Fig. 1

Characteristics of SARS-CoV-2-specific T-cell immune responses towards Omicron variant. a Schematic presentation of four main groups of included participants with different SARS-CoV-2 infection or vaccination statuses. Previously infected individuals, solely vaccinated individuals, infected and initially vaccinated individuals, vaccinated and boosted individuals were selected for SARS-CoV-2-specific T-cell immune responses analysis. b, c Effector T-cell reactivity to the SARS-CoV-2 Omicron and Delta variants. The percentage of individuals whose effector T-cell response was escaped from by the Omicron or Delta variant was analyzed for the general population (b) and for the groups with no vaccination, pre-booster, and post-booster vaccination with or without an infection history (c). Effector T-cell immune escape was defined as the individual who show a > 50% (0.3 log 10) reduction in effector T-cell response towards antigens from Omicron or Delta. d, e Memory T-cell immune escape and potential mechanism. CD4⁺ T-cell- and CD8⁺ T-cell-specific carboxyfluorescein succinimidyl ester (CFSE) proliferation assay results showed that CD4⁺ memory T cells had robust proliferative responses against Omicron spike, but escape from CD8⁺ memory T-cell responses were more frequent (d). Sequence alignment or binding affinity analysis for HLA class I epitopes predicted by NetMHCpan4.1 confirmed the mutations in epitope sequences and the decrease in HLA class I binding affinity (e). f Effector T-cell responses to Omicron are preserved even in individuals without detectable neutralizing antibodies of Omicron. A portion of vaccinated individuals with or without prior infection was T-cell response-positive but neutralizing antibody-negative from IFN-γ ELISpot and pseudovirus neutralization assay. The data (b–f) are reproduced from the original article and supplementary materials. Panels b–f are adapted from figures and data in the article by Naranbhai et al.¹