TGF-β promotes stem-like CD8 ⁺ T cells during chronic viral infection. (A) Experimental design. (B) At indicated days after infection, representative FACS profiles of pre-gated donor P14 T cells are shown (six repeats, n = 4–5/each). (C) The percentage of Tcf-1⁺ cells in P14 T cells is shown. (D) The percentage of Tcf-1⁺ (left) and Tcf-1⁻ (right) donor P14 T cells in total splenic CD8⁺ T cells is shown. (E) The percentage of IL-2 producing cells in IFN-γ⁺ P14 T cells is shown. (F and G) Day 7 (F) and day 10 (G) after infection, representative FACS profiles of pre-gated Tcf-1⁺ and Tcf-1⁻ P14 T cells are shown (three repeats, n = 4–5/each). (H and I) Mean fluorescence intensity (MFI) of integrin α4β7 (H) and MFI of integrin β1 (I) on Tcf-1⁺ and Tcf-1⁻ P14 cells are shown. The number in H was calculated as the ratio of MFIα4β7 on Tgfbr2^−/− over MFIα4β7 on co-transferred control P14s in each recipient mouse. Each pair of symbols in C–E, H, and I represents the results from an individual recipient. Combined results from three (C, total n = 8–10/time point), six (D, n = 10–18/time point), three (E, n = 7–9/time point), and three (H and I, n = 5/time point) independent experiments are shown. *, P < 0.05; **, P < 0.01; ***, P < 0.001; and ****, P < 0.0001 by paired Student’s t test for each time point.