(A) Chimeras were constructed with graded p14⁺ T_N numbers (2 × 10² to 2 × 10⁵; color legend in panel B), and p14⁺ T_E expansions were quantified in the MedLNs on days 3–4 (connected data points, respectively). (B) Kinetics of p14⁺ T_E expansion/contraction and p14⁺ T_M development in blood (5 combined experiments; n = 3–6); data for day 0 indicate p14⁺ T_N retrieved in the absence of infection, and vertical colored lines indicate respective p14⁺ T_E peak expansions. (C) Serum IFN-γ as a function of p14⁺ T_N input number. (D) Absolute numbers of transferred p14⁺ T_N (day 0), T_E (day 8) and T_M (day 109) in spleen; values indicate fold difference between p14⁺ T_N and T_M cellularity. (E) CD127 and CX3CR1 expression by splenic p14⁺ T_E/M recovered from respective chimeras on days 8, 44, and 109. (F) Kinetics of phenotypic p14⁺ T_E/M differentiation as function of p14⁺ T_N precursor frequency. Analyses of splenic p14⁺ T_E (day 8) and T_M (days 44 and 109) were conducted as above; data points from p14⁺ T_E/M analyzed at the same time point are connected by a line, and statistics compare p14^2e2 vs. p14^2e3-p14^2e5 chimeras. For comparative purposes, the graded background shading demarcates the spread of respective marker expression from young (Y, light) to old (O, dark) D^bNP₃₉₆⁺CD8⁺ T_M in B6 mice (Figure 4 and Supplemental Figures 5–14). (G) Summary of preceding analyses comprising 48 markers categorized according to similarity between p14⁺ T_M from young p14^2e5 chimeras (~7 weeks) and old D^bNP₃₉₆⁺CD8⁺ T_M (≥80 weeks). (H) AT/rechallenge experiments were performed with 2 × 10³ p14⁺ T_M purified from respective p14-titration chimeras infected ~7 weeks earlier, AT, LCMV Armstrong challenge and quantification of II° p14⁺ T_E expansions 8 days later (n = 3; representative of 3 similar experiments). *P < 0.05, **P < 0.01, and ***P < 0.001 by 1-way ANOVA or Student’s t test.