was characterized by elevated expression of IFN-γ, which was linked with clonotype specificity in the CD8⁺ T cell lineage. Collectively, these findings identify a molecular hallmark of hybrid immunity and suggest that vaccination after infection is associated with cumulative immunological benefits over time, potentially conferring enhanced protection against subsequent episodes of COVID-19.2023-01-01T00:00:00Z2023 Dec2025-05-29T20:32:47.464Z2025-05-29T20:32:47.464ZS-EPMC76155873806456910.1126/sciimmunol.adh0687