Spike protein–specific CD4 and CD8 T cell responses after vaccination of aged rhesus macaques . (A) Spike protein–specific T cell responses as measured in 40 NHP PBMC samples (20 NHPs and two time points) by ICS at indicated time points. Frequency of CD4⁺CD69⁺ T cell–expressing cytokines. The geometric mean response per group is indicated with a horizontal line. The dotted line indicates the technical threshold. Open symbols denote samples at technical threshold. (B) Spike (S) protein–specific T cell responses as measured by ICS at indicated time points. Frequency of CD8⁺CD69⁺ T cell–expressing cytokines. The geometric mean response per group is indicated with a horizontal line. The dotted line indicates the technical threshold. Open symbols denote samples at technical threshold.