Impact of anti-PD-1 mAb on lymph node Tfh cells, Tfr cells, B cells, and CD8 ⁺ T cells. C57BL/6 mice were injected s.c. with MC38-OVA tumor cells. After 10 days, tumor-bearing mice were treated or not with anti-PD-1 mAb (250 µg, i.v.). Draining lymph node flow cytometry analysis was performed 3 days later. (A) Representative dot plots showing CXCR5 and CD84 expression in CD4⁺ BCL6⁺ PD-1^high T cells compared with CD4⁺ BCL6⁻ PD-1⁻ T cells. (B and C) (B) Representative FACS dot plots and (C) quantification of CXCR5⁺, PD-1^high cells among CD4⁺ T cells. Compiled from three independent experiments with a total of 11 mice per group. (D and E) (D) Representative FACS dot plots and (E) quantification of BCL6⁺Foxp3⁻ and BCL6⁺FoxP3⁺ among CD4⁺ T cells (n = 7 mice per group). (F–H) (F) Quantification of GL7⁺ CD19⁺ B cells. Representative dot plot (G) and quantification (H) of B220⁺ IgD⁻ cells among CD19⁺ B cells. Compiled from two independent experiments with a total of eight mice per group. (I and J) C57BL/6 mice were injected s.c. with MC38-OVA tumor cells. After 10 days, mice were adoptively transferred by GFP-expressing OT-I CD8⁺ T cells and treated or not with anti-PD-1 mAb (250 µg, i.v.). (I) Tumor-bearing mice received either two doses of the BCL6 inhibitor FX1 or a vehicle as a control. On day 3, OT-I T cells were quantified at the tumor site. (J) The small fraction of BCL-6 expressing specific CD8⁺ T cells in the lymph node do not preferentially expand upon anti-PD-1 treatment. Statistical analyses were performed using t test (C, F, H, and J), one-way ANOVA (I), or two-way ANOVA (E). ns, non significant; **, P < 0.01, ***, P < 0.001.