Anti-PD-1 mAb activity in the draining lymph node is BCL6 dependent. (A and B) C57BL/6 mice were injected s.c. with MC38-OVA. After 10 days, mice were treated or not with anti-PD-1 mAb (250 µg, i.v.) and received either three doses of the BCL6 inhibitor FX1 or a vehicle as a control. Representative FACS dot plots (A) and quantification (B) of H2-K^b-OVAp tetramers⁺ CD8⁺ T cells 5 days after treatment. Compiled from two independent experiments with five to eight mice per group. (C and D) C57BL/6 mice were injected s.c. with MC38-OVA. After 10 days, mice were adoptively transferred by CTV-labeled OT-I CD8⁺ T cells and treated or not with anti-PD-1 mAb (250 µg, i.v.) and received either two doses of the BCL6 inhibitor FX1 or a vehicle as a control. OT-I CD8⁺ T cell proliferation was assessed 3 days later. (C) Representative histograms showing CTV dilution in OT-I CD8⁺ T cells. (D) Quantification of OT-I CD8⁺ T cell replication index in lymph nodes. Compiled from two independent experiments with 6–11 mice per group. (E and F) C57BL/6 mice were injected s.c. with MC38-OVA. After 10 days, mice were treated or not with anti-PD-1 mAb (250 µg, i.v.). Some mice were injected every 2 days with FX1 or vehicle until day 10. (E) Evolution of tumor volume between day 0 and day 10. (F) Survival curves for the indicated groups. The dashed line corresponds to 50% survival. Compiled from two independent experiments with a total of 9–10 mice per group. Statistical analyses were performed using two-way ANOVA (B and D) or a log-rank test (F). *, P < 0.05; **, P < 0.01.