(A) The number of TCRs from YF45 tet⁺ T cells from the indicated donors, before and 14 days after YFV vaccination. (B) TCRs from cells in A were compared to T_MN-derived TCRs in the day 210–242 post-vaccine samples. Bar graphs show the percentages of cells with or without a match. (C) Each circos plot represents TCRs from T_MN YF45 tet⁺ cells and TCRs from the same specificities, before and 14 days after YFV vaccination, from the same donors. Cells are ordered by frequency within each arc. Gray marks cells expressing unique TCRs; other colors represent expanded or shared sequences. Connecting lines highlight shared TCRs between a T_MN cell and cells in a previous time point. (D) The number and phenotypes of T cells in the day 14 sample that matched a T_MN-derived clonotype from the memory time point. (E) Clonal dynamics of a TCR expressed by a T_MN cell in the 14-day post-vaccine sample. Plot shows the number and phenotypes of T cells that expressed the same TCR sequence at the indicated time points. ND, not detected. (F and G) The frequencies of CD45RO^–CCR7⁺ YFV-specific T cells before and after vaccination for the corresponding populations (F). Post-vaccine CD45RO^–CCR7⁺tet⁺ cells were separated into T_SCM or T_MN subsets based on CXCR3, CD95, CD11a, or CD49d staining (G). (H) Plot compares the frequencies of CD45RO^–CCR7⁺tet⁺ cells before vaccination with the frequencies of T_MN cells in the corresponding population from the post-vaccine sample. (I) The post-vaccine T_MN frequency of each tet⁺ population was divided by its initial CD45RO^–CCR7⁺ frequency before vaccination. The ratio is defined as a gain if above 1 and a loss if below 1. Pie chart shows the numbers of populations that had gained or lost naive T cells after vaccination. (J) Plot shows the fold-change in tet⁺ frequency, from the pre-vaccine baseline to the memory time point, for populations that had gained or lost naive cells. For F, H, and J, n = 27 tetramer⁺ populations. Welch’s t test was performed. *P < 0.05, **P < 0.01.