Figure 3. Cell-Intrinsic Defect in CD8⁺ T Cell Memory in the Absence of PD-1.

(A) (top) Representative plots of WT (black) and PD-1 KO (red) P14 cells in the lung and spleen 7 days after X31-GP33 infection. Numbers indicate frequencies of P14 cells as percentages of CD8⁺ T cells (top). Summaries of frequencies and numbers of P14 cells (bottom). (B) Flow cytometric analysis of BrdU incorporation by WT and PD-1 KO P14 cells at day 7 p.i. Numbers indicate the fraction of BrdU⁺ P14 cells. Representative plots from the spleen (left). Summary of BrdU⁺ P14 cells in the indicated organs (right). (C) Longitudinal analysis of WT and PD-1 KO P14 cell numbers in the lung during primary X31-GP33 infection. (D) Representative plots of intracellular cytokine staining for IFNγ and TNF-α (left) in WT and PD-1 KO P14 cells from spleen (top) and lung (bottom) at day 47+ p.i. and quantification (right). (E and F) Longitudinal analysis of KLRG1 and CD127 (E) and CD122 (F) expression on transferred PD-1 KO and WT P14 cells on days 8, 20, and 30 p.i. in the lung. (G) Representative plots of WT and PD-1 KO P14 cells at day 35 p.i. with X31-GP33 (day 35, left) and 7 days after rechallenge with PR8-GP33 (day 42 after primary infection, right). Numbers indicate frequencies of P14 cells as percentages of CD8+ T cells. A summary of numbers of P14 cells pre- and post-rechallenge is shown (right). Numbers above the bars indicate the fold change between day 35 and day 42 (7 days after rechallenge). Data are representative of 3–4 independent experiments with 4–6 mice per group and represented as mean ± SEM. Significance was assessed using Student’s t test; ns, not significant; *p < 0.05, **p < 0.01, ***p < 0.001. See Figures S5 and S6 for supporting data.