Fig. 5: TGFβ-mediated suppression of CXCR3 limits CD8⁺ T cell chemotaxis and anti-tumor effect.

ChIP was carried out using human Jurkat cells (a) and mouse primary CD8⁺ T cells (b) with anti-SMAD2 and anti-SMAD3 antibodies +/− TGFβ1 treatment, n = 2–5 technical replicates/condition. Experiment shown is representative of 3 independent experiments, displayed as mean +/− SD. ****p < 0.0001 using one-way ANOVA with Sidak’s multiple comparison correction. c Linear regression analysis of SMAD2 and CXCR3 gene expression levels from a cohort of TCGA colorectal cancer patients. P-values derived from Spearman and Pearson correlations. d MC38 survival (i) and tumor growth curves (ii–iv) in WT (n = 14), ALK5^ΔCD8 (n = 11)^, and ALK5^ΔCD8 + αCXCR3 blocking antibody (n = 12). The ratio of cured/total mice in each group is in the upper right. Shown is a composite of two independent experiments. P-value derived from log-rank test. *p = 0.0388. e Representative FACS plots of tumors from one C57BL/6 mouse each from untreated or αCXCR3 treated groups harvested 4 days after the last dose. Shown is CD4 and CD8 expression gated on viable CD45⁺CD3⁺ cells. f Schematic representing hypothesis for LY2157299 mechanism of action. Naïve T cells exposed to LY are more susceptible to activation by low-avidity antigen in the lymph node. CXCR3 is upregulated upon activation, and by loss of TGFβ-mediated suppression, which allows for better homing to CXCR3 ligands produced in the tumor microenvironment endogenously and following radiation. Once in the tumor, those TGFβ-resistant CD8 T cells have improved cytotoxicity.