(A) Tumor growth curves of UPFL1 subcutaneous syngeneic tumors treated with the indicated treatments when tumor reached 150 to 300 mm³ in volume. Significance testing was performed by 1-way ANOVA with post hoc Tukey’s HSD. *P < 0.05, **P < 0.001. (B) FFPE tumors were sectioned and dual stained for CD8 and with Masson’s trichrome. Immune phenotyping was performed and the phenotype/CD8 intensity call was plotted as the proportion of each treatment group. Flow cytometry was performed on UPFL1 syngeneic tumors following 1 week of treatment. CTRL, control. (C) Box-and-whisker plots of percentage of cells in each treatment group of CD45⁺, CD3⁺, and CD8⁺ cytotoxic T cells after 1 week of treatment. (D) Box-and-whisker plot of percentage of cells in each treatment group of CD4⁺ cytotoxic T cells and CTLA-4⁺ cells after 1 week of treatment. (E) Cell types were assigned to scRNA-seq data from either control or erdafitinib-treated UPFL GEMM tumors using SingleR. The frequency of each immune cell type was plotted as a proportion of all immune cells. The inset percentage represents the percentage of T cells as a proportion of the total immune population. (F) The T cell subset of cells were plotted by the scRNA expression values for Icos, a marker of active/proliferative Tregs. (G) FoxP3⁺GFP⁺ cells were isolated from murine spleens and cocultured in the presence or absence of APCs and increasing doses of erdafitinib (n = 3 for each group). (H) Bulk RNA-seq data (GSE135390) from flow-sorted T cells (naive, Th, and Treg) were plotted for FOXP3, FGFR1, FGFR2, and FGFR4. Plots show the IQR and midline at the median. Error bars represent Q1/Q3 ± (1.5 × IQR). Two-sided t tests followed by Bonferroni’s correction to account for multiple comparisons were preformed, with the P values shown above the given comparison.