OX86-induced tumor rejection is lost in CCR7-KO mice. Effect of OX86 treatment in CCR7-KO mice. (A) 5 × 10⁴ CT26 cells were injected s.c. into the right flank of WT (top) or CCR7-KO (bottom) mice. Tumors grew without difference between the two groups. At 3–4 mm in size, mice received intratumor injection of anti-OX40 mAb or rat IgG as control. Each line represents individual tumors. The number of tumor-free out the total number of treated mice is reported. The pooled data of three independent experiments are shown. (B) T cell infiltration in tumors from CCR7-KO mice. CD4⁺ T cells were purified from a pool of CT26 tumors grown in CCR7-KO mice (TILs). As controls, splenocytes of tumor-free CCR7-KO mice were analyzed (STF). (top) On gated CD4⁺ T cells, the percentage of CD25⁺ versus Foxp3⁺ T cells was evaluated by flow cytometry. (bottom) OX40 and Foxp3 expression were analyzed in the gated CD4⁺ CD25⁺ population. Both Foxp3⁺ and Foxp3⁻ subsets were mostly OX40⁺, similarly to WT mice (Fig. 3A). However, in contrast to WT mice, TILs from CCR7-KO mice contain a higher percentage of OX40⁺ Foxp3⁻ T cells, representing activated effector T cells.